It is quite common for the upper surface of the leaves of certain maple trees, primarily silver maple (Acer saccharinum) and red maple (Acer rubrum) but sugar maples (Acer saccharum) are less bothered, to be covered with small, reddish, round wart-like structures about 1/16 to 1/8 inch in diameter. They tend to appear by mid-May and are green at first. Eventually, they turn a reddish color.

The smaller type of gall are called bladder galls and are caused by spider mites of the species, Vasates quadripedes. Taller, upright growths called spindle galls are the result of damage by the mites in the species, Vasates aceriscrumena.

The mites over winter as adults and feed on the developing leaf buds in the early spring. This feeding results in the development of the galls which are somewhat equivalent to tumors in animals.

As mentioned above, the key symptoms are the small, often very numerous, galls that grow on the top surface of the maple leaves.

Plant Resistant Maples - If the presence of these galls bothers you a lot, you can avoid them by planting types of maples that are resistant to them

1. Do Nothing - This is another of those critters that are an aesthetic nuisance rather than any threat to the health of the tree. The galls do reduce the photosynthetic surface of the leave but by just a tiny, tiny percentage. The tree doesn't even notice it!

2. Dormant Oils - IF you have a prime specimen tree that is seriously infested and you do not want to put up with the situation, you can try spraying the tree with dormant oil. This must be done on a warm day after the leaves have dropped. The intent is to kill the over wintering mites hidden in the bark crevices of the tree. The success of this option may vary considerably depending on the proximity of other susceptible trees.

3. Insecticides/Miticides - There are probably standard insecticides or miticides labeled for use for this problem. Again, this is generally not recommended since this is an aesthetic problem.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

Types of Insects

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