What Are Red Bumps on Maple Tree Leaves?
- The red maple is one of many maple species.Liquidlibrary/liquidlibrary/Getty Images
Maple tree is a general term given to a variety of shrubs and trees in the genus Acer. Red bumps on maple tree leaves, caused by insect species that lay eggs on the surface of maple leaves and by spider mites, are a common problem of many maple cultivators. Early identification and treatment are vital for reducing damage and further infection on maple trees. - Red spider mites are small arachnids, related to spiders and ticks, which grow up to one-twentieth of an inch, according to the University of California Integrated Pest Management Program (UCIPM). Because of their size, red spider mites appear as small red bumps on the foliage and bark of maples. The mites suck nutrients from individual tree cells, causing localized dead areas. A minor spider mite infestation does not cause substantial or lasting damage to maples; however, a severe infection can cause leaf drop and tree death. To prevent a severe infestation, water maples regularly to prevent water stress. Water stress occurs when plants do not get enough water, thus making it more vulnerable to spider mites. Control consists of physically removing the mites with a water hose, soaps and insecticidal oils, according to UCIPM. However, avoid using broad-spectrum insecticides because they can reduce natural predators, thus causing a more severe infestation.
- When certain insects or mites lay eggs on plant leaves, a hormone interaction causes the leaves to produce abnormal growths, known as galls, according to The University of Kentucky College of Agriculture (UKCA). The maple bladder gall, caused by mites, is largely an aesthetic problem of red and silver maples. Symptoms of a maple bladder gall consist of red circular bumps on the upper surface of leaves, leaf curl and leaf drop. According to UKCA, gall activity usually lasts from the spring months to July. Control for infestations of maple bladder galls consists of physically removing and burning infected leaves and the use of insecticides. However, only use insecticides if the infestation is severe enough to cause continuous damage to the maple tree.
- Maple spindle galls, caused by the mite Vasates aceriscrumena, afflict sugar maples. Unlike maple bladder galls, elongated bladders protruding from the leaf surface identify maple spindle galls. The bladders first appear as green, but change to red, thus appearing as elongated red bumps. Damage from maple spindle galls consists of leaf damage, unsightly leaf appearance and premature leaf drop, according to the Ohio State University Extension Fact Sheet. However, the galls typically do not cause severe damage and do not warrant control. Standard and systemic insecticides are effective at preventing galls, but limit use to only at-risk maples.
