Weed Control in Christmas Trees with Flumioxazin and Other Residual Herbicides Applied Alone or in Tank Mixtures

Abstract

Four studies were conducted from 2001 to 2004 in Michigan to determine Christmas tree tolerance and weed control with flumioxazin and other herbicide treatments. In Study 1, fraser fir (Abies fraseri) leader length was greater with fall-applied flumioxazin (0.38 lb/acre) than with halosulfuron (0.21 lb/acre), isoxaben (1 lb/acre), oxyfluorfen (1 lb/acre), simazine (2 lb/acre), or sulfentrazone (0.5 lb/acre). Flumioxazin applied in the fall provided preemergent control of common ragweed (Ambrosia artemisiifolia), field violet (Viola arvensis), and hoary alyssum (Berteroa incana) 79% to 98% the following summer. Preemergence weed control with the other herbicides was more variable. In Study 2, fraser fir treated in the spring with oxyfluorfen had the shortest leader length (terminal stem growth of the current growing season) at 4.3 inches. Trees treated in the spring with flumioxazin, isoxaben, simazine, and sulfentrazone had leader lengths of 6.7 to 8.7 inches. Flumioxazin applied preemergence in the spring controlled common ragweed 80%, but controlled field violet, hoary alyssum, and white campion (Silene alba) only 43% to 64%. In Study 3, fall-applied flumioxazin alone did not injure colorado blue spruce (Picea pungens). However, mixtures of flumioxazin plus pendimethalin (3 lb/acre) caused 5% and 6% tree injury at 6 months after treatment (MAT) and sulfentrazone plus pendimethalin caused 9% and 23% injury at 6 MAT in 2003 and 2004, and 52% injury at 9 MAT in 2004. There was no significant injury to the trees treated with isoxaben plus pendimethalin, oxyfluorfen plus pendimethalin, or simazine plus pendimethalin in 2003 and 2004. Leader length was reduced by sulfentrazone plus pendimethalin compared with flumioxazin plus pendimethalin and oxyfluorfen plus pendimethalin. Flumioxazin plus pendimethalin provided 84% to 88% preemergence control of annual grasses, common catsear (Hypochoeris radicata), horseweed (Conyza canadensis), and virginia pepperweed (Lepidium virginicum). In Study 4, spring-applied mixtures of flumioxazin plus pendimethalin resulted in minor (2%–10%) visual injury to colorado blue spruce, although leader length at the end of the season did not differ significantly from the control. In summary, flumioxazin controlled several weed species with acceptable selectivity in colorado blue spruce and fraser fir Christmas trees.