Trees Suffer During Prolonged Drought.

• Position: WATER SHORTAGES

August usually is hot and humid, bringing about a certain lethargy when it comes to yard work. 'Who wants to work outside in this heat?" you may ask as you settle down in the shade of a tree with a pitcher of your favorite soft drink--but to keep that shade oasis growing healthy in your landscape, it is important to take some simple proactive steps to ensure its longevity, especially during times of drought.

"While it's impossible to keep every tree in good health during severe drought, taking a proactive approach for a prized tree or one for which you have sentimental attachment can prevent long-term damage," advises Tchukki Andersen, staff arborist with the Tree Care Industry Association, Londonderry, N.H. "A tree that is supported with good cultural practices, preemptive monitoring for pests and diseases, and appropriate responses to warning signs will have an increased chance of survival."

A drought's effects start beneath the soil line, in the form of root damage, long before any outward signs of trouble. After a tree's unsuccessful attempt to conserve water by closing leaf stomata (pores), its feeder roots die back, sometimes so drastically that the tree is unable to absorb enough water to support itself.

Such drought stress may lead to tree death, but usually the signs of stress are much less dramatic. "Leaves are undersized and may wilt, yellow, curl, or crinkle, and may be marginally scorched or even turn brown and drop early," explains Andersen. "Emergent shoots are short. In an effort to right the imbalance caused by root loss, crown dieback or a general thinning of the canopy occurs."

This is when "opportunistic" pests make their move. Boring insects are thought to be drawn to the chemical and acoustic signals of stressed trees. The sound of the tree's breaking water columns cues the borer to invade the tree and lay eggs.

Andersen recommends applying a three-inch layer of composted wood chip mulch on the ground over the root zone at least out to the drip line (the ground under the outer edge of the branch spread). This will hold moisture longer for stressed roots to access, and will provide a long-term nutritional source for the soil. Prized or important trees may be protected from wood-boring insects with spray or injection chemicals, but they should be treated before becoming drought-stressed.

Stressed trees also are vulnerable to fungal pathogens. Andersen notes that, when a...