The gall wasp, Andricus quercuslanigera, causes a woolly gall on the midrib of the leaves of live oak.Oaks in general have a flourishing fauna of gall wasps associated with them. The abnormal growths developing in oak tissue are due to the powerful enzymes given off by the immature gall-forming insect as it grows. Galls are abnormal swellings of plant tissue, usually on leaves and stems. Each gall, produced by single aphid, later becomes filled with offspring. This typically causes the leaves to appear scorched. The resulting larvae cause oblong blister-like galls to develop on the leaves. Mature aphids with wings leave the galls in late spring and early summer and fly to … Gall midges (Cecidomyiidae) are a large group of small (usually less than 1/4 inch long), delicate flies that cause bud galls, blister galls, and galls on leaves and other plant tissues. For example, the oak-apple gall appears as fairly large, round, apple-like growths. They may be caused by insects, mites, bacteria, fungi, or nematodes. These are caused by a very small wasp. Most insect and mite galls are caused by chemicals produced by the egg laying and feeding activities. The chemicals cause the affected plant cells to swell. A sunken scar marks the spot of the gall. These eriophyid mite-caused galls … These spores are spread by the wind and splashing rain to the bark or buds of other camellias where they’ll lie dormant until next year and cause infection next spring. They grow to the size of a golf ball and have an interesting life cycle. As these galls mature, several layers of the lower leaf surface will peel away revealing a white color, which is the spores of the fungus. Most leaf galls on oak are not damaging. However, twig or branch galls may cause injury or even death to a heavily infested tree. Some may affect twigs, such as the gouty oak gall, and actually cause some dieback. In general, most gall wasps on oak trees don’t affect the trees' health. If enough galls form on a leaf, the leaf may die back. The adults emerge from the gall in early summer and lay eggs on the leaves of the tree. One Extension agent … The maple spindle gall mite, V. aceriscrumena, causes galls to form on the upper surface of sugar maple, A. saccharum foliage. Leaves of hackberry trees often have the hackberry nipple gall, caused by an … 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. Most leaf galls on oak cause little or no harm to the health of a tree. The gall in this tree is a Horned Oak Gall. Neuroterus irregularis causes an irregular gall on the leaves of post oak. This gall is caused by an aphid that passes the winter in eggs laid on twigs of the plant. Galls may drop from leaves, leaving only the damaged foliage. 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