Disease Management in Organic Vegetables

Sally Miller

Department of Plant Pathology

April 19, 2007Tri-State Organic IP VideoProgram Session III

Organic Disease Management Importance of diseases varies among crops,

locations “Diseases are the Achilles heel of organic tomato

production” Diver, Kuepper & Born 1995

Management requires an integrated [systems] approach

Choose the Best Site Well-drained fields

Water molds Pythium, Phytophthora Good air movement

Promote rapid plant drying Physical separation from other crops

Potatoes: late blight Peppers: bacterial leaf spot Conventionally produced crops

Improve Soil Quality Reduce diseases by soilborne pathogens Enhance composition of “beneficial”

organisms Increase the abundance and diversity of the soil

microbial community

Increase soil organic matter Cover crops/Green manures Composts/Animal manures

Effects of Compost on Plant Health

Treatment % Plants with Sclerotinia

No compost

26.9 a

Compost 5.8 b

P value 0.0033

High Tunnel Tomato

Increases soil suppressiveness to diseases

Induces disease resistance (“healthier plants”)

Improves soil tilth

Improves soil moisture-holding capacity

Good Quality Compost C:N ratio 30:1 at the beginning

Finished compost C:N ratio = ~10:1-14:1 90-120 days Temperature 131-170F, 3 days in a static

aerated pile or 15 days in a windrow Temperature> 15F above ambient indicates

unstable compost Turn to assure entire pile reaches 131-170F

Maximizing Disease Suppression Compost

Cure 4 or more months Incorporate into soil several months before

planting Inoculate with beneficial microorganisms, e.g.

Trichoderma Application

5-10 tons (dry weight)/A - rule of thumb Apply every year until significant organic matter

improvement observed; watch for increases in P

Rotate Crops Break the life cycles of pathogens

> 3 yrs between crops in the same family Some pathogens cause disease among

multiple plant families

Include appropriate rotational crops to increase soil organic matter

Exclude Pathogens Destroy vines, etc. post-season

Removes sources of inoculum Sterilize plant stakes between crops Clean tools, equipment frequently Prohibit tobacco use

Make Life Difficult for Pathogens Mulches

Plastic or plant-based Reduce splash dispersal of pathogens Protect fruit from soilborne pathogens

Row orientation Maximize air movement Minimize leaf wetness periods

Irrigation management

Variety Selection Use resistant or tolerant varieties

wherever possible

Angular Leaf Spot - Cucumber Favored by cool, wet

weather

Affects foliage and fruit

Seedborne

Some cultivars advertised as resistant

Cultivar Foliar AUDPC

Fruit incidence

(%) Classy R 408.4 dy 0.2 d Slice More - 563.4 cd 1.0 bcd Talladega - 571.6 dc 6.7 a 2409 - 600.9 bcd 2.9 a Thunder - 733.7 a-d 7.2 a Thunderbird R 799.8 a-d 3.7 ab Stonewall T 902.0 abc 4.7 a Sassy R 907.0 abc 0.7 cd Green Slam - 926.9 abc 0.3 cd Indy R 985.4 ab 4.6 a Intimidator R 1074.1 a 7.5 a Speedway R 1129.3 a 4.5 a

Mildews of Cucurbits Downy mildew

New strains appeared in 2004 More aggressive on resistant varieties

Powdery mildew Always appears in the Midwest in mid-

summer Defoliates and predisposes plants to

other diseases

Disease resistance tables: http://vegetablemdonline.ppath.cornell.edu/Tables/TableList.htm

Best performers - NCSU trials 2006 (slicing cucumbers)**

Variety DM rating* Powdery mildew

NC-Stratford- NCSU 5-6 ?

Dasher II 5-6 √

Talladega 5-6 √

Thunder 5-6 √

Speedway 5-6 √*Rating: 0=none; 1-2=trace; 3-4=slight; 5-6=moderate; 7-8=advanced; 9=dead plant

**http://cuke.hort.ncsu.edu/cucurbit/cuke/cukemain.html

Use “Clean” Seeds

Sanitizing seed treatment may be needed: hot water treatment

Fact sheet: http://ohioline.osu.edu/hyg-fact/3000/pdf/3086.pdf

Water Bath Temperatures and Treatment Times

Seed F Minutes

Brussels sprouts, eggplant, spinach, cabbage, tomato

122 25

Broccoli, cauliflower, cucumber*, carrot, collard, kale, kohlrabi, rutabaga, turnip

122 20

Mustard, cress, radish 122 15

Pepper 125 30

Lettuce, celery, celeriac 118 30

* Cucurbit seeds may be damaged by hot water treatment

Seed Treatment Cautions Use new, high quality seed Treat a small sample first and test for

germination Treat close to time of planting (within

weeks) Treat only once Fact sheet: http://ohioline.osu.edu/hyg-

fact/3000/pdf/3086.pdf

Producing Healthy Transplants

Practice good sanitation in the greenhouse Use new or sanitized plug trays or flats and

pathogen-free mixes Sanitize equipment Install solid flooring; raise seedling trays Limit movement of personnel and equipment

between greenhouses Clean benches, greenhouse structure thoroughly

after the crop; close up greenhouse

Prevent Damping-off

Don’t overwater Incorporate 10%

stable compost into planting mix Significantly reduces

damping-off Drench or

incorporate biocontrol products

Prevention of Pythium damping-off

% damping-off Treatment

Pre-emergence

Post-emergence

Untreated control w/o Pythium 6.3 j 0.0 d Composted cow manure 39.6 h 0.5 cd Omega Grow 47.9 g 0.5 cd Trichoderma hamatum 382 56.8 ef 1.1 bcd Prestop 64.1 de 3.2 abc Phosphonate 66.7 cd 2.1 a-d Serenade ASO 1.0% 66.7 cd 4.2 a Serenade ASO 2.0% 69.8 bcd 1.6 a-d Untreated control + Pythium 70.3 bcd 0.5 cd Omega Grow Plus 72.9 abc 0.5 cd Serenade ASO 0.5% 74.5 abc 3.7 ab Seacide 75.5 ab 0.5 cd Mycostop 77.1 ab 2.6 a-d

Prevention of Rhizoctonia damping-off

% Damping-off Treatment Pre-

emergence Post-

emergence Untreated control w/o R. solani 1.6 k 0.0 b Composted cow manure 4.7 jk 0.0 b Trichoderma hamatum 382 9.4 ijk 1.1 ab Omega Grow Plus 16.7 hi 1.1 ab Serenade ASO 0.5% 30.2 def 1.6 ab Untreated control w/ R. solani 33.3 cde 2.6 ab Serenade ASO 1.0% 56.8 b 2.1 ab Serenade ASO 2.0& 74.0 a 0.5 ab

Preventing Other Diseases

Do not raise exotic or experimental vegetable varieties, or plants from saved seed, in the same greenhouse with commercial seedlings unless all seeds are treated

Avoid raising or holding ornamental plants and vegetables in the same greenhouse

Exclude insects (may carry viruses)

Maintain conditions in the greenhouse that do not favor disease development

Maintain relative humidity as low as possible Good air circulation Proper temperatures

Handle plants as little as possible

Field Options: Pre-plant Biofumigation

Mustards, broccoli residue Muscodor Broad-spectrum activity

Biocontrols Contans

Narrow-spectrum (Sclerotinia only)

Post-Planting Options

Bringing out the Band-Aids

Biological products Chemical products Plant extracts/oils Compost teas

Treatment % Foliar

disease Control- water to run off 66.0 ab

Humega 75.9 a Timor 67.6 ab StorOx 61.4 ab Biodynamic 508- Equisetum arvense 59.0 ab Kaligreen 47.9 abc Sonata + Champion WP 45.6 abc Serenade 44.3 abc Timorex 44.1 abc Trilogy 39.5 bcd Garlic Barrier 39.4 bcd SW-3 37.1 bcd Sonata 37.0 bcd StorOx alternated with Champion WP 25.0 cde Serenade + Champion WP 21.4 cde Champion WP 10.8 de Bordeaux mixture 5.0 e

Disease Management Alternatives for Organic Tomatoes

Disease Management:Squash Winter squash ‘Taybelle’

Floating row covers + pyrethrum to protect plants from beetles

Foliar sprays Armicarb Milk Stylet oil Neem oil Serenade Compost tea Sulfur

Powdery Mildew Management

Treatmen t and rate % Powdery mildew

Serenade Max 1 lb/A + Kocide 2 lb/A 2.9 g Serenade Max 2 lb/A + Kocide 2 lb/A 2.2 g Sulfur 16 lb/A 5.0 g Whole milk 50% 5.9 g Mineral oil (stylet-oil) 3.5 qts/100 gals 11.8 ef Armicarb- 100 5.0 lb/A+ Biolink 1.5 qt/100 gal 11.6 f Armicarb-100 2.5 lb/A + Biolink 1.5 qt/100 gal 14.7 ef Soil soup compost tea 100% 17.0 e Neem oil 0.75 % 23.1 d Soil soup compost tea 33% 31.8 c Untreated control, protected 52.9 b Untreated control, non-protected 80.7 a

Bacterial Wilt

Bacterial wilt

Treatment and rate

% wilted

Armicarb- 100 5.0 lb/A+ Biolink 1.5 qts/100 gal 0.0 b**

Armicarb-100 2.5 lb/A + Biolink 1.5 qts/100 gal 3.3 b

Whole milk 50% 0.0 b

Mineral oil (Stylet-oil) 3.5 qts/100 gals 1.7 b Neem oil 0.75 % 0.0 b

Serenade Max 1 lb/A + Kocide 2 lb/A 0.0 b

Serenade Max 2 lb/A + Kocide 2 lb/A 0.0 b

Soil soup compost tea 33% 0.0 b

Soil soup compost tea 100% 0.0 b

Sulfur 16 lb/A 0.0 b

Untreated control, protected 0.0 b

Untreated control, non-protected 13.3 a

National Organic Standards/Related Subjects The National Organic Program

http://www.ams.usda.gov/nop/

USDA links to organic-related material http://www.ams.usda.gov/nop/nop2000/nop2/

fedorganlinks.htm

Organic Materials Review Institute http://www.omri.org/

Additional Information….. ATTRA (Appropriate Technology Transfer for

Rural Areas) http://www.attra.org

Organic Agriculture Consortium http://www.organicaginfo.org

NEON (Northeast Organic Network) http://www.neon.cornell.edu/

Anusuya Rangarajan Department of Horticulture121 Plant Science Building Cornell

University, Ithaca, NY 14853 Phone:(607) 255-1780

ATTRA Sustainable Management of Soil-borne Diseases http://attra.ncat.org/attra-pub/soilborne.html

Compost Production and Use (MSU) http://www.hrt.msu.edu/course/HRT491/Compost/CombinedCompost.pdf

Composting at Home (OSU) http://ohioline.osu.edu/com-fact/0001.html

http://www.oardc.ohio-state.edu/millerlab