Powdery mildew on lilacs in the fall doesn't hurt them

Backyard Q&A

October 11, 1998

Q. I've finally learned what powdery mildew looks like, and I'm sure I have it on my lilacs, dogwoods and crab apple trees. How bad a disease is it and what should I be doing about it?

A.Powdery mildew is a generic term for several fungal pathogens that attack a wide range of plants at different times of the growing season.

Powdery mildew that arrives late in the season on lilacs will not harm your plants. It's unsightly, but no action need be taken. As for dogwood and crab apple trees, powdery mildew attacks blooms and new foliage early in the season.

If untreated, your trees will be weakened. Apply a summer rate of horticultural oil to your trees just as new leaves emerge. See this rate on the product label and closely follow all label directions.

Q. I have some basil in my garden that I know will be killed by the first frost. We love fresh basil. Is there a way to grow it indoors?

A.Sure, just take some cuttings and place them in glass jars with water. They will root and grow easily in a bright kitchen window. You can also pot some of the cuttings in a loose, soil-less growing medium.

Q.My neighbor has a tree that is covered with millions of red insects. It's a spectacular sight, but I'm worried about them eating my trees. What's the insect?

A. It's box elder bug time! The box elder tree is a weedy native species; it has compound leaves with three leaflets that resemble poison ivy leaves. The female tree has large clusters of winged seed pods.

Box elder bug nymphs and adults congregate in early fall on the female trees. They only feed on box elder trees, but this feeding does not damage the trees.

In their search for protected areas in which they can over-winter, box elder bugs may head for your house. Your biggest problem may be bugs clinging to the sunny side of your house or entering your home in search of warm, sunny areas. Seal up all cracks around vents, windows and foundation.

This Week's Checklist

* Don't worry if some of the needles on your evergreens are yellowing and dropping. It's natural for the older needles to die off now. As long as the remaining needles are green, there's no cause for alarm.

* Harvest small ornamental squashes before the first frost. Clean them gently with a damp rag.

Garden tips are provided by the Home and Garden Information Center of the Cooperative Extension Service of the University of Maryland. For additional information on these questions, or if you have questions of your own, call the center's hot line at 800-342-2507, or visit its Web site at www.agnr.umd.edu/users/hgic.

Pub Date: 10/11/98

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