Late Season Pests in Apples

Although it is tempting to put away the sprayer at this time of year and focus solely on apple harvest, it is not always the best thing to do. The heavier rainfall that often occurs in August and September is favorable for pathogen development, resulting in increased apple scab and fruit decay (black rot).

Apple Scab

Late season apple scab infections may occur due to wet weather before and during harvest. These late season infections can cause a build up of scab on the leaves after harvest, thereby increasing the inoculum for the following season. Fruit may be infected with scab late in the season, causing rough, black, circular lesions to develop in storage. These lesions (also known as pinpoint scab) are very small in size and may not be visible to the naked eye at harvest, but enlarge after the fruit has been stored for several months. At optimal temperatures (62 - 76°F) it takes 8 - 10 days for scab symptoms to develop after infection, so maintaining a good scab program until harvest is important in managing this disease.

Figure 1. Apple scab on fruit.

Black Rot

Black rot infections on apple fruit also become more obvious later in the season. Although black rot infections often occur early in the season, the symptoms of these infections become more obvious as the fruit mature. After petal fall, black rot infections first appear as small, red specks on the fruit that develop into purple pimples. As the fruit begins to mature, these blemishes begin to grow, turning into dark, brown, necrotic lesions. Recent infections on mature fruit are often dark black in color and are surrounded by a red halo. Late season black rot infections often develop on fruit adjacent to black rot mummies or old fire blight cankers from conidia. Removing dead wood, mummies and cankers from the trees can help to manage the disease. In orchards with a history of black rot problems, fungicides should be used from silver tip until harvest to help manage this disease.

Figure 2. Late season black rot infection on fruit.

Figure 3. Black rot infection on fruit: note concentric rings

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