Producers are interested in tactics for managing crop residues when growing corn after spring wheat. We compared five systems of managing spring wheat residues: conventional tillage, no-till, strip-till, cover crop (hairy vetch) with no-till, and cover crop with strip-till following spring wheat. Conventional tillage consisted of chisel plowing and disking, whereas strip-till consisted of tilling a 15-cm band centered on corn rows, which were spaced 76 cm apart. Plots were split into weed-free and weed-infested subplots. Grain yield in weed-free conditions did not differ among treatments. However, weed-free yield was nearly 40% greater than weed-infested corn in conventional tillage. In contrast, weeds reduced yield only 15% with strip-till. Weed density and biomass was twofold greater with conventional tillage compared with the no-till and strip-till treatments. Weed seedlings also emerged earlier with conventional tillage. Increased weed tolerance with strip-till may be related to fertilizer placement. Corn growth and tolerance to weeds in no-till systems may be improved if a starter fertilizer is placed in the seed furrow.

Competitive crops or cultivars can be an important component of integrated weed management systems. A study was conducted from 2003 to 2006 at four sites across semiarid prairie ecoregions in western Canada to investigate the weed-suppression ability of canola and mustard cultivars. Four open-pollinated canola cultivars, four hybrid canola cultivars, two canola-quality mustard cultivars, two oriental mustard cultivars, and two yellow mustard cultivars were grown in competition with indigenous weed communities. Yellow mustard was best able to suppress weed growth, followed in decreasing order of weed competitiveness by oriental mustard and hybrid canola, open-pollinated canola, and canola-quality mustard. Competitive response of cultivars, assessed by weed biomass suppression, was negatively correlated with time to crop emergence and positively correlated with early-season crop biomass accumulation (prior to bolting) and plant height.

Field trials were conducted over two spring seasons (2005 and 2006) to investigate the interference between American black nightshade and watermelon in polyethylene-mulched and nonmulched (bare ground) trials. Competition studies were performed with watermelon at 1 plant/m in-row and American black nightshade grown at 0, 2, 4, 6, and 8 plants/m2 in-row. Watermelon yield reductions started to plateau at only 2 American black nightshade plants/m2. Yield reduction was 80, 89, 96, and 98% and 54, 67, 81, and 85% at 2, 4, 6, and 8 American black nightshade plants/m2 in mulched watermelon production in 2005 and 2006, respectively. When watermelon was grown on bare ground, yield reduction was 100% at 2 American black nightshade plants/m2 in 2005 and 68, 81, 89, and 93% at 2, 4, 6, and 8 American black nightshade plants/m2 in 2006, respectively. Watermelon fruit numbers were reduced due to American black nightshade interference, but no significant differences in individual fruit weight were observed.

An experiment was conducted to determine the population dynamics of barnyardgrass under a range of weed management treatments in glyphosate-resistant (GR) cotton in Australia. These treatments consisted of glyphosate herbicide only (Glyphosate only), glyphosate herbicide plus a combination of conventional or integrated weed management practices (Glyphosate + IWM), glyphosate herbicide plus a reduced residual herbicide program (Glyphosate + Res.), glyphosate herbicide plus a grass herbicide (Glyphosate + Grass), and a combination of conventional weed management practices (IWM only). The experiment investigated the effects of weed management on the weed seed bank, weed emergence patterns, and weed populations. After three years, all treatments resulted in commercially acceptable control of barnyardgrass. However, treatments containing soil-applied residual herbicides proved more effective over the period of the experiment. Seed bank reductions were in the order of 100-fold over the period of the experiment for treatments that received residual herbicides compared to 10- to 20-fold reductions for treatments that did not. The experiment highlighted the importance of early-season weed control, as well as the importance of an integrated approach to weed management with residual herbicides to control later-emerging weeds in GR cotton.

Four field trials were conducted over a 2-yr period at Exeter (2005, 2006), Harrow (2006) and Ridgetown (2006), Ontario to evaluate the tolerance of pinto and small red Mexican (SRM) bean to the POST application of bentazon, imazethapyr, or their combination. Bentazon applied once or twice (to simulate a spray overlap in the field) at 840 g ai/ha and imazethapyr applied at 37.5 g/ha caused minimal injury (6% or less) in pinto and SRM bean and had no adverse effect on plant height, shoot dry weight, seed moisture content, and yield. Imazethapyr applied twice at 37.5 and all single and repeat applications containing 75 or 150 g/ha caused 15 to 44% injury to dry bean. These injuries were persistent and reduced plant height by as much as 21% and shoot dry weight by as much as 34%, but caused no adverse effect on maturity and yield, except for imazethapyr applied twice at 150 g/ha, which delayed maturity and reduced yield 16%. The addition of bentazon to imazethapyr applied as a tankmix reduced injury by as much as 23%. Imazethapyr at 37.5 or 75 g/ha combined with bentazon at 840 g/ha applied once or twice caused 3 to 23% injury but had no adverse effect on plant height, shoot dry weight, maturity, or yield. Two applications of imazethapyr at 150 g/ha plus bentazon at 840 g/ha reduced plant height 16% and shoot dry weight 28%.

Certified Crop Advisors of Arkansas and members of the Arkansas Crop Consultants Association were surveyed in fall 2006 through direct mail to assess the current situation of the red rice problem and early impact of imidazolinone-resistant (IMR) rice technology on red rice infestation. The information generated represented 40% (226,800 ha) of rice production areas in Arkansas. Barnyardgrass and red rice were the most problematic weeds, with 62% of fields infested with red rice. The estimated economic loss due to red rice averaged $274/ha. Red rice infestation was prevented mostly by crop rotation (96%) and use of certified seed (86%). Of the red rice–infested fields, 38% had light infestation and 26% had severe red rice problems before adopting IMR rice. Thirty-seven percent of infested fields had been planted with IMR rice once and 43% at least twice. Approximately 85% of the consultants reported > 90% red rice control when using IMR rice. The majority (92%) of IMR rice growers rotate to other crops, mostly soybean. Unsuitable field condition was the main reason for growing only rice. After 3 seasons, the consultants perceived that red rice infestation level declined by 77% on average. The herbicide-resistance gene had escaped to red rice in some fields, and 90% of growers are exerting effort to mitigate outcrossing.