How to Manage Pests

Pests in Gardens and Landscapes

Botrytis rot (gray mold) on lettuce—Botrytis cinerea

Leaves on or near the soil or in the dampest areas of the garden turn light brown and develop a gray or brown fuzzy growth of fungal spores. Plants shrivel and rot and often develop flattened hard black masses, called sclerotia, under rotted parts.

Identification

Symptoms of Botrytis crown rot are similar to sclerotinia rot: lower leaves of plants infected with Botrytis yellow, and eventually the whole head wilts and rots. A watery, brown decay develops on the underside of the head at the crown. A dense gray or light brown sporulation appears over the damaged areas when moisture is abundant; this gray sporulation distinguishes Botrytis from lettuce drop. Occasionally, the fungus produces small, black, usually flattened sclerotia on the plant's underside.

Life cycle

The fungus that causes gray mold, Botrytis cinerea, survives in decaying plant material in or on the soil and as sclerotia. Botrytis infects primarily through germination of its airborne spores. An injury or dead or dying tissue must be present for the fungus to invade. On lettuce, aging wrapper leaves or older leaves at the bottom of plants are usually first infected. Wrapper leaves often provide entry sites for crown rot. Head rot may develop on sites damaged by aphids or downy mildew or other diseases.

Solutions

Plant on well-drained, raised beds, use furrow irrigation whenever possible, and try to keep the surface of vegetable beds as dry as possible. When sprinkling plants, do so in the morning so that foliage will dry quickly during the day. Harvest in advance of rainy or humid, cool conditions whenever possible. Remove diseased plants as soon as they appear and dispose of them. Discard plant residue left in the garden to prevent infection of the next planting.

 

 

Lettuce crown damaged by Botrytis rot
Lettuce crown damaged by Botrytis rot

Wilt caused by Botrytis rot
Wilt caused by Botrytis rot


Statewide IPM Program, Agriculture and Natural Resources, University of California
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