Abstract: The present invention relates to the use of diquat bromide as a root control agent. It is based, at least in part, on the results of green house testing in which application of diquat bromide as a dense foam to tree roots resulted in the destruction of the test roots without causing damage to the upper portion of the trees. Without being bound to any particular theory, it is believed that by applying diquat bromide to produce a high local concentration on the target root, the inactivating effects of local organic substances are overcome, and the diquat bromide kills root tissue by its dessicating activity. The inactivation of diquat bromide by organic materials, under these circumstances, becomes an advantage, as it prevents toxic levels of diquat bromide from traveling downstream from the point of application.