EFFECT OF COMMONLY USED TURFGRASS HERBICIDES ON BERMUDAGRASS (CYNODON-DACTYLON) ROOT-GROWTH

Experiments were conducted in 1990 and 1991 to determine bioavailabili ty of PRE herbicides at three soil profile depths and two soil types i n established common bermudagrass sods. Prodiamine and oryzalin reduce d 'Tifgreen' bermudagrass root growth in the 5- to 7.5-cm layer of a B osket very fine sandy loam soil at 2 and 4 wk after treatment in 1991. These herbicides decreased bermudagrass root weight in both the Boske t and Marietta sandy clay loam both years in samples taken from the 2. 5- to 5-cm depth layer. In the O- to 2.5-cm soil layer, all herbicides reduced root weight in 1990. In a bioassay, prodiamine caused decreas ed Tifgreen bermudagrass root growth at concentrations as low as 4 ppb by wt in the very fine sandy loam soil, while 8 ppb was necessary in the sandy clay loam soil. Prodiamine was detected in the very fine san dy loam at 4 wk after treatment at all depths in 1991 (65, 45, and 39 ppb in the O- to 2.5-, 2.5- to 5-, and 5- to 7.5-cm soil layers, respe ctively). Oryzalin was also detected at all depths in 1991 when sample d at 2 and 4 wk after treatment in the very fine sandy loam. Pendimeth alin was present in concentrations of 38, 39, and 37 ppb in the sandy clay loam at 2 wk after treatment in the O- to 2.5-, 2.5- to 5-, and t he 5- to 7.5-cm soil layers, respectively. Pendimethalin was also dete cted in the very fine sandy loam at 2 wk after treatment at concentrat ions of 55, 69, and 36 ppb in the O- to 2.5-, 2.5- to 5-, and 5- to 7. 5-cm soil layers, respectively.