EC Diseases of Nebraska's Field Crops

Transcription

1 University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Historical Materials from University of Nebraska- Lincoln Extension Extension 2001 EC Diseases of Nebraska's Field Crops Loren J. Giesler University of Nebraska Lincoln, lgiesler1@unl.edu Robert M. Harveson University of Nebraska Lincoln, rharveson2@unl.edu Jim Stack University of Nebraska-Lincoln John E. Watkins University of Nebraska-Lincoln Jennifer L. Chaky University of Nebraska, Lincoln Follow this and additional works at: Part of the Agriculture Commons, and the Curriculum and Instruction Commons Giesler, Loren J.; Harveson, Robert M.; Stack, Jim; Watkins, John E.; and Chaky, Jennifer L., "EC Diseases of Nebraska's Field Crops" (2001). Historical Materials from University of Nebraska-Lincoln Extension This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.

2 Leaf Rust on Wheat Bean Pod Mottle Virus on Soybean Aphanomyces Root Rot on Sugarbeet Anthracnose on Alfalfa Rhizopus Head Rot on Sunflower Gray Leaf Spot and Southern Rust on Corn Loren J. Giesler Extension Plant Pathologist Robert M. Harveson Extension Plant Pathologist James P. Stack Extension Plant Pathologist John E. Watkins Extension Plant Pathologist Jennifer L. Chaky Extension Educator Alfalfa Corn Dry Beans Potato Small Grains Sorghum Soybeans Sunflower Sugarbeets Diseases of Nebraska s Field Crops University of Nebraska Cooperative Extension EC

3 Table of Contents Introduction... 2 Alfalfa Diseases... 3 Corn Diseases... 5 Dry Bean Diseases... 9 Potato Diseases Small Grains (Barley, Oat, Rye, Wheat) Diseases Sorghum Diseases Soybean Diseases Sugarbeet Diseases Sunflower Diseases Introduction Each year, plant diseases are an important factor in reducing yields of Nebraska s field crops. The purpose of this publication is to provide concise information in an easy to use table for many of Nebraska s field crop diseases. The disease information is organized by crop. Diseases covered in this publication include the four main groups of plant pathogens: fungi, bacteria, viruses and nematodes. Fungi: Many fungi can cause plant diseases. Fungi grow by producing small thread-like filaments called hyphae. These tubular-shaped structures collectively are referred to as mycelium and make up the vegetative stage of the fungal life cycle. Many fungi also produce spores that serve for propagation and survival. Spores often move by wind or water, or if the spores are soil-borne, by activities that move soil. Most spores require moisture to germinate and initiate infection on host plants. Many fungi can survive in the soil or on plant debris and serve as a source of inoculum to initiate disease. Bacteria: Many bacteria can cause plant diseases. Bacteria often require an opening in the plant, such as a wound, in order to initiate infection. Moisture favors disease development, as the bacteria can multiply rapidly under such conditions and cause more disease. Bacteria can spread among plants through water splashing and machinery movement (e.g. cultivating) when the crop is wet. Bacteria can survive in the soil or on plant debris and serve as an infection source. Viruses: Viruses cause plant disease by infecting host cells and disrupting normal cellular processes by causing the host cells to replicate the virus. Insect vectors acquire viruses from infected plants and transmit them to healthy plants when they feed. Only certain insects can transmit certain viruses. To control insect-vectored plant viruses, it is important to understand the life cycles of the insects that move viruses from plant to plant. Organisms that transmit viruses include aphids, mites, other insects, nematodes and fungi. Nematodes: Nematodes are microscopic worm-like animals that can cause plant diseases. They often damage plant roots by feeding on or in the roots. This feeding activity can distort or gall roots. Symptoms of nematode feeding are often seen above ground, as plants are usually stunted because of the reduced root mass. Some plant parasitic nematodes damage plant foliage, but most are root-feeders. Cover Photo Credits Phytophthora root rot on soybean seedling, courtesy of X.B. Yang, Iowa State University; all other photos courtesy of faculty in the NU Institute of Agriculture and Natural Resources. 2

4 Alfalfa Diseases Conditions Favoring Pathogen Survival and Bacterial Wilt Thinning of stand during second Cooler weather in spring and Bacteria are soilborne and enter Plant resistant varieties; maintain Clavibacter michiganense year and thereafter; plants early summer enhances disease plant through wounds from balanced soil fertility; prevent subsp. insidiosum stunted with slow regrowth. development; ample moisture winter injury, clover root root and crown injury; do not Leaves yellow and wilt during also favors disease; mowing curculio feeding, and mow when plants are wet. warm weather; yellowish-tan wet fields introduces bacterium mechanical damage. discoloration of top root into cut stems. vascular tissue. Seedling Blights Seed decay before and after Pythium and Phytophthora are Pathogens are soilborne and Plant resistant varieties; maintain Pythium spp. emergence; soft watery rot of favored by cool, wet, poorly persist indefinitely through balanced soil fertility; prevent Fusarium spp. roots and stems; seedlings drained soils; Fusarium and resistant fungal structures. root and crown injury; use Phytophthora megasperma yellow and die rapidly. Rhizoctonia are favored by seed-applied fungicide. f. sp. medicaginis warm, wet weather. Rhizoctonia solani characteristic symptoms. between tile lines show or mefenoxam seed treatment. well-drained fields; use metalaxyl proper seedbed; maintain balanced soil fertility; establish on Plant resistant varieties; prepare Fusarium Root Rot Damage to roots varies from Symptoms increase during Fungus is soilborne and persists Maintain plants in vigorous Fusarium spp. irregular brown rotted areas to periods of severe moisture or as chlamydospores in soil and growing condition; maintain complete destruction of root and heat stress. plant material. proper cutting schedule and crown; as symptoms progress, control insect pests. plants yellow, wilt and die. Anthracnose Light to dark brown diamond- Infection spreads rapidly during Fungus persists on crown and Plant resistant varieties; clean Collectotrichum trifolii shaped lesions on stems warm, humid weather in summer stems; spores spread by wind. harvesting equipment of debris containing small black bodies; and early fall. Crown rot phase Dirty harvesting equipment can before going from infected to new young dead shoots may develop of this disease is often more spread infection from an old to or non-infected fields. a shepherd s crook ; dead, serious in hot, dry weather; new stand. straw colored stems scattered anthracnose in the crown lowers throughout field; dry rot of winter hardiness and infected crown with bluish-black plants die during winter. discoloration associated with winter stand loss. 3

5 Crown Rot Plants stunted with bleached, Environmental, mechanical and Fungi are saprophytic in soil and Harvest when soil is dry, allow for Several fungi yellow leaves that wilt under other factors that promote injury enter crowns through wounds inches regrowth after last moisture stress. Red to black to crowns. Rot commonly cutting; use good fertilizer discoloration of crowns; rotted develops slowly with age of management; do not graze stands; tissue interspersed with healthy stand, but stresses can accelerate use adapted winter hardy varieties tissue; crown may be hollowed; development. with a history of good gradual thinning of stand. performance; control insects. Fusarium Wilt Irregularly shaped patches in Disease favored by high soil Fungus survives in the soil as Fusarium oxysporum field; wilting of shoots followed temperatures; soil moisture f. sp. medicaginis by bleaching of leaves and does not alter disease severity. in tap root. brown-to-red discolored streaks reddish tinge; cinnamon stems; leaves may develop a roots through wounds. chlamydospores and enters Grow resistant varieties. Verticillium Wilt Wilting of upper leaves on warm Cool, moist weather favors Fungus survives on crop debris Grow resistant varieties if Verticillium albo-atrum days; leaves and stems become infection and spread; spread and is seed borne; spores are available; harvest infested fields pale yellow; leaflet tip has within and between fields wind-borne and spread on last and clean harvesting V-shaped discoloration as an primarily by harvesting blowing trash and harvesting equipment after infested field is early indication; taproots have a activities; can spread from equipment; survives up to 3 harvested; 2-3 year rotation will dark ring in cross section. infected hay stacked in a field. years in dry hay. reduce inoculum. Common Leaf Spot Small, circular, black or brown Disease develops during moist Fungus survives on crop residue; Harvest at one-tenth bloom; Pseudopeziza medicaginis spots on leaves; leaves turn periods of cool to moderate spores are spread by wind. destroy volunteer plants in fence yellow and drop as disease temperatures. rows; plant resistant varieties. progresses. Stemphylium Leaf Spot Dark, sunken, oval to irregular- Warm moist weather in July and Fungus survives on crop residue; Plant resistant varieties; harvest Stemphylium botryosum shaped spots on leaves; older August favors infection. spores spread by wind. at one-tenth bloom if leaf drop is spots are large and concentrically severe. ringed with yellow halo. Spring Black Stem Black, irregular spots on leaves Cool moist weather in May Fungus survives on crop residue; Plant resistant varieties no Phoma medicaginis and stems; stem lesions enlarge favors this disease; usually only spores spread by wind. high level of resistance is until lower stem appears black; a problem on first cutting; available; harvest at one-tenth young shoots may die; petiole fungus may spread to crown bloom or earlier if leaf drop is infection causes defoliation; and cause crown rot. severe. stunted plant growth. Summer Black Stem Large, circular ash-gray spots Warm, moist weather favors Fungus persists in old stems; Plant resistant varieties no Cerecospora medicaginis on leaves; spots surrounded by disease development; second spores spread by wind. high resistance level available; yellow halo; brown to black and third cutting most affected harvest at one-tenth bloom or lesions appear on stem. especially if harvest is delayed. earlier if there s severe leaf drop. 4

6 Leptosphaerulina (Lepto) Small roughly circular leaf spots More prevalent in spring; Fungus overwinters in leaf Grow varieties less susceptible Leaf Spot with tan centers, a brown border favored by cool, wet conditions debris; spores blown onto resistance not available; cut at Leptosphaerulina briosiana and surrounded by a yellow halo; following harvest when new leaves. one-tenth bloom. mostly on young leaves. growth is infected. Rust Dark reddish-brown rust pustules Infections occur in late summer Wind blown spores from Harvest stand timely to reduce Uromyces striatus form on leaves, petioles and or early fall; warm days and cool southern states where disease loss and remove inoculum; stems; leaves on heavily rusted nights that result in heavy dews overwinters; reaches Nebraska destroy volunteer plants in fence plants shrivel and fall favor infection. typically in August. rows. prematurely; stems attacked when harvest is delayed. Downy Mildew Light green to yellow blotches on Cool, moist weather in spring Fungus persists from season to Plant resistant varieties; harvest Peronospora trifoliorum leaves; leaves twisted and margin and fall. season in crowns; spores spread first cutting early; use metalaxyl curled down; grayish-white by wind. or mefenoxam seed treatment. fungal growth on leaf surface. Alfalfa Mosaic Light green to yellow leaf Symptoms most evident during Virus transmitted by aphids or Use certified seed; grow aphid- Alfalfa Mosaic Virus (AMV) mottling; stunted shoots; leaf cool weather in spring and fall; up to 10% by seed. resistant cultivars. and petiole distortion. not evident in summer. Stem Nematode Stunted plants with white shoots Cool, wet weather promotes Nematode survives in infested Grow resistant varieties; plow Ditylenchus dipsaci scattered through a field; plants nematode reproduction and stems in dry hay and alfalfa under infected stands and use crop have bushy appearance; crowns plant infection; nematode crowns and soil; spread is by rotation for 2-3 years when swollen, spongy and easily requires free moisture to move machinery and free-flowing severe; harvest field when dry and detached; swollen buds; mostly up outside of plant and feed in water. do not irrigate right before or after a problem in first cutting. the buds. harvest. Corn Diseases Conditions Favoring Pathogen Survival and Seed Rots and Seedling Blight Symptoms range from embryo These diseases are prevalent in Fungi causing seedling blights Seed treatment; use high quality Pythium spp. death before germination to poorly drained soils during persist in soil and can grow uncracked seed; proper seedbed Fusarium spp. small rotted areas on the roots periods of cold, wet weather; through soil to contact roots preparation. Diplodia spp. of seedlings; above ground soil temperatures of o F or seed. Pythium produces Rhizoctonia spp. symptoms are yellowing, wilting, favor seedling blight. spores that move in soil water. and death of seedling leaves. 5

7 Gibberella Stalk Rot Symptoms on roots, base of Moderate to high temperatures Fungus survives as perithecia Plant stalk rot resistant varieties; Gibberella zeae stem, and first-third internodes; with high moisture following on stalk residue or as mycelium maintain balanced soil fertility; (asexual stage Fusarium pith becomes shredded and a tassling favors disease and spores in soil and on crop use recommended plant graminearum) reddish color; plants ripen development. High plant residue; spores spread by wind populations; use full season prematurely and often lodge; population and continuous and rain. hybrids; harvest at maturity; plant symptoms become evident as corn may increase damage. adapted hybrids. plants mature. Fusarium Stalk Rot Symptoms vary; pith becomes Dry conditions early in season Plant stalk rot resistant varieties; Fusarium verticillioides shredded, tan to pinkish in color; accompanied by warm, wet maintain balanced soil fertility; F. proliferatum plants ripen prematurely and weather 2 to 3 weeks after use recommended plant often lodge; symptoms appear as silking; high nitrogen, low populations; use full season plants mature; often associated potassium, hail and disease or with corn borer damage. insect damage predispose plants populations. to infection; high plant adapted hybrids. hybrids; harvest at maturity; plant F. subglutinans by wind. crop residue; spores are spread Fungus survives in soil and on Charcoal Rot First appears as brown to black Moderate soil temperature and Fungus survives as sclerotia on Maintain adequate soil moisture Macrophomina phaseolina lesions on roots of seedlings and moisture favor infection; high crop residue in soil; hyphae of after tasseling; maintain balanced young plants; spreads into soil temperatures ( o F) fungus grow through soil to soil fertility; plant adapted, full crown and lower internode as and low soil moisture favor contact and infect plants. season hybrids at recommended plants mature; grayish streaks on symptom development. plant populations; harvest at lower internode and internal maturity. shredding of pith; small black sclerotia on shredded stalk tissue. Diplodia Stalk Rot Brown discoloration of the lower Warm wet weather favors Fungus survives as perithecia Maintain adequate soil moisture Stenocarpella maydis 1-2 internode regions. Black infection. on stalk residue or as mycelium after tasseling; maintain balanced (syn. Diplodia maydis) perithecia may appear below the and spores in soil and on crop soil fertility; plant adapted, full surface of the stalk; plants ripen residue; spores spread by wind season hybrids at recommended prematurely and often lodge; and rain. plant populations; harvest at symptoms appear as plants maturity. mature. Diplodia Ear Rot Grayish-white fungal growth Warm wet weather favors Fungus survives as perithecia Rotate crop and use fall tillage to Stenocarpella maydis between and on kernels; black infection. on stalk residue or as mycelium reduce inoculum. (syn. Diplodia maydis) perithecia produced on kernels; and spores in soil and on crop husks may be bleached. residue; spores spread by wind and rain. Fusarium Kernel Rot Symptoms appear as a pinkish Dry conditions early in season Infection from wind-borne Control corn earworms; maintain Fusarium verticillioides discoloration of caps of kernels accompanied by warm, wet spores usually follows injury balanced soil fertility. F. proliferatum followed by the formation of weather 2 to 3 weeks after to ear from corn earworms, F. subglutinans cottony pink mold growth. silking. birds, etc.; fungus survives in the soil and on crop residue. 6

8 Bacterial Stalk Rot Tan to dark brown, water-soaked High temperatures and rainfall, Bacteria survive as saprophytes No satisfactory method of control; Erwinia spp. soft rot at lower nodes; produce hail, sprinkler irrigation, wet on crop residue in soil; bacterial some hybrids may be partially Pseudomonas spp. offensive odor; stalks collapse soils and poor air circulation propagules are rain splashed or resistant. and twist in midseason causing aid disease development. wind-borne onto plants. plants to lodge. Aspergillus Ear Rot A. niger appears as a black mold All Aspergillus spp. grow on Spores are wind-borne and may Dry corn to below 15% moisture Aspergillus spp. growth; A. flavus as a greenish- corn stored at a moisture be insect transmitted. soon after harvest; reduce stress yellow mold growth; A. glaucus content of 15% or above; and insect injury during growing as a greenish mold growth. fungus may grow in earworm season. Minimize mechanical tracks or at ear tips. damage pre and post harvest. Common Smut Symptoms occur on all above Dry conditions and temperatures Avoid mechanical injury to Smut spores overwinter in soil; Ustilago maydis ground parts; galls first appear of o F favor smut plants; maintain balanced soil initial infections from wind-borne as shiny green to gray raised development; high nitrogen fertility. spores. areas which enlarge, forming and injury favor disease large gray galls containing black development. powdery spore masses. Downy Mildew (Crazy Top) Excessive tillering, rolling and Disease develops where soils Fungus survives in soil; new Provide adequate soil drainage; Sclerophthora macrospora twisting of upper leaves; tassel have been saturated for 24 to infections from soil-borne avoid planting in low, wet areas. resembles mass of leafy tissue; 48 hours shortly after planting. spores. stunted, narrow leaves. Eyespot Small, translucent, tan, oval to Cool, humid weather favors Spores are produced on crop Grow resistant hybrids; manage Kabatiella zea round leaf spots with dark disease development. residue and blown onto leaves. residue where feasible; rotate margins. Yellow halo around crops. lesion with reverse lighting. Physoderma Brown Spot Large chocolate brown to Infection requires moisture in Fungus survives in crop residue Grow resistant hybrids; manage Physoderma maydis reddish brown, irregular blotches whorls or behind leaf sheaths and in soil, spores are spread by residue where feasible; rotate at the base of leaves. along with high temperatures. wind, water, insects and crops. equipment. Common Rust Brownish-red oblong pustules Cool temperatures and high Spores are wind-blown with Plant resistant varieties. Puccinia sorghi on leaves; spores rub off on humidity favor infection. new infections occurring every fingers. Lesions primarily on 7 to 14 days. both leaf surfaces. Southern Rust Light cinnamon, circular rust High temperatures and high Spores are wind-borne. Grow resistant hybrids; apply Puccinia polysora pustules on upper leaf surfaces; relative humidity favor disease. foliar fungicide if rust is severe in distinguished from common rust seed production fields. only by microscopic examination. 7

9 Gray Leaf Spot Symptoms vary with hybrid Warm (75-90 o F) humid Spores are windblown from leaf Manage with tolerant hybrids; Cercospora zeae-maydis genetics; early symptoms easily conditions (>95% RH) favor to leaf, plant to plant, and field crop rotation and tillage help; confused with other foliar disease. to field. Fungus survives in fungicides are effective in seed diseases. Rectangular lesions crop residue on soil surface. production fields. most common leaf symptom on leaves. Yellow Leaf Blight Large tan to brown, oval to Cool, wet spring weather Fungus survives as pycnidia on Phyllosticta maydis elliptical leaf spots with a dark favors disease development. crop residue; spores are wind- margin and surrounded by a borne to leaves. within spots. specks (pycnidia) may form wide yellow halo; tiny black Plant resistant hybrids; manage residue; apply foliar fungicide if leaf spot is severe; rotate crops. Northern Corn Leaf Spot Symptoms range from small Moderate temperatures with The fungus survives on corn Plant resistance is effective for Bipolaris zeicola (syn. circular spots to narrow elongated high relative humidity favor residues and grain left in the most races. Fungicides are Helminthosporium carbonum) lesions depending on pathogen disease; in Nebraska, symptoms field. Spores from the residue effective for seed corn production. race and plant genotype; causes usually develop 3-4 weeks prior are wind blown onto plants. Crop rotation and cultivation can stalk rot in stressed plants. to tassling. be effective. Northern Corn Leaf Blight Long, elliptical gray to tan Temperatures of o F Fungus survives on crop Plant resistant varieties; apply a Exserohilum turcicum (syn. lesions originating on the lower accompanied by heavy dews residue; initial and secondary foliar fungicide if varieties are Helminthosporium turcicum) leaves and progressing upward during the growing season infections from wind-blown susceptible. on plant. favor disease. spores. rain. spread by wind and splashing susceptible. foliar fungicide if varieties are Plant resistant varieties; supply Holcus Spot Round to oval spots on lower Warm temperatures, wet, windy Bacteria survive on crop residue, Plant resistant varieties; rotate Pseudomonas syringae leaves; spots dark green at first weather early in season favor spread by splashing rain, crops. then becoming light tan and later disease. blowing soil particles, and turning brown with reddish- cultivation during heavy dews. brown margins. Stewart s Wilt Seedling phase: leaf striping and Mild winters that allow high Bacteria overwinter within the Plant resistant hybrids; seed Pantoea stewartii blight; tan to brown lesions survival of corn flea beetle gut of and are vectored by the applied insecticides are effective (syn. Erwinia stewartii) extend the length of the leaf; vector favor disease; high corn flea beetle; flea beetles for seed corn production. necrotic cavity in crown; temperatures and high nitrogen overwinter in grassy areas seedlings may wilt and die; and phosphorus fertility beside field. Second phase: Gray-green then increase severity. tan to brown lesions extend the length of the leaf. 8

10 Goss s Bacterial Wilt and Blight Shiny dark green to grayish tan Warm, moist weather. High Bacteria survive on crop Plant resistant or tolerant Clavibacter michiganense areas on leaves containing many Goss Wilt incidence is often residue; thought to be seed- varieties; rotate crops. subsp. nebraskense small dark spots (freckles); pith associated with a hail storm. borne to a limited extent; contains orange streaks; severely spread by hail, splashing rain infected plants stunted. and blowing soil particles. Maize Chlorotic Mottle Yellow streaks, mosaic and slight Environmental conditions that Primary vector unknown. Plant tolerante hybrids, rotate Maize Chlorotic Mottle mottling of leaves. Greatly favor early development and Beetles can transmit the virus, crops, use fallow period. Virus (MCMV) reduced kernel number; kernels high populations of beetle but a soil fungus or insect also enlarged and distorted. Plants vectors; history of virus in may be involved. sometimes killed. the field. Corn Lethal Necrosis Bright yellow mottling of leaves Environmental conditions that MDMV is insect transmitted. Grow tolerant hybrids; rotate Maize Chlorotic Mottle followed by a necrosis inward favor early development and Mechanism of transmission for crops. Virus (MCMV) from the margins; premature high populations of aphid and MCMV is unknown. Maize Dwarf Mosaic Virus death of husks; popped kernels. beetle vectors; history of (MDMV) MCMV in field and influx of aphids carrying MDMV. Nematodes Above-ground symptoms are Nematodes most active at Maintain balanced fertility; crop Root Lesion-Pratylenchus spp. stunted, off-colored plants and moderate to high temperatures; Dagger-Xiphinema spp. an unevenous to the field; root sandy soils more conducive Lance-Hoplolaimus spp. symptoms include a proliferation to nematode activity. of fibrous roots, pruning of feeder roots and thickening of smaller roots. Sting-Belonolaimus spp. Stubby Root-Trichodorus spp. above threshold levels. nematicides if nematode levels are rotation; weed control; apply Nematodes are soilborne. Dry Bean Diseases Conditions Favoring Pathogen Survival and Root Rots Reddish-brown to dark brown Mid to late season disease Fungi persist in soil and attack Rotate crops; provide adequate Rhizoctonia solani, rotted areas on taproot at or favored by dry, compacted soil. roots during favorable weather irrigation; minimize soil Fusarium solani f. sp. phaseoli below soil line; plants stunted; conditions; spread by anything compaction by subsoiling; treat Fusarium oxysporum f. sp. may or may not yellow. that moves soil. seed for seed decay and seedling phaseoli blight. 9

11 White Mold Infection first seen as small, Long hours of dew or light Partial control by fungicide Sclerotinia sclerotiorum water-soaked spots on stems, frequent rains; lush, viny growth application at full bloom; avoid pods, and leaves; spots enlarge and late irrigations. late season irrigation; rotate crops; to become rotted watery mass avoid using irrigation runoff from often covered by white moldy fields with history of white mold; growth; plants wilt and die; stems contain small black bodies (sclerotia); seeds are a chalky color and lightweight. certified seed. grow less viny cultivars; plant fields should be well drained; water; spores wind-blown. sclerotia spread by irrigation sclerotia can mix with seed; crop residue as sclerotia; Fungus survives in soil and on Bacterial Blights On leaves common blight Warm, moist weather favors Use certified seed, 3-year Common: Xanthomonas appears as irregular areas of common blight; cool rotation; avoid entering field when campestris pv. phaseoli brown, dead tissue surrounded temperatures favor halo blight; foliage is wet; treat seed with Halo: Pseudomonas syringae by a narrow lemon yellow hail can predispose plants to streptomycin; plant varieties pv. phaseolica border; halo blight has small infection; volunteer beans in tolerant to common blight, avoid water-soaked spots that become adjacent fields can harbor irrigation water reuse; control reddish brown lesions disease. volunteer beans; early application surrounded by a large greenish- yellow halo; infected seed are shriveled and discolored; water-soaked spots on pods. common blight. controls halo blight but not of copper fungicides partially Bacteria seed-borne and spread by splashing rain, small animals, insects, cultivation, and irrigation water; survive on bean residue for 2 years; bacteria can infect or be on the surface of volunteer beans. Rust First symptoms are chlorotic Cool nights and warm days Spores wind-borne with new Apply foliar fungicide when Uromyces appendiculatus flecks on leaves that develop into favor disease development; pustules produced every infection is first visible but not 3 dark red pustules containing heavy dews or light rains that days; fungus survives in to 4 weeks before harvest; control spores that rub off onto fingers wet foliage favor infection; crop debris. volunteer beans; manage crop and clothing. volunteer beans in adjacent fields residue. can serve as initial disease source. Bacterial Brown Spot Dark brown necrotic spots of Moderate, wet weather favors Plant certified seed treated with Pseudomonas syringae varying sizes on leaves; lacks infection; volunteer beans in streptomycin; incorporate crop pv. syringae water-soaking or a halo; brown adjacent fields can serve as debris; avoid reusing irrigation spots on pods. initial disease source. water; control volunteer beans; fungicides reduces spread. foliar application of copper bacteria survive in crop residue and are seedborne. promote infection and spread; Rain and sprinkler irrigation Bacterial Wilt Leaf symptoms similar to Warm temperatures accompanied Bacteria are seed-borne and Plant disease-free seed from Curtobacterium flaccumfaciens common blight; wilt occurs at by heavy dews, driving rains, survive for 2 years on crop certified fields; rotate crops; subsp. flaccumfaciens any growth stage; wilted leaves and hail favor disease residue; spread by wind, cultivate to reduce crop residue; dry and turn brown; dark green development. irrigation water, splashing rain, plant tolerant varieties. lesions on pods; seed discolored, and hail. shrunken, and wrinkled. 10

12 Potato Diseases Conditions Favoring Pathogen Survival and Black Leg Symptoms may appear at any time Erwinia carotovora pv. Most common transmission is Use clean seed tubers; plant in Erwinia carotovora pv. atroseptica during season; infected plants atroseptica is more active below through infected seed pieces; well-drained moist soil; eliminate Erwinia carotovora pv. wilt during hot weather; stems 70 o F, Erwinia carotovora pv. bacteria survive in infected cull piles and control weeds and carotovora turn grayish brown to black carotovora is more active above tubers, roots or other crops and potato volunteers; allow tubers to progressing to inky black; stems 70 o F; wet conditions favor weeds, and in surface irrigation mature before harvest. become soft and mushy at soil line. spread. water. Bacterial Soft Rot Tuber decay not always Erwinia carotovora pv. Most common transmission is Use clean seed tubers; plant in Erwinia carotovora pv. atroseptica associated with plants showing atroseptica is more active below through infected seed pieces; well-drained moist soil; eliminate Erwinia carotovora pv. black leg symptoms; tuber 70 o F, Erwinia carotovora pv. bacteria survive in infected cull piles and control weeds and carotovora symptoms vary from slight carotovora is more active above tubers, roots or other crops and potato volunteers; allow tubers to vascular discoloration to 70 o F; spread is favored by wet weeds, and in surface irrigation mature before harvest. complete soft rot. conditions. water. Bacterial Ring Rot Symptoms first appear on middle Ring rot develops in tubers most The bacterium overwinters in Certified seed and strict sanitation Clavibacter michiganense and lower leaves; leaf margins rapidly at o F; does not infected tubers, but not freely in involving all equipment that subsp. sepidonicum turn from pale green to brown usually spread from tuber to soil; infects new tubers through touches tubers. giving a scorched appearance; tuber in storage, but affects wounds and is very contagious. most characteristic symptom is several tubers around pockets vascular ring decay in tubers. of ring rot-infected tubers. Root-Knot Nematode Infected plants stunt and wilt In general, not as important in Nematode survives in soil and Rotation with non-host crops such Meloidogyne spp. under moisture stress; knots or cooler climates and usually more weed hosts; spread by irrigation as grasses; soil nematicides; weed galls of varying sizes form on common in coarse, sandy soils; water and contaminated soil on control; field sanitation measures. roots, and when densities are Northern root-knot nematode machinery. high, tubers appear warty. (Meloidogyne hapla) has an optimum temperature of 68 o F. Lesion Nematode Plants are less vigorous than High temperatures increase Nematodes survive in roots and Crop rotation ineffective because Pratylenchus spp. normal and yellow; reddish- sensitivity of P. scribneri/ soil; wet soils favor disease; of nematodes large host range, brown root lesions that coalesce Verticillium dahliae interaction. often associated with wilt- particularly small grains; nonand turn black; most species do causing fungi like Fusarium spp. fumigant nematicides more not attack tubers. and Verticillium spp. effective than fumigants. Corky Ringspot Two symptom types; the first Disease incidence is highest in TRV is transmitted by feeding Plant certified seed tubers; Tobacco Rattle Virus (TRV) rings of dark, corky layers that coarse, sandy soils; nematode of stubby-root nematode. eliminate weed hosts; control alternate with healthy layers; activity is greatest at o F stubby-root nematode. the second consists of small, with 15-16% soil moisture; brown flecks scattered activity decreases as soil throughout the infected tubers. moisture decreases. 11

13 Mosaic Disease Symptoms consist of vein Infection and spread of disease Virus transmitted by many Plant certified seed tubers; control Potato Virus Y (PVY) banding (development of brown depend on winged aphids; different aphids; it also infects weed hosts and volunteer streaks along veins); shows a mottling symptoms may be many weeds and solanaceous potatoes; eliminate cull piles; mosaic mottling. masked at temperatures below plants. prevent aphid buildups. 50 o F or above 70 o F. Mosaic Disease Some strains produce no visible Low temperatures (60-68 o F) Virus is carried in tubers, or is Potato Virus X (PVX) symptoms, others may cause enhance mosaic symptoms. mechanically transmitted by mild mottling at low light intensity; PVY and PVX together give severe leaf wrinkling known as rugose mosaic. to plant contact. equipment or sprayers) or plant machinery (seed cutting Use certified seed tubers; avoid mechanical transmission. Leafroll Younger leaves become upright, Infection requires either aphid Monitoring aphid populations; Potato Leafroll Virus (PLRV) rolling upward, and turning vectors or planting infected controlling weed hosts and potato yellow; chronic infections tubers; current season infection develop symptoms on lower occurs by aphids; chronic infections arise from planting infected tubers and are more infections. severe than current season and leathery. leaves which become pale, stiff, tubers; systemic insecticides. volunteers; use certified seed occurs at o F. Maximum symptom expression Early Blight Infections characterized by Primarily a disease of aging or Fungus survives in potato Avoid harvesting immature or Alternaria solani brown, circular lesions (1/8"-3/8" stressed plants; spore germina- residue, soil, tubers, or weed wet tubers; use late maturing in diameter) that appear on older tion and infection requires hosts; infection spreads by varieties; avoid nutrient leaves first; the lesions consist moist, warm weather; however, windblown spores. deficiencies; timely application of concentric rings of dead dry conditions favor wind of foliar fungicides. tissue, resembling a target-like transmission of spores to other or bull s eye appearance. plants; alternating wet and dry weather leads to rapid spread. Late Blight Small, water-soaked spots on Spores survive in infected Plant certified seed tubers; Phytophthora infestans leaves that expand to large, foliage, cull piles or uncovered remove cull piles and volunteers; brown to purple-black lesions; tubers and can spread by wind hill to keep tubers covered; apply lesions may kill entire leaflet or or water splashing to other spread over whole plant; greasy plants. under favorable conditions. causing wilting and death dark lesions appear on stems where possible. fungicide; use resistant cultivars rapid spread and severe disease. temperatures (<78 o F) favor High humidity and cool 12

14 Fusarium Dry Rot Small brown areas appear on Infection requires wounds from Pathogens are common soil Proper tuber handling and curing; Fusarium solani wounds after tubers are stored; field operations; dry rot inhabitants; they enter tubers prevent bruising or wounding; Fusarium roseum skin over rotted area sinks and develops over several months; through wounds and disease treat tubers with fungicide if becomes wrinkled; internal damp conditions in storage develops during storage. harvested under adverse lesions are brown, dry and spongy encourage secondary bacterial conditions. in texture; can also predispose tuber rots. tubers to secondary bacterial rots. Rhizoctonia Canker Reddish-brown lesions on Soil temperatures below 54 o F Fungus overwinters in soil or Avoid planting in wet, cold soils; (Black Scurf) stolons and underground parts maximize disease development, residue; infects roots of plants rotate crops; allow crop residues Rhizoctonia solani of the stem; severe infections infection and damage decrease in cool, wet soil. to decompose before planting. result in wilting, stunting, or at higher temperatures. leaf curling. Verticillium Wilt Plants yellow, wilt and die Warm soil temperatures (72-80 o F) Fungi overwinter in soil as Treat seed tubers with fungicides; Verticillium dahliae prematurely; single stems or favor growth of Verticillium sclerotia or in plant debris; rotate with cereals or legumes; Verticillium albo-atrum leaves may wilt first on one side dahliae; Verticillium albo-atrum infection occurs in roots through fumigate soil; control weeds. of stem; vascular tissue of stems is relatively more pathogenic wounds or root hairs. becomes discolored or light between o F. brown in cross-section. Scab Tuber surfaces have brown, Low soil ph (<5.5) and high Pathogen survives in soil or on Avoid planting scabby tubers; Streptomyces scabies roughened areas that may be moisture levels inhibit scab fleshy taproots of beets, sugar maintain high soil moisture during raised and warty, level with development. beets or carrots; it invades and after tuber set; avoid surface or sunken. tubers through lenticels. over-liming and high soil ph; treat to lower soil ph. Small Grains (Barley, Oat, Rye, Wheat) Diseases Conditions Favoring Pathogen Survival and Loose Smut Black smutty spore masses Cool, cloudy wet weather at Wind carries smut spores to Plant certified seed; treat seed Ustilago tritici-wheat replace both grain and chaff; flowering; smutted seed. healthy plants at flowering; with a systemic fungicide. U. nuda - Barley smutted heads emerge earlier spores germinate and infect from the boot than healthy heads. developing grain; smut fungus carried internally within seed to next crop. Semi-Loose Smut Grain replaced by powdery mass Cool, wet weather during seed Spore masses break during Treat seed with a fungicide; plant Ustilago avenae of black smut spores; usually germination; planting smutted threshing and collect on seed resistant varieties; use certified Barley, Oats entire head affected; spore seed. and in soil; spores germinate seed. masses shattered easily by and infect young seedlings; rain and wind. may also penetrate superficial tissues of developing kernel. 13

15 Covered Smut Grain replaced by powdery Cool, moist weather during Spore masses break during Plant resistant varieties; use Ustilago segetum-oats mass of black smut spores seed germination. threshing and collect on seed certified seed; treat seed with a U. hordei - Barley contained within a thin and in soil; spores germinate fungicide. membrane; spore masses do and infect young seedlings not shatter easily. following planting. Common Bunt Grain is replaced by black Cool, moist weather during Smut balls break during Treat seed with a fungicide. (Stinking Smut) powdery spore mass; smut seed germination; contaminated threshing and spores collect Tilletia tritici, balls give off fishy odor. seed. on seeds and in soil; spores Tilletia laevis germinate and infect young Wheat, Rye seedlings following planting. Fusarium Head Blight (Scab) Presence of one or more Scab develops in warm, humid Rotate with crops other than Fusarium spp. blighted spiklets after weather during flowering and wheat, corn, barley or rye; Wheat, Barley, Rye flowering; orange conidial grain ripening; wheat following manage stubble to hasten masses form a ring at base of corn or sorghum. decomposition; scabby wheat is toxic to most nonruminant animals; adjust combine air flow to blow out scabby kernels during harvest. may cause seedling blight. kernels shriveled; infected seed spiklets or along glume edges; cereal and grass residues in soil; infection from wind-borne spores. Fungus survives on infested Ergot Grass and cereal symptoms are Cool, wet weather favors Mow roadside grasses adjacent Claviceps purpurea similar; amber colored honey infection; grasses adjacent to small grain fields before Wheat, Barley, Oats, dew followed by hard, black heading; clean seed before Rye planting; cultivate to bury sieving. grain by gravity separation or sclerotia; remove sclerotia from sclerotia in place of kernels. to field. Spores are wind-borne to wheat heads during flowering. Black Point Black point shows brown or Wet weather after the wheat Causal fungi grow as Harvest promptly; do not plant Alternaira spp. and Bipolaris black discoloration of the matures; wheat prematurely saprophytes on crop debris; black-pointed seed or treat it with spp. and Sooty Mold Alternaria embryo region of the seed; killed by frost, take-all or other spores produced from debris a systemic fungicide before spp. and Cladosporium spp. sooty mold shows superficial diseases is prone to sooty mold; are carried by wind. planting. Wheat, Rye gray-black mold growth over the contaminated seed. surface of the head after maturity. Crown (Leaf) Rust Elongated orange-yellow Cool nights combined with Orange spores are wind-borne, Plant resistant varieties; apply Puccinia coronata pustules on the leaf sheaths warm days and 6 to 8 hours of new infections occur every 7 to systemic foliar fungicide if rust avenae - Oats and heads; heavy infections free moisture on leaves; 14 days during growing season. potential is high; avoid late cause lodging and premature growing susceptible varieties. planting. ripening. 14

16 Leaf Rust Circular to oval reddish-orange Mild winter; cool nights Orange spores spread from Plant resistant varieties; apply Puccinia triticina - Wheat, Barley pustules on leaves, stems, and combined with warm days and plant to plant by wind; spores systemic foliar fungicide if rust P. hordei - Barley head; orange spores will rub 6 to 8 hours of free moisture appear every 7 to 14 days potential is high and varieties are off onto fingers. on the leaves; growing during growing season. susceptible. susceptible varieties. Stem Rust Reddish-brown oblong pustules Mild winter; growing Rust spores are wind-borne; Plant resistant varieties; apply a Puccinia graminis tritici - on leaves, stems, and heads; susceptible varieties; cool nights new infections occur every 7 to systemic foliar fungicide if rust Wheat, Barley spores will rub off onto fingers; combined with warm days and 14 days during growing season. potential is high and varieties are P. graminis avenae - Oats pustules more elongate and 6 to 8 hours of free moisture susceptible. P. graminis scealis - Rye darker than leaf rust pustules. on the leaves and stems. Stripe Rust Bright yellow linear rust uredia Rust develops during wet, cool Rust spores are wind-borne to Plant resistant or partially Puccinia striiformis tritici -Wheat form on leaves and heads; weather in spring; growing healthy plants. resistant varieties; usually not a P. striiformis hordei - Barley symptoms usually appear early susceptible varieties. serious disease in Nebraska. before those of leaf or stem rusts. Septoria Leaf Blotch Lesions on leaves are elongate Cool, wet weather favors disease Fungus survives as mycelia in Manage stubble where feasible; Septoria tritici - Wheat tan-to-reddish brown, irregular- development; continuous living plants and as pycnidia on apply a systemic foliar fungicide S. secalis - Rye shaped spots surrounded by a cropping maintains wheat stubble; infection is from wind- if leaf spot potential is high. yellow margin; older lesions residue on soil surface. borne spores. contain small black specks (pycnidia). Septoria Leaf and Glume Blotch Small, grayish to brown spots on Warm, wet weather favors Fungus is seedborne, survives Manage stubble where feasible; Stagnospora nodorum - Wheat glumes; light brown spots with disease; continuous cropping as mycelia in living plants and as one application of a systemic S. passerinii-barley dark brown margins on leaves; maintains wheat residue on pycnidia on stubble; infection is foliar fungicide if disease S. avenae-oats older lesions contain small black soil surface. from wind-borne spores. potential is high. specks (pycnidia). Leaf Blotch and Crown Rot Reddish-brown spots on leaves Cool, wet weather favors Fungus is seedborne; conidia Treat seed with a fungicide; Drechlera avenacea - Oat which develop into longitudinal infection and disease produced on leaf lesions; wind- practice crop rotation and residue stripes; discoloration of plant development; continuous borne to healthy leaves. management. crowns. cropping. Net Blotch Long, narrow, tan spots on Moderate, humid weather Fungus overwinters on barley Apply a systemic foliar fungicide Brenophora teres - Barley leaves with longitudinal and favors disease development; stubble; spores are splashed or if leaf spot potential is high. transverse spots within the continuous cropping. wind-borne from crop residue to spot producing a net effect; healthy leaves. yellowing. Scald Large oval-shaped, grayish tan Disease develops during cool, Pathogen survives on crop Plant resistant varieties; manage Rhynchosporium secalis lesions surrounded by a dark wet weather; continuous residue; spores are splashed or residue where feasible. Barley, Rye brown border. cropping. wind-borne from crop residue to healthy leaves. 15

17 Speckled Blotch Circular to elongate light yellow Cool, wet weather favors Fungus overwinters on stubble Plant resistant varieties; manage Stagonospora avenae - Oats to gray lesions surrounded by infection; continuous cropping. and straw left in field; in spring, residue where feasible. a dull brown border on leaves; spores are blown to green plants. severe stem infections can cause lodging; centers of spots contain small black bodies (pycnidia). Spot Blotch Small dark, oval-shaped spots Moderate, wet weather in spring Conidia produced on crop Apply a systemic foliar fungicide Cochliobolus sativus on leaves later developing a favors infection; continuous residue are blown to leaves; if leaf spot potential is high; plant Barley, Wheat light tan center. cropping; contaminated seed; conidia can also spread from certified seed. infected brome grass adjacent pasture and roadside grasses to to small grains. small grains. Tan Spot (Yellow Leaf Spot) Disease first appears on leaves Cool, wet weather favors disease Pathogen overwinters in wheat Manage stubble where feasible; Pyrenophora tritici-repentis as small, dark, oval lesions with development; continuous stubble as small, raised, black apply a systemic foliar fungicide Wheat, Barley, Rye light centers; later develops into cropping. perithecia; new infections from if tan spot potential is high. large tan blotches with yellow wind-borne ascospores; border; leaves die from tip secondary spread by wind-blown toward base. conidia. Powdery Mildew White fluffy mildew pustules Moderate, humid, overcast Wind-borne conidia; new Plant resistant varieties; apply a Erysiphe (Blumeria) on leaves, stems and heads. weather; high nitrogen infections occur every 7-10 days. systemic foliar fungicide to graminis tritici - Wheat fertilization and high seeding susceptible varieties grown under E. graminis hordei - Barley rates that create a dense canopy. intense management; usually not E. graminis avenae - Oats a serious disease in dryland E. graminis secalis - Rye wheat. Bacterial (Halo) Blight Spots with dead centers Cool, wet weather favors Bacteria overwinter in seed and Plant resistant varieties; plant Pseudomonas syringae surrounded by pale yellow disease; continuous cropping on infected crop residue; crop certified seed; manage stubble coronafaciens - Oats green halo-like margins. that maintains oat residue on residue is main source of where feasible. soil surface. infection in spring. Bacterial Stripe Blight Elongate, water-soaked stripes Cool, wet weather favors Bacteria survive in infected Manage stubble if feasible; plant Pseudomonas syringae pv. or blotches with narrow yellow disease development; residue; bacterial cells are resistant varieties if available. striafaciens - Barley, Oats margins; white, scaly bacterial continuous cropping. splashed or blown onto leaves. exudate forms on stripes. Black Chaff (Bacterial Stripe, Translucent water-soaked Warm, wet and humid weather; Contaminated seed and rain a Bacterial Leaf Streak) streaks and spots on leaves; sprinkler irrigation favors splashed water containing Xanthomonas campestris pv. streaks become covered with bacteria; plant to plant and translucens - Wheat, Barley, droplets of yellow exudate; Oats, Rye darkening of glumes and a and green unaffected tissue. with alternating dark lesions barber pole effect on awns spreads bacteria. animal to plant contact infection; contaminated seed. serious disease in Nebraska. Plant certified seed; usually not 16

18 Cephalosporium Stripe During heading plants show Wet, acid soils and fluctuating Pathogen is soil-borne, Grow winter wheat in a 2- to Cephalosporium gramineum longitudinal chlorotic stripes winter temperatures favor associated with crop residue 3-year rotation with spring Wheat, Barley, Rye on leaves; stripes later become infection; freezing and thawing and enters plant through cereals, row crops or forages; tan to brown; stripes continue of soil; continuous wheat with wounds in roots. plant tolerant varieties where down culm on leaf sheath; minimum tillage or irrigation. available; delay fall planting. plants are yellowed and stunted. Symptoms first appear on 50 o F soil temperatures during Pathogen is seed-borne in seed Grow resistant varieties; plant second or third leaf and on seed germination; high coat and pericarp; wind-borne certified seed; treat seed with a most leaves produced there- humidity during flowering; conidia from infected leaves systemic fungicide; usually not a after as yellow to tan stripes contaminated seed. enter head during flowering. leaf; stunted plants. extending the length of the parallel to the midrib often serious disease in Nebraska. Barley Leaf Stripe Pyrenophora graminea Barley Take-all Stunted plants become evident Wet spring weather, poor soil Fungus directly associated with Rotate crop with legumes; Gaeumannomyces graminis during heading in more or less conditions and use of nitrate crop residue in the soil; infected maintain balanced soil fertility; Wheat, Barley circular patches in fields; plants fertilizers favor disease grasses may also contribute delay planting; destroy wheat take on a bleached dead straw development; planting wheat fungal inoculum. residue and control of volunteer color and heads are empty; into an area previously planted wheat in continuous wheat; some black streaks form on lower to perennial grasses. systemic seed treatments are stem and crown. effective. Common Root Rot, Seedling Yellowing of leaves; roots and Drought stress increase Fungi survive in the soil and Treat seed with fungicide; plant Blight, Dryland Foot Rot, crown rot; crowns are tan to susceptibility to infection; on plant debris. certified seed; follow date- Crown Rot brown in color; plant dies or dry falls and open winters favor of-planting recommendation; Cochliobolus sativus becomes stunted; poor tillering; crown and root rot development; plant into a firm mellow seedbed; Fusarium spp. partial loss of stand during loose seedbeds contribute to plant adapted varieties. Wheat, Barley, Oats, Rye winter. plant stress; cold injury to crowns; continuous wheat. Eyespot (Strawbreaker) Eye-shaped, honey-brown Continuous cropping into Rain splashes spores from Manage stubble; rotate crop; Pseudocercosporella lesions at base of stem; gray standing stubble; high nitrogen stubble to the base of the stems balance fertility; rarely occurs in herpotrichoides fungal structures in center of fertility; prolonged humid, cool of growing wheat. Nebraska. Wheat, Barley lesion. weather; mild winters. Sharp Eyespot Pale cream oval lesions with a Early planting and continuous Rain splashes spores from Manage stubble; rotate crop; Rhizoctonia cerealis darker brown margin. May wheat; cool, wet conditions stubble to the base of the stems delay planting; rarely damaging Wheat, Barley, Oats, Rye cause lodging and whiteheads. favor infection. of growing wheat. in Nebraska. 17

19 Wheat Streak Mosaic Light green to yellow mosaic Hail at medium dough stage Destroy volunteer wheat that Wheat Streak Mosaic Virus streaks on leaves; plants resulting in volunteer wheat; results from a hail storm at the (WSMV) stunted and rosetted; field symptoms appear when medium dough stage; follow Wheat, Barley, Oats, Rye appears yellowed; symptoms temperatures remain above 75 o F date-of-planting recommendation; evident in late spring and for several days; early planting early summer. and failure to control volunteer stubble fields after harvest. wheat and grassy weeds in stubblefields. practice good weed control in oats, green foxtail are potential sources. mite; volunteer wheat, corn, Transmitted by the wheat curl High Plains Yellow areas in fields in spring Hail at medium dough resulting Transmitted by the wheat curl Destroy volunteer wheat that High Plains Virus and early summer; leaves with in volunteer wheat. Warm falls mite; volunteer wheat serves as results from a hail storm at Wheat, Barley, Oats mosaic of yellow spots and and wet summers; presence of the summer green host bridge medium-dough; avoid early streaks; infected plants may die volunteer wheat and grassy between wheat crops. planting; control weeds in prematurely, particularly when weeds; early planting. stubble fields after harvest. present with wheat streak mosaic. Wheat Yellow Mosaic Symptoms appear in early spring Cool, wet spring weather Transmitted by a soil-borne Avoid early planting; grow (Wheat Spindle Streak Mosaic) as a distinct light-green to enhances symptom expression; fungus that invades wheat roots resistant varieties. Wheat Spindle Streak yellow, spindle-shaped dashes continuous cropping. in fall. Mosaic Virus and short streaks on younger Wheat leaves; stunted plants; yellowing. Soil-borne Wheat Mosaic Light to yellow irregular Symptoms evident during Transmitted by a soil-borne Plant resistant varieties; avoid Soil-borne Wheat Mosaic Virus blotches on the leaves; extended cool temperatures fungus that invades wheat early planting. (SBWMV) symptoms most evident in low (below 60 o F) in spring. roots in fall. Wheat, Barley, Rye areas in field; plants stunted and infected area takes on a yellowed appearance. Barley Yellow Dwarf Symptoms highly variable; leaf Early planting and volunteer Several aphid species transmit Plant at proper time; control Barley Yellow Dwarf Viruses tip turns a bright yellow often wheat; moderate weather that the virus; some grasses serve volunteer wheat and grassy weeds (RPV, MAV, PAV, SGV, RMV) accompanied by a red to purple favors aphid multiplication and as alternate hosts. in the stubble following harvest; Wheat, Barley, Oats, Rye color; midrib remains green. migration; high populations of resistant varieties; seed treatment Patches of yellow plants at aphids in the fall. with an insecticide that kills heading. aphids. Blast Sterility at heading in the form Nonparasitic disease associated Avoid late planting of spring oats. Physiological of white empty hulls on lower with extremes in temperature, Oats half of head. rain, soil fertility, and light from tillering to flowering. Bends Necks and stems are bent or Unknown; possibly frost, cold, Physiological crinkled; weakened stems. hail, herbicides, insects. Wheat 18

20 Color Banding Banded seedlings have distinct High or low temperature stress; Physiological yellow white transverse bands rapid drying of water-soaked or Barley, Oats, Rye, Wheat on coleoptiles and leaves. frosted leaves; deep planting depth. Frost and Winter Injury Partial loss of stand during Repeated freezing and thawing Environmental winter; kinking at the joints; during winter; freezing Barley, Oats, Rye, Wheat trapped heads; sterility. temperatures most damaging when they coincide with tiller elongation, heading or flowering. Hail Damage Random kinking and severing of Damage varies with growth Environmental plant parts; trapped heads; spike stage. Barley, Oats, Rye, Wheat bruising; shattering of kernels. Herbicide (2,4-D) Injury Missing florets; branched Application of 2,4-D during Proper timing of herbicide Chemical spikes; shortened heads; jointing after the developing application. Barley, Oats, Rye, Wheat head trapping. head begins moving up the stem. Melanism (Brown Necrosis) Brown-black streaks or Usually a response to Physiological blotches on glumes. nonspecific stress; varies with Wheat different varieties. Physiological Leaf Spot Small chlorotic to tan spots Mineral imbalances or Physiological on leaves. environmental stress. Barley, Oats, Rye, Wheat Sorghum Diseases Conditions Favoring Pathogen Survival and Fusarium Stalk Rot Plants may die prematurely and Damage most severe during Fungus survives in soil and on Maintain balanced soil fertility; Fusarium thapsinum lodge; pith disintegrates in area cool wet weather following hot, crop residue. use recommended plant Fusarium spp. where stalk has broken and is dry periods. populations; sorghum grown in an red in color. ecofallow cropping system develops less stalk rot. Fusarium Head Blight Heads are dull and grain is Extended periods of wet Fungus survives in soil and No plant resistance. Sorghum Fusarium spp. light weight; reddish-brown weather prior to pollenation on crop residue. grown in an ecofallow cropping streaks may occur on rachis favor disease development. system may get less head blight. branches; panicle may lack rachis branches on one side. 19

21 Charcoal Rot Premature ripening followed by Favored by low soil moisture Fungus survives as hyphae and Plant adapted varieties; maintain Macrophomina phaseolina lodging; pith is dark, shredded and high temperatures. tiny black sclerotia in soil and balanced soil fertility; use and filled with black specks in crop residue. recommended plant populations. (sclerotia). Bacterial Leaf Diseases Bacterial stripe appears as tan Excessive moisture and warm Bacteria spread by wind, Rotate crops and cultivate to Stripe: to brick-red to dark purple temperatures. splashing rain, insects, hail, reduce crop residue if applicable. Burkholderia andropogonis stripes generally on tips of blowing dust, etc. (Pseudomonas andropogonis) lower leaves. Bacterial streak Streak: occurs as light yellow to red Xanthomonas holcicola streaks on leaves, surrounded by narrow dark margins; some streaks may form large oval spots with tan centers and red margins. Bacterial Spot Lesions have a dark red margin Disease develops after a hard The bacteria survives in Rotate crops. Pseudomonas syringae with a tan necrotic center. These rain with moderate-to-high infested crop residue and is symptoms are easily confused winds and is favored by low disseminated by rain. with other diseases and temperatures and high humidity. chemical injury. Sooty Stripe Disease first appears on older Warm, humid weather. Fungus survives from season to Cultivate to reduce crop residue. Ramulispora sorghi leaves as small purplish-tan season on crop residue; spores spots that enlarge rapidly and are spread by wind and are surrounded by a broad splashing rain. yellow margin; leaves often turn yellow and die. Zonate Leaf Spot Symptoms vary with hybrid High rainfall and moderate The fungus survives as Rotate crop and control tillage to Gloeocercospora sorghi genetics; dark red-to-black temperatures favor disease sclerotia in crop debris or free reduce residue-borne inoculum. concentric zones of development. in soil; spores are rain splashed Hybrids vary in susceptibility. discoloration occur on leaves; onto plant. lesions may encircle the leaf sheath, killing the leaf. Rust Early lesion color depends on Warm temperatures and Fungus survives on several Host plant resistance. Puccinia purpurea plant type. Mature lesions are intermittent dew periods favor alternate and perennial hosts. dark red to brown and occur on disease development. Spores are blown great distances upper and lower leaf surfaces. by wind. Elongated lesions on peduncle. 20

22 Head Smut Entire head transformed into Cool, dry soils. Smut spores survive in soil; Resistant varieties. Sphacelotheca reiliana black powdery mass of spores infection occurs from soil-borne or portion of head sterile or spores. leafy; smut first becomes evident at heading. Maize Dwarf Mosaic A mottled or striped pattern of Weather that is conducive to Virus is aphid transmitted. Grow cultivars resistant to Maize Dwarf Mosaic Virus light and dark green on younger high aphid populations; cool common strains of the virus in (MDMV) leaves; mottling replaced by a nights favor symptom your area; control grassy weeds. red leaf symptom on some expression. sorghums. Soybean Diseases Conditions Favoring Pathogen Survival and Seedling Blights Seed decays before or after Environmental conditions Fungi survive in soil and on Plant clean undamaged seed into a Pythium spp. emergence; seedlings wilt and favoring root rot range from crop residue and attack properly prepared seedbed; use Fusarium spp. die; roots and lower portion of cold, wet soils in spring for seedlings when environmental fungicide seed treatment in fields Rhizoctonia solani stems rot; rot confined to outer Pythium spp. to warm drier soils conditions favor infection. with history of problem or when root surface. in summer for Rhizoctonia field is planted early in cool soils. and Fusarium. Phytophthora Root Rot Seed decays before or after Disease occurs mostly in low, Fungus survives from season to Plant race-specific resistant Phytophthora sojae seedling emergence; seedlings poorly drained areas but also season in the soil and on crop varieties; improve field drainage; wilt and die with discolored can occur on higher ground residue as oospores; 45 races of tillage in non-mandated stem pith; plants become during wet weather; heavy, clay the pathogen have been conservation tillage regions; use yellowed, wilt and show a dark soils; compaction; favored by identified. metalaxyl or mefenoxam seed discoloration of the lower stem; continuous soybeans; develops treatment. roots of older plants rot. most rapidly at soil temperatures above 75º F. Pod and Stem Blight Symptoms on plants nearing Wet, warm weather at mid-pod Fungus survives on pods and Plant disease-free seed; treat seed; Diaporthe phaseolorum maturity are numerous, small stage or later. stems left in field and is also apply foliar fungicides between var. sojae black dots on lower stems, seed-borne; spread by wind and mid-flowering and late-pod stage. petioles, and pods; speck-sized rain-splashed spores. fruiting structures usually arranged linearly. Stem Canker Symptoms present from mid-july Moderate temperatures with Fungus survives in soil, on Plant high quality disease-free Diaporthe phaseolorum to maturity as light brown extended wet weather early in crop residue and is seed-borne; seed; rotate crops; avoid var. caulivora sunken areas usually near a the season; conservation tillage; spread by wind-blown spores conservation tillage in fields with lower leaf node; dead plants favored by continuous and infected seed. a history of stem canker. with dried attached leaves. soybeans. 21

23 Brown Spot Angular dark brown to red Warm, moist weather favors Fungus survives on crop Rotate with nonsusceptible crop; Septoria glycines spots mostly on lower leaves; disease development; most residue and in infected seed; use disease-free seed; cultivate to infected leaves become yellow severe with continuous spread by wind and splashing reduce crop residue. and drop prematurely. soybeans. rain. Small, shallow, elongated, Warm, wet weather favors Fungus is carried on seed and Plant disease-free seed or treat reddish brown lesions or large infection and disease overwinters in crop residue; infected seed; rotate crops; avoid dark lesions on stems; stems of development; typically occurs spores are wind-borne (5 h of mature plants covered with late in season; more severe in drying reduces spore black acervuli; premature narrow rows with irrigation. germination by 98%). reduce germ. defoliation; seed infection can severe. mandated areas if disease is conservation tillage in nonmature Colletotrichum truncatum Anthracnose severe. mandated areas if disease is through main and lateral roots. in the soil; infection occurs Fungus survives on crop residue Charcoal Rot Leaves of infected plants yellow, Seedling disease greatest at Carried over as sclerotia in dry Rotate crops; avoid high plant Macrophomina phaseolina wilt and remain attached; red- high temperatures; continuous soil and residue; infects through populations to reduce moisture brown discoloration of taproot soybeans favor disease; hot, roots; fungus can infect at the stress; keep soil moisture high vascular tissue extending up the dry weather favors disease seedling stage and remain latent with irrigation in late growth stem; small black bodies development on older plants, until plant is stressed. stages. (sclerotia), beneath the stem which is why this disease is also epidermis giving it a gray-black known as dry-weather wilt. color. Sclerotinia Stem Rot During pod development leaves History of Sclerotinia stem rot The fungus overwinters as Plant tolerant varieties; use row Sclerotinia sclerotiorum wilt and turn gray-green before in the field; cool, wet conditions sclerotia in debris or soil; spacing of 15 inches or wider; do turning brown and drying; white during flowering favors sclerotia germinate to form not hold seed from infected fields fungal growth on stems and disease development. apothecia which release airborne for planting. pods; diseased stems are spores; can be moved with seed. bleached; sclerotia on and inside stem. Sudden Death Syndrome (SDS) Interveinal necrosis; spots High yield environments favor The fungus overwinters in the Plant resistant varieties; avoid Fusarium solani f. sp. glycines coalesce to form brown streaks SDS, especially during cool, soil as chlamydospores and early planting; use ridge-till; between the leaf veins with wet weather; more severe in mycelium in plant residue; reduce compaction. yellow margins; leaf drop with saturated soils; soil compaction spread by anything that moves petiole (leaf stem) remaining; and high fertility levels soil. deteriorated tap-roots and associated with increased SDS. lateral roots; root cortex is light-gray to brown and may extend up stem. 22

24 Soybean Cyst Nematode (SCN) Heavily colonized plants may Optimum development at soil Nematodes survive in soil as Plant resistant varieties; rotate Heterodera glycines be stunted and chlorotic; root temperatures between 75 o and eggs within cysts formed by crops; sample soil in fields with system reduced with poor 82 o F; reproduction of female bodies; spread by yield drag to test for SCN; avoid nodulation; yellow to brown H. glycines is greater in coarse- anything that moves soil. moving soil from infested to cysts visible on roots textured soils than in fine- non-infested fields. (pin-head size). textured soils. Bacterial Blight Small angular water-soaked Cool, wet weather favors Bacteria survive in crop residue Plant disease-free seed; rotate Pseudomonas savastanoi spots on leaves, later turning disease; hot dry conditions and in seed; spread by crops; do not cultivate when pv. glycinea brown; spots surrounded by halt disease development. splashing water, leaf contact foliage is wet. yellow borders; centers of old and cultivating wet fields. lesions fall out giving shot-hole appearance. Bacterial Pustule Small, pale green spots with Warm weather with wet Bacteria survive in crop residue, Plant resistant varieties; plant Xanthomonas axonopodis raised centers; raised pustule conditions favors disease; seed, and wheat roots; spread disease-free seed; rotate crops; do pv. glycines is typically on lower leaf unlike bacterial blight, high by splashing water, leaf contact, not cultivate when foliage is wet. surface; may be spots or temperatures do not slow and cultivating wet fields. irregular brown areas without disease development. water soaking. Bean Pod Mottle Green to yellow mottling of Symptoms appear during cool Virus is transmitted by bean leaf Plant virus-free seed; control bean Bean Pod Mottle Virus (BPMV) younger leaves; leaf mottling weather and rapid growth, may beetles; seed transmitted at leaf beetles; cultural practices may disappear as leaves mature; be masked at high temperature. 0.1% level; host range limited such as planting late and trap stunted plants; misshapen pods to legumes. crops are not yet scientifically with mottling; green stem at evaluated. harvest; seed coat discoloration same color as hilum; small seed. Plants infected before flowering, Disease occurs over a wide Virus transmitted by Eliminate other hosts (alfalfa, apical bud and shoot turn range of environmental grasshoppers, immature thrips, sweet clover, red clover, pigweed, brown, curve downward, and conditions; producing soybeans and dagger nematodes; also become dry and brittle and do in fields with high numbers of seed transmitted at varying not produce seed; plants dagger nematodes may increase levels depending on when dwarfed. Infection at flowering problem as they are a known produces small undeveloped or vector. at harvest. maturity leads to green stem aborted pods; infection after producing plant. infection takes place in seed soybeans; plant virus-free seed. areas along with volunteer ragweed, sunflower) from nearby Tobacco Ringspot Virus (TRSV) Bud Blight 23

25 Soybean Mosaic Light and dark green mosaic Symptoms most pronounced Virus transmitted by aphids Plant seed from virus-free fields; Soybean Mosaic Virus (SMV) pattern on leaves; leaf has during cool weather and and also seed-borne less than plant resistant varieties; avoid late crinkled appearance; leaf disappear during hot weather; 5% in most varieties; planting; practice effective weed margins curl downward; plants planting bin run seed from overwinters in some perennial control. stunted; seed coat discoloration infected fields. weed species. same color as hilum; small seed. Phomopsis Seed Decay Infected seed shriveled, More prevalent in lower pods; Fungus survives in crop debris Use resistant varieties; crop Phomopsis longicolla elongated, and cracked; seed virus infection, insect damage, and soil; moved with seed. rotation; harvest promptly at appears white and chalky; and delayed harvest with wet maturity; control virus and insect poor germination if planted. conditions. problems. Purple Seed Stain Pale to dark purple discoloration Infection occurs during warm, Treat seed to improve Carried on seed; spores produced Cercospora kikuchii of seed coat; reduced seedling humid weather; pod infection germination; avoid holding seed on infected cotyledons and during pod emergence. requires 8 hours of dew. from infected fields. seed set. Sugarbeet Diseases Conditions Favoring Pathogen Survival and Rhizoctonia Root and Early symptoms are permanent Disease occurs throughout the Fungus survives in soil and Rotate crop; control weeds; Crown Rot wilting and blackening of growing season during warm roots of certain weeds. certain varieties are resistant. Rhizoctonia solani petioles followed by extensive weather. rotting of crown and root tissue. Powdery Mildew Light gray mold growth Warm, dry weather favors Wind spreads fungal spores. Sulfur sprays or dusts if symptoms Erysiphe polygoni covering leaf surface; leaves disease development. appear before September 1. yellow, become dry and collapse. Cercospora Leaf Spot Small, brown to gray spots Warm temperatures combined Fungus survives on crop Plant resistant varieties; rotate Cercospora beticola with purple borders appear on with high humidity or dew residue; spores spread by wind crop; cultivate to reduce crop leaves and leaf stems; spots favors disease. and rain splashing. residue; use foliar fungicide on merge, leaves turn yellow then susceptible varieties. brown and finally collapse. Fusarium Yellows Leaves curl upward, become Disease occurs throughout the Pathogen survives in the soil; Lengthy crop rotation; apply Fusarium oxysporum f. sp. betae yellow, mottled, necrotic and growing season independent infects through the root. adequate nitrogen fertilizer. die in upright position; fleshy of weather. root develops discolored vascular rings; plants die through season. 24

26 Aphanomyces Root Rot Seedling phase exhibits thin Warm weather and water- Rotate crop; limit irrigation; treat (Black root) black hypocotyls that may saturated soils favor disease. seed with fungicide for seedling Aphanomyces cochlioides extend to cotyledon; late of taproot. black lesions on basal part wilting of leaves; brown to infection show yellowing and phase. plant debris. Fungus survives in soil and in Rhizomania Yellowed, erect leaf posture; Warm weather and water- Virus survives in and is Resistant varieties; irrigation Beet necrotic yellow root stunting with lateral roots saturated soils favor disease. transmitted by the soil-borne management; soil fumigation. vein virus (BNYVV) proliferation resulting in a fungal vector, Polymyxa betae. bearded appearance. Curly Top Leaves dwarfed, crinkled and Climate influences disease by Virus has extensive host range Plant resistant varieties; control Beet curly top virus (BCTV) cupped inward and upward; affecting weed hosts and and survives in natural vector; reduce vector breeding veins on underside of leaves movement of leafhopper vector. vegetation in western U.S. areas and viral host sources. roughened with spine-like outgrowths. Sugarbeet Nematode Distinct areas in field with Nematode survives in soil as Use nematicides in combination Heterodera schachtii stunted or dead plants, small, cysts and on weed hosts; with crop rotation; use field pinhead-sized, white cysts spread by irrigation water and attached to feeder roots; above contaminated soil on machinery. wilted leaf petioles. yellow plants with sprawling, ground symptoms are small weeds. sanitation measures; control temperatures of o F. Nematode most active at soil Root-Knot Nematode Symptoms become evident in Nematode survives in the soil Nematode survives in the soil Use nematicides in combination Meloidogyne spp. mid-season; foliage yellows and and on weed hosts. and on weed hosts; spread by with crop rotation, weed control, wilts on warm days; galls form irrigation water and by use field sanitation. on taproot and lateral roots. contaminated soil on machinery. Nebraska Root Gall Nematode Beets in heavily infected fields Nematode most active when Nematode survives in soil, crop Use nematicides in combination Nacobbus bataiformis stunted and wilt prematurely; soil temperatures are o F. residue and on certain weed with crop rotation; weed control; numerous galls on lateral roots; hosts; spread by irrigation field sanitation measures; early galls on small rootlets cause water and soil contaminated planting. hairy or whiskery appearance. equipment. 25

27 Sunflower Diseases Conditions Favoring Pathogen Survival and Downy Mildew Dwarfing and chlorosis start as Systemic root infection occurs Fungus overwinters in soil and Extended rotations; eradication of Plasmopora halstedii yellowish areas near midribs and early in poorly drained clay can infect roots soon after volunteers; avoid poorly drained expand outward; conditions of soils; high humidity and water emergence; secondary spread soil; plant when soil temperatures high humidity causes white splashing spreads to occurs via wind or rain favor rapid seedling growth. growth on underside of leaves. neighboring plants. splashing. Phoma Black Stem Large black lesion on lower Moist conditions during and Fungus overwinters; in infected Crop rotation reduces pathogen Phoma macdonaldii stem (several inches in length); after flowering. debris and is spread by insects populations; some hybrids have leaves wilt, dry and stalks or splashing rain. tolerance; insect control limits become dark brown to black spread. with small black spots (fruiting structures); when stems are girdled, premature ripening occurs. Phomopsis Stem Canker Lesions on stems larger than Moist conditions during and Fungus overwinters in infected Long rotations. Phomopsis helianthi those of Phoma (up to 6 inches); after flowering. debris and is spread by insects also lighter in color (tan to or splashing rain. brown) than Phoma; stems become soft and crush easily with thumb pressure. Charcoal Rot General wilting with stalks High temperatures and low Fungus survives as sclerotia in Avoid water stress; use planting Macrophomina phaseolina becoming grayish at base; pith soil moisture. soil or plant debris; can also dates and hybrids that avoid decays and vascular bundles survive in other crops host flowering and seed fill in hottest are covered with small black range of 200+ plant species. part of season. structures called sclerotia. Alternaria Leaf Spot, stem Infects all plant parts; produces Warm, humid conditions and Both species are seedborne Crop rotation and practices that lesion and head rot, dark brown, oval, necrotic extended periods of leaf and survive in stem residue. stimulate residue decomposition. Alternaria helianthic spots; spots can eventually wetness; plants more Alternaria zinniae cover large areas of tissue; susceptible at flowering and defoliation and lodging during seed-fill. frequently occur. Red Rust Appears first as yellow spots High moisture conditions with Spores are windblown from Disease resistant hybrids; crop Puccinia helianthi on upper leaf surfaces; temperatures below 90 o F. alternate reservoirs such as sanitation; avoid late planting; brownish-cinnamon colored volunteers and wild sunflowers. avoid high nitrogen rates and high spots form on underside of plant populations. leaves that eventually turn black; severely affected leaves wither and die. 26

28 White Rust Raised, yellowish-green spots High rainfall and temperatures Extended rotation; weed Fungus overwinters as oospores Albugo tragopogonis on upper leaf surface; on lower below 90 o F. management. in residue, soil or on infected surface a creamy-white weeds in milder climates. pustule forms below yellowish lesion. Symptoms include wilting, High moisture and cool Fungus survives in soil as Long rotations of non-host crops; stalk rot, and head rot; stalk temperatures favor apothecia sclerotia; they can germinate control weeds; avoid excessive and head rot result in snowy and ascospore formation. and infect roots; the fungus white fungal growth with sclerotia forming during humid weather; wilting and bleaching of stalks and heads are common. that colonize plant tissues. release windblown ascospores structures (apothecia) that also produces mushroom nitrogen. White Mold Sclerotinia sclerotiorum Rhizopus Head Rot Back of head becomes brown High humidity and wet weather. Disease development correlates Avoid wounds; control head moth Rhizopus arrihizus and soft; thread-like strands are with sunflower head moth at or near flowering. Rhizopus stolonifer visible with small dark spore- infestation or mechanical filled structures called sporangia damage from hail or bird in rotted head during wet feeding. weather. 27

29 University of Nebraska Lincoln Extension educational programs abide with the nondiscrimination policies of the University of Nebraska Lincoln and the United States Department of Agriculture. Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska Lincoln cooperating with the Counties and the United States Department of Agriculture. Common Bacterial Blight on Dry Beans Zonate Leaf Spot and Rust on Sorghum Wheat Streak Mosaic Virus on Wheat Phytophthora Root Rot on Soybean Seedling Scab on Potato Fusarium Root Rot on Dry Beans Common Smut on Corn