Pests and diseases: Botrytis Blight or Gray-Mold

Photo courtesy of Dion Mundy

Life Cycle: Botrytis Blight or Gray-Mold is a common fungus disease found in many greenhouses and field crops. Caused by Botrytis cinerea, the disease is often referred to as gray-mold due to the gray, fuzzy-appearing spores which cover the surface of infected plant tissue. Botrytis can cause dampening off, fruit rot, root rot, leaf, and flower blight. Some species of Botrytis can develop sclerotia in dead plant tissue in which it can overwinter. The sclerotia can then germinate in the spring, if in the field; sclerotia can be spread from one plot to another in soil stuck to equipment (plows, tillers, etc.).  Fungal mycelium can also overwinter in dead plant debris, creating a host for conidia (infectious spores) to develop. These conidia can be windborne or splash onto host tissue from overhead watering or rain.

Germination, infection, and disease development is dependent on a specific range of temperature and humidity. In order for the germination of spores and infection of the plant, a film of moisture (dew) must coat the plant for 8-12 hours with humidity of 93% or greater and temperatures between 55-75°F/13-24°C. Gray-mold is much more common in spring and fall months. It can infect plants at any stage, but freshly injured tissues, new, tender growth or aging, dead tissues are preferred.
   
Plants Affected: Vegetables, ornamentals, fruits, and herbs.

Symptoms: Brown lesions on plant material that develops after periods of cool, drizzly, rainy weather. Look for masses of fluffy, silver-gray spores on dead and dying tissues and/or tiny black sclerotia.

Controls: In greenhouse settings, maintaining strict sanitation practices is always key. Remove all dead/dying plant debris off of benches, floors and plants themselves. Empty trash/compost everyday to eliminate places for Botrytis to thrive.  Inspections of all crops in greenhouses should be done on a weekly, if not daily basis. Not only will this help you spot Botrytis, but other plant pests as well.

Sanitizing benches, work areas, utensils and reused pots with a fungicide such as Oxidate will also help to kill any gray-mold spores.  Correct spacing of plants on benches/floors will also help by promoting good air circulation and by reducing humidity within the plant canopy.  Reducing the humidity with proper ventilation and heat can also play a major role in preventing an infection of gray-mold, and other plant diseases.  The use of circulation fans, even in a closed greenhouse can help reduce moisture on plants, by creating a more uniform temperature.  Thus reducing the chances of cool spots in the greenhouse in which dew can form on plants.  Avoiding overhead watering can also be very helpful in preventing infection.  If overhead watering, misting, etc., can not be avoided, good air circulation can again benefit plants by promoting rapid drying of vegetative surfaces.

In field crops, cleaning equipment in between plots can be very helpful, but time consuming.  Washing hand hoes, spades, plows, tillers, etc with water can remove dirt or plant debris that could contain, conidia or sclerotia.  Removing all infected plant material from the field during crop growth by way of culling or pruning can also be very helpful.

Remember, Botrytis can overwinter in several forms, so bagging and trashing culls or burning them is always the best method of disposal.  If culling or pruning is not an economically favorable control method, a fungicide such as Champ or Kocide 3000 can be applied by means of spraying.  When using any type of pesticide read product label in full and follow label instructions as specified by that particular product.

More information:
Benzimidazole management strategy
UMass Extension Pest Management: Botrytis Blight of Greenhouse Crops
Article by Sonya Reynolds, Greenhouse Coordinator, Johnny’s Selected Seeds