Relax -- your trees aren't dying

Backyard Q&A

browning was caused by cicadas

In The Garden

July 04, 2004|By Jon Traunfeld & Ellen Nibali | Jon Traunfeld & Ellen Nibali,Special to the Sun

What happened to the trees? It looks like they're all dying. What's going on?

The cicadas may be gone, but we'll see their impact all summer. The "flagging" injury you're seeing -- lots of dead twigs at the ends of branches -- resulted from the millions of small slits made by females for depositing their tiny white eggs. This disrupted the vascular system of the twigs, preventing water and nutrients from reaching the ends of branches. Although the results can look alarming, usually it amounts to no more than a benign tip pruning by Mother Nature. Cicadas are a native insect, and their 17-year tip pruning has occurred for eons. Unsightly dead tips can be pruned off, but they'll fall off eventually with no hardship to the tree.

We have an asparagus patch of about 300 feet of rows. The plants are 5 years old and filled with grass and weeds. Is there any application (other than hand weeding) we could use now that is safe and effective and that will kill the grass and weeds, but not adversely affect the asparagus plants?

There is no herbicide labeled for home garden use that can be sprayed after asparagus shoots emerge in the spring. At this point, we recommend that you hand-pull or cut the weeds with a hoe.

Weeds should be removed every spring before the first shoots come up, to avoid breaking off the spears. Then a thick layer of mulch (3"-4") should be applied to the bed. You can mulch with grass clippings or weed-free straw. Any weeds that come through the mulch should be removed immediately.

There is a pre-emergent herbicide called Preen that prevents certain grassy and broadleaf weeds from germinating. (The key here is that the herbicide must be labeled safe for use on asparagus.) This herbicide can only be applied before spear emergence of established plants next spring. Check the label for a listing of weeds controlled.

Other organic methods of weed control include spraying with vinegar (5% acetic acid). The spears and fronds would have to be protected. Burning, with a hand-held propane flamer sold as a weed control device, also could work.

For more information on Preen, do a Web search, visit www.preen.com or call 800-233-0626.

My Japanese snowbell tree is getting weird little protrusions from the bark. They look like pencil lead, but are very fragile and crumble when touched. Should I be concerned?

The protrusions you see are frass (sawdust and fecal material) pushed out by an ambrosia beetle as it bores into the tree. Ambrosia beetles will bore into many tree species when the trees are stressed, but also they will attack healthy snowbell (Styrax) and yellowwood. There are two generations yearly. The first does the most damage, though it is not necessarily fatal. It is too late to treat your tree now.

Beetle populations vary greatly from year to year; there seems to be an abundance of these pests this year. Ambrosia beetle populations are monitored each spring using traps.

If you have lost a tree, call the HGIC hot line (see below) in March or April to determine the year's population. If numbers are high, you may want to have a preventative insecticide applied by a certified pest control operator.

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 to www.hgic.umd.edu. (You can also download or order publications and diagnose plant problems online).

Checklist

1. Pinch out aster and chrysanthemum buds before they open to increase their fall flower display.

2. For a keen edge, sharpen hoes and other garden tools with a belt sander.

3. Pull off tomato fruits with large brown or black spots on the bottom (blossom end rot). Water your plants deeply and regularly. Next season, add a small handful of lime to the planting hole.

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