JANUARY PLANT PROBLEM REPORT FROM THE AUBURN PLANT DIAGNOSTIC LAB JANUARY PLANT PROBLEM REPORT FROM THE BIRMINGHAM PLANT DIAGNOSTIC LAB

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1 EXTENSION PLANT PATHOLOGY, EXTENSION HALL, AUBURN UNIVERSITY, AL February 11, 2002 PP-521 JANUARY PLANT PROBLEM REPORT FROM THE AUBURN PLANT DIAGNOSTIC LAB JANUARY PLANT PROBLEM REPORT FROM THE BIRMINGHAM PLANT DIAGNOSTIC LAB DISEASE POSSIBILITIES FOR FEBRUARY Jackie Mullen Extension Plant Pathology Specialist Jim Jacobi Extension Plant Pathology Specialist Auburn Plant Disease Report-January (J. Mullen) January started out seasonably cold, but warmed up to spring like conditions by the end of the month. Some azaleas and Japanese magnolias in Auburn had begun to show flowers opening! Our thirty plant samples in January came from landscapes and greenhouses. Phytophthora cinnamomi root rot is a fairly well-known root disease of azaleas, rhododendrons, and related plants. Roots become brown, soft, and have a wet decay. The fungus is active at soil temperatures that range usually from 16 C-32 C. It usually causes problems during the warmer months of June, July, and August, but it will form resistant spores that will survive temperatures lower and higher than the C range of normal growth and activity. It is not common for this disease to be active in January. The plant was sent from a Mobile area landscape, and it is possible that root disease may have been actively developing in January, but it is more likely that this disease had been most active last summer and fall. Obvious foliage symptoms may not have developed until roots were seriously damaged in late fall-early January. Foliage showed the lower leaf yellowing and browning along with dieback that is typical of root damage in woody ornamentals. Control of Phytophthora cinnamomi in landscapes involves removal of damaged plants; improved soil drainage and/or reduced irrigation, if appropriate. 1

2 There are several azalea cultivars that show some resistance to Phytophthora. See ANR-571 for a listing of these cultivars. If planting a Phytophthora-susceptible cultivar is planned, some soil replacement in the area may be helpful. Protective fungicide drench treatments are not usually recommended in landscape areas. These protective products are recommended in nurseries and sometimes in large landscape azalea plantings. See ANR-571 for more comments on control of this disease in nursery settings. Downy mildew is a commonly seen problem in the early spring on a variety of vegetables. Crucifers in greenhouses and gardens are often bothered by this disease when conditions are cool and wet. Leaf infections usually begin as pale yellow or pale white irregular spots of varying size and shape. A thin gray mold may be seen on the lower surfaces of leaf spots when conditions are humid and wet. Use of a hand lens in the >field= will greatly enhance the ability to see this mold. As spots age, they typically become dark gray or black. The downy mildew leaf spots we saw were dark gray-black. Moist chamber incubations produced the diagnostic gray mold with spores of Peronospora parasitica. Plants we examined also showed some irregular bleached areas or blotches on leaves and stems. These spots were not typical of disease, and we suspect that some type of spray burn may have occurred. Downy mildew problems in a greenhouse or garden can usually be controlled well by a regular spray schedule with a protective fungicide. See the AL Pest Management Handbook for a listing of these products. Pansy diseases this past month included landscape problems with Colletotrichum leaf spot and Pythium crown rot. Also, cold damage was noted on some plantings in Montgomery. Colletotrichum leaf spot is usually seen in spring and fall, but some periods of January were springlike. Leaf spots are typically white, round, and about 2-4mm diameter. Sometimes the tiny black fruiting bodies of the fungus can be seen scattered over the leaf spot surface. This disease is usually controlled by sanitation and sometimes protective fungicide applications are recommended. See the AL Handbook or ANR Pythium root rot is a common problem at wet locations. The lower stem becomes light brown in color; tissue is soft and rotted and pulls apart easily, leaving the plant foliage neatly separated from the root ball! This disease is very similar to Phytophthora crown rot. Root rots may also develop. See ANR-1214 or the AL Handbook for protective fungicide drench treatments which are typically used only in greenhouse situations or very large landscape plantings. Damaged plants should be removed and water in the area should be reduced if appropriate. If pansies are to be replanted and the area will continue to be wet from time to time, soil replacement or fungicide treatment may be needed. The cold damage appeared as large bleached areas at stem tips, leaf edges, and on large areas of leaves and stems. Newest growth appeared to be normal. Primula bacterial soft rot appeared as a brown, wet rot at the lowest stem areas of the plants. The symptoms could be confused with Pythium or Phytophthora crown rot. Microscopic study showed the presence of abundant quantities of bacteria, and culture work showed that fungal agents were not active. Usually soft rot bacterial decay follows after a wounding or other injury or weakness of the plant tissue. We are not sure what might have brought about this problem. There is no pesticide treatment typically recommended for control of bacterial soft rot. Complete 2

3 removal of damaged plants was recommended. As insects may cause injuries, plants should be watched for indication of insect presence. Brown patch (caused by Rhizoctonia solani) and take-all patch (caused by Gaeuammnomyces graminis var. graminis) disease spread and development on St. Augustine grass are not typical occurrences in January, but warm weather of this past January in locations of mid or southern state sections could have provided conditions favorable for fungal activity. See ANR-493 and ANR-823 for details and control of these diseases. Phytophthora cactorum on strawberry is the >other= Phytophthora crown/root rot disease of strawberry. P. fragariae causes a disease of strawberry called red stele root rot, and it is this reddiscoloration crown/root rot disease that is usually seen in Alabama. The Phytophthora cactorum present in the strawberry sample we received showed a very mild crown discoloration on the surface of the crown. Some foliage dieback and leaf edge scorch and discoloration was also present. Culture work on the crowns produced P. cactorum. Wet conditions and warm temperatures favor disease development. Short daylengths (less than 13 hours) also are reported to favor disease activity. Control usually involves removal of diseased plants, management (reduction) of water conditions, and applications of protective fungicide treatments. See the Alabama Handbook, or Ed Sikora. Table 1. January 2002 Plant Diseases Seen In The Plant Diagnostic Lab at Auburn. Plant Disease County Azalea Phytophthora cinnamomi Root Rot Mobile Broccoli Downy Mildew (Peronospora parasitica) * Indian Hawthorn Colletotrichum Leaf Spot Montgomery Pansy Colletotrichum Leaf Spot Montgomery Pythium Crown Rot Madison Primula Bacterial Soft Rot * St. Augustine Brown Patch (Rhizoctonia) Coffee Take-All Patch (Gaeumannomyces graminis graminis) Coffee, Montgomery 3

4 Plant Disease County Strawberry Phytophthora cactorum Crown & Baldwin Root Rot *Counties are not reported for greenhouse and samples. Birmingham Plant Disease Report-January (J. Jacobi) We received 50 samples for the month. Most of the samples were received in the last 10 days of the month as above normal temperatures prevailed. Botrytis blight was seen on several greenhouse-grown plants. Botrytis can attack all above ground parts of a plant at all stages of growth, but damage is most common on the more succulent tissues during cool, moist conditions. Symptoms on diseased tissues range from small, distinct, light-colored, water-soaked spots to extensive blighting and decay of blooms, leaves, and shoots of a wide range of plants (annuals, perennials, and woody ornamentals). This disease is an especially common problem in greenhouses. Botrytis produces masses of gray spores clusters on diseased plant tissue and can often be seen with the aid of a hand lens. Management of Botrytis in the greenhouse depends upon good sanitation and reduction of relative humidity. Routine fungicide sprays used against Botrytis have fostered the development of fungicide-resistant Botrytis strains, so check with your county extension agent for the latest recommendations when selecting a fungicide. Extension publication, ANR-753, ( provides additional information on the identification and control of Botrytis blight. Conditions were also favorable for Pythium blight on ryegrass. This disease is often seen during periods of favorable weather (extended periods of moist conditions with temperatures F) from fall through spring. Symptoms include small, distinct, circular to irregular, grayish-green, watersoaked spots, usually several inches in diameter. These spots often appear greasy or slimy, and may enlarge to 1-foot in diameter on highercut turfgrass. ANR-594 ( 594/anr-594.html) provides information on how to make an accurate diagnosis and manage this disease problem. Table January Problems Seen in the Birmingham Plant Diagnostic Lab. Plant Problem County Azalea Cercospora Leaf Spot Poor Drainage Shelby Jefferson Basil Botrytis Cutting Rot * Rhizoctonia Stem Rot * 4

5 Plant Problem County Boxwood Phytophthora Root Rot Jefferson Poor Drainage Jefferson Camellia Tea Scale, Undetermined Virus Jefferson Cherrylaurel, Carolina Cercospora Leaf Spot Jefferson(2) Southern Red Mite Coleus Botrytis Blight * Pythium Root Rot Cryptomeria, Japanese Phyllosticta Needle Blight Jefferson Forget-Me-Not Flea Beetle * Geranium, Zonal High EC, Pythium Root Rot * Low ph * Holly x >Emily Brunner= Tea Scale Jefferson Holly, Japanese >Helleri= Black Root Rot (Thielaviopsis) Jefferson JuniperPoor Drainage, Mites Jefferson Lavender Botrytis Blight * Pansy Pythium Root and Crown Rot Etowah Ryegrass, perennial Pythium Blight Jefferson, Shelby Thyme Rhizoctonia Stem Rot * *Counties are not reported for samples from commercial greenhouse and nursery operations. 5

6 Disease Possibilities For February Powdery mildews and Botrytis may be a problem in greenhouses where temperatures are on the moderate to cool side. Also downy mildew (yellow spotting, sometimes defoliation) on rose and bedding plants and vegetable transplants may develop when temperatures are moderately cool (60-70 F). Powdery mildew disease spread requires a high relative humidity. Botrytis and downy mildew require high relative humidity and free moisture for disease spread. If temperatures are F, some leaf spots on grasses may develop. The list below includes some common disease problems received in the lab in February of the past few years. Comments on control practices are brief. Refer to appropriate fact sheets, or timely information sheets for details of disease control. Table 1. Disease Descriptions and Brief Control Comments on Some Common Diseases Often Seen in February. Plant Disease Description Control Aglaonema Rhizoctonia Crown Rot Brown dry decay of lower stem. Sanitation; Cleary's 3336 protective treatments. Alfalfa Spring Black Stem and Leaf Spot (Phoma) Numerous black spots on lower leaves, petioles, and stems. Leaf spots often coalesce and become medium or light brown. Spotted leaves become yellow and fall. Lesions may completely girdle stems and petioles and cause death to the foliage beyond. Phoma may also cause a crown and root rot. -- Arbor-vitae Cold Damage, Pestalotiopsis Tip Blight Tips of damaged (brown) twigs develop tiny black bodies just barely visible (about 3-amm diameter). Azalea Cercospora Leaf Spot Brown, roughly circular leaf spots, diameter. Sanitation; See the Ala. 6

7 Begonia Botrytis Blight Brown, water-soaked or dry tissue blight. See the Ala. Bentgrass Brown Patch (Rhizoctonia) Patchy areas become brown. Individual leaves show brown spots, larger blotches, or complete leaf blight. See ANR-492 or the AL Pythium Root Rot Roots become brown and water-soaked and then dry. Pythium Blight Quickly spreading, brown blight (wetlooking) of grass blades. See the Ala. Pest Manage-ment See Ala. Pest Management Bermuda Helminthosporium Spots Brown elliptical or elongated rectangular, usually small (but spot coalescence often occurs) leaf spots. Sometimes decay occurs at the stem near the soil line and then whole plants die rapidly. Often, spots remain localized on the leaves. See ANR-621. Rhizoctonia Blight Patchy areas become brown. Individual leaves show brown spots, larger blotches, or a complete leaf blight. See ANR-492 or the AL Slime Mold Thin, translucent, rumpled sheets of gelatin-like material. Physical removal. 7

8 Boxwood Macrophoma Blight Brown or reddish leaves (often begins at branch tips and moves to older foliage.) develop black specks that are fruiting bodies of fungus. Many of these bodies cover discolored leaf surfaces. Phytophthora Crown & Root Rot Broccoli Downy Mildew (Peronospora) Camellia Algal Leaf Spot (Cephaleuros) Anthracnose (Colletotrichum) Botrytis (Sclerotinia) Flower Blight Lower trunk is brown and rotted. Initially the decayed tissues are water-soaked but later the dead tissues are dried. Faded, yellow blotches on upper leaf surfaces show gray, powdery masses of fungal growth on lower leaf surfaces in areas corresponding to yellow spots. Green or reddish colored, slightly raised, circular spots. See the AL Pest Management Light to medium brown, circularirregular (0.2-1 cm diam.) spots develop on leaves. Brown, small-large, irregularly-shaped lesions. See AL Maintain vigorous plants. Improve soil drainage and/or decrease irrigation. See Alabama Pest Management Handbook for fungicides recommended for nursery situations & some large scale landscape plantings. Reduce humidity; raise temperatures; see Ala. Sanitation; Protective fungicides labelled on camellia such as Cleary's Sanitation of fallen blossoms; see Ala. Pest Management 8

9 Ring Spot Virus Carolina Cherry Laurel Cherry Leaf Spot (Blumeriella jaapii, formerly Coccomyces hiemalis) Yellow rings appear on foliage; plants may become slightly stunted. Brown-purple leaf spots with most of leaf spot centers falling out leaving the typical shot hole symptom. Collard Black Rot (Xanthomonas) Yellow, V-shaped lesions on leaf edges become darkened. Bacteria spread into the vascular system and cause leaf veins to darken. Eventually, tissue death and decay spreads into the central vascular system with the lower center stalk becoming rotted. Crop rotation away from crucifers for 2 years. Daylily Kabatiella Leaf Spot Red brown elongated spots (approx. c-3 inch diam.). Dusty Miller Alternaria Leaf Spot Dark brown angular spots ( cm) on foliage. Cleary's 3336 may help. English, Ivy Anthracnose (Colletotrichum) Circular or irregular, dry, brown spots or blotches on leaves. Leaf spots often begin at leaf edges. Brown stem lesions may also develop. See the AL Pest Management Handbook or ANR Euonymus Anthracnose (Colletotrichum) Large (3-2 inch diam.; cm) brown, circular spots. Fescue Pythium Foliage Blight Dark, water-soaked spots and blotches. See Ala. See Ala. 9

10 Scab (Elsinoe) Brown, raised, slightly corky spots ( cm) develop on foliage. Sanitation; Cleary's 3336 may help. Geranium Oedema Small ( cm diam.), raised corky spots scattered on lower leaf surfaces. Upper leaf surfaces corresponding to corky spots often show yellowed spots. Reduce watering schedules when weather is cloudy and cool. Gerbera Daisy Powdery Mildew Leaves show some necrosis and white powdery dusting on leaf surfaces. Sanitation; Cleary's Pythium Root Rot Plants become stunted and yellowed. Usually lower leaves become yellowed first. Roots become brown and water- soaked. Sanitation of damaged plants. In some situations, removal of contaminated soil or media is recommended. Protective fungicide drenches in greenhouse situations. Greenhouse/Nursery Crops Peat Mold (Chromelosporium) Tan-orange-yellow spore masses often develop on the surface of potting mix or at the edge of potting mix next to the pot rim. Extensive fungal growth may cause the potting media to become water repellent; that is, the media will not absorb water. Holly, Foster Bacterial Leaf Spot Small, black, angular leaf spots. 10

11 Holly, Japanese Phomopsis Dieback Cankers on twigs and small branches with dieback resulting. Hydrangea Powdery Mildew White dusty coating on upper leaf surfaces. Leaf yellowing and blight; some new growth distortions. Fungicide spray treatments. See AL Phytophthora Pythium Root Rot & Roots brown and water-soaked initially, then dried. Sanitation; improve soil drainage and/or reduce irrigation; Banrot or Banol are recommended in some nursery situations. Impatiens Impatiens Necrotic Spot Virus Black, circular leaf spots; stunted growth. Sanitation; control. thrips Phytophthora Crown Rot Plants become stunted. Older leaves turn yellow. Roots become brown and watersoaked. Sanitation of plants and sometimes removal of contaminated soil or media. Adjust watering practices and/or improve water drainage through soil or media. Fungicide drenches are often recommended in greenhouse situations. Pythium Crown Rot See Phytophthora comments. See Phytophthora comments. Impatiens, Guinea New Botrytis Stem Rot Dark, water-soaked leaf blight & stem rot. Sanitation; See Ala. Impatiens Spot Virus Necrotic New growth is stunted; circular black, greasy spots develop. Remove damaged plants; control thrips. 11

12 Indian Hawthorn Cercospora Leaf Spot Circular, dark brown spots (approx. c inch diam.) Sanitation; Mancozeb fungicide. Entomosporium Leaf Spot Red-black spots. See the Ala. Suspect Bacterial Leaf Spot Red-black spots. angular Irish Potato Scab (Streptomyces scabies) Scurf (Rhizoctonia) Slightly raised, rough, corky, cortex-colored spots, lesions (smalllarge) on tubers. Black, irregular, hard slightly raised roughsurfaced scabs on tuber surface. Crop rotation. Keep soil ph at , if possible. Crop rotation. Terraclor. See E. Sikora. Ivy, English Anthracnose (Colletotrichum) Black irregularly shaped leaf spots. Sanitation; See AL Bacterial Leaf Spot (Xanthomonas) Brown-black, angular, wet-looking spots (c- 3 inch diam.; cm). Sanitation; See Ala. Ivy Leaf Geranium Oedema Upper leaf surface shows diffuse yellow spots; lower leaf surface shows brown, corky, slightly raised spots (less than c inch diam.; cm). Decrease schedule. watering Kalanchoe Botrytis Blight Brown, gray spots, blotches on the foliage. Infected areas may become limp. Spots look grayer when spore production occurs. Apply protective fungicide drenches. See the Ala. Decrease humidity. Increase temperature. 12

13 Lantana Foliar Leaf Spot Nematode Angular, brown-black leaf spots. Leyland Cypress Seiridium Canker Sunken, elongated cankers with oozing sap. Pruning. See comments in AL Lily, Easter Lily Symptomless Virus & Cucumber Mosaic Virus Yellow and brown flecks on foliage; plants stunted; leaves curl under. aphids. Control Magnolia Algal Leaf Spot (Cephaleuros) Greenish or reddish slightly raised spots (0.1-1 cm) on upper leaf surfaces. Spot edges are often irregular or wavy in appearance. Old spots are usually cream colored in the center. Control measures are usually not necessary. Bordeaux mixture may be used. See the Ala.. Marigold Botrytis Canker Dark brown, elongated cankers form on stems. See the Ala. Oats Helminthosporium Leaf Spot/Blotch On seedlings, oblong to elongate, lightreddish-brown spots appear on seedling leaves. Seedling leaves may also be twisted. On older leaves, spots start as small, brown flecks that develop into longitudinal flecks of dead tissue. Tissue outside of the leaf spot become brown, yellow or red. Sometimes these discolored areas around the spots spread to involve the major portion of the leaf blade. See the Small Grains Recommendations for seed treatment; rotate crops; plow under residue. 13

14 Crown Rust (Puccinia coronata) Orange-colored pustules form on leaves, mainly; severely infected plants will turn yellow and grow poorly. Contact A. Hagan. Pansy Botrytis After Cold Damage Brown leaf spots/ blight; gray mold. Sanitation; protective fungicide sprays. See AL Cercospora Leaf Spot Brown-black circular spots. Sanitation; Cleary's Phytophthora Crown/Root Rot See comments for Impatiens. Pythium Crown/Root Rot See comments for Impatiens. Peach Botryosphaeria Canker (Gummosis) Gummy, "bleeding" or oozing spots of sap develop on bark surfaces where sunken, darkened lesions occur in the wood. Lesions are often cracked around the edge. Sanitation; Benlate sprays on the trunk. Cytospora Canker Sunken lesions on branches and trunk. Prune off lesions making cuts 3-4 inches beyond margin of decay. Phomopsis Blight Twig Gray sunken cankers, dieback. Check with Ed Sikora. 14

15 Peas, Austin Sclerotinia Blight A dark wet-looking rot develops at lower stem area near soil. A white fungal mat may develop. Small (1/16 inch or less) black, hard, flat, irregularshape bodies may develop in the fungal mat. Infected plants wilt and die. Pentas Bacterial Leaf Spot Dark brown, angular leaf spots, 1/16-1/8 inch diam. Crop rotation. Photinia Entomosporium Leaf Spot Small reddish spots (3-2 inch diam.; cm) often coalesce into larger red spots with dark red centers and bright red, diffuse borders. Sanitation; See the Ala. Pine, Loblolly Needle Rust (Coleosporium) Cream-white pustules (c inch diam.; cm) on needles. No control recommended. Pine Loblolly Seedlings, Phytophthora Root Rot Plants become stunted. Older growth becomes yellowed. Roots become brown and water-soaked. Sanitation of infected plants and sometimes media/soil replacement is recommended. Correct water problems. Fungicide drenches are recommended in nursery situations. Pine, Virginia Lophodermium (Ploioderma) Needle Cast Small (1/32-1/16 inch diam.; 0.15 cm or less; just barely visible), black, football-shaped slightly raised fruiting bodies scattered on needles; needles brown and drop. See Ala. 15

16 Poa trivialis Pythium Blight Foliage blight. Decrease water content of soil. Apply fungicide treatments as listed in the Alabama Hand-book for turf grasses. Pothos Rhizoctonia Stem Rot Stems near or touching the soil (potting mix) developed a dark brown canker or lesion (0.3-1 cm). Rhododendron Botryosphaeria Dieback Branch tips dieback to canker areas that are usually sunken and cracked around edges. Rosemary Pythium Root Rot Roots become brown and soft rotted. Ryegrass Pythium Root Rot Grass turns yellow, withers and dies; roots show a wet, brown decay. Take-All Patch Individual plants become yellow and die. Roots develop dead areas and lesions. Affected plants are usually in patchy areas of landscape. Protective sprays of Cleary's Pruning and sanitation. See the Ala. Pest Management Handbook or ANR-594. Manage soil ph and nitrogen appropriately. Apply fungicide treatment when economically feasible. See ANR-823. St. Augustine Brown Patch (Rhizoctonia) Irregular areas become brown due to browning of individual grass blades. See the Ala. Pest Management Handbook or ANR-492. Take-All Patch See comments under Ryegrass. Snapdragon Root-Knot Nematode (Meloidogyne) Stunted, wilted plants; roots develop irregular galls. Sanitation; See AL 16

17 Spinach Pythium Root Rot Roots become light brown and soft rotted; foliage wilts and dieback occurs. Sanitation; Improve soil drainage and reduce irrigation if appropriate. Spirea Powdery Mildew Leaves show a white powdery dusting on upper leaf surfaces and young shoots Cleary's Strawberry Common Leaf Spot (Mycosphaerella) Red to red-black leaf spots. Sanitation; See AL Pythium Root Rot Roots brown and water-soaked. Tomato Bacterial Leaf Speck Very small (1/16 inch diam.) angular, dark brown spots often with a diffuse yellow halo. Turnip Cercospora Leaf Spot Small, off-white, irregular spots which may enlarge into 3-2 inch diam. ( cm). Verbena Bacterial Leaf Spot Angular, water-soaked black or dark green leaf spots. See E. Sikora. See Ala. See Ala. Myrothecium Crown Rot Foliar Nematode Plants collapse after decay at crown. Angular brown leaf spots; sometimes these symptoms can be confused with bacterial disease. Pythium Root Rot Roots brown and water-soaked when infections are new. Sanitation; improve water/soil situation so soil does not remain wet. 17

18 Wheat Bipolaris Leaf Spot Brown elongated lesions (typically c-3 inch long) on foliage. -- Powdery (Erysiphe) Mildew A white to light brown (buff) dusting or slightly raised powdery patches on foliage. Affected leaf areas eventually turn yellow and die. Infection of the flag leaf will severely affect plant development and yield. See the Ala. Pest Management Handbook and/or A. Hagan. Soilborne Mosaic (SBWMV) Wheat Virus Green-yellow mosaic pattern (short, narrow stripes) on leaves; stunting; reduced tillering; possible plant death. Crop rotation. 18