How to Manage Pests

Pests in Gardens and Landscapes

Botrytis leafspot (leaf blight) on onions—Botrytis cinerea or other spp.

Botrytis leafspot, also called leaf blight, occurs on onions. White sunken spots on leaves are usually signs of infection; spots are small and tend to be oval. They sometimes have a light green halo and may appear water soaked. The epidermis around the spots may be silvery. When numerous spots are present, leaf tips die back and whole leaves may be killed.

Life cycle

Botrytis cinerea spores land on leaf surfaces and, in the presence of moisture, germinate and produce enzymes that kill leaf tissue and provide an entry point for the fungus. The fungus damages the leaf by causing leaf spotting. Leaf surfaces must be wet by dew or rain for long periods (20 hours or more) for leafspot to develop. Optimum temperature for germination of spores is 59°F; optimum temperature for mycelial growth is between about 73 and 77°F.

Solutions

To reduce the level of disease inoculum in the soil, use a 3-year rotation scheme away from onions, garlic, and related crops and destroy volunteer onions during this period.

Leaf spotting and dieback of leaf tips
Leaf spotting and dieback of leaf tips

White sunken spots on leaves
White sunken spots on leaves

Silvery lesions
Silvery lesions


Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2016 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

Accessibility   /PMG/GARDEN/VEGES/DISEASES/botryslfspot.html revised: September 20, 2016. Contact webmaster.