University of Maryland Extension

Reducing Botrytis in Greenhouses

In the spring during extended periods of cloud cover, rain and generally poor selling conditions for bedding plants, Botrytis is hard to avoid. Greenhouses can stack up with plants and air circulation drops rapidly. With these conditions the fungal spores can spread quickly and infect many plants.

Botrytis infection on geranium flowersBotrytis spores on geranium leaf

Here are some things you can do to help reduce Botrytis:

Keep plants and greenhouse surfaces as dry as possible. Irrigate plants early in the morning so that wet foliage dries quickly. Overwatering also increases problems with fungus gnats and shore flies.

Good air circulation is always very important. Keep HAF fans on to increase air movement in greenhouses. Increased plant spacing will also help to reduce Botrytis problems. Keep an eye out for areas of the greenhouse where water drips down from overhead (i.e. condensation, leaks in the structure) and avoid placing plants in those areas.

Keep the greenhouse as clean as possible. Botrytis is a great survivor – the pathogen can colonize just about any piece of plant tissue. Clean up dropped leaves, spent flowers, and other debris under and on greenhouse benches. Keep lids on any containers used for discarded plant debris.

Protectant fungicides may be necessary when weather favors disease development and cultural practices alone are not enough. See the Botrytis section in the in the Total Crop Management for Greenhouse Production manual for chemical control options.

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