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Gall Mite Identification
Gall mites are translucent, cigar shaped, microscopic mites that feed on many different plants. There are over 2000 species of eriophyid mites. Some are host specific, others feed on a wide variety of plants. The adult females overwinter as fertilized adults and reproduction is continuous. When buds begin to break open in spring, the mites emerge and begin to feed on new growth.
Gall Mite Symptoms
The salivary secretions from the mites spark increased production of plant growth hormones, which result in increased cell size and leads to galls. This mostly occurs when the plant is an accelerated growth period (late spring, early summer). Feeding can cause abnormalities like leaf curling, blisters, rusts, slivering, fruit russeting, and deformed buds, finger-like galls, and pocket pocket galls. The feeding of the mites forms galls. Gall mites cause ash flower gall, maple bladder gall, spindle galls on maple and linden, velvet galls on maple, along with many other plants. These mites don’t often affect mature plants.
Gall Mite Treatment & Control
Since gall mites cause no real harm to the plants they feed on, treatment is generally not recommended. However, if the unsightly deformations bother you, or if repeated infestations are affecting your plant’s growth, there are some measures you can take. Monitoring plants, using plants less susceptible to gall mites, removing infested leaves and branches and heavily infested plants (like corn or wheat), can help keep infestations down. Pesticides formulated for mites can be used if absolutely necessary. Spraying plants at the period when buds begin to break open is a good time to spray. Remember to read instructions and keep in mind that you may reduce the populations of natural predators for other pests.
Information via DoMyOwnPestControl.com experts, Colorado State Extension, and Utah State University Extension.
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Do your maple trees have gall mites? You may have noticed unsightly growths on the leaves of your silver or sugar maple trees this summer. Some folks have been coming into our Naperville shop telling us they have something that looks like chicken pox on their plants! Clusters of small, raised bumps that start out green and then turn red and black are the signs that gall mites have been building homes there. In some cases the galls cause leaves to turn yellow and fall prematurely. While looking alarming, the galls will not cause long-term harm to your tree. There is no need to treat for this condition; you simply need to wait for the process to take its course.
Eriophyid mites are often the culprits causing galls. Tiny enough to be invisible to the naked eye, these parasites are drawn to leaf buds in the spring before they open. They build the galls and then feed inside them and females lay eggs. Usually, by July the mite activity is finished for the season. Other causes of galls can be fungus or bacteria. More information about plant galls can be found at the Morton Arboretum website, http://www.mortonarb.org/trees-plants/plant-clinic/help-pests/plant-galls
Some of our customers have asked about this and other conditions as a result of the excessive rain we’ve received this spring and summer. Be assured that plant galls can occur in any weather condition, and your maple trees should not be adversely affected. Sometimes young trees can show signs of deformed growth after an infestation. You can remove the affected branch if desired.
This year’s cool, wet weather has caused some concern about diseases affecting our trees and shrubs. We will talk about some of these and how to treat them in future blogs. Remember, your outdoor living space and the trees, shrubs and plants in them will bring you years of enjoyment and add value to your property. Taking a little time to maintain them will pay off for years to come.
For over 45 years, O’Donovan and Sons Landscaping has been designing, installing and maintaining residential landscapes in Naperville and surrounding areas. We can help you design and install your new outdoor living spaces. Call us at 630-355-3370 to schedule an appointment!
Leaf Galls on Maple
Maple, Acer spp., leaves are often infested with a wide variety of brilliantly colored, odd-shaped galls and blotches. Some of these abnormal plant cell growths called galls, are caused by very small eriophyid mites in the family Eriophyidae (Fig. 1). Members of this family of mites are commonly referred to as eriophyid mites. Several species of eriophyid mites cause leaf galls on maple. They are the maple bladdergall mite, Vasates quadripedes Shimer, maple spindle gall mite, V. aceriscrumena (Riley), and some erineum gall mites, Eriophyes spp.
Figure 1. An eriophyid mite, greatly magnified.
The maple bladdergall mite, V. quadripedes , is a native pest in eastern North America on silver maple, A. saccharinum , and red maple, A. rubrum foliage. Foliar feeding by this species results in the formation of green or red globular growths that are about 2.5-3 mm in diameter on the upper leaf surface (Figure 2). These galls are usually noticed during May, about the time the leaves are fully expanded. At first, these growths are green, then they turn red, and eventually black. In some cases, galls become so abundant that infested leaves become deformed.
The maple spindle gall mite, V. aceriscrumena , causes galls to form on the upper surface of sugar maple, A. saccharum foliage. These galls are small, elongate, projecting growths that give the leaf a spiked appearance.
Erineum galls are caused by several species of eriophyid mites in the genus Eriophyes . These eriophyid mite-caused galls are crimson-red patches on the lower and upper leaf surfaces of silver and sugar maples. Erineum galls vary in size and shape, usually resembling patches of red felt. When viewed under magnification, these galls look like the beaded surface of a slide projection screen..
Figure 2. Maple bladdergall mite caused galls on the upper surface of a silver maple leaf.
Eriophyid mites that infest maple foliage overwinter as adults under bark scales and other protected sites on the host tree where they are able to withstand severe weather conditions. Early in the spring they migrate to newly expanding leaves and begin to feed.
Eriophyid mites that are responsible for the formation of bladder galls and spindle galls feed on the lower leaf surface. At first, a slight depression results from their feeding, followed by the leaf rapidly producing a pouch-like gall that encloses the mites. An opening remains on the underside of the leaf. The mites continue to feed and mature within the leaf gall. Mating and egg deposition also takes place within the gall. Young mites hatch from the eggs and remain within the gall until they reach maturity. At that time, they move to new leaves to start other galls.
In general, these galls are not harmful to the health of a tree. The brilliant red color associated with these galls generally alarms some people who believe the trees are “diseased” or seriously damaged. Feeding by eriophyid mites appears to stimulate the formation of galls on the upper and lower surface of the leaves. Occasionally, photosynthesis (food making process by plants) may be reduced in individual leaves that are heavily infested. If many leaves on a tree are heavily infested, there may be some reduction in growth.
In general, leaf galls do not seriously affect the normal growth of a tree. Thus, chemical control is seldom suggested. If indicated, the best time to treat an infested tree with a registered insecticide applied according to label directions for management of eriophyid mites is mid-April, before buds swell. Adults move from their overwintering sites to new growth at this time of the year. This treatment may help reduce the eriophyid mite population on an infested tree.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Greg Hoover, Sr. Extension Associate
Revised March 2004