7/2/2013 - By Dr. Raymond Snyder

This month we will be covering a disease that is sure to show up in the next couple of months… Botrytis. Botrytis is also known as “Gray Mold” because of the gray fuzz that appears when the pathogen is present. This pathogen is a necrotrophic fungi, which means it kills its host and then feeds off of the dead tissue.

This time of year the gray fuzzy mold is often seen on plants under crowded and bunched conditions where air circulation is poor. These pathogens thrive in cooler, damper conditions, and seem to do best between 60-75?F, and when humidity is above 90%. The lack of sunlight and decreased airflow in covered greenhouses during the fall and spring months can also help to contribute to the disease's spread.

Botrytis overwinters as sclerotia on fallen plant debris and in the top layers of soil. Good sanitation is key to controlling this disease. Try to keep any fallen debris picked up and encourage substantial airflow when feasible. Heavily infected plant tissue should also be removed to help eliminate disease spores. Botrytis will attack many different parts of the upper portion of a plant including leaves, flowers, buds, and even stems. Some insects can also help spread this disease; pests like aphids encourage plants to produce a sugary substance called honeydew when they feed on them. This honeydew can act as a food source for some strains of Botrytis, and disease outbreaks can occur very rapidly. Sooty mold can also be found growing on honeydew and should not be confused with Botrytis.

Botrytis spores have a very unique structure which is key to diagnosising the disease. When looked at through a hand lens, this fungi looks like tiny trees that have clusters of round spore pouches (called conidia) on top. Botrytis will often attack plants that are in post-harvest storage conditions, like cut flowers and fruits and vegetables. Some finer wines are even made from grapes that have been infected with “Noble Rot” or a Botrytis strain. The fungus removes the liquid from the grape and leaves behind a more concentrated and intense flavor.

Botrytis is usually easy to control when fungicides are used preventatively. Products such as Palladium and Daconil work well this time of year. Pageant, Iprodione, and thiophanate methyl also work well. Coppers work well when the disease is present and spreading. Encourage growers to apply these products prior to covering their greenhouses, and it should pay dividends for them through the cooler months.