2005 Year in Review

Drought and Heat Stress

Source: James Schuster (708) 352-0109; Contact: Bob Sampson, Extension Communications Specialist, Phone (217) 244-0225; rsampson@uiuc.edu

Drought and heat stress can be tough on plants, and some trees respond by shedding their green leaves or leaflets until the foliage is re-balanced to available moisture, said a University of Illinois Extension horticulture educator.

"Some maple and ash trees are very prone to shedding the green leaves and leaflets," said James Schuster. "Other trees hang onto their leaves, but then the leaf tissue farthest from the veins dries out, turns brown, and dies. The hotter and drier it stays, the more leaf tissue is killed.

"Scorching is the name given to the appearance of leaves that are partially alive and dead due to drying out."

However, Schuster cautioned that sometimes scorched leaves can be confused with diseases. 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 his or her trees before the hot, dry weather. Anthracnose likes wet weather."

Ironically, both drought and drowning often cause a similar appearance on the above-ground plant parts. When plants are too wet, the roots may suffocate or drown or the excessively wet soil may encourage root rot.

"As the roots die, the above-ground plant parts do not get enough water from the surviving roots," said Schuster. "Therefore, the plants developed scorched foliage. Homeowners often see wilting due to drowning and think the plants are not getting enough water. They then water--increasing the drowning of roots. When plants are in drought stress, there just is not enough moisture to keep all the foliage alive. Therefore, either scorched leaves appear or leaves are dropped green."

To minimize scorching, Schuster said it is important to make sure plants have adequate drainage. Plants growing on the side of a slope or hill do not necessarily have good drainage, he noted.

"Avoid over-watering, especially with an underground sprinkler system," he said. "During drought, water deep but not frequently. Plants that are watered properly should be able to go a week or more between waterings. Plants that are mulched correctly can go even longer between waterings.

"For most trees and shrubs, try to water 12 or more inches deep and go deeper on sandy soils. Clay soils do not absorb water as quickly as sand so water trees growing on clay at a slower rate to avoid or reduce run-off. On large trees, start several feet out from the trunk and water as far as the tree is tall in all directions or as far as property lines, roads, houses, and so forth allow."

by  Editor, theCity1.com
June 29, 2005