Pome Fruit Disease - Blue Mold

Blue mold is the most important postharvest disease of apples worldwide. Some strains of blue mold secrete patulin, which is a mycotoxin. Patulin levels are regulated, but blue mold is an economic concern for the fresh fruit industry and the fruit processing industry. Aside from losses in fruit caused by rot, sound fruit in the same container as decaying fruit may absorb a moldy odor and flavor.

Symptoms

Blue mold appears as soft, light brown, watery spots that begin around injuries or lenticels on the outer surface of fruit. Rotted fruits have a characteristic moldy odor and flavor. When the relative humidity is high, grayish blue masses of spores may appear on the fruit surface.

Disease Cycle

Spores of the soft rot fungus are present almost everywhere and can survive long periods of unfavorable conditions. Bulk bins, field crates, packhouse lines, and storage rooms are usually contaminated. Injuries to fruit, especially during picking and handling operations, are the primary points of entry. At ordinary temperatures, infected fruit can rot in 2 weeks or less.

Disease Management, Cultural

To control blue mold, it is important to prevent fruit from becoming injured during picking and handling.

It is also essential to move harvested fruit into cold storage as rapidly as possible. Packing line equipment and storage rooms should be cleaned, and clean water maintained in water dumps and anti-scald solutions.

Disease Management, Chemical

Picking bins and boxes can be disinfected with fungicides or steam. Disinfectants or fungicides can be used in fruit dips and combined with wax applications. Preharvest applications of Merivon or Pristine (FRAC Groups 7 and 11), which are labeled for blue mold control, will also help mitigate blue mold occurring on apples in storage. Postharvest fungicides that are most effective include the following active ingredients: pyrimethanil (FRAC Group 9); fludioxonil (FRAC Group 12); and the premix difenoconazole and fludioxonil (FRAC Groups 3 and 12). When using postharvest fungicides, practice fungicide resistance management by rotating modes of action from season to season.