Weed control systems for no-till crop rotations in the Central Texas Blackland Prairie

Abstract

Experiments were conducted to evaluate weed control practices in no-till cropping systems for the Central Texas Blackland Prairie. Herbicide placement techniques for preemergence applications of pendimethalin [N-(1-ethyl-propyl)-3,4-dimethyl-2,6-dinitrobenzenamine] were developed for grain sorghum [Sorghum bicolor (L.) Moench.]. Despite intense, simulated rainfall within 24 hours after planting, a row shield technique prevented sorghum injury for preemergence applications of pendimethalin at 1.1 kg/ha. A second technique, which consisted of a double off-center spray nozzle unit mounted on the rear of the planter, allowed successful establishment of no-till sorghum at pendimethalin rates of 1.1 and 2.2 kg/ha. In a related growth chamber experiment, preemergence applications of pendimethalin had minimal effects on sorghum under hot, dry conditions, but such applications caused severe injury to sorghum emerging in wet soils. In field experiments, glyphosate [N-(phosphonomethyl) glycine] applications in June, August, and September, following wheat harvest were evaluated for johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control. The addition of ammonium sulfate at 3.3 kg/ha enhanced the activity of low rates of glyphosate when environmental conditions were less than ideal for johnsongrass growth. June applications provided excellent initial control, but at one location reinfestation occurred due to subsequent emergence of seedlings and regrowth of treated plants. In other field experiments, prior-fall applications of glyphosate provided excellent johnsongrass control at the time of sorghum planting. Systems which included fall applications of glyphosate coupled with spring foliar and residual treatments, resulted in increased yields compared to those systems which consisted of only spring treatments. Glyphosate and paraquat (1.1'-dimethyl-4,4'-bipyridinium ion) applied in the spring were ineffective for controlling johnsongrass. In a grain sorghum-cotton (Gossypium hirsutum L.)-wheat (Triticum aestivum L.) rotation experiment, effective johnsongrass control required intensive herbicide inputs, including fall and/or spring herbicide treatments. The most predominant weeds escaping control measures were johnsongrass and browntop panicum [Panicum fasciculatum Sw. # PANFA].