The German firm BASF, the largest chemical manufacturing company in the world, markets Plateau herbicide, which contains the active ingredient imazapic. Plateau is formulated to control annual and perennial broad-leaf weeds and grasses on pastures, range land, non-crop land, non-residential turf, golf courses, and beside ditches, highways and railroads. It can be used with caution around and under most trees.
General Guidelines for Use
Up to 12 ounces of Plateau per acre may be used to control weeds in and around established trees in pastures, range land, prairies, roadsides, windbreaks and wildlife refuges.
Plateau and Trees
Trees that are stressed because of disease, insect damage or drought are more susceptible to injury from Plateau. Contact with Plateau can cause some trees to have yellowing at the tip of their leaves and minor dead spots. Severe injury can kill trees
Plateau can cause severe injury or death if applied below the foliage of azalea, basswood, black cherry, choke cherry, lilac, and American linden. Spraying Plateau on the leaves may defoliate or kill box elder, cottonwood, narrow leaf cottonwood, grey dogwood, gooseberry, hawthorne, western snowberry, and willow. BASF says that Plateau should not be used on or around the following trees because of insufficient testing data: red mulberry, white mulberry, black oak, southern red oak, white oak, osage orange, apple, blue ash, Ohio buckeye, sweet cherry, peach, and yellow poplar.
To avoid injuring trees, fall applications of Plateau should be made after the leaves begin to turn color or after they drop. Species of conifer trees are usually tolerant to applications with Plateau in the fall.
Tips and Warnings
BASF suggests that growers concerned about the effect of Plateau on their trees should test the herbicide on a limited basis to make sure it does no harm. The Plateau label contains a full list of common trees that tolerate the herbicide used at the rate of 12 ounces per acre. The list is for trees that are at least 2 inches in diameter at breast height.
Removing a third to half of the new growth on coniferous evergreens to create a denser, fuller plant, is called candling. Plateau applied to a Douglas fir or lodgepole pine just before or during candling may injure or kill the tree.