2009 Year in Review

Drought and Heat Stress on Trees

Summer's hot temperatures can pose challenges for trees, said a University of Illinois Extension plant pathology specialist.

"Some trees, such as maples and ashes, instead of scorching, shed their leaves or leaflets while they are green until the trees rebalance the remaining foliage to available moisture the tree can take up," said James Schuster. "Some maple and ash trees are very prone to shedding the green leaves and leaflets. Other trees hang onto all their leaves but then the leaf tissue farthest from the veins dries out, turns brown and dies. The hot and drier it stays, the more of the leaf tissue is killed.

"Scorching is the name given to the appearance of leaves that are partially alive and dead due to drying out." Sometimes scorched leaves can be confused with diseases, he added.

An example would be anthracnose. Anthracnose on oak, maples and ashes seem to be more commonly confused with scorching especially, if the homeowner was not paying attention to their trees before the hot dry weather. Anthracnose likes wet weather.

Drought and drowning often cause similar appearance on the above-ground plant parts," he said. "When plants are too wet, the roots may suffocate or drown or the excessively wet soil may encourage a root rot. As the roots die, the above-ground plant parts do not get enough water from the surviving roots.

"Therefore the plants develop scorched foliage. When plants are in drought stress, there just is not enough moisture to keep all the foliage alive. Therefore scorched leaves appear."

To minimize scorching, make sure plants have adequate drainage and are watered correctly during droughts, he said.

"Plants growing on the side of a slope or hill do not necessarily have good drainage. Avoid overwatering, especially with an underground sprinkler system," Schuster noted.

"During drought, water deep and infrequently. Plants that are watered properly should be able to go two weeks or more between waterings."

Plants that are mulched correctly can go even longer between watering. For most trees and shrubs, try and water nine to twelve inches deep at least (deeper on sandy soils). Clay soils do not absorb water as quickly as sand or silt so water trees growing on clay at a slower rate to avoid or reduce runoff.

"On large trees start several feet out from the trunk and water as far out as the tree is tall in all directions or as far as property lines, roads, houses, and so forth allow," he said.

by  Editor, theCity1.com
May 21, 2009