CONTROL OF ANNUAL WEEDY GRASSES IN A BENTGRASS GREEN WITH TREATMENT PROGRAMS OF TRI-CALCIUM ARSENATE

A creeping bentgrass (Agrostis palustris Huds. 'Penncross') green was treated with flowable tri-calcium arsenate (Ca-Ars) in increment levels of 17 or 34 kg.ha-1 in 12 multiple treatment date programs. Treatments were made over 4 years to determine effectiveness of initial applications and accumulated residues in controlling annual bluegrass (Poa annua var. annua L.) and large crabgrass (Digitaria sanguinalis L. Scop.) and to evaluate the phytotoxicity to the bentgrass. Multiple treatments of Ca-Ars at increments of 17 or 34 kg.ha-1 effectively controlled annual bluegrass and large crabgrass when cumulative application amounts totaled at least 136 kg.ha-1. Excellent control of annual bluegrass was achieved by timing treatments and soil residue buildup totals to coincide with the major germination and regrowth period of late winter to early spring. Optimum timing included treatments during the fall and spring. This treatment sequence also gave excellent control of crabgrass. Sustained control of both weeds was achieved when continued low level follow-up applications totaled > 136 kg.ha-1. Penncross bentgrass appeared tolerant of Ca-Ars treatments totaling as high as 272 kg.ha-1. Arsenic apparently influenced thatch accumulation by killing earthworms.