Question
should i worry, i have green and black sac like growths on my silver maples, it is causing brown spots on the leaves. worried it may be something besides mites.

Answer
Galls are irregular plant growths which are stimulated by the interaction between plant hormones and growth-regulating chemicals produced by some insects and mites. The maker receives food and protection from the gall tissue. Gall populations fluctuate from year to year, occasionally becoming very abundant. Despite the aesthetic impact and premature leaf drop during outbreaks, tree vigor is not affected significantly.



Gall makers must attack at a particular time in the year to be successful. Otherwise, they may not be able to stimulate gall production. Generally, initiation of leaf galls occurs around "bud break" or as new leaves begin to unfold in the spring. Once the symptom or gall appears, the organism is protected in the structure, making remedial actions ineffective.

Most galls occur on early spring foliage that develops near the trunk and on larger branches. Additional galls are formed on newly developing leaves later in the summer but mites are most active early in the season. Galls usually form on a small proportion of the leaves and tree health is unaffected.

Leaf galls are fairly common on trees and shrubs. A gall is actually plant tissue that has developed as the result of feeding or other activity by insects or mites. Plant hormones are involved when the pest interferes with leaf development in the spring. There are also galls caused by fungi, bacteria and other organisms.

Once the gall appears on the leaf, there is no way to control it. Preventing most leaf galls is extremely difficult. However, other than being unsightly, most leaf galls are not harming the tree or shrub.

I would not worry about these they are not really effecting the overall health of the tree.