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Heat, drought likely causes of early leaf drop

More than 90 percent of the leaves have fallen off our 30-year-old English walnut trees. They started falling several weeks ago, and two neighbors also have this problem. What is wrong, and what can I do about it?

We are getting many reports of mature trees of assorted species dropping leaves. We suspect that this is a result of stress from the repeated droughts and excessively high temperatures this summer. Other plants are displaying early autumn behaviors, too, such as apples, which are maturing much earlier than normal.

Your trees have had an opportunity all summer to carry on photosynthesis and store carbohydrates in their roots. Because this leaf drop is occurring so late in the growing season, they should be fine. Since you cannot control our warming climate, try to help your trees benefit naturally as much as possible. Mow fallen leaves so they decompose and feed the tree. Let lawn clippings lie.

A landscaper planted bamboo on our property several years ago. Supposedly, the shade would control the growth. Now we need to know how to eliminate this noxious grass so we can plant new plants and bushes.

Running bamboo is not native and can become very invasive, especially when grown in full sun. The best method of control is to spray with a nonselective herbicide containing glyphosate at a 2 percent rate in October, after you've cut it down in spring and let it grow over the summer. Cut down all growth again next spring and spray any regrowth with glyphosate. It may take two to three years to completely kill it. Our bamboo publication includes control strategies and is available on our website, or it can be sent to you.

University of Maryland Extension's Home and Garden Information Center offers free gardening and pest information. Call 800-342-2507 or send a question to the website at

Plant of the week

Sweet Potato

Ipomoea batatas

Old recollections of sweet potatoes conjure marshmallows and brown sugar, but now we learn that sweet potatoes are packed with vitamins and minerals. Even the foliage and flowers are delicious and nutritious. Though technically a perennial, we typically treat them as annuals in Maryland. They are only distantly related to white potatoes but close relatives of morning glories. Yams are an entirely different species.

To raise sweet potatoes for eating, it is best to purchase certified disease-free sweet potatoes. (Store-bought potatoes can be treated to prevent them from sprouting.) Sweet potato vines prefer lots of heat and sunlight and well-drained soil, so avoid heavy soils that stay wet after rainstorms. They do not require much fertilizer, so don't bother feeding them more than a handful of bone meal when you plant. If the soil is very acidic, it would also be appropriate to add some limestone at that time.

Sweet potatoes can take 90 to 120 days to develop, and are harvested after the first frost or when the foliage browns and begins to die. — Lew Shell

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