Disease Control

For effective disease control it is important to accurately identify the causal agent. If uncertain, bring specimens with various stages of disease to your local Extension agent or diagnostician. Management practices that will reduce disease are: the use of resistant varieties, sanitation, fungicides and cultural practices that keep the humidity below 90%.

NOTE:  For the disease control products listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, days to harvest (dh), REI, and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 22 and Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

Bacterial Canker (Clavibacter michiganensis pv. michagenensis)

Initial symptoms are often a wilting and/or scorching of half of a leaf or one side of a plant. When these symptoms occur, remove the entire plant, including roots from the greenhouse. Wash hands with soap and water before handling healthy plants. There are few effective bactericides to control this disease. If extensive bacterial canker occurs in the greenhouse, steaming of the soil is advised. Pruning, harvesting and handling, especially when plants are wet, spreads the bacterium down the row. See discussion of bacterial canker on Tomato (Outdoor).

Botrytis Blight (Botrytis cinera)

Control over the environment is very important in controlling this disease. Keep humidity below 80% by heating and ventilating, especially at night. Avoid wetting the foliage during times when drying is slow. Practice strict sanitation, removing senescent tissues and infected crop debris. Pruning of lower leaves to clean-cut stubs aids in disease prevention by improving air circulation through the crop. Fungicide rotations and combinations are important because strains resistant to benlates, dichloran, captan, and iprodione have been reported.

copper plus mancozeb (Cuprofix Disperss): 1.75-7.25 /100 gal water. (5 dh, REI 24h, Group M1 & M3). Do not apply in spray solution having a pH less than 6.5. Crops grown in the greenhouse may be more sensitive to copper injury; user should determine crop sensitivity.

dichloran (Botran 75W): 1.0 lb/43,560 sq ft. (10 dh, REI 12h, Group 14).

mancozeb (Dithane F45): 1.2 to 1.6 qt/100 gal. (5 dh, REI 24h, Group M3). Apply when disease first appears and repeat as necessary on a 7- to 10-day schedule.

pyrimethanil (Scala SC): 7 fl oz/A. (1 dh, REI 12h, Group9). Use only in a tank mix with another effective fungicide recommended for Botrytis. Apply Scala SC only in well ventilated plastic tunnel houses or glass houses. Ventilate for at least two hours after application.

Leaf Mold (Fulvia fulva)

This disease occurs in both soil or hydoponic production and is most important in poorly ventilated plastic greenhouses. The pathogen produces large numbers of conidia on infected tissue; the disease can spread rapidly throughout a greenhouse by air currents, water, insects, and workers. Start with certified disease free seed. Use resistant cultivars. Improve air circulation by adequate row/plant spacings and removal of lower leaves. Avoid the formation of water droplets on leaves by watering in the morning. Reduce relative humidity by a combination of heating and venting, especially at night. Avoid excessive nitrogen fertilization. Remove diseased leaves, place in plastic bag, and destroy. At the end of crop cycle, remove all plant residue and destroy and disinfest the entire greenhouse.

copper hydroxide (Kocide 3000): 0.75-1.75 lb/150 gal water. (0dh, REI 24h, Group M1). Do not apply in a spray solution having a pH less than 6.5 or tank mix with Aliette.

copper plus mancozeb (Cuprofix Disperss): 1.75-7.25 /100 gal water. (5 dh, REI 24h, Group M1 & M3). Do not apply in spray solution having a pH less than 6.5. Crops grown in the greenhouse may be more sensitive to copper injury; user should determine crop sensitivity.

mancozeb (Dithane F45): 1.2 to 1.6 qt/100 gal water. (5 dh, REI 24h, Group M3). Apply when disease first appears and repeat as necessary on a 7- to 10-day schedule.

pyrimethanil (Scala SC): 7 fl oz/A. (1 dh, REI 12h, Group 9). Use only in a tank mix with another effective fungicide with a different mode of action. Apply Scala SC only in well ventilated plastic tunnel houses or glass houses. Ventilate for at least two hours after application.

Powdery Mildew

Powdery mildew of tomato is emerging as an important disease of greenhouse crops. This pathogen is favored by low light and cool temperatures. In contrast to other fungal plant pathogens, it does not require free water to germinate and cause diseases. DeRuiter’s Seeds has recently released the cultivar Grace which has resistance to powdery mildew.

copper hydroxide (Kocide 3000): 0.75-1.75 lb/150 gal water (0dh, REI 24h, Group M1). Do not apply in a spray solution having a pH less than 6.5 or tank mix with Aliette.

potassium bicarbonate (Armicarb 100): 2.5 to 5 lb/100 gal water (0 dh, REI 4h, Group N/A). Apply 10 to 20 gallons of solution per 4350 sq ft. Reapply at 10- to 14-day intervals as needed. Use material within 12 hours of preparation.

potassium salts of fatty acids (M-Pede): 1 to 2% solution (0 dh, REI 12h, Group N/A). Apply at 7- to 14-day intervals (not more than three sprays). See label for precautions. OMRI listed.