Crape Myrtle showing signs of herbicide damage.
Beware of lawn-care herbicides damaging trees!
Herbicide damage in landscape trees seems to be a growing problem. For the past few years, every spring and early summer I receive a series of calls from homeowners with herbicide damaged trees. In most cases, injuries occur as a result of misunderstandings or misapplied herbicides. However, many calls also coincide with lawn-care products being used to control weeds in landscape lawns.
Herbicides are useful products designed to control undesirable plants in landscapes. However, care must be taken before using these products to avoid damage or death to unintended plants and trees. In a matter of minutes, an uninformed gardener can erase trees that have taken decades or in some cases centuries to grow and forever alter their landscapes.
While herbicide damage can be difficult to identify in trees, the most common symptoms are twisted, deformed, discolored and cupped leaves. Defoliation is common of the entire tree or select branches. Re-sprouting leaves will often be tiny, a yellowish color and tightly clustered. Below I outline some important lessons that every gardener must keep in mind when using herbicide products around trees to avoid disfiguring or killing their trees.
Cupping leaves can be a sign of herbicide damage.
Lesson 1: There are no “antidote” for herbicide damage
Once herbicides have been absorbed, options become very limited and it’s a waiting game to see how trees will react and whether they survive. Depending on the herbicide and the dose applied, the time can range from a few weeks to several years, during which time trees exhibit declining health. If you suspect you have misapplied an herbicide, water the tree regularly to flush the soil and help the tree grow past the herbicides in its system. If the herbicide misapplication is recent, consult a Certified Arborist about using activated charcoal. Activated charcoal can be incorporated into the soil to help absorb and chemically bind herbicides. Please note, however, these products have variable success.
Lesson 2: 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 I have seen warnings for tree damage placed near the end. Use only the specified rates as over-application of many products could cause damage. If you have lost your label and need information on a specific herbicide, visit this website: www.cdms.net.
Lesson 3: Understand the difference between foliar and soil active herbicides
The ‘activity’, or how plants absorb herbicides, is very important to avoid damaging trees. Herbicides are absorbed in two primary ways. First, is foliar, meaning the herbicide must be sprayed onto the foliage. This means that for the herbicide to work, it must be sprayed directly on the plant. 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. So 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.
Lesson 4: Beware, 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, I suggest going twice the drip-line. Roots can extend two to three times a tree’s drip-line and to ensure large high value trees are not damaged, I recommend erring on the side of caution.
Lesson 5: Only spray the target plants
While this may seem obvious, there are a few common mistake made that result in non-target plants being sprayed. First, beware of spraying on windy days. Wind can cause herbicides to drift where you don’t want them. Second, beware of spraying the trunk or exposed roots of trees because they can absorb herbicides. Thirdly, 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.
Crape Myrtle showing patchy and stunted foliage.
Lesson 6: “Weed and Feeds” contain herbicides that can damage trees
The term “weed” in lawn care “weed and feed” products contain various types of herbicides to control a variety of unwanted weeds. Unfortunately, many of these products are also damaging to trees. In the last few months, I have seen several cases of damaged trees as a result of these products. Common herbicides to control weeds in lawns that have the potential to damage trees include atrazine, 2-4D, dicamba, MCPP, imazaquin and metsulfuron. Do not apply these products within the dripline of trees, and preferable twice the dripline. Read labels carefully as the warnings for using these products around trees are often in small letters and buried deep within the document.
Lesson 7: Question your lawn-care professional
Ask your lawn care professionals about the products they are using. I have encountered multiple cases of trees damaged by herbicides used to control lawn weeds by professional companies. Applicators are required to carry the label and Material Safety Data Sheet (MSDS) with them when they use the product. So they are able to access the information you need.
Lesson 8: Use other means to improve the health of your lawn
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 your trees. In areas where grass is desired, pruning can thin tree canopies to improve light penetration. Always hire Certified Arborists to prune trees, as improper pruning can result in unhealthy or unsafe trees.
For additional information, contact Beau Brodbeck at the Baldwin County Extension Office in Bay Minette Alabama by email at firstname.lastname@example.org or by phone at 251-937-7176.