Herbicide damage in landscape trees seems to be a growing problem. During the spring and summer over the last few years, many calls have come in from homeowners about herbicide-damaged trees. In most cases, injuries occur as a result of misapplied herbicides in both landscape beds and lawns.  

Herbicides are useful products designed to control undesirable plants in landscapes. However, care must be taken before using these products to avoid damage to unintended plants. In a matter of minutes an uninformed gardener can erase trees that have taken decades or centuries to grow, forever altering their landscapes.

Symptoms 

While herbicide damage can be difficult to identify in trees, the most common symptoms are twisted, deformed, discolored, and cupped leaves. Defoliation of the entire tree or select branches is also common. Re-sprouting leaves will often be tiny, exhibit a chlorotic, yellowish color and be tightly clustered. The exact symptoms will depend on the type of herbicide used. Below are some important lessons for homeowners to follow when using herbicides around trees. 

There is No Antidote for Herbicide Damage

Once a herbicide have been absorbed, options become limited. It then becomes a waiting game to see how the tree will react and whether it will survive. Depending on the herbicide and the dose applied, this waiting period can range from a few weeks to several years. If an herbicide misapplication is suspected, water the tree regularly to flush the soil and help the tree grow past the herbicide damage.

If the herbicide misapplication is recent, consider using activated charcoal. Activated charcoal can be incorporated into the soil to help absorb and chemically bind organic herbicides. Please note these products are not guaranteed and have variable success. Herbicide injury can lead to other problems (pests, diseases, etc. ) and can take trees years to fully recover from. 

Read Product Labels Carefully

Herbicide labels are there for a reason. They not only outline where and how to use the product, but also provide application rates and a list of safety considerations. In most cases they also warn about possible damage if used around trees. Be sure to read the entire label as some warnings for tree damage are placed near the end.

Use only the specified rates as over application of many products could cause damage. Note that some products have small quantities of soil active herbicides and can damage trees at higher rates. If the label is lost, the website: www.cdms.net can be used to search most available products. 

Understand the Difference Between Foliar and Soil Active

Knowing the activity, or how plants absorb herbicides, is important to avoid damaging trees.  Herbicides are absorbed in two primary ways. First, is foliar, meaning the herbicide must be sprayed onto the foliage or plant. Second, is soil active herbicides, which are absorbed by roots.

Using soil active herbicides is where most people get into trouble. These herbicides are either applied as a liquid or granules and are absorbed by roots. This means this product will affect any roots growing under the sprayed area. An application to kill weeds in grass can also result in trees absorbing the herbicide. Note that some herbicides are both foliar and soil active. 

Tree Roots are Far Reaching

While many products that are soil active recommend staying outside the tree’s drip–line, or the farthest-reaching branches, it might be more prudent going twice the drip–line. Roots can extend two to three times a tree’s drip–line. To ensure large high value trees are not damaged, it might be best to error on the side of caution. 

Only Spray the Target Plants

While this may seem obvious, there are a few common mistakes made that result in non-target plants being sprayed. First, beware of spraying on windy days. Wind can cause herbicides to drift onto non-target plants, especially if droplet sizes are small. Second, beware of spraying the trunk or exposed roots of trees. The bark and roots, especially thin barked tree species, are able to absorb herbicides. Third, beware that herbicides can volatilize. Some herbicides have a tendency to go from liquid to gas after application on hot summer days. Volatilized herbicides can rise and cause damage to tree canopies. For these chemicals, such as 2-4D, do not spray during hot days over 85 degrees.  

“Weed and Feeds” Contain Herbicides That Can Harm Trees

The term weed in lawn care “weed and feed” products contain various types of herbicides to control a variety of unwanted weeds. Additionally, post-emergent landscape herbicides used to control broadleaf species in grasses should also be used with care around trees. Unfortunately, many of these products are soil active and can be damaging to trees when misapplied.

Common herbicides to control weeds in lawns that have the potential to damage trees include:

• atrazine
• 2-4D
• dicamba
• MCPP
• imazaquin
• metsulfuron

Read all labels carefully as warnings for using these products around trees can be buried deep within the document. Also, pay attention to soil type, soil PH, tree species, and outside temperatures as these can influence the interaction between herbicides and trees. Damage from these products may be more subtle when misapplied. If in doubt, consider alternative products.    

Beware of Products with Additional Soil-Active Herbicides

In recent years, commonly used landscape herbicides have added additional herbicide products that should be used cautiously, if at all around trees. Glyphosate products with the words max control or extended control have the active ingredients Imazapic and Diquat, both of which are soil active. For the unsuspecting consumer, these products often spell trouble as many only assume the glyphosate rate has increased.

Read the labels of these products carefully and use caution, as Imazapic at certain rates can be very damaging to trees. The glyphosate extended control product allows for use under trees at certain rates. However, if the rate is exceeded or soil condition are not favorable (sandy, high PH) it could lead to damage. 

Use Other Means to Improve Lawn Health

The management of landscape grasses and trees are often at odds. Trees produce dense shade, which increases weed problems. Furthermore, the herbicides that control weeds in grasses can be damaging to trees. Consider replacing struggling lawns with mulched beds and shade tolerant landscape plants. The mulch will improve the health of the trees. In areas where grass is desired, pruning can thin tree canopies to improve light penetration.