Improperly Applied Weedkillers Can Damage or Kill Oak and Loblolly Pine

On May 3, 1968, a farmer's wife near Starkville, Miss., in an effort to control the lateral growth of native grasses along sidewalks to her home, sprayed a commercial weedkiller. The weedkiller (a white powder containing diuron, dimethyl urea, sodium trichloroacetate, bromacil, chlorinated benzoic acid and trichlorobenzoic acid), was applied at about 1 to 1.5 times the rate recommended to kill grasses along highways, around mailboxes, power line poles and the like. The weedkiller did eradicate the woman's grass in a 1.5 ft. wide strip. Where no weedkiller was applied, the native grass remained healthy. However by May 14, the weedkiller had also killed most of the already well developed foliage on four of 14 large oaks, 3.5 to 5 feet in diameter (DBH) and 40 to 50 feet tall, and moderately injtted six others of like size growing in the yard at various distances (15 to 48 feet) from the point of weedkiller application. The dead leaves stayed on the trees for about 1 1/2 months, and then dropped. The. farther an oak was from the point where the weedkiller was applied, the less severe the injury. Four oaks showed no injury. There seemed to be little or no relationship between the type and amount of injury and the species of oak. Rose bushes and other flowering shrubs growing 15 feet from the application point remained unaffected. Pecan trees 30 feet away were not injured.

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Author(s): G. K. Parris

Publication: Tree Planters' Notes - Volume 23, Number 1 (1972)

Volume: 23

Number: 1