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Summer Heat Stress

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Larry Sagers Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved

Summer Heat Stress Soaring temperatures, hot winds and no rain mean serious problems for the plants in the garden. You and I take refuge in the shade or inside and air-conditioned building. We might also add cool lemonade to increase our comfort but our plants have to tough it out wherever they may be. Typically these tips would be in July and August but the recent early heat wave is stressing plants now.

High temperatures and wind also cause scorch on many woody plants. These problems, coupled with lack of or poorly functioning irrigation systems are responsible for many cases of burned plants each year. The plants that are most likely to be damaged are those with large leaves. Maple, horse chestnut, walnut, poplar, aspen and linden are susceptible.

The most common symptom is browning of the edges of the leaves and between the veins of the leaves. Leaf scorch is usually not fatal but the symptoms remain until leaves drop. Scorch on evergreens is a more difficult to diagnose problem because the symptoms do not usually show up until long after the events have taken place to cause the scorch are over.

Scorching is not just a matter of lack of water. In many cases there is sufficient water in the soil but the tree cannot move it to the top of the plant quickly enough to avoid damage. In some cases well-meaning gardeners actually aggravate the problem by applying so much water that the absorbing roots are destroyed and the plants cannot take up sufficing water to prevent leaf scorch.

Newly transplanted trees are particularly vulnerable. They have small root systems that will not absorb enough water to prevent the plants from drying out. Several way to reduce the problems include transporting the trees inside covered vehicles rather than drying along the freeway at 75 MPH and keeping them watered until they are planted.

Large black pots can get very warm and cook the roots inside so keep them out of the sun or stand a board along the south side. Use care in handling the plants so the bark is not damaged because that interferes with water uptake.

Scorch is aggravated by any condition that interferes with water uptake. The water system of the tree is a gigantic plumbing system for moving water and nutrients from the roots to the leaves. In the leaves food is manufactured and then distributed to all parts of the plant. Anything that interferes with the plumbing or the growth of the tree is a potential cause of leave scorch to the plant.

Because this condition is so complex, it is often difficult to determine what is causing the trees to scorch. The accompanying chart lists several frequent causes of leaf scorch and possible solutions for each of the problem. If your trees are showing stress, some preventive medicine will likely help solve the problem and prevent future problems.

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