11/13/2022 0 Comments Maple leavesThere are several different species of mites that cause different types of galls. Because pesticides have limited impact on the mites, it is better to put efforts into good horticultural practices, such as watering and fertilizing, as needed, rather than spraying. These should be applied prior to bud break. Because the mites overwinter on the host trees, dormant oil sprays can be quite effective (although oil sprays should not be used on sugar maple, Japanese maple and other oil-sensitive trees such as birch, hickory and walnut because of phytotoxicity problems). Application to the lower leaf surface should be made on a warm day in the spring when the leaves are about 1/4 expanded and again 10 days later. Infestations are often worse on leaves nearest the overwinter sites on the bark.įor trees with extreme infestations, preventative treatments in very early spring to control overwintering mites – as they begin feeding on the expanding leaves but before the galls have enclosed them – may reduce the incidence of galls but are generally of limited value. Once the galls have formed, the mites are protected within the galls, so sprays will not be effective. Damaged leaves can be handpicked to reduce mite populations. However, on newly planted trees with less foliage, galls may be a significant stress. Control is generally not recommended for this primarily cosmetic problem on established trees. Although the galls may look dramatic, they actually have very little effect on plant health, even in severe infestations. Homeowners are often concerned when they notice the highly conspicuous and sometimes colorful growths and want to do something to correct the problem. But usually the mites and their galls cause little harm. Heavy infestations may deform the leaves or cause premature yellowing and drop. Abundance also varies greatly from year to year, with galls appearing sporadically. The leaves closest to overwintering sites are most heavily infested. The extent of infestations can vary greatly, with large concentrations of galls on some trees or portions of trees, and very little on adjacent trees or the other part of a single tree. Heavy infestations may cause leaf deformity. There may be several generations during a growing season. At this time they head for the trunk and branches to overwinter in roughened areas on the bark, bud scales, or other protected places. Once the tree has stopped new growth, usually in early summer, the mites are unable to stimulate the abnormal growth to produce the galls. They then exit through an opening on the underside of the leaf to crawl to newly developing leaves and begin the cycle again if the tree still has new leaf growth. They remain within the galls, feeding on the gall tissue until they have matured into adults, usually within a few weeks. The eggs hatch into whitish-orange, carrot-shaped nymphs with two pairs of legs. #MAPLE LEAVES FULL#Once the leaf has expanded completely and reached its full size, the adult mites lay numerous eggs within the galls and die. Mite feeding causes the abnormal cell growth that causes gall formation. The mites get nutrients from the inner gall tissue and are protected from natural enemies (and also pesticides). Each mite species produces slightly different substances, resulting in the different characteristic gall shapes. This abnormal growth forms the galls that gradually enclose the mites. As they feed on the developing leaf tissue, growth regulating chemicals produced by the mites interact with plant hormones causing an abnormal stimulation of cell growth. The adult mites become active very early in spring, just as buds begin to open. The mites, less than 2mm long, are too small to be seen without magnification. These strange swellings are plant galls caused by the feeding of tiny eriophyid mites on newly developing foliage. If you have a maple tree, you may have noticed weird growths on the leaves in some years. Bumpy growths caused by maple gall mites cover silver maple leaves.
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