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The Drought, Act II

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By Adrian Higgins
Thursday, March 27, 2008; Page H01

Those lovely cues of the dawning spring -- the smell of mulch, the sight of pale blossoms, the sweet softness of the greening grass -- all point to the celebration of a new growing season.

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Enjoy the moment, for the year ahead will be a tough one in the garden.

We may have forgotten what happened last year, but our plants have not, especially the biggest of them. "It's hard to talk to someone about drought when it's pouring with rain," said entomologist Rex Bastian. "But the trees remember."

They remember weeks of little or no rainfall, of the soil hardening around their dying roots and the leaves turning and dropping early. The ill effects of one of the worst dry spells on record will be seen this spring and summer and may linger for years. Look for symptoms of delayed drought stress in your woody plants so you can help them, and be prepared for some to die.

"Trees don't react quickly and often tend to show effects after the damage has occurred," said Bastian, vice president of field education for the arborists group the Care of Trees.

Amid the splendid ornament and fertility of spring, spare an eye for old, arboreal friends, and be prepared for such symptoms as dead branches, stunted growth and worse. "A lot of symptoms probably won't show up until the summer," said horticulturist David Yost, who runs a plant clinic at Merrifield Garden Center in Fair Oaks.

Some are already evident, however. Yost said a customer arrived recently with a sad sample of an azalea bush bearing the effects of a September with just six-tenths of an inch of rainfall. "Growth was poor, color was poor and the flower buds had not set," he said.

Barbara Bullock, curator of the azalea collection at the National Arboretum, said she is not seeing so much bud loss in Washington's favorite spring flowering shrub as the death of branches. "Major branch dieback in mature azaleas," she said. "We have been pruning lots of dead wood."

Bastian said you don't have to remove every dead twig from a tree, but major limbs that are dying or dead should be removed, not just for the health of the tree but to prevent a hazard to people and property. The removal of large tree limbs is a perilous job best left to the professionals.

Canker diseases are another drought-related malady, seen as sunken areas beneath bark or as parts of the trunk eaten away. If allowed to spread, the decay can kill branches or a whole tree.

In addition, drought stress can bring on a root rot disease that, once present, will slowly spread and kill a tree. The fungus, armillaria, is also called shoestring fungus for the strands that kill roots and cause cankers at the base of the trunk.

One of the most damaging insect pests to drought-stressed trees is the borer, numerous species of beetles whose larvae tunnel into the vascular system of a tree and, if present in sufficient numbers, can kill it. A species called the two-lined chestnut borer is particularly pesky and targets oaks as well as chestnuts. Often, the damage is in the tree canopy and not apparent, but the insect can also attack the base of the tree, where it is even more lethal.


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