Herbicide Damage to Trees
Herbicide Damage to Trees Wednesday, April 18, 2018
Author(s): Laurie Stepanek, Justin Evertson, Kyle Martens
Herbicides can be effective tools for controlling unwanted weeds in the landscape. However, in recent years the Nebraska Forest Service has seen a significant increase in unintended herbicide damage to trees and other landscape plants. You can assist us in documenting damage across Nebraska. Please note the NFS is not a regulatory agency.
Damage symptoms vary with the type and concentration of herbicide, the plant exposed and its stage of growth, and environmental factors. Common symptoms may include:
- Deformed foliage: leaf cupping, curling, twisting, puckering, strapping (narrow, elongated growth)
- Twisted, curled or stunted stem and branch growth
- Clusters of stunted shoots or leaves
- Discolored foliage: yellow, white, reddish, purplish, or abnormally light or dark green
- Leaf scorch (leaf edges turn tan to brown), flecking, or complete browning and death of leaves
- Defoliation (leaves or needles drop from the tree)
- Branch dieback or death of entire tree
Damage from weather, insects, and diseases can be confused with herbicide damage. Your local extension office, the Nebraska Forest Service, or the Nebraska Department of Agriculture may be able to assist with identifying herbicide injury.
Sources of herbicide exposure
Drift: Herbicides can move through the air from the site of application to nearby areas, causing damage to trees and other plants.
Possible sources of drift include the use of 2,4-D and dicamba in spring in an effort to control dandelions and other weeds in home lawns and for control of winter annual weeds in crop fields. These herbicides can be particularly damaging to tender foliage emerging in spring, especially on sensitive trees such as oaks, redbud, honeylocust, Kentucky coffeetree, elms, and maples.
Many formulations of dicamba and 2,4-D are quite volatile. This means the herbicides can form a gaseous vapor during or following application— sometimes even days later. Warmer temperatures (typically above 85 degrees) increase volatility, and may result in the vapor moving long distances from the application site on warm spring and summer days.
Root uptake: Tree damage can also occur through root uptake from herbicides that move through the soil. These include herbicides used to control roadside vegetation or to keep the ground “clean” around buildings, along fence lines, and on sidewalks, driveways and gravel strips. Many are labeled for control of “brush and woody weeds” and can cause significant damage to trees. Even trees located some distance from the application site may be affected since tree roots can extend well beyond the canopy of the tree. Dicamba, picloram (Tordon), bromacil (Hyvar), and prometon (Pramitol) are just a few common examples.
Another “bare-ground” herbicide, glyphosate (Roundup), controls most weeds when applied to the foliage. Glyphosate is generally inactive in soils; however, some Roundup products contain different or additional active ingredients, which may be picked up by roots. Check the label!
Root uptake by trees can also occur with many lawn herbicides, particularly those for control of clover, violets and other tough broadleaf weeds. Care must be taken to apply the appropriate rate when used in landscapes with trees.
Steps you can take
To lessen the likelihood of herbicide damage to your trees and those of your neighbors, follow these guidelines:
- Read and follow ALL herbicide label directions, particularly restrictions that help limit drift, vaporization, and runoff. Look for precautionary statements regarding trees.
- Be aware of surrounding properties with sensitive vegetation including parks, gardens, windbreaks, landscape nurseries, orchards, vineyards, organic farms, and native woodlands and other natural areas. Visit Driftwatch.org for locations of growing operations near you.
- Most damage occurs in spring when trees and other plants are leafing out with susceptible new growth. Try to shift weed control to fall when many weeds are more easily controlled and damage to trees is reduced.
- Monitor temperature, wind speed, and wind direction. Avoid spraying on warm, windy days.
- Adjust sprayer nozzles to a coarser spray to reduce drift.
- Be especially careful using herbicides that control “woody brush” or include trees or shrubs on the list of weeds controlled.
- Keep in mind the extensive reach of tree root systems—often well beyond the canopy edge.
- Use extreme caution when treating stumps located near desirable trees. Over-application may contaminate the soil around the stump. Alternatively, the chemical may move into the soil from the stump roots.
- When possible use alternate methods of weed control such as cultivation, mulching, use of cover crops, and mowing weedy tree sprouts.
- Though trees can sometimes be killed relatively quickly by unintended herbicide damage, some of the worst damage builds slowly over several growing seasons. Trees often can recover from light and occasional damage, but repeated damage year after year will almost certainly shorten the lifespan of our most important trees.
- Become familiar with the more common herbicides and how they may be safely used. Homeowner herbicides include 2,4-D, dicamba, triclopyr, MCPP, and glyphosate. Professional herbicides include these plus imazapyr, picloram, bromacil, prometon, tebuthiuron and many others.
To learn more about potential herbicide damage to trees and other non-target plants contact your local UNL Extension Office or visit this website.
Growers of specialty crops can register at Driftwatch.org to raise awareness of their operation to surrounding applicators.
- Diagnosing and Preventing Herbicide Injury to Trees
- Diagnosing Herbicide Injury on Garden and Landscape Plants
- Precautions for using dicamba herbicides in dicamba-resistant soybeans
Photo courtesy: University of Nebraska-Lincoln, Pesticide Safety Education Program.