Summer heat leaves trees hurting

By David Coltrain

Walnut Creek Extension

This summer has been especially hard on trees and shrubs. High temperatures, strong winds and drought conditions have certainly taken a toll across Kansas. Normally summers in Kansas have some days and weeks that are miserable, but 2006 has been a scorcher.

Trees are very important to people in western Kansas and these harsh environmental conditions are causing many trees to show scorch problems. Scorch affects trees in different ways, but in general on deciduous trees the leaves turn yellow or brown on the edges and conifers exhibit brown needles. Leaves and needles can be affected enough by scorch that they completely turn brown and fall off trees.

Symptoms usually appear after drying winds in conjunction with periods of hot, dry weather. Scorch usually is a warning that some condition has occurred or is occurring that is adversely influencing the plant. In some cases it is simply an indication that a particular tree is unsuited to the local climate or has been given unsuitable exposure.

When water is lost from leaves faster than it can be replaced, the resulting condition appears as leaf scorch. Nearly all water reaching leaves is supplied by veins, and leaf margins and interveinal areas cannot get water as rapidly as areas next to veins. Therefore, marginal areas dry up while tissues adjacent to veins remain alive.

When leaf scorch is noticed, the tissue has usually dried past the point of recovery, but several steps can be taken to prevent more severe damage and improve the condition in subsequent years. Thorough, deep watering will usually help increase water uptake. Conserve soil moisture by mulching trees and shrubs with rotted leaves, bark, or other material. And if watering is necessary, be sure to water thoroughly because mulches absorb water from the surface. Light waterings will do no more than wet the mulch.

Leaf scorch is a noninfectious condition caused by unfavorable environment. There is no chemical control, so the most effective defense is good management. Scorch is often called a disease but is not caused by fungus, bacteria, or virus, nor does it result from insect attack. However, these problems may add to the seriousness of scorch.

The fact that scorch is not caused by a pathogen is a sure indication that spraying trees with natural or synthetic chemicals is an unnecessary practice. "This time of year spraying would not do any good even if a disease were present," commented Jim Strine, northwest area forester for K-State Research and Extension. "I have looked at many trees and have seen very little diseases, but a great amount of scorch," said Strine. As an illustration about spraying at the correct time, a disease affecting pines is tip blight that can only be controlled by spraying a copper fungicide during springtime.

If you are concerned about your trees, get a sample and send it to the K-State diagnostic lab so you can have peace of mind. Spraying trees unnecessarily only takes money from your pocket and will not likely help your trees. Using natural products with no scientific unbiased research results are especially a waste of money. Spraying trees that contain fertilizer may cause trees to green up, but this is only a temporary non-significant factor for improving the health of trees. In fact, fertilizing now could hurt trees by encouraging new growth that might winterkill and hurt trees future health.

The August Green Thumb News newsletter is now available. It contains 11 articles including: Watering Newly Planted Trees and Shrubs, Fertilizing Strawberries, Reviving Annual Flower Beds, Powdery Mildew Infecting Many Plants, and Soil-applied Systemic Insecticides for Borers. If you would like to receive an electronic copy of the newsletter, please e-mail me at coltrain@ksu.edu.

Date: 8/22/06

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