Morningglories currently infest approximately 0.5 million acres of cotton in Texas at levels severe enough to negatively impact yield and quality of the crop. They are gaining the reputation of being one of the most difficult to control weeds in Texas cotton. Traditionally preplant and preemergence herbicide treatments offer approximately 65% control of the morningglory species present. At crop harvest this control often cannot be detected.

Following unsuccessful attempts to identify a single herbicide treatment for morningglory control in cotton, research was initiated to evaluate Probe (methazole) as a postemergence directed applications in a herbicide control system for this troublesome weed. In the morningglory control system Prowl (pendimethalin) at 0.5 lb ai /A was applied preplant incorporated and Caparol (prometryn) at 0.8 lb ai/A was applied preemergence. Probe applied at 0.5, 0.75 and 1.0 lb ai/A as a postemergence directed application to 3 inch cotton provided 78, 86, and 90% control, respectively, with little crop injury. The addition of MSMA at 1.6 lb ai/A with Probe at 0.5 lb/A improved control to 88% in 1 ate season evaluations. A second postemergence directed treatment of Probe + MSMA at the same rates when the cotton was 6 inches tall resulted in 90% morningglory control. Probe applied without MSMA at this stage gave 93% control but crop injury was 20%. When Bladex (cyanazine) at 0.6 lb ai/A was substituted for the Probe at the 6 inch application stage, control was improved 96 %. However, visual crop injury at harvest ranged from 15 to 20% and yield was reduced by more than 200 1 b/A for the sequential treatments. No treatment applied postemergence directed gave acceptable control of morningglories when applied in absence of Caparol applied preemergence. Caparol in the absence of a postemergence directed treatments provided only 66% control.

In summary, the most effect morningglory control system with good crop safety was Caparol at 0.8 lb/A applied preemergence followed by Probe + MSMA at 0.5 + 1.6 lb/A applied in 3 inch cotton. Probe at 0.75 lb/A applied at the 3 inch stage also provided good control and crop safety.