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Bitter Pit

Bitter pit once went by the name "Baldwin spot" in America, and in Germany it is known as Stippen. This is not a disease, but a calcium-related disorder, and it often becomes apparent postharvest, in storage. The probable causes of bitter pit are various, ranging from fruit size to tree age, and the disorder is not yet fully understood. Many home growers will not consider it a matter of concern because they do not intend to store their apples for any significant length of time or because they are not bothered by minor flaws. However, if you are looking for immaculate apples that last all winter, read on.

The disorder displays as small dark circles scattered on the skin, concentrated toward the calyx, or circular, brown, corky areas in the flesh just under the skin, or both. In time, surface blemishes become sunken and the apple starts to look like it has been attacked by an angry hole puncher. The spots usually remain superficial, and they can generally be peeled off without sacrificing too much of the apple. Bitter pit is so named because these spots, if eaten, will have a bitter taste. If an apple is destined to develop bitter bit, it will typically appear within two months of being placed in storage, often sooner.

Bitter pit appears to result from a complex interaction of nutrition, tree vigor, and climate. Recommended strategies for management include avoiding overpruning and overthinning, as this can result in excessive vegetative growth at the expense of providing nutrition to the fruit. Trees should not be overfertilized for similar reasons. Maintaining a regular water supply enables trees to uptake calcium and transport it to fruit. For those whose are willing to try supplemental calcium, this is most effective when applied to the leaves rather than the soil. Finally, certain highly susceptible varieties are easily avoided: Honeycrisp, Northern Spy, Gravenstein, Grimes Golden, and, of course, Baldwin.

For more information, see The Pacific Northwest Pest Management Handbook Factsheet on Bitter Pit.

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