Dandelions were blooming a few weeks ago and many gardeners sprayed their lawns with herbicide.

The dandelions died, but in some cases there was collateral damage. Nearby trees and shrubs may have been exposed to the herbicide. Leaves started curling, cupping, twisting and stretching (see photos).

In most cases, the herbicide drifted onto the foliage of the trees. Once this happens, there is not much we can do about it. The herbicide is readily absorbed in the leaves and it cannot be rinsed off.

In some cases, the herbicide was absorbed by the roots of the plants. This can happen with dicamba, a powerful chemical found in Trimec and other herbicide mixes. Leaf cupping is the textbook symptom of exposure to dicamba (see top photo).

In either case, woody plants usually survive accidental exposure to herbicide because they were not exposed to the full lethal dose. Plants will be weakened, but subsequent growth is typically not affected.

In the future, use herbicides only when needed and when they are most effective. Herbicides are most effective in September and applications are rarely needed more than once a year. Especially be careful with dicamba, which may persist in the soil for several months.

Avoid spraying when the weather is windy. Reduce evaporation of the chemical by using amine (not ester) formulations and avoid spraying on hot days. Avoid spraying with a fine mist, which is more likely to drift. 

Shield trunks from exposure to sprays. This is especially important for young trees and shrubs, which have thinner bark and are more vulnerable to damage. 

Written by Tom Kalb, Extension Horticulturist, North Dakota State University (NDSU). Photos courtesy of Yolanda Schmidt, Extension Agent, NDSU.