Common cocklebur (Xanthium strumarium) seed were collected from cotton fields in Orrville and Polk, AL, where long-term applications of the arsenical herbicides MSMA and DSMA had been applied. Seed were separated from the bur and treated with a 1 percent ethephon solution (v/v) prior to planting. Seeds were planted into a soilpeat moss mixture contained in 32 ounce cups, thinned to 2 per cup after emergence, and allowed to grow until 2-leaf or 6-leaf stages before treatment. Treatments included MSMA at 0.5, 1.0, 2.0, and 4. 0 lbs. ai per acre, fluometuron (Cotoran) at 1.0 lb. ai per acre, and methazole (Probe) at 0.5 lb. ai per acre. Nonionic surfactant at 1/4% (v/v) was added to fluometuron and methazole treatments. The MSMA formulation used contained a nonionic surfactant. Treatments were applied in a spray volume of 15 gallons of solution per acre using a flat fan 8001 nozzle positioned directly over the top of the plants. Treatments were applied to four cups of plants at each growth stage. Visual weed control on a scale of 0 to 100 percent, where 0 = no control and 100 = complete control, was obtained 10 days after treatment. Plant shoots were harvested after visual ratings and dryed for 7 days at 130F. Air temperatures and relative humidities were 85 to 9OF and 45 to 55%, respectively, during the greenhouse trials.

Cocklebur responded differently to treatment based on seed source, growth stage, herbicide, and rate. Cocklebur from Orrville was controlled better at the 6-leaf stage (63%) than at the 2 leaf stage (12%) by MSMA rates of 0.5 and 1.0 lb., respetivley. However, the reverse was observed for cocklebur from Polk where better control of 2-leaf that 6-leaf cocklebur was obtained at the two lower MSMA rates. Cocklebur control was approximately equal (70%)using MSMA rates of 2.0 and 4.0 lbs per acre with both seed sources. Regrowth from axial buds on lower portions of the treated plants was observed after initial burndown from MSMA treatments at all rates in some cases. Good spray coverage on the lower stem appeared to decrease regrowth. Fluometuron and methazole controlled cocklebur from Polk, AL better than cocklebur shoots closely approximated visual ratings.