Thursday, August 23, 2007

Think of the summer-long drought as a very large cloud with a very thin silver lining.

The lining? For many gardeners, the absence of water has reduced the populations of mosquitoes and slugs, and suppressed the type of foliar fungal diseases and root and crown rots of shrubs and perennials common in wet years.

Rock-hard soil has also been tough on Japanese beetles, which can be a scourge to turf grass and ornamental shrubs. They prefer soft soil in which to lay eggs in early summer. The dryness reduces the survival rate of both the eggs and those larvae that do hatch, said Michael Raupp, an entomologist at the University of Maryland.

Don't rejoice too much, however, if you live close to a condo community, golf course, retirement home or any other property with an efficient irrigation system, where you can still expect to see large beetle populations next summer. "Those Japanese beetles were as happy as clams in the ocean," Raupp said.

Now for the cloud: Gypsy moth caterpillars have been held in check in recent years by a parasitic fungus. "Because we have had compounded years of drought, the fungal populations have declined, and gypsy moth populations are back with a vengeance," Raupp said. This is bad news for the shade trees defoliated in late spring by this voracious pest. Couple defoliation with drought stress, he said, and you have a secondary pest moving in -- the two-lined chestnut borer and other borers -- to kill off old trees.

It may be too late to save many trees and shrubs, whose decline may take a season or two to occur. But Raupp suggested watering again soon if this week's rain has not broken the pattern of drought. If the rain "shuts off next week, I will be irrigating my trees and shrubs to help them get ready for the winter," he said.

Adrian Higgins