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Diagnosing Herbicide Injury In Plants

Herbicides work well when they’re used correctly. But sometimes because of wind, rain, and other factors out of your control, they can cause injury to other plants. The trick is knowing if the plants were affected by the herbicide or something else.

Gail Ruhl is a senior plant disease diagnostician at Purdue University. She says when diagnosing herbicide injury, the first step is to identify the plant species you’re concerned about and then to look for similar symptoms on plants nearby. The second is to know the particulars about the herbicide used or suspected, when it was applied, the mode of action, and how it affects a plant.

"The ones that are drifting or volatilizing, you’ll usually see that damage within a couple of days. But there are some that are known as total vegetation killers or soil sterilants, and those are taken down into the soil and might spread as the water moves them along and they’re taken up throughout the roots and up into the plant," says Ruhl. "So you might not see the symptoms there for weeks, months, down the road."

The signs of plant damage depend on the herbicide.

"If it is a growth regulator like 2,4-D, or dicamba or banzo, that would be a twisting and a cupping, or a strapping of the leaf," she says.

Before you blame the herbicide, rule out other causes. Ruhl says insects, mites, disease, misapplications of fertilizer, and adverse weather conditions can mimic the symptoms of herbicide damage. If you’re not sure what you’re dealing with, contact your local extension office for help.