Extension Logo
Extension Logo
University of Minnesota Extension
extension.umn.edu

Gray mold of tomatoes

Quick facts

  • Gray mold thrives in the high humidity found in high tunnel and greenhouse tomato production.
  • Gray mold is rare in Minnesota field grown tomatoes. 
  • The fungal pathogen infects all above ground plant parts. 
  • It can be highly destructive when environmental conditions favor disease.

How to tell gray mold apart from other issue

Gray mold infection on a tomato leaf
Gray mold infection on tomato stems
Small white rings on tomato fruit indicate failed gray mold infections
  • Gray mold occurs in cool temperatures (between 60-75°F) and high humidity (greater than 80%) 
  • In high humidity, fluffy gray spores cover infected plant parts.
  • Leaves have irregular to V-shaped brown blotches, often starting at the margin of the leaf.
  • Die-back symptoms appear as infection progresses from leaves, through petioles, towards the main stem.
  • Brown, oval lesions can girdle the stem.
  • Infected flowers turn brown and die.
  • The spores are light brown-gray on black stalks.
  • Infected fruit develop a pale, soft, watery rot, or have white rings or halos on the fruit, called ghost spots.
  • Fruit symptoms occur on green and red fruit; while on the plant and post-harvest.

Biology

  • Gray mold is caused by the fungus Botrytis cinerea
  • Disease develops in temperatures between 60-75°F (60-70°F optimum). Temperatures greater than 82°F suppress fungal growth and sporulation.
  • Gray mold requires high humidity (greater than 80%).
  • Spores are most likely to germinate when leaves remain wet for 5-8 hours.
  • The fungus survives on numerous weed hosts, on dead plant material, and as hard resting structures (sclerotia) in plant debris and soil.
  • Spores are spread short and long distances by wind and rain, equipment and workers.
  • Infections begin on weak, dying or wounded plant tissue.

Managing Gray Mold in Home Gardens

 | 

Managing Gray Mold on Farms

 | 

Marissa Schuh, Horticultural IPM Extension Educator, Angela Orshinsky, Extension plant pathologist and Michelle Grabowski, Extension educator

Reviewed in 2021

Page survey

© 2024 Regents of the University of Minnesota. All rights reserved. The University of Minnesota is an equal opportunity educator and employer.