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Ask Dayle

10/11/2012 - West Side Leader
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By Dayle Davis

Shown are symptoms of dogwood leaf scorch.
Photo courtesy of Donald Multer
Dogwoods are under-story trees best planted within the shady protection of a larger tree’s canopy, the shady side of a home or at the edge of a woodland.
Photo: Dayle Davis
Q: I have three dogwood trees in my yard, two of which have turned dark green leaves and red berries. One of these trees [shown at near right] has developed black spots on the tips of the leaves, has no berries and the leaves have not turned dark green like the other two. What is causing this and is there a treatment for this?

A: Dogwoods are one of the first landscape trees to suffer when conditions border on drought. Your dogwood is exhibiting symptoms of leaf scorch, which starts as a brown band around the outside of the leaves.

Browning leaf edges are a common reaction of dogwood — and eventually other trees — to the hot, dry weather and lack of rainfall we experienced this past summer. The leaves may also droop, turn reddish and curl. Some of the leaves may develop fairly large brown spots or turn completely brown if enough water is not supplied.

The scorch develops when evaporation of water from the leaves exceeds the absorption of water by the roots. This can occur because of several reasons: dry soil, a weak root system, injury to the trunk of the tree, hot temperatures, or a layer of root-sustaining soil that does not penetrate the ground deeply enough to sustain tree root health.

If leaf scorch is due to drought, the good news is that it does not ordinarily kill dogwoods. However, it can weaken them. Help to prevent leaf scorch by planting dogwoods in partial shade and keeping the soil slightly moist during hot weather periods.

In general, wilting leaves are the first sign that a dogwood is suffering. To help prevent the development of leaf scorch, water deeply once a week at the first sign of wilting or stress. Water only in the early morning. This time of day helps to prevent other diseases from taking hold by allowing any wet foliage to dry during the day. Avoid keeping the soil totally saturated, which will suffocate the roots and quickly lead to root or crown rot. Also, watering in the heat of the day will cause loss of water to evaporation.

Aim for the application of 1 inch of water per week. Be sure to water your dogwood at ground level, covering the entire base of the tree completely out to the edge of the drip-line, or canopy. A soaker hose used at the drip line will allow the water to be absorbed into the ground before it runs off into the outer surrounding area.

Many homeowners make the mistake of planting dogwoods in full sunlight. Know that the native habitat of a dogwood is wooded areas. This means that dogwoods are under-story trees that grow best in the shade. When planting dogwoods, situate them at the edge of a woodland or in the shade at least 4 to 6 feet away from the trunks of other landscape plants and trees.

Keep the surrounding soil of the dogwood clear of vegetation; do not under-plant it with shrubs or flowers. Rather, add 2 to 3 inches of chunky organic mulch to keep the root zone cool and conserve moisture. Do not use stones or rock mulches around the tree, as this type of material will absorb heat and potentially add to the development of heat stress.

Since your other two dogwoods appear unscathed by leaf scorch, the base cause of this particular dogwood’s stress may be related to its particular location in the yard. Perhaps it receives more sunlight per day than the other two; perhaps it is situated a bit higher in the soil, which would cause rapid water drain-off; perhaps the soil is less enriched than the other areas in your yard. In any event, see carefully to its water needs. You may wish to withhold fertilizer until next year, then fertilize at half strength in spring or regular strength in the fall.

For future plantings, consider the kousa or Chinese dogwood, which are a bit tougher than native dogwoods and keep their green foliage in better shape during drought conditions.

For details on native small trees and large shrubs of Ohio, call The Ohio State University Summit County Extension Hotline Tuesdays between 9 a.m. and noon at 330-928-4769, ext. 3, and Request Bulletin 865, “Native Plants of Ohio.” Please note there is a fee for bulletins. Many bulletins are available online at ohioline.osu.edu and can be printed from home or accessed at a public library.

 

Dayle Davis is a freelance writer and avid perennial gardener, with a B.A. in communications and coursework in botany, geology and wildflowers. Davis is certified as a Master Gardener under The Ohio State University’s Horticultural Extension. Readers can send in questions regarding lawn and garden issues, which could be featured in a future edition, as well as about the OSU Master Gardener program. Questions can be emailed to kcollins@akron.com, faxed to 330-665-9590 or sent to Leader Publications, 3075 Smith Road, Suite 204, Akron, OH 44333. Please do not send any leaves, seeds or other organic material. Inquiries about area garden clubs or groups should be sent directly to the particular organization in question.

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