1. Managing Diseases in the Greenhouse
October 21, 2008
Managing Diseases
in the Greenhouse
Kenny Seebold
University of Kentucky
Plant Pathology Department
Presenter: Kenny Seebold

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. Managing Diseases in the Greenhouse
October 21, 2008
Successful management of greenhouse diseases
begins with prevention…
Host
Pathogen
Environment
Presenter: Kenny Seebold

4. Managing Diseases in the Greenhouse
October 21, 2008
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 F for at least 30 min
Presenter: Kenny Seebold

5. Managing Diseases in the Greenhouse
October 21, 2008
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
Presenter: Kenny Seebold

6. Managing Diseases in the Greenhouse
October 21, 2008
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
Presenter: Kenny Seebold

7. Managing Diseases in the Greenhouse
October 21, 2008
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.
Presenter: Kenny Seebold

8. Managing Diseases in the Greenhouse
October 21, 2008
Recommended Temperatures and Soaking Times for Hot-Water Disinfection of Selected Vegetable Seeds
Presenter: Kenny Seebold

9. Managing Diseases in the Greenhouse
October 21, 2008
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
Presenter: Kenny Seebold

10. Manipulating the Environment
Managing Diseases in the Greenhouse
October 21, 2008
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)
Presenter: Kenny Seebold

11. Manipulating the Environment
Managing Diseases in the Greenhouse
October 21, 2008
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
Presenter: Kenny Seebold

12. Suppressing Pathogens
Managing Diseases in the Greenhouse
October 21, 2008
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
Presenter: Kenny Seebold

13. Managing Diseases in the Greenhouse
October 21, 2008
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
Temps in mid- to high 40’s C common in top 4 inches (45C = 13F)
Presenter: Kenny Seebold

14. Limitations of Solarization
Managing Diseases in the Greenhouse
October 21, 2008
Limitations of Solarization
Not practical in northerly climates (fewer “sunshine” days than in southern areas
Unproductive during summer
Disposal of plastic
Presenter: Kenny Seebold

15. Chemicals for Disease Control
Managing Diseases in the Greenhouse
October 21, 2008
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…
Presenter: Kenny Seebold

16. Managing Diseases in the Greenhouse
October 21, 2008
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
Presenter: Kenny Seebold

17. Greenhouse Fungicides & Bactericides for Vegetables
Managing Diseases in the Greenhouse
October 21, 2008
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)
Presenter: Kenny Seebold

18. Greenhouse Fungicides & Bactericides for Vegetables
Managing Diseases in the Greenhouse
October 21, 2008
Greenhouse Fungicides & Bactericides for Vegetables
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)
Presenter: Kenny Seebold

19. Greenhouse Fungicides & Bactericides for Vegetables
Managing Diseases in the Greenhouse
October 21, 2008
Greenhouse Fungicides & Bactericides for Vegetables
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)
Presenter: Kenny Seebold

20. Greenhouse Fungicides & Bactericides for Vegetables
Managing Diseases in the Greenhouse
October 21, 2008
Greenhouse Fungicides & Bactericides for Vegetables
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
Presenter: Kenny Seebold

21. Managing Diseases in the Greenhouse
October 21, 2008
Fungicides for Greenhouse Use ‘Soft’ Chemistries / Organic-approved
Bacillus subtilis: broad-spectrum fungicide
Serenade Max
Approved for most greenhouse vegetables
Peroxides (hydrogen): broad-spectrum fungicide bactericide
Oxidate
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
Presenter: Kenny Seebold

22. Managing Diseases in the Greenhouse
October 21, 2008
Diseases Caused by Fungi
Presenter: Kenny Seebold

23. Managing Diseases in the Greenhouse
October 21, 2008
Damping-off Pythium spp., Phytophthora spp., Rhizoctonia solani
Tomato
Photomicrograph: NCSU Plant Pathology
Pepper
Presenter: Kenny Seebold

24. Managing Diseases in the Greenhouse
October 21, 2008
Damping-off Development 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
Presenter: Kenny Seebold

25. Managing Diseases in the Greenhouse
October 21, 2008
Powdery Mildew Oidium spp.
Tomato
Cucurbit
Presenter: Kenny Seebold

26. Managing Diseases in the Greenhouse
October 21, 2008
Botrytis Gray Mold Botrytis cinerea
Stem canker
‘Ghost spots’ on fruit
Tomato
Fruit rot
Leaf blight
All images:
Plant Management Network
Presenter: Kenny Seebold

27. Managing Diseases in the Greenhouse
October 21, 2008
Botrytis Gray Mold Botrytis cinerea
Lettuce
Presenter: Kenny Seebold

28. Managing Diseases in the Greenhouse
October 21, 2008
Early Blight Alternaria solani
Presenter: Kenny Seebold

29. Managing Diseases in the Greenhouse
October 21, 2008
(Gray) Leaf Mold Fulva fulva
Tomato
Presenter: Kenny Seebold

30. Managing Diseases in the Greenhouse
October 21, 2008
Timber Rot Sclerotinia sclerotiorum
Stem rot + sclerotia (black seed-like structures)
Presenter: Kenny Seebold

31. Managing Diseases in the Greenhouse
October 21, 2008
Foliar Blights Management
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)
Presenter: Kenny Seebold

32. Managing Diseases in the Greenhouse
October 21, 2008
Diseases Caused by Bacteria
Presenter: Kenny Seebold

33. Managing Diseases in the Greenhouse
October 21, 2008
Bacterial Spot Xanthomonas campestris pv. vesicatoria
Tomato
Pepper
Presenter: Kenny Seebold

34. Managing Diseases in the Greenhouse
October 21, 2008
Bacterial Canker Clavibacter michigensis subsp. michiganensis
Foliar symptoms on greenhouse-grown transplants
Presenter: Kenny Seebold

35. Managing Diseases in the Greenhouse
October 21, 2008
Bacterial Canker
Wilting
Stem canker
Pith necrosis
Pith necrosis
Presenter: Kenny Seebold

36. Managing Diseases in the Greenhouse
October 21, 2008
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
Presenter: Kenny Seebold

37. Managing Diseases in the Greenhouse
October 21, 2008
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
Presenter: Kenny Seebold

38. Managing Diseases in the Greenhouse
October 21, 2008
Diseases Caused by Viruses
Presenter: Kenny Seebold

39. Managing Diseases in the Greenhouse
October 21, 2008
Tobacco Mosaic Tobacco mosaic virus (TMV)
Fruit symptoms
Typical mosaic symptoms on foliage
TMV is seedborne & survives well on surfaces & plant debris
Easily transmitted by mechanical means
Presenter: Kenny Seebold

40. Managing Diseases in the Greenhouse
October 21, 2008
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
Presenter: Kenny Seebold

41. Managing Diseases in the Greenhouse
October 21, 2008
Tomato Yellow Leaf Curl Tomato Yellow Leaf Curl Virus (TSWV)
Uncommon in KY, but has occurred in 2005 and 2008
Vectored by whiteflies
Presenter: Kenny Seebold

42. Managing Diseases in the Greenhouse
October 21, 2008
Viral Diseases Management
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
Presenter: Kenny Seebold

43. Managing Diseases in the Greenhouse
October 21, 2008
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.
Presenter: Kenny Seebold

44. Questions?