Controlling annual weeds such as pigweed and Russian thistle is the major challenge as producers move toward conservation tillage systems on the Texas Southern High Plains. A test was established in 1991 near Lamesa, Texas, to evaluate chemigation, strip-till, preemergence, and lay-by applications of trifluralin in a terminated wheat-cotton system. Wheat was planted after cotton harvest in November 1990 and terminated with Roundup in April. Treatments included chemigation applications of Treflan in 1.0" of irrigation water at 1.0, 1.5, and 2.0 lb ai/acre. Strip-till (rolling cultivator) incorporated trifluralin treatments were applied at 0.5 and 0.75 lb ai/acre alone or in combination with chemigation treatments. Other combinations included chemigation plus preemergence (scratched in behind planter) and lay-by treatments. Two sweep cultivations, (including one to incorporate lay-by treatments) were performed in July and August.

No treatment had any adverse effect on cotton stand or caused any crop injury, even at the highest rates. Effective early-season pigweed was achieved with all treatments except strip-till treatments alone. Best control of both pigweed and Russian thistle resulted from the combination of strip-till and chemigation. As the season progressed, weed control declined for chemigation alone treatments, even at the 2.0 lb ai/acre rate. Excellent season-long control (>90%) was achieved with chemigation + strip-till, and chemigation + preemergence treatments. Even with heavy rains i in August, late season weed germination was minimal and the lay-by treatments applied were not necessary this year. Little difference in cotton yields were found between treatments. Highest yields resulted with the strip-till plus chemigation treatments which gave best weed control. Lowest yields occurred with the strip-till alone at 0.5 lb ai/acre, which had significant weed competition.