Background and Description
Apple rust mite (Aculus schlechtendali, ARM) may occur wherever apples are grown, but it is usually not a significant pest in Southeastern orchards because it almost never causes significant damage. In addition, it provides an alternate food source for mite predators when other prey species (such as European red mite) are not present, and therefore under normal conditions it can even be considered a beneficial organism.
ARM adult females are minute (1/150 inch or 0.17mm long) and cannot be seen without magnification. Males are slightly smaller. The body is yellowish and wedge-shaped, tapering at the abdomen. Eggs and immatures are extemely small and are unlikely to be observed.
Adult female ARM overwinter in crevices, especially on bud scales. In springs females become active, feeding on the undersides of leaves and laying eggs that will develop through two instars relatively quickly (10 to 14 days from egg to adult). There may be several generations before overwintering females are produced in July or August.
Like other Southeastern mite pests, ARM feed on leaves. If populations build to 200 or more mites per leaf, leaves may become silver and curl lengthwise, as if the tree is under drought stress. Fruit may also become russeted, though this occurs only under extremely high populations.
Monitoring and Control
ARM is rarely a concern in North Carolina orchards. To monitor, use at least a 15x hand lens or microscope to observe 100 leaves (10 leaves x 10 different trees), examining primarily the midrib near the base. If an estimated average exceeds 200 mites per leaf, a pesticide application may be necessary. Smaller populations do not require treatment and in fact may be beneficial by providing food to predatory mites that will in turn control more significant mite pests, such as European red mite or twospotted spider mite.
Publication date: Feb. 23, 2015
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