TEMPERATURE THRESHOLDS FOR BUD SPROUTING IN PERENNIAL WEEDS AND SEED-GERMINATION IN COTTON

Experiments were conducted to establish low temperature thresholds for initiation of bud sprouting in dormant vegetative propagules of johns ongrass, purple nutsedge, and yellow nutsedge, and seed germination in cotton. Weed propagule sprouting and cotton seed germination response s to temperature were determined in a series of experiments conducted on a temperature gradient bar. Four calculated indices were used to qu antify germination: mean percent germination per day, reciprocal media n response time, and two versions of germination rate index. Data were analyzed as a series of regressions of germination indices against te mperature, maximum and minimum temperatures for germination were deriv ed directly from the regressions and compared among species. Yellow nu tsedge had the lowest temperature threshold (6 C), while the other spe cies had low temperature thresholds of 11 to 12 C. Upper temperature t hresholds were similar among species and ranged from 42 to 44 C. The l ower low temperature threshold of yellow nutsedge sprouting compared t o those for cotton, johnsongrass, and purple nutsedge suggests that ea rly establishment by yellow nutsedge is an important factor in competi tiveness in mixtures of these species. The results presented here sugg est that application of principles derived from studies in seed biolog y might advance our understanding and ability to manage perennial weed s.