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Ministry of Agriculture, Food and Rural Affairs

Blue Mold

Blue mold on apples
Click to enlarge.

Beginner

Scientific Names
Penicillium expansum and P. solitum

Identification

  • The symptoms begin as soft watery light brown areas around injuries or lenticels on the fruit surface.
  • The older lesions may be covered by bluish-green spores that initially are nearly snow white in colour.
  • The musty odour and formation of conidial tufts spores (coremia) on the surface of well developed lesions are characteristic features of P. expansum.
  • Under cold storage conditions, lesions expand 2.5-3.8 cm in diameter after 8-10 weeks after infection.

Often Confused With

  • Gray mold - 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. Blue Mold initially has snow-white spores that turn to blue-green. It has musty odour.

Period of Activity
Wound pathogen that invades fruit during picking and handling operations.

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

Thresholds
None established.

Advanced

Blue mold is the most common storage disease in Ontario.

Scientific Names
Penicillium expansum and P. solitum

Identification           
The symptoms begin as soft watery light brown areas around injuries or lenticels on the fruit surface. The older lesions may be covered by bluish-green spores that initially are nearly snow white in colour. The musty odour and formation of conidial tufts spores (coremia) on the surface of well developed lesions are characteristic features of P. expansum – the most predominant species causing blue mold of apple in Canada. Under cold storage conditions, lesions expand 2.5-3.8 cm in diameter after 8-10 weeks after infection. The spores are important in spreading the disease to other apples in storage. The spores are resistant to drying and survive on the surfaces of the storage walls and on packing equipment. Spores also build up in post-harvest drench solutions, and in flotation tanks used to float fruit, following long-term storage, onto packing lines.

Often Confused With

  • Gray mold - 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. Blue Mold initially has snow-white spores that turn to blue-green. It has musty odour.

Biology
The blue mold fungus is a wound pathogen. The pathogen most frequently enters through the wounds caused during picking and handling operations. Spores are present almost everywhere and survive long periods of unfavourable conditions. These spores also survive from season to season on picking boxes, contaminated bins and on storage walls. The pathogen also invades lenticels of fruit that are over mature at harvest or fruit held in storage too long.

Period Of Activity
Wound pathogen that invades fruit during picking and handling operations.

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

Thresholds
None established.

Management Notes

  • General sanitation and avoiding conditions favourable to infection are important in controlling post-harvest blue mold of apple.
  • Take precautions in harvesting and handling of fruit to minimize bruising and wounding. Disinfect contaminated bins and storage walls before reuse.
  • Harvest fruit at optimum maturity and move harvested fruit to cold storage as rapidly as possible. Remove decaying fruit daily from packing houses. In many areas, Penicillium has developed resistance to the benzimidazole fungicides used in pre-harvest sprays and post-harvest dips.
  •  In recent years, new classes of fungicides have been registered for the control of post-harvest blue mold and gray mold in Canada.
  • For information on pre-harvest application of fungicides and post-harvest fungicides for the control of post-harvest blue mold and gray mold, consult OMAFRA Publication 360, Guide to Fruit Production - Chapter 3 Apples (PDF) or Apple Calendar only (PDF) :