Long-term control of aspen poplar and western snowberry with dicamba and 2,4-D

Seven- and nine-year studies were conducted in northeastern Saskatchewan to compare the long-term control of aspen poplar (Populus tremuloides Michx.) and western snowberry (Symphoricarpos occidentalis Hook.) following single and multiple applications of 2,4-D ester (2,4-DE) or amine (2,4-DA) mixed with dicamba. The area was bulldozed free of trees and was subsequently invaded by aspen poplar and western snowberry regrowth, native forbs and grasses. Herbicides were applied to 2- and 4-yr-old regrowth of aspen poplar, growing with a small uniform stand of western snowberry. A single application of dicamba with either 2,4-DE or 2,4-DA applied at 1.5 + 2.2 kg (a.i.) ha −1 was as effective as two or three consecutive yearly applications for the control of aspen poplar. In one experiment, two consecutive applications of dicamba + 2,4-D controlled western snowberry whereas in the other experiment a single application was adequate. The highest forage production of grasses and forbs occurred following dicamba + 2,4-DE treatments. Following a single dicamba + 2,4-DE application, grass production, averaged over 7 and 9 yr, increased from 38 to 98 g m −2 and from 31 to 83 g m −2 , whereas forb production decreased from 48 to 25 g m −2 and from 58 to 48 g m −2 , respectively. Key words: Aspen poplar, Populus tremuloides, western snowberry, Symphoricarpos occidentalis, 2,4-D dicamba