Herbicides are used to control the growth of weeds in forests and garden areas. A drawback to these chemicals is their potential to damage surrounding trees and plants if misapplied. Identification of herbicide damage is difficult. Proper herbicide application prevents the dangers of herbicide poisoning.
Identification of herbicide damage can be difficult, as normal signs of damage are difficult to differentiate from disease. Ruling out insect damage is the first step in diagnosing herbicide damage. If pests are not present, disease is the next most likely cause. Attention should be paid to the tree's location and whether herbicide poisoning is possible in its location to the spraying area.
The most common cause of herbicide poisoning is herbicide drift, when spray is caught on the breeze and travels past its intended location. Heavier weights of application pose a more present danger than small applications. Trees require a great amount of drift before poisoning is likely, but thin-bark trees or those with delicate foliage can be damaged by stronger herbicides.
Although identification can be difficult, there are some common effects. Foliage that has turned yellow, brown or a rusty color may have been damaged by herbicide. Unfortunately, this is also a common symptom in many tree diseases, as foliage is the most common place to find symptoms. Extreme damage such as defoliation cannot be ruled out. Damage on only one side of the tree may indicate drifting of herbicides.
If there is doubt as to whether damage to a tree is from disease or herbicide, the best testing method is to send a sample of the tree to a local forestry protection service or to a university extension. Several samples of healthy and damaged leaves, as well as portions of branches, may be required.
Preventing Herbicide Damage
Calm days, with little wind or rain, are the best times to apply herbicide. Covering trees with plastic, especially young or thinly barked varieties, is an effective, although costly and time-consuming, method of prevention.
Trees will likely recover over time if new growth is apparent. Trees that appear to grow sicker may not survive. Reducing other stresses to the tree will reduce the likelihood of it dying. The plant should be provided the proper amount of water, and if it has not received nutrients in a long time, an application of fertilizer. Overfertilization and overwatering can be just as damaging as an herbicide.