Botrytis Blight in Vegetable Greenhouse and Plant Beds

Plant Pathology Information Note 118 (PPIN-118)
Charles W Averre, Extension Plant Pathologist

Botrytis blight is caused by a fungus (Botrytis cinerea) that attacks many succulent plants. In most years it causes considerable damage in a few operations to seedlings in plant beds and producing tomatoes in greenhouses. This disease usually affects plants at the tip of the younger leaves, causing a water-soaked area. The infected areas of the leaves enlarge and the fungus appears to grow down the leaf petiole into the main stem. The diseased area becomes covered with a fluffy, brownish-gray mold. The disease has not been observed as a problem in the field in Eastern North Carolina. On producing tomatoes it causes foliar blight, stem rot, and fruit spotting and rot.

Botrytis blight is associated with excessive moisture and high humidity as a result of poor ventilation in covered plant beds and greenhouses. Growers are urged to take every precaution to provide adequate and continuous ventilation, especially during periods of cool, cloudy and wet weather. Most growers are able to avoid serious Botrytis blight problems without the use of fungicides by keeping humidity low in the structure. Specific steps include: (1) wider plant spacing, (2) continuous introduction of some cold air when house is closed, (3) continuous forced air movement with fans when house is closed, (4) use of "speeding trays" in racks above ground or placed on rocks or plastic ground sheets on the ground, (5) good soil drainage, (6) covering ground with plastic sheets, and (7) not using sprinkler irrigation.

There are few registered fungicides for use in covered plant beds and greenhouses. Fungicides must be used with caution in order to avoid health hazards during application, illegal residues on commodities, and buildup of Botrytis resistance to the fungicide. Be sure to read the label carefully, and be sure that the fungicide selected is registered for the intended crop.

Fungicides occasionally used to control Botrytis blight on vegetables in covered plant beds and greenhouses. Read the label carefully and be sure the fungicides is labeled for the specific, intended crop. Follow all precautions on label.

Chlorothalonil 20% smoke generator (Exotherm Termil) 3.5 oz can per 1000 sq ft Locate generator where smoke will disperse evenly in structure. Commence weekly application at first appearance.
Dichloran 75% (Botran 75W) 1.0 lb (formulated) per 100 gal water (.16 oz/gal) Commence weekly spraying when disease first appears.
(Dyrene 75W) 1 to 2 lb (formulated) per 100 gal water (.16 to .32 oz/gal) Commence weekly spraying when disease first appears. Do not use when structure is covered.
Benlate 50W (benomyl 50%) 0.5 to 1.0 lb (formulated) per 100 gal water Apply spray two or three times on 7-day schedule only if disease cannot be controlled with humidity control and standard fungicides. Simultaneously continue using standard fungicides. Regular and overuse of Benlate will cause the fungus to become immune.

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Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data. All recommendations for pesticide use were legal at the time of publication, but the status of registration and use patterns are subject to change by actions of state and federal regulatory agencies. Last printed 02/91

Published by North Carolina Cooperative Extension Service. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Reformatted Dec. 2000 by A.V. Lemay