Greenhouse - Botrytis Control

Botrytis is the most common disease of flowering greenhouse plants. The following is an article on this disease and its control from the New England Greenhouse Update newsletter.

Closely spaced plants, overcast cloudy weather, and flower drop from overhead hanging baskets have encouraged Botrytis Blight on New Guinea Impatiens, Garden Impatiens, geraniums and many other susceptible ornamental crops. Botrytis infections often begin when spent flowers drop from hanging baskets above susceptible crops. The flowers provide a source of food for the developing fungus. Tender flowers, leaves, and stems are often infected.

The familiar fuzzy grayish-brown spores are easily spread on air currents and by water splash. Botrytis is best managed by combining proper sanitation practices with environmental controls.
Promptly remove infected plants, keep weeds under control, and place cull piles as far away from your greenhouse as possible. Keep garbage cans covered so spores are not released into the greenhouse via air currents. Some growers place netting below hanging baskets to catch the spent flowers.

Water early in the day, so foliage can dry rapidly. As plants are sold, provide more space to your existing crops to reduce humidity levels within your crops. Reduce humidity by heating and venting several times in the evening and in the morning.

Apply preventative fungicides before cleaning up plants so spores are not released as workers handle plants. On ornamental crops, a number of fungicides are labeled for use against Botrytis. The New England Recommendation Guide lists the following fungicides under Botrytis Management: trifloxystrobin(MOA Group 11) (Compass), fenhazamid (MOA Group 17)(Decree), iprodione (MOA Group 2) (26GT), chlorothalonil (MOA Group 5)(Daconil Weather Stik) or (Daconil Ultrex), mancozeb (MOA Group 3) (Dithane Rainshield WF), azoxystrobin (MOA Group 11) (Heritage), fludioxonil (MOA Group 12) (Medallion), Protect T/O (MOA Group 3), triflumizole (MOA Group 3)(Terraguard) or iprodione (MOA Group 2)(Sextant).
(Before treatment, read labels carefully to see if there is potential damage to flowers and other safety precautions to avoid potential phytotoxicity!)

Reprinted from the May 2006 edition of the New England Greenhouse Update.