Archive for Thursday, July 6, 2006

Invisible invader can damage landscape

July 6, 2006


This time of year, many trees, shrubs and flowers show signs of abuse and neglect. Hail, strong winds, drought and insects tatter leaves and shred stems. However, the maltreatment does not end there. Oftentimes damage is caused by an invisible invader - one that passes through without you ever knowing it was there. Herbicide drift and misapplication can cause various plant problems.

So if you have trees, shrubs or flowers with twisting or yellowing leaves, or branches that are dying back, here's what you need to know about identifying herbicide drift in your landscape:

Many broadleaf weeds in home lawns, pastures and right-of-ways are controlled using hormonal-type herbicides such as 2,4-D, triclopyr or dicamba. If applied during windy or hot weather, these chemicals may drift as far as five miles and cause severe damage to nontarget plants. Look for symptoms such as severe twisting and distortion of foliage - often in the shape of a curlicue, a leathering or thickening of the leaf tissue, leaf yellowing or branch dieback.

Drifting herbicides often damage more than one plant species in the landscape. If you see twisting or cupping on multiple plants, then it is a good bet the damage is herbicide and not disease. Redbud, grape and tomato are highly sensitive to 2,4-D drift and can be used as indicator plants. If herbicide drift is suspected, nothing can be done to "fix" the plant. Badly affected plants may need to be removed because they do not usually recover.

Likewise, stump killers can cause damage as well. The chemical Tordon (picloram) often is used to prevent regrowth of cut stumps or to kill unwanted sprouts from roots. Unfortunately, people forget how damaging this stump treatment can be. Sloppy treatment of cut stumps can lead to soil contamination. Picloram can be washed through the soil by rain or irrigation water and affect nontarget trees many feet away.

Other points to remember are never to treat sprouts coming off a root system of a tree that you wish to keep. For example, honey locust, black locust, hackberry, western soapberry, persimmon, crabapple and, occasionally, maples send up sprouts from their roots. Cutting and treating these sprouts with an herbicide contaminates the entire roots system, oftentimes resulting in tree death. Similarly, trees of the same species growing next to one another may have a common root system as a result of root grafting. Treating one tree in the group is like treating all of the trees. So don't be surprised if you spray one stump and several trees nearby die as well. Long story short: Be very careful when using stump killer treatments. If there are any doubts or desirable trees nearby, don't use them.

Finally, liquid weed edgers can cause major damage to various landscape plants. Herbicides such as glyphosate (Round-up) and glufosinate (Finale) are used along fences, on sidewalks or gravel drives to stop plant growth. If used properly, these rarely cause damage unless they are directly sprayed on the foliage of a desired tree or shrub. There are other liquid weed-edger products, called soil sterilants, that are much more toxic and have a long residual (measured by years) in soil and are highly toxic to trees and shrubs.

Once plants take up these products through their roots, they're toast; the damage can't be reversed. Symptoms include chlorosis, marginal leaf scorching, branch dieback and tree death. Never use soil sterilants in areas where tree roots may be exposed. Remember that tree roots extend two to three times beyond the distance of the so-called drip-line. Some gardeners assume that it is fine to apply sterilants on sidewalks, gravel drives or brick walks or drives because tree roots will not be underneath. Not so. Soil sterilants are mobile in soil and can be washed down slopes many feet killing plants the entire way.

- Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.


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