Problem Pests of Potatoes

Problem Pests of Potatoes Problem Pests Workshop 2017 Late Blight vs Early Blight Common skin diseases Common Scab / Rhizoctonia Tuber Flea Beetles Colorado Potato Beetles Outline Late Blight Disease / Life cycle Symptoms Conditions Favouring Disease / Insect Development Phytophthora infestans Affects all aboveground plant parts, plus infects tubers Requires living tissues to overwinter Serious disease of Solanaceous plants Primary Hosts Potatoes Tomatoes Secondary Hosts Eggplant, peppers, petunia Solanaceous weeds (nightshade, wild tomato) Needs 2 mating types Needs free water for germination Late Blight Strains Preferred Host Metalaxyl Resistance Mating Type Environment US8 Potato Resistant A2 Wet / Cool In Season US11 Potato Resistant A1 Wet / Cool US22 Tomato Susceptible A2 Moist / Warm A2 mating type not in AB US23 Tomato/Potato Susceptible A1 Dry / Hot US24 Potato Intermediate A1 Moist / Warm CA15 Potato Susceptible A2? US 23 (A1) in AB this last season Table by Dr. Larry Kawchuk, AAFC 1

Dark, water soaked lesions SYMPTOMS Lesions are not contained by leaf veins Photo by K. Al Mughrabi Lesions may have a yellow edge Lesions are not contained by leaf veins Lesions become brown & brittle within a couple of days Photo by K. Al Mughrabi Lesions move in from leaf tip or margin LB on tomato Lesions move in from leaf tip or margin LB on tomato 2

Sporulation may occur under moist conditions on older lesions Photo by K. Al Mughrabi Photo by K. Al Mughrabi Sporulation may occur under moist conditions on older lesions Photos by R. Howard Photo by K. Al Mughrabi Sporulation may occur under moist conditions on older lesions Plants may be rapidly defoliated & die Lesions may also develop on stems, tomato fruit or potato tubers Rot penetrates deeply Disease develops rapidly in field Rot may have a reddishbrown colour Disease may spread to healthy tubers in storage 3

Photos by R. Howard Late blight tuber rot LB on tomato fruit Photo by K. Al Mughrabi LB on tomato fruit Note sporulation on surface Conditions Favouring Disease Development Moderate temperatures & wet/humid conditions 16 21 C day / 10 16 C night Extended periods of leaf wetness favour spore germination & lesion development Dew Irrigation Photo by K. Al Mughrabi Conditions Favouring Disease Development cont d Disease transfers from infected living tissues Tubers (seed potatoes, cull piles) Volunteer potatoes or weeds Transplants (tomatoes) A little bit of late blight Infected seed tubers = significant risk point 1% infection level in seed = 100 150 tubers/acre 5% infection level = 550 725 tubers/acre 1 plant can infect 10 foot diameter of surrounding plants 4

Conditions Favouring Disease Development cont d Spores are spread through: Wind (many miles 50+) storm fronts Rain/water splash in field Soil in water films / on equipment (short time) Detection / Monitoring Spore trapping Visual / Digital images not very accurate Quick immunostrip tests Phytophthora specific Lab diagnosis accurate Phytophthora Immunostrip Test Kits Late blight Surveillance Quick test kits followed by detailed lab tests Spore traps Plant resistant tomato varieties (if also growing spuds) Mountain Magic, Defiant PHR, Mountain Merit, and Iron Lady Control volunteers and Solanaceous weeds Adjust plant density to reduce humidity Water using drip or flooding to reduce wetting foliage Prevent overwintering on living tissues Avoid introduction of infected materials Manage cull piles Use clean seed potatoes Use care when bringing in transplants from other regions where late blight may exist 5

Dispose of infected material as soon as detected Bury / freeze infected tissues Tarp compost piles Top kill to reduce tuber infection & continued spread Cull potato tubers heavily before storage Apply PROTECTIVE applications of fungicides Mancozeb based seed treatments Contact sprays on a preventative basis to fields, as required Alternating chemistry for resistance management If disease found, kill the hot spot and an area around it (minimum = 2x size of infected area) Desiccant or physical removal Follow with a trans laminar or kick back product alternately with the contact spray to manage the rest of the field Frequency depends on environmental conditions and the amount of inoculum present LATE BLIGHT IS A COMMUNITY DISEASE Early Blight EARLY BLIGHT Alternaria solani Very common disease Hosts Potato Tomato Pepper Eggplant Solanaceous weeds 6

Tuber lesions Concentric Rings Limited by veins Yellow border Photos by R. Howard Conditions Favouring Disease Development Persists on crop residues, in the soil, on infected tubers and on other hosts Spores are spread by contact of leaves with soil or through wind or water splash Cool, moist or dewforming nights favor spore formation Disease development greatest at 20 C More prevalent on older leaves and vines and on stressed plants Wounded tubers can become infected Dispose of infected vines Maintain good soil fertility Maintain a 2 3 year crop rotation Ensure tubers are fully mature when harvested Don t harvest when soil is wet Avoid mechanical injury during harvest Application of registered chemical fungicides can slow disease development and protect plant tissues RHIZOCTONIA 7

Rhizoctonia solani Hosts Wide range of host crops Potatoes Cruciferous vegetables Other Rhizoctonia Causes a range of diseases Damping off Wirestem (cruciferous veggies) Black Scurf (potatoes) Crater Rot (cruciferous root crops) Bottom Rot (cabbage) Rhizoctonia canker (potatoes) Potatoes may fail to emerge Aerial tubers may be visible on infected stems Reddish brown & sunken root / stem / stolon cankers Cankers can kill sprouts & girdle stems Black Scurf The dirt that doesn t wash off Superficial dark brown to black, irregularly shaped sclerotia on tuber surfaces Sclerotia DO NOT penetrate the tuber Disease Cycle / Conditions Favouring Disease Development Overwinters as sclerotia on tubers and in the soil Sclerotia germinate and mycelium infect tissues No spores are produced Cold and wet soils Short rotations Does not develop/spread in storage Ensure minimum 3 year rotations Rotate with grasses and cereals Plant clean seed tubers Seed treatments can control seed borne inoculum, but will not protect shoots from soil borne inoculum Top killing and early harvesting can reduce scurf development on tubers 8

Stem/stolon cankers Plant into soil and in conditions which favour rapid emergence and good plant growth Avoid cool soils Warm seed Seed shallow and hill after emergence Delay irrigation until after sprouts emerge Avoid overwatering COMMON SCAB Common Scab Streptomyces scabies Fungus like bacterium Soil borne disease Hosts Potatoes Various root vegetables Carrots, beets, parsnips, rutabagas, turnips, radishes Disease Cycle Persists in the soil for 8 10 years Typically infects tubers during the 1 st 5 weeks of tuber development Via the lenticels Colonizes several layers of cells Does not spread or increase in storage Lesions vary in form Shallow and superficial Underground stems & stolons may also be affected Photo by inspection.gc.ca Round, irregular, brown lesions on the tuber surface Typically less than 1cm across Initially form around lenticels Deep & pitted Photo by inspection.gc.ca Raised & erupting Almost impossible to distinguish from Powdery Scab 9

Raised, corky lesions Pitted scab Various other looks for scab (caused by the same organism) Netted scab Conditions Favouring Disease Development Severity of Symptoms: Strain of pathogen Potato cultivar Soil organic matter Crop rotation Environmental conditions Moisture availability Photos by inspection.gc.ca Conditions Favouring Disease Development Warm, dry conditions at or after tuber formation can increase incidence Reduces levels of antagonistic bacteria Soil ph can influence scab formation Prefers soil ph of 5.5 7.5 Use less susceptible cultivars There is a wide range of scab resistance between varieties Generally russet types = more resistant than smooth skinned types See Handouts for Variety Resistance Tables Minimum 4 year crop rotation between host crops Maintain adequate & uniform levels of moisture, especially around tuber development Alter soil ph Difficult to accomplish, as soil buffers and pathogen and host both reduced at lower or higher ph levels Avoid introducing pathogen Use clean seed Avoid applying manure from animals fed scabby produce Seed treatments can provide some control of tuber borne scab Does not provide protection for daughter tubers 10

Tuber Flea Beetle TUBER FLEA BEETLE Epitrix tuberis ** Epitrix cucumeris (potato flea beetle) Epitrix subcrinata Hosts Potatoes Solanaceous plants (weeds, crops) Adults: Small, black beetles Up to 2mm long Jump when disturbed Larvae: Slim, white Up to 5mm long Feed on roots and tubers Burrow under skin of tubers Agriculture Canada, Ottawa, Bugwood.org Agriculture Canada, Ottawa, Bugwood.org Whitney Cranshaw, Colorado State University, Bugwood.org Characteristic shothole damage caused by flea beetle adult feeding Whitney Cranshaw, Colorado State University, Bugwood.org Agriculture Canada, Ottawa, Bugwood.org 11

Life cycle Adults overwinter in the soil in and around fields Adults may fly into new fields 1st generation emerges in mid May to early June to feed and mate on foliage Once soils start to warm up Eggs are laid on soil surface 1st generation larvae emerge (~10days) and feed on tubers through mid July Larvae pupate in the soil Typically single generation per year Life cycle Adults are typically found on the undersides of leaves They jump when disturbed Damage Adult feeding causes shothole symptoms on leaves Feeding by larvae result in cosmetic damage Reduced marketability and down grading Storability may be affected Damage is most common in mid to late harvested crops Damage may become more obvious as crops age in storage Monitoring Populations tend to be highest closer to field margins Scout from crop emergence to 30cm plant height Examine individual sample plants for beetles or use sweep net for larger plants (later season) Thresholds are: 1 beetle/60 plants (early) 1 beetle/10 sweeps Regular crop rotations Keep crops separated from each other Ensure fields are free from volunteer potatoes and Solanaceous weeds Removal of plant residues (in small scale situations) can reduce overwintering Early crops tend to have less damage Apply chemical controls to try and reduce adult populations prior to egg laying Apply early in the season Control of larvae is not possible 12

Colorado Potato Beetle COLORADO POTATO BEETLE Leptinotarsa decemlineata Hosts Solanaceous crops (potato, tomato, eggplant) Solanaceous weeds (nightshades, wild tomato) Cabbage pepper Pigweed, thistle, lamb s quarters One of most important pests of potato in Canada Single generation per season Colorado Potato Beetle - adult Photo by B. Elliott Photo by B. Elliott Colorado Potato Beetle 3 rd instar larva Monitoring Begin monitoring early in season when plants begin to sprout look for larvae and adults Inspect 10 feet (3m) of row in minimum 10 locations, regardless of field size Record the number of plants in each section with at least 1 larval colony (determine total for 10 sites) Potatoes are most sensitive to feeding damage around peak flowering Chemical treatment at 10% defoliation (potatoes can tolerate up to 20 25%) Ensure rotation between chemistry to avoid development of resistance Crop rotation can reduce populations 13

QUESTIONS??? Rob Spencer, BSA, MSc, P.Ag. Commercial Horticulture Specialist robert.spencer@gov.ab.ca Alberta Ag Info Centre 310 FARM 14