Disease Management in Organic Vegetables Sally Miller Department of Plant Pathology 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 Tri-State Organic IP Video Program Session III April 19, 2007 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 Good Quality Compost Increases soil suppressiveness to diseases Induces disease resistance ( healthier plants ) Improves soil tilth Improves soil moistureholding capacity High Tunnel Tomato Treatment No compost Compost P value % Plants with Sclerotinia 26.9 a 5.8 b 0.0033 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 1
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 2
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/ta blelist.htm Best performers - NCSU trials 2006 (slicing cucumbers)** Variety NC-Stratford- NCSU Dasher II Talladega Thunder Speedway DM rating* Powdery mildew? *Rating: 0=none; 1-2=trace; 3-4=slight; =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/hygfact/3000/pdf/3086.pdf Water Bath Temperatures and Treatment Times Seed Brussels sprouts, eggplant, spinach, cabbage, tomato Broccoli, cauliflower, cucumber*, carrot, collard, kale, kohlrabi, rutabaga, turnip Mustard, cress, radish Pepper Lettuce, celery, celeriac F 122 122 122 125 118 Minutes 25 20 15 30 30 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/hygfact/3000/pdf/3086.pdf * Cucurbit seeds may be damaged by hot water treatment 3
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 Prevention of Rhizoctonia damping-off 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 4
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 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 Bacterial Wilt 5
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/fedor ganlinks.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 Soilborne Diseases http://attra.ncat.org/attrapub/soilborne.html Compost Production and Use (MSU) http://www.hrt.msu.edu/course/hrt491/com post/combinedcompost.pdf Composting at Home (OSU) http://ohioline.osu.edu/com-fact/0001.html http://www.oardc.ohio-state.edu/millerlab 6