Temperature-mediated responses of flumetsulam and metosulam on Raphanus raphanistrum

The effect of temperature and light after spraying on the activity of flume tsulam and metosulam when applied to seedlings of Raphanus raphanistrum was evaluated under controlled environments. Flumetsulam and metosulam were ap plied at 0.01-3 times the recommended doses and the plants were subjected t o a range of temperatures after spraying. Herbicide activity was estimated from dose-response curves of fresh weight. Varying the temperature after sp raying from 1 to 20 degrees C increased the activity of flumetsulam and met osulam, as determined by comparison of ED50, by a factor of 97 and 7 respec tively. Large increases in herbicide activity occurred in the 1-5 degrees C range and smaller but significant increases at temperatures greater than 5 degrees C, No significant differences in the activity of the herbicides we re found when the plants were subjected to light or dark conditions at 5 de grees C after spraying. The influence of temperature on activity may lead t o opportunities for rate adjustment of flumetsulam and metosulam based on t he temperature prevailing around the time of spraying.