Using Herbicides Near Trees and Shrubs

Many homeowners use herbicides, commonly known as weed killers, to battle persistent plants like ragwort, pigweed, crabgrass, dandelion, purslane, clover, poison ivy, and others. Of the wide variety of herbicide products available, not all contain the same ingredients. With that in mind, these products should not be used universally. The weed being treated, site, and surrounding plant material should all be considered when choosing a product.

We have recently seen a number of cases of plant damage and death due to misapplication of some new extended-control products that are available in retail stores and contain the compounds imazapyr or imazapic. Though the herbicide products may seem familiar, the addition of imazapyr or imazapic is a notable difference. These compounds are water soluble and persistent in the soil, which means they can be taken up by weeds and desirable woody ornamentals alike. Given these characteristics, it is important to understand that products containing imazapyr or imazapic can severely damage or kill trees and shrubs when applied nearby.

Abnormal ‘tufted’ growth is a typical symptom when imazapyr or imazapic are absorbed by a plant’s root system.

Abnormal ‘tufted’ growth is a typical symptom when imazapyr or imazapic are absorbed by a plant’s root system.

Look for words like ‘extended control’ or ‘kills weeds for up to one year’ on the container. A long-lasting herbicide product may sound good, but there are dangers in applying these products the same way older herbicides have been applied.

Complete defoliation resulting from misapplication of herbicides.

Complete defoliation resulting from misapplication of herbicides.

Trees and shrubs impacted often grow strappy, small and twisted tufts of foliage. These symptoms may appear almost immediately or manifest in the subsequent growing season depending on the time of year the herbicide is applied as well as a number of other factors (soil type, amount of rainfall, temperature, plant species, to name a few). Dieback in the crown or death of the tree may also result.

Flowering dogwood before and after exposure to new 'extended control' herbicides

Flowering dogwood before and after exposure to new ‘extended control’ herbicides.

Plants exposed to this type of herbicide should be irrigated and the root zone mulched to reduce moisture stress. Keep root collars exposed, monitor for insects and diseases and treat infestations as needed. Fertilize according to soil nutrient analysis after herbicide damage symptoms subside.

When using an herbicide, it is always extremely important to read the entire label thoroughly, including all directions and warnings, and apply products specifically as directed to prevent damage to desirable plants. If you are using the product near trees and shrubs, be sure to check the label to see if it can be applied to the root zones of ornamental trees and shrubs.

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