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

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Presentation on theme: "Managing Diseases in the Greenhouse Kenny Seebold University of Kentucky Plant Pathology Department."— Presentation transcript:

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 Dont allow field soil into the greenhouse – Dont 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 F 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 Dont 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 Dont 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 – Dont 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 Dont 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 Soil covered with clear plastic mulch Heated by sunlight Max 45-52ºC at 4-6 in soil depth Shown to suppress numerous soilborne diseases Solarization

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, dont 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 Greenhouse Fungicides & Bactericides for Vegetables Pesticides that do not specifically prohibit greenhouse use can be used if labeled for the crop in question. Chlorothalonil: Exotherm Termil – 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)

18 EBDCs (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 – EcoMate Armicarb 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 Photomicrograph: NCSU Plant Pathology Damping-off Pythium spp., Phytophthora spp., Rhizoctonia solani Tomato Pepper

24 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 Damping-off Development and Spread

25 Powdery Mildew Oidium spp. Tomato Cucurbit

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

27 Botrytis Gray Mold Botrytis cinerea Lettuce

28 Early Blight Alternaria solani

29 (Gray) Leaf Mold Fulva fulva Tomato

30 Timber Rot Sclerotinia sclerotiorum Stem rot + sclerotia (black seed-like structures)

31 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) Foliar Blights Management

32 Diseases Caused by Bacteria

33 Bacterial Spot Xanthomonas campestris pv. vesicatoria TomatoPepper

34 Bacterial Canker Clavibacter michigensis subsp. michiganensis Foliar symptoms on greenhouse-grown transplants

35 Bacterial Canker Wilting Pith necrosis Stem canker Pith necrosis

36 Bacterial Spot & Canker Development 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. Dont handle plants if foliage is wet – If watering overhead, do so early; dont 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 Mosaic Tobacco mosaic virus (TMV) - TMV is seedborne & survives well on surfaces & plant debris - Easily transmitted by mechanical means Typical mosaic symptoms on foliage Fruit symptoms

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

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

42 There are no chemical options Tomato seed can be treated with trisodium phosphate to kill TMV Cultural: – Use resistant varieties if available (TMV) – Dont 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 Viral Diseases Management

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 – ID-36 ( Veg. Production Guide for Commercial Growers) – Plant Pathology Dept. – Hort. Dept.

44 Questions?


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