Herbicide vapor can travel far

Q. My tomato plants are not growing. They curl, wither up and die. What can I do?

Ralph from Boardman

A. Every July we have tomato plants come into the clinic in the same condition. The leaves are curled and distorted. The leaves never get to full size and easily break in half as if they are brittle. The problem is not a disease or disorder, it is an herbicide issue.

The likely culprit we see every summer is 2,4-D damage. This is the common lawn herbicide that is used to kill all of the weeds that are not grass. These broadleaf weeds include everything from dandelions to clover that are unwanted in the lawn.

Volatilization can occur with herbicides, meaning the herbicides change from a liquid to a vapor, allowing them to move off-target. The chemical 2,4-D has a high vapor pressure. Thus, when the temperature increases and the humidity is low, the product readily drifts as a vapor onto non-target sites. At our clinic, we’ve had samples where the chemical has drifted across other lawns to a vegetable garden two houses away.

The lesson? Don’t spray 2-4,D in the heat of the summer! Many factsheets and labels for this product specifically state not to spray it when the temperature exceeds 85‚∞F. This would be most of the summer here in the Mahoning Valley.

Most 2,4-D applications occur in the spring before it gets hot. This is why we do not see issues in early or late spring. Most late applications are being applied for an outbreak of clover or birdsfoot trefoil (yellow flowers). Both of these weeds tend to get a second wind in lawns during July. For those of you with lawn weeds, consider other methods of reducing weed pressure, such as mowing at 3 inches high, irrigation and proper fertilization to keep the turf happy and healthy.

Forgetting to clean garden sprayers can lead to misapplication and drift as well. Sprayers should be rinsed at least three times after use. Gardeners should have a separate sprayer for any insecticide or fungicide applications to avoid any accidental application of an herbicide.

But don’t just assume a problem is herbicide injury. Some viruses and other diseases can have similar symptoms. Get the plant examined to be sure of the problem.

For complete details on safe use of pesticides in the home landscape, go to http://go.osu.edu/safeuse.

For details on proper use of 2,4-D, go to http://go.osu.edu/properuse.

To learn about the effects on the produce itself, go to http://go.osu.edu/whattodo.

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Call the office hotline at 330-533-5538 to submit your questions. Regular clinic hours are 9 a.m. to noon Mondays and Thursdays.