University of Maryland Extension: Garden Q&A
A: Galls are very common on oaks and maples. These growths are abnormal swellings of plant tissue, usually leaves and twigs, caused by insects, mites, bacteria, fungi, or nematodes.
Most insect and mite galls result from chemicals introduced by the egg laying and feeding activities of the organism. The chemicals cause the affected tree cells to swell. Though galls appear in many strange forms, they rarely do any harm. They do not affect the health of the tree and are more of a cosmetic issue. Chemical control is not recommended.
Q: Help! This has occurred now the second year. I just let my dogs out and looked at the garden for ten minutes and, even through my stockings, I must have five welts like mosquito bites. I don't see a thing. This occurs only on one side of the garden.
A: If you can eliminate fleas as the culprit, mosquitoes are the best bet. The Asian Tiger Mosquito, a recent arrival to our shores, is extremely pesky. It feeds during the day (unlike her more nocturnal cousins), is a persistent repeat biter, and worst of all, is a carrier of West Nile virus.
Wear suitable clothing when in the yard and spray exposed skin with a repellent containing 'deet.' Scout your home and landscape often and eliminate any sources of standing water. There are many surprising places. Check drain pipes, flower pot saucers, indentations in tarps, rain gutters, etc. All Asian Tiger mosquitoes need is a teaspoon of water to reproduce. Refresh bird baths weekly or more often. Keep high grass and weeds to a minimum.