Dealing with drought, heat stress in trees

The early summer heat and lack of rainfall can affect landscape trees in our area. The sight of scorched tree leaves caused by drought and/or heat stress can be alarming to homeowners and quite often can sometimes be confused with diseases.

Anthracnose Disease on oak, maple, and ash varieties seems to be more commonly confused with scorching especially if the homeowner was not paying attention to the trees before the hot, dry weather set in. Anthracnose likes wet weather.

Some trees respond to a lack of adequate moisture and excess heat by shedding their leaves or leaflets when still green until the trees re-balance their foliage to available moisture.

Other trees hang onto all their leaves but then, the leaf tissue farthest from the veins starts drying out, turns brown, and dies. The hotter 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 due to drying out.

Drought and too much water (drowning), ironically enough, often cause similar appearances on the aboveground plant parts. When plants are too wet, the roots may suffocate or drown, and 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. Therefore, the plants develop scorched foliage.

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

To minimize scorching, make sure plants have adequate drainage. Avoid overwatering, especially with an underground sprinkler system. Avoid overhead watering which wets the leaves. And, during drought, water deeply but not too frequently. Plants that are watered properly should be able to go a week or more between watering. Plants that are mulched correctly can go even longer between watering.

Container plants out on the patio however can really be stressed by the heat wave since they have much less buffering of temperature extremes on the root system. Providing that the container has adequate bottom drainage, you can water container plants more frequently in hot weather. The bonus to containers is your ability to relocate them unless their size/ weight prevents this. If you notice scorched leaves on your container flowers, shrubs and/or small trees move them to a spot that will provide afternoon shade, if possible, which will help to keep them a bit cooler.

Trees surrounded by asphalt and growing in parking lots or next to large buildings that have reflective surfaces are at much greater risk for heat stress than trees surrounded by landscape plants or even bare soil.

Typical signs of drought and heat stress include wilting leaves, scorched leaves, leaf drop, branch dieback, sunscald on branches and trunks, reduced or no new growth and potential plant death. While some symptoms will be apparent during or after extended drought or extreme heat, in trees, reduced growth or mortality may also occur in subsequent years.

For most trees and shrubs, try to water at least 6 to 8 inches deep and deeper on sandy soils. Clay soils do not absorb water as quickly as sand or silt so plants that are growing in clay should be watered at a slower rate to avoid or reduce the water runoff. One of the best methods for deep, slow watering is to coil a soaker hose around the tree several feet away from the trunk all the way out to the drip line and let it run to get the required depth of moisture.

4-H information

There are several 4-H Clubs for Garland County youths who are 5 to 19 years old. For more information on all the fun 4-H activities available, call Carol Ann McAfee at the Extension office, 501623-6841, or email cmafee@uada.edu.

Master Gardener information

Master Gardener meetings are held on the third Thursday of each month at the Elks Lodge. They’re open to the public and guests are welcome. For more information call Luke Duffle at 623-6841 or email him at lduffle@uada.edu.

EHC information

Are you interested in joining an existing Extension Homemakers Club? EHC is the largest volunteer organization in the state. For information about EHC, call Alison Crane at 501-623-6841 or email acrane@uada.edu.