Managing Diseases in the Greenhouse

1. Managing Diseases in the Greenhouse • Kenny Seebold • University of Kentucky • Plant Pathology Department

2. The Greenhouse: A Plant Disease “Factory” • Most GH vegetables are susceptible to one or more diseases • Humidity tends to be high in the greenhouse • Greenhouse temperatures tend to favor one or more pathogens • Contaminated material can be brought in from outside sources • Plants share virtually the same space – sometimes in tight quarters • Plants may share the same water (sometimes recirculated) • Pesticide options are limited • Plants are handled frequently • Two of three elements of the disease triangle are always present • Susceptible host • Favorable environment

3. Successful management of greenhouse diseases begins with prevention… • Host • Pathogen • Environment

4. Sanitation • Sound sanitary practices make a difference! • Goal is to eliminate carryover or introduction of disease-causing organisms • Before planting: • Remove all plant debris & weeds inside structure • Discard trash (inside AND outside) • Sanitize benches, work surfaces, and tools with 10% bleach or quaternary ammonia (Quattro, Greenshield) • If possible, maintain a 30-ft “weed-free” zone around greenhouse to eliminate refuges for pathogens and insects • Don’t allow field soil into the greenhouse • Don’t store trays & pots on bare soil • Grow on raised benches if possible • Clean shoes before entering structure • Install concrete or gravel walkways; cover soil under benches with gravel or landscape cloth • If field soil is to be used, sterilize by heating to 160-170F for at least 30 min

5. Sanitation • Keep greenhouse tidy during the growing season • Wash hands regularly and avoid using tobacco products in the greenhouse • Avoid handling plants if foliage is wet • End of season: • Remove all plant debris & weeds inside structure • Discard trash (inside AND outside) • Sanitize benches, work surfaces, and tools with 10% bleach or quaternary ammonia (Quattro, Greenshield) • Close greenhouse for several weeks to promote high temperatures – this will help kill off weeds & insects

6. Exclusion • Minimize the movement of pathogens into the greenhouse… • Sanitation helps address the issue of exclusion • Don’t grow ornamentals & vegetables in the same greenhouse • If this must be done, keep separated on different benches or parts of greenhouse • Control insects and weeds in and around greenhouse • Potential sources of plant pathogens • Don’t use water from ponds, creeks, and rivers • Source of Pythium and other pathogens • Pathogen-free planting material • Grow transplants from seed if possible • Buy seeds from reputable source • Don’t save seed OR treat to minimize threat from fungal, bacterial, and viral pathogens

7. Hot Water Treatment • Can be used with many vegetables (see ID-36) • Not safe for legumes or cucurbits other than cucumber • Will inactivate most pathogens except those that have become associated with the embryo • Temperature and soaking time depends on crop • Critical factors -> poor efficacy or crop damage can occur… • Invest in a quality thermometer • Must agitate water to maintain uniform temperature • Use weighted mesh bag to hold seed • Dip in cold water to cool quickly • Dry completely before storage / planting Images – S.A. Miller, Ohio State U.

8. Recommended Temperatures and Soaking Times for Hot-Water Disinfection of Selected Vegetable Seeds

9. Chemical Soaks • Bleach • Use 1 qt commercial-grade bleach to 3-4 qt of water • Add 1-2 drops of dish detergent to decrease surface tension • Use ~1 gallon of solution per lb. of seed -> soak time is 1 minute • Rinse thoroughly afterward; spread to dry • Trisodium phosphate (TSP) • Concentration of solution = 10% (1 part TSP, 9 parts water) • Use ~1 gallon of solution per lb. of seed -> soak time is 15 minutes • Rinse thoroughly afterward; spread to dry

10. Manipulating the Environment • Goal is to make the greenhouse environment less favorable to pathogens • Temperature: • Avoid temperature extremes • Minimizes stress & makes plants less susceptible to disease • Humidity: • Goal is to keep relative humidity below 90% • Minimize long periods of leaf wetness • Avoid tight plant spacing • Provide good ventilation & airflow (vents, side-curtains, fans) • In cool weather, flush humid air in the early morning & late afternoon (will help reduce dew formation & condensation)

11. Manipulating the Environment • Watering & irrigation are critical • Don’t over- or under-water • Excess moisture can promote root and foliage diseases • If watering overhead, do so early to allow for rapid drying of foliage • Apply gently to minimize splash • Avoid the use of “float” systems • Promotes disease • No chemicals labeled to control diseases of vegetables grown in these types of systems

12. Suppressing Pathogens • Sanitation, exclusion, & environmental control are important • Resistant varieties: • Along with cultural controls, can significantly reduce disease in the greenhouse • Resistance available varies by crop & pathogen • Solarization

13. Solarization • Soil covered with clear plastic mulch • Heated by sunlight • Max 45-52ºC at 4-6 in soil depth • Shown to suppress numerous soilborne diseases

14. Limitations of Solarization • Not practical in northerly climates (fewer “sunshine” days than in southern areas • Unproductive during summer • Disposal of plastic

15. Chemicals for Disease Control • As with other practices, don’t rely solely on chemicals to manage disease! • Timely applications are critical • Apply before symptoms appear OR at first signs • Maintain a regular schedule • Proper calibration & nozzles • Safety & protective clothing • Re-Entry Interval after spraying • Follow REI guidelines on product labels • Post warnings on entrance to greenhouse • Choices of active ingredient are limited…

16. Soil Treatments • Methyl bromide not longer available • Basamid G (9-13 oz/100 sq. ft) • Incorporated into soil • Allow time for fumigant to dissipate (> 4 weeks is ideal) • Oxidate / Terracide (hydrogen peroxide) • Results variable • Microbial amendments • Gliocladium (SoilGard) ; Trichoderma (T-22); Bacillus subtilis (Subtilex); Streptomyces (Mycostop) • Results may be variable • Composts • Results variable for control of damping-off

17. Pesticides that do not specifically prohibit greenhouse use can be used if labeled for the crop in question. Chlorothalonil: ExothermTermil No longer cleared for use in the greenhouse on vegetables Copper compounds*: bactericide / broad-spectrum fungicide (protectant) Kocide, Champ, Cuprofix, Nu-Cop Numerous crops labeled (not lettuce) Greenhouse Fungicides & Bactericides for Vegetables

18. EBDC’s (Mancozeb / maneb): broad-spectrum fungicide (protectant) Dithane DF / Maneb Numerous crops labeled Sulfur*: powdery mildew / miticide (protectant) Dusting sulfur (various brands) Wettable sulfur (various brands) Numerous crops labeled (not lettuce) Greenhouse Fungicides & Bactericides for Vegetables

19. Botran 75W (Control of Botrytis) Cucumbers, lettuce, tomatoes Decree: (Control of Botrytis) Fruiting vegetables (tomatoes, peppers), cucurbits, leafy greens Previcur Flex (Pythium, Phytophthora damping-off) Tomatoes, peppers, cucurbits, lettuce Drench or drip-applied Scala: (Control of Alternaria & Botrytis) Tomatoes Terramaster EC: (Control of Pythium) Tomatoes Greenhouse Fungicides & Bactericides for Vegetables

20. PCNB: (damping-off, root/stem rots caused by Rhizoctonia) Applied to media or soil Turfcide 10G / Terraclor 75W For cabbage, cauliflower, broccoli, Brussels sprouts, pepper, and tomato plants grown in containers Greenhouse Fungicides & Bactericides for Vegetables

21. Bacillus subtilis: broad-spectrum fungicide Serenade Max Approved for most greenhouse vegetables Peroxides (hydrogen): broad-spectrum fungicide bactericide Oxidate Approved for most greenhouse vegetables Low residual activity (frequent applications needed) Potassium bicarbonate: powdery mildew Kaligreen EcoMateArmicarb “O” Milstop Cleared for use on most greenhouse vegetables Low residual activity Fungicides for Greenhouse Use‘Soft’ Chemistries / Organic-approved

22. Diseases Caused by Fungi

23. Damping-offPythium spp., Phytophthora spp., Rhizoctoniasolani Tomato Photomicrograph: NCSU Plant Pathology Pepper

24. Damping-offDevelopment and Spread • Pathogens are soil- or water-borne • Spread in irrigation systems, splash, contaminated soil & media, soil on old trays & containers • Will affect most greenhouse crops • Favored by high soil moisture (saturation) • Sanitation is the key to control • Fungicides are available for certain crops

25. Powdery MildewOidium spp. Tomato Cucurbit

26. Botrytis Gray MoldBotrytis cinerea Stem canker ‘Ghost spots’ on fruit Tomato Fruit rot Leaf blight All images: Plant Management Network

27. Botrytis Gray MoldBotrytis cinerea Lettuce

28. Early BlightAlternariasolani

29. (Gray) Leaf MoldFulvafulva Tomato

30. Timber RotSclerotiniasclerotiorum Stem rot + sclerotia (black seed-like structures)

31. Foliar BlightsManagement • Use quality, pathogen-free seed • Employ good sanitation in the greenhouse • Ensure adequate ventilation / air circulation • Eradicate weeds and volunteers around greenhouse • Use adequate fertilizer to encourage vigorous, but not rank, growth • If irrigating overhead, allow for time to plants to dry • Apply fungicides if needed (see labels for timing)

32. Diseases Caused by Bacteria

33. Bacterial SpotXanthomonas campestrispv. vesicatoria Tomato Pepper

34. Bacterial CankerClavibactermichigensis subsp. michiganensis Foliar symptoms on greenhouse-grown transplants

35. Bacterial Canker Wilting Stem canker Pith necrosis Pith necrosis

36. Bacterial Spot & CankerDevelopment and Spread • Plants susceptible at all stages • Seed- and transplant-borne • Overwinters on plant debris, stakes, etc. • Easily spread by mechanical contact & water splash • Can be carried to the field – serious outbreaks can result

37. Management of Bacterial Spot & Canker • Prevention is the primary tool to manage bacterial diseases • Use pathogen-free seeds and transplants • Avoid saving seed from previous crops • Heirloom growers: hot-water or bleach soaks (ID-36) • Resistant varieties: pepper only • Sanitation & prevention of spread • Remove and destroy diseased plants • Keep heirlooms in an “isolated” spot • Clean benches, tools, stakes, etc. • Don’t handle plants if foliage is wet • If watering overhead, do so early; don’t over-water • Apply streptomycin on a 5-7 day interval • Fixed copper + mancozeb/maneb(1.5-3 lb/A): 5– 7 day intervals

38. Diseases Caused by Viruses

39. Tobacco MosaicTobacco mosaic virus (TMV) Fruit symptoms Typical mosaic symptoms on foliage • TMV is seedborne & survives well on surfaces & plant debris • Easily transmitted by mechanical means

40. TSWV & INSV INS Thrips - vector TSW Tomato spotted wilt virus & Impatiens necrotic spot virus (TSWV) vectored by thrips and can occur together in the greenhouse

41. Tomato Yellow Leaf CurlTomato Yellow Leaf Curl Virus (TSWV) Uncommon in KY, but has occurred in 2005 and 2008 Vectored by whiteflies

42. Viral DiseasesManagement • There are no chemical options • Tomato seed can be treated with trisodium phosphate to kill TMV • Cultural: • Use resistant varieties if available (TMV) • Don’t plant ornamentals and vegetables in close proximity • Avoid handling tobacco products; wash hands frequently • Clear weeds around fields and greenhouses • Control insect vectors in the greenhouse

43. Greenhouse Resources • County Extension Offices • ANR and Hort. Agents • Short Courses, demonstrations, Master Gardener programs • Publications • Video Tapes & DVDs • Soil Tests • Plant Disease Diagnostic Labs (Lex. & Princeton) • Disease, Insect, Weed ID and control • Web Resources • KY Pest News • http://www.uky.edu/Ag/kpn/kpnhome.htm • ID-36 (2006-2007 Veg. Production Guide for Commercial Growers) • http://www.ca.uky.edu/agc/pubs/id/id36/id36.htm • Plant Pathology Dept. • http://www.ca.uky.edu/agcollege/plantpathology/index.html • Hort. Dept. • http://www.ukyu.edu/Ag/Horticulture

44. Questions?