Evaluation of Fall and Spring Burndown Application Timings on Control of Glyphosate Resistant Horseweed in No-Till Cotton

Glyphosate resistant horseweed has been a consistent problem for growers in Tennessee. Many failed attempts to control GR horseweed with burndown applications close to planting have inspired growers to go out earlier with herbicides targeting smaller weeds. Often, these applications have proven themselves worthy. However, they have had some degree of inconsistency due to certain factors in the environment. Recent research has shown that horseweed can germinate nine months out of the year with the most consistent times occurring in the fall (September) and the spring (March). It is evident that when producers make spring burndown applications they are often targeting dense, large fall emerged horseweed populations. Therefore, a study was initiated to determine the efficacy of fall burndowns for GR horseweed. The study was conducted in 2006 and 2007. Cotton variety used was a Phytogen 485 WRF. Fall burndown applications went out in Nov. and spring applications went out in early March. Experimental design was a randomized complete block with four replications. Percent control and seed cotton yields are reported.