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Ministry of Agriculture, Food and Rural Affairs

Gray Mold

Gray mold in apples (Dr. Deena Errampali, Agriculture and Agri-Food Canada)
Click to enlarge.

Beginner

Scientific Name
Botrytis cinerea

Identification

  • Affected areas on the fruit appear light brown to dark brown and colour is similar across the decayed area.
  • The infected area is spongy, and diseased tissue is not separable from the healthy tissue.
  • On mature lesions and under high relative humidity conditions, fluffy white to grey mycelium and dark grey spore masses appear on the decayed area.
  •  Unlike blue mold, gray mold does not have a distinct odour, but in advanced stages decayed apples have a “cedar-like” smell.
  • When the disease spreads through the whole fruit, the entire decayed fruit appears “baked” and eventually turns softer.

Often Confused With

  • Blue mold - Blue mold initially has snow-white spores that turn to blue-green. It has musty odour. Gray mold does not have a distinct odour but in advanced stages have a cedar-like smell. Gray mold has fluffy white grey mycelium and dark grey spores masses on the decayed area.

Period of Activity
The gray mold fungus enters fruit through wounds caused during the harvest and handling processes.

Scouting Notes
Symptoms do not appear in the orchard so can’t be monitored.

Thresholds
None established.

Advanced

Scientific Name
Botrytis cinerea

Identification           
Affected areas on the fruit appear light brown to dark brown and colour is similar across the decayed area. The infected area is spongy, and diseased tissue is not separable from the healthy tissue. On mature lesions and under high relative humidity conditions, fluffy white to grey mycelium and dark grey spore masses appear on the decayed area. Unlike blue mold, gray mold does not have a distinct odour, but in advanced stages decayed apples have a “cedar-like” smell. When the disease spreads through the whole fruit, the entire decayed fruit appears “baked” and eventually turns softer.

Often Confused With

  • Blue mold - Blue mold initially has snow-white spores that turn to blue-green. It has musty odour. Gray mold does not have a distinct odour but in advanced stages have a cedar-like smell. Gray mold has fluffy white grey mycelium and dark grey spores masses on the decayed area.

Biology
The fungus colonizes organic matter in the orchard floor. Conidia of the fungus are dispersed mainly by air currents and water splash. The gray mold fungus enters fruit through wounds caused during the harvest and handling processes. The fungus also invades stems of apple fruit and cause stem-end rot. Botrytis, also known as the nesting fungus, spreads from fruit to fruit in the storage bins and causes significant losses. Mycelial growth and secondary infection from fruit-to-fruit spread is enhanced by high relative humidity. The fruit affected by the secondary infection may not have visible symptoms at the time of packing, and infected fruit may be packed but symptoms develop on packed fruit during storage or transit.

Period of Activity
The gray mold fungus enters fruit through wounds caused during the harvest and handling processes.

Scouting Notes
Symptoms do not appear in the orchard so can’t be monitored.

Thresholds
None established.

Management Notes

  • Orchard sanitation is an important step in the management of gray mold of apple. The removal of decayed fruit and organic debris from the orchard floor reduces inoculum levels of B. cinerea from building in the orchard.
  • Good harvest management practices that minimize punctures and bruises on the fruit skin help prevent wound infections.
  • Harvest apple cultivars at their optimum maturity to minimize splits at the stem bowl.
  • Move harvested fruit to cool storages as soon as possible. Daily removal of decaying fruit reduces the production and spread of spores in packing houses.
  • Due to the persistent use of benzimidazole fungicides in the orchard and in storage, some strains of gray mold fungus have developed resistance to the benzimidazole fungicides.
  • In recent years, new classes of fungicides have been registered for the control of post-harvest gray mold in Canada.
  • For information on pre-harvest application of fungicides and post-harvest fungicides for the control of post-harvest gray mold, consult OMAFRA Publication 360, Guide to Fruit Production - Chapter 3 Apples (PDF) or Apple Calendar only (PDF):