Botrytis
Tuesday, 04 October 2011 10:17
Recent cloudy, rainy weather has been favorable for Botrytis infections on crops in greenhouses.
Generally, Botrytis spore germination and infection of the crop is dependent on a film of moisture for 8 to 12 hours, relative humidity 93% or greater, and temperatures between 55 - 75 F. Regulation of temperature, humidity and leaf wetness duration can prevent disease development.
On poinsettias, Botrytis can cause leaf blights and then move from the leaf petiole into the stem, causing a stem canker. When reducing temperatures as plants mature, avoid night temperatures below 60F. Later in the season, tender bracts are also prone to infection.
Proper plant spacing, good sanitation practices (removing plant debris and placing this debris in a covered garbage can) help prevent Botrytis blight. Proper environmental management by using horizontal air flow (HAF) fans to promote air circulation and minimize cold spots is critical to managing this disease. Be sure to water early in the day and heat and vent as needed to reduce humidity levels. Some poinsettia varieties, especially those with white colored bracts, are more prone to Botrytis infections, so these varieties are best placed in your less humid houses.
Many fungicide sprays will injure or discolor sensitive bracts. Read fungicide labels carefully before application for information on plant safety. If unsure, contact the technical representative from the company for more information. Apply fungicides (such as Decree with capsil to help minimize visible residue or Phyton 27) only under good drying conditions, early in the morning, preferably on clear days. Even overhead applications of plain water, can injure the sensitive bracts!
Botrytis is also a problem on greenhouse tomatoes. For details and photo links see: Foliar Diseases on Greenhouse Tomatoes
Fact Sheet: Reducing Humidity in Greenhouses
Photos: Botrytis on Poinsettias
