Herbicide effects on bermudagrass lawn recovery and crabgrass control during spring root decline in the north-south transition zone

A bermudagrass [Cynodon dactylon (L) Pers. X C. transvaalensis Burtt-Davy 'Tifgreen'] lawn in the transition zone (about lat. 35 degrees N) was treated in late March for 3 years with a high and a low level each of benefin, bensulide, DCPA, oxadiazon, and siduron. Objectives were to determine if relationships exist between field environment and dates of preemergence herbicide applications for large crabgrass (Digitaria sanguinalis L. Scop.) control, the spring root decline (SRD) phenomenon, and herbicide phytotoxicity to the bermudagrass. Herbicide treatments in late March generally controlled large crabgrass, reduced total weed competition, and appeared to aid bermudagrass spring growth following winter dormancy. Herbicide injury to 'Tifgreen' bermudagrass roots during SRD does occur under practical field conditions and was more severe when bermudagrass spring green-up occurred closer to the herbicide treatment date, as in 1982. Bermudagrass stand density was significantly reduced with the high level of siduron in 1980 and 1981, and with both levels of oxadiazon and siduron in 1982. Bensulide and oxadiazon, at both levels, gave 92% to 100% crabgrass control during all three treatment years. The high levels of benefin and DCPA in 1980, both levels of benefin and the high level of DCPA in 1981, and both levels of DCPA and the high level of benefin in 1982 gave crabgrass control in excess of 95%.