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Market Diseases of Apples, Pears, and Quinces
Diphenylamine Injury |
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Diphenylamine (DPA), applied as a dip, drench, spray, or wrap, is used to control ordinary scald of apples. A small amount of chemical injury is likely to develop when the material is applied as a dip or a drench to loose fruits in bins or field boxes. Toxic concentrations of the chemical may accumulate where some of the liquid is trapped in the calyx cups, between fruits, or in the bottom of the container. Symptoms appear as small black spots, rings of darkened tissues surrounding areas of sound tissues (top photo), solid areas of killed discolored skin (second photo), or a discoloration in the calyx. Generally, only the skin is affected, but in cases of severe injury the underlying flesh may be darkened to a depth of 1/8 inch or more. Affected areas may become sunken when moisture is lost through the injured skin.
On Golden Delicious, DPA wraps or sprays produce a bluish-gray scald-like disorder which is confined largely to the cheeks and shoulders of the fruit. The distinctive color and the development of longitudinal streaks on the shoulders of the fruits help to distinguish this injury from senescent scald on this variety. DPA injury may be reduced by carefully draining excess liquid from the bins and boxes before the fruits are placed in storage. Ethoxyquin should be substituted for DPA to control senescent scald on Golden Delicious. |
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