Conditions favor Botrytis on vegetable transplants in the greenhouse

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

The recent overcast and humid conditions are very favorable for Botrytis development on vegetable transplants being held in the greenhouse. Do not wait for this gray mold to develop. It is better to be proactive with cultural and fungicide applications to prevent this disease from becoming established.

Botrytis gray mold can infect all vegetable transplants causing an irregular brown spotting or “blight” of leaves and stem cankers. This is the same Botrytis that infects a wide range of floriculture crops producing gray masses of powdery spores. In vegetable transplants, Botrytis is a threat when plants grow and form a canopy of leaves, keeping the relative humidity high that favors disease.

Since the fungus that causes gray mold depends on water to germinate on the plant surface, increasing air circulation through fans and reducing the relative humidity by venting or heating (depending on outside temperatures) will help prevent condensation of water on plant surfaces and thereby reduce the occurrence of gray mold. Watering early in the day will help ensure that the plants dry by evening, reducing the occurrence of disease. The fungicides Scala, Botran and Decree can be used on tomatoes in the greenhouse to protect against Botrytis. Also, Exotherm Termil will provide protection against Botrytis and can be used for tomatoes (Note: Other forms of chlorothalonil such as Daconil are not registered for use in the greenhouse on vegetable transplants.). Although Botran 75-W is registered to control Botrytis on tomato seedlings, this fungicide should be used with caution due to concern regarding occasional sensitivity of the plant stem. Decree can also be used on cucumber transplants.

Dr. Hausbeck’s work is funded in part by MSU‘s AgBioResearch.

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