The objective of this study was to compare the effectiveness of single and sequential applications of monosodium methanearsonate (MSMA) with single applications of fenoxaprop {(±)-2 [4-({6-chloro-2-benozoxazolyl} oxy) phenoxy) propanoic acid} for postemergence control of crabgrass (Oigitaria spp.). MSMA applied at 2.2 kg ha-1 twice on a 14-day interval or 1.1 kg ha-1 applied three times on a 7-day interval provided exceptional (99 percent) control of mature (i. e., three or more ti1l. ers) c rabgr ass, but elicited unac ceptable levels of discoloration. When MSMA was a pplied at O. 6 kg ha-1 th ree times on a 7-day in ter val or at 1.1 kg ha-1 t wice on a 14-day interval, fair (78 to 79 percent) to good (88 percent) control was achieved without unacceptable discol. oration of turf. Uowever, a single MSMA application at 2.2 kg ha-1, did not effectively control crabgrass. Penoxaprop (0. 28 kg ha-1) provided fa ir (78 percent) to excellent (93 percent) levels of control when applied to mature crabgrass. The erratic performance of fenoxaprop in control of mature crabgrass was attributed to environmental conditions as such conditions affected the vigor of crabgrass. Single applications of fenoxaprop (0.20 and 0.28 kg ha-1) in early summer when crabgrass was relatively immature provided exceptional (91 to 99 percent) control and eliminated weeds as a problem for the remainder of the season. Effective control of mature crabgrass with fenoxaprop (0.28 or 0.56 kg ha-1) can be achieved if rainfall or irrigation is not limiting and crabgrass is growing vigorously.

Weed control in turfgrass is best accomplished by maintaining a dense stand through employment of sound cultural practices. However, because of budget limitations, proper mowing frequency, fertility, and other management inputs in low maintenance, highway turfgrass areas are often neglected. Budget restrictions, as well as mechanical disturbances, environmental and biotic stresses, and poor soil conditions invariably lead to deterioration of turfgrass stand density and weed invasion. For these reasons, herbicides are used to supplement cultural practices in controlling weeds. Weed control in highway turfs is important because it provides the following benefits: