This study examines the economic performance of rainfed cropping systems endemic to the Southern Great Plains under weed competition. Cropping systems include tilled and no-till wheat-fallow, wheat-soybean, and wheat-sorghum rotations. Net returns from systems are compared under different levels of weed pressure. Producers operating over longer planning horizons would choose to double-crop regardless of the tillage method used and weed pressure level. Producers operating under shorter planning horizons would implement wheat-fallow systems when weed pressure is high and double crop when weed pressure is low.

Grape hyacinth is a perennial bulbous species in the Liliaceae. It is commonly grown as an ornamental plant, but it can spread into agricultural fields and become weedy, potentially interfering with harvest and fall-planted crops. There has been limited research on controlling grape hyacinth in cropping systems. Fall and spring applied field-research studies were conducted to determine grape hyacinth control with herbicides labeled for use in wheat or winter fallow before planting soybean. Among fall-applied herbicides, paraquat resulted in the greatest initial grape hyacinth control (90% to 100%). Grape hyacinth control, 16 months after application (MAA), was variable, but the top-performing treatments were glyphosate and metsulfuron plus paraquat, resulting in 65% and 50% control, respectively. After spring applications, grape hyacinth control in November (7 MAA) was variable, but top-performing treatments were glyphosate and metsulfuron, which resulted in at least 26% control. Spring-applied paraquat, carfentrazone, metsulfuron, and sulfosulfuron resulted in 73%, 68%, 69%, and 60% reductions in grape hyacinth bulb counts, compared with the nontreated control 7 MAA, and were the top-performing treatments. Despite product-label prohibitions on rotation to soybeans, no soybean yield reductions were observed from any treatment in either study. Single applications of certain herbicides in the fall or spring can result in good control (>80%) of grape hyacinth initially, but long-term control is poor, and additional research is required.

Glyphosate-resistant Palmer amaranth has become a major threat to soybean production in the southern United States. Arkansas soybean producers rely heavily on glyphosate-resistant soybean; hence, an alternative solution for controlling resistant Palmer amaranth is needed. A field experiment was conducted at Marianna, AR, during 2009 and 2010 in which soybean production systems were tested in combination with deep tillage and no tillage to determine the impact on Palmer amaranth emergence. To establish a baseline population, 250,000 glyphosate-resistant Palmer amaranth seeds were placed in a 1-m2 area in the middle of each plot and incorporated in the soil, and emergence was evaluated five times during the season. Production systems of full-season soybean with a rye cover crop or soybean double-cropped with wheat, which had high amounts of plant residue on the soil surface reduced Palmer amaranth emergence more than systems without deep tillage and a cover crop or wheat. When used in combination with deep tillage, these systems reduced Palmer amaranth emergence by 98 and 97%, respectively, in 2009 and by 73 and 82%, respectively, in 2010. Deep tillage alone caused an 81% reduction in emergence averaged over both years. Soybean double-cropped with wheat used in combination with deep tillage provided a 95% reduction in Palmer amaranth emergence over the 2-yr period. This research shows that deep tillage in combination with soybean production systems that have high amounts of residue on the soil surface are alternative means for providing a high level of control of glyphosate-resistant Palmer amaranth and could lessen the dependence on chemical weed control.