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Botrytis bunch rot (Botrytis cinerea) or gray mold is caused by a ubiquitous and opportunistic fungus with a wide host range. It colonizes dead and damaged tissue before spreading to nearby healthy tissue. Blossoms, young berries, injured tissue, and overripe fruit are susceptible to infection. Berry infections can occur early in the season and remain latent (dormant) until berry ripening; blossoms and young clusters are highly susceptible to infection. Symptoms during ripening vary with weather conditions: during dry weather, berries dry out, but in wet or humid weather, gray moldy growth develops on berry surfaces. Infected shoot tips wither and become blighted. Spore production occurs during wet or humid conditions; spores spread by wind or rain. Infections continue as long as moisture and susceptible tissue are present. The pathogen overwinters as sclerotia (which develop in autumn) in infected buds, in debris, or in rachises and fruit mummies.

Botrytis bunch rot between berries.

(Photo: Julie Beale, University of Kentucky)

Botrytis bunch rot advanced symptoms.

(Photo: Chris Smigell, University of Kentucky)

Botrytis bunch rot advanced symptoms.

(Photo: John Hartman, University of Kentucky)

Management:

• Practice proper sanitation (remove infected berries, remove damaged and infected tissue).
• Increase air circulation to encourage drying of plant tissues (pruning, thinning, spacing, managing weeds).
• Apply fungicides (especially before cluster closure).

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