Galls on oaks and maples do no harm to the trees


July 10, 2005|By Jon Traunfeld and Ellen Nibali | Jon Traunfeld and Ellen Nibali,Special to the Sun

My pin oak has little nutlike growths on its leaves. What should I do?

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 egg laying and feeding. 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.

What is the thorny nonflowering vine climbing up my trees and through my fence? I spray every year with glyphosate but can't rid of it completely. My neighbors have it as well but don't seem concerned at all.

It might be greenbrier if its leaves are medium-sized and glossy and the stems stay green in winter. In a natural area, greenbrier is a desirable native vine that feeds wildlife. However, in ornamental landscapes, mature greenbrier can be objectionable and difficult to eliminate. Herbicide does not adhere well to the glossy foliage, unless a spread-sticker is added to the herbicide. An efficient and economical way to tackle woody plants like greenbrier is to cut down the stems and apply high strength glyphosate or triclopyr to only the freshly cut stem within 5 minutes. Early fall is a prime time to apply herbicide because it moves well to roots then. Greenbrier is especially hardy because of a nutlike nodule on the roots that stores energy and can reach inches in diameter. It must be dug up when all else fails.

I grew cosmos from seed and now three of them, 18 inches tall, have keeled over about 3-4 inches above the ground. Looks like something was inside the stem, turning the inside brown and weakening the stem. Could ants do this? Is there anything I can do now?

The ants are innocent. Cosmos can get a couple of stem borers. (One is the common European corn borer.) With borers, you should see expelled borings coming from a hole, or, if you slit the stem, you should find the borer inside. If it's borers, it may be too late this year to save your cosmos. Preventative sanitation is important. Remove any infected stalks plus weeds where the borers could overwinter. Rotating the planting sites of cosmos is helpful.

On the other hand, your cosmos may have a stem rot, which is most common when temperatures are high and plants are overwatered. This is a soil-borne disease. Remove infected plants plus the surrounding pocket of soil or else plant elsewhere next year. Provide good air circulation by keeping plants well spaced, avoid overwatering, keep mulch a few inches back from plant bases, and plant in amended soil that drains well.

Jon Traunfeld, regional specialist, and Ellen Nibali, horticulture consultant, work at the University of Maryland Cooperative Extension's Home and Garden Information Center. The center offers Maryland residents free gardening information and answers to plant and pest questions. Call its hot line at 800-342-2507 (Monday through Friday, 8 a.m.-1 p.m.) or e-mail questions through the Ask a Question feature on the Web site at (You can also download or order publications and diagnose plant problems online.)


1. Pinch off basil flower buds to keep plants bushy and productive.

2. Prevent mosquito problems by dumping out standing water wherever it collects outside your home.

3. Remove tree branches that overhang your home to keep squirrels from gaining access to your attic.

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