Gardening Help FAQs

Here are answers to some of the most common questions we receive about garden plants. You will find concise information on general gardening techniques as well as plant selection and care. For detailed information on specific plant pests and problems refer to our Common Garden Pests and Problems page.

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Horticulture Questions and Answers

What are these bumps on my maple tree's leaves?

In early spring, maple leaf tissue may develop irregular, spherical, or bladder-like growths, known as galls, on the upper surfaces of the leaves. Leaves next to the trunk and on large branches are most affected. The galls are yellowish green at first, but later turn pinkish to red and finally black. If the galls are numerous, leaves become deformed and may turn yellow and drop prematurely.

Bladder and spindle gall are caused by tiny mites, too small to be seen with the naked eye. Each gall contains one mite. The mites congregate on buds just before they open in the spring. As the buds open, each mite punctures and enters a leaf on the underside, injecting a growth-promoting substance that causes abnormal tissue formation. A gall encloses the mite, with an opening remaining on the underside. The mites feed, and females lay eggs inside their galls. The eggs hatch, and as they mature, the young mites crawl out through the opening and infest new leaves. In late summer, mite activity stops and the mites migrate to the bark to spend the winter.

Gall growths on leaves are unattractive and may cause concern, but damage to the tree is purely cosmetic. Because the tree's health is not involved, homeowners need to decide if spraying is really necessary. Large trees are difficult to spray and you may need a professional to do a proper job of spraying. The number of galls will fluctuate from year to year and may disappear on their own. If young trees suffer regular damage, consider spraying buds, branches, and trunk with a dormant oil spray or Kelthane before the buds begin to open in spring.