Herbicides are products designed to kill undesirable weeds, however, misapplied herbicides can cause injury to desirable landscape plantings. Symptoms of herbicide injury often involve discolored or distorted leaves and can easily be confused with other cultural or environmental problems, as well as insect, mite, disease problems, or another pesticide injury. Diagnosis is often difficult because information about specific symptoms on ornamentals is limited. In addition, the dose received by the plant and how it was applied will often influence symptom expression. Some herbicides are more readily absorbed through plant roots while others are only absorbed through leaf and stem tissue. Tissue and soil analysis for herbicide residues is often not available, impractical or very costly.
Herbicide injury usually occurs when weed control spray drifts onto nearby plants.
- In some cases, herbicides can drift many feet from the site of application.
Damage attributable to herbicides should be suspected when:
- More than one type of plant is affected
- Symptoms appear only on one portion of the plant or plants
- Other causes of damage have been ruled out, (such as nutrient deficiencies, air pollution, insects, diseases or virus)
Symptoms of some commonly misapplied herbicides:
- 2,4-D and MCPP: Twisted and bent shoots and petioles
- Dicamba: Dwarfed, distorted and/ or discolored foliage
- Glyphosate: Plants stop growing, remain green for several days, may develop yellow leaves and then turn to a uniform brown. Leaf distortion and bleached or dead spots may occur.
- Symptoms may not appear for 7 to 10 days after exposure.
- Trifluralin: Roots may be swollen or club-shaped, roots may appear shortened with fewer secondary roots present.