Metabolism of 2,4-dichlorophenoxyacetic acid contributes to resistance in a common waterhemp (\u3ci\u3eAmaranthus tuberculatus\u3c/i\u3e) population

BACKGROUND: Synthetic auxins such as 2,4-D have been widely used for selective control of broadleaf weeds since the mid-1940s. In 2009, an Amaranthus tuberculatus (common waterhemp) population with 10-fold resistance to 2,4-D was found in Nebraska, USA. The 2,4-D resistance mechanism was examined by conducting [14C] 2,4-D absorption, translocation and metabolism experiments. RESULTS: No differences were found in 2,4-D absorption or translocation between the resistant and susceptible A. tuberculatus. Resistant plants metabolized [14C] 2,4-D more rapidly than did susceptible plants. The half-life of [14C] 2,4-D in susceptible plants was 105 h, compared to 22 h in resistant plants. Pre-treatment with the cytochrome P450 inhibitor malathion inhibited [14C] 2,4-D metabolism in resistant plants and reduced the 2,4-D dose required for 50% growth inhibition (GR50) of resistant plants by 7-fold to 27 g ha-1, similar to the GR50 for susceptible plants in the absence of malathion. CONCLUSIONS: Our results demonstrate that rapid 2,4-D metabolism is a contributing factor to resistance in A. tuberculatus, potentially mediated by cytochrome P450. Metabolism-based resistance to 2,4-D could pose a serious challenge for A. tuberculatus control due to the potential for cross-resistance to other herbicides

Guide for Weed Management in Nebraska

Each year we strive to provide a publication that is updated, informative, and easy to use. Last year’s edition has been revised to include the latest research-based information and several new sections outlined below. We hope you find these revisions useful and that they make this guide an even better resource than the previous edition

Guide for Weed Management in Nebraska

Each year we strive to provide a publication that is updated, informative, and easy to use. Last year’s edition has been revised to include the latest research-based information and several new sections outlined below. We hope you find these revisions useful and that they make this guide an even better resource than the previous edition

2006 Guide for Weed Management in Nebraska

2006 Guide for Weed Management in Nebraska. Includes special sections on weed control in corn, soybean, wheat, other small grains, sorghum, turfgrass, and alternative crops. Also includes sections on integrated weed management, classificationof herbicides by mode and site of action and chemical family, herbicide application and sprayer recommendations, weed response ratings to specific herbicides, herbicide hazards, herbicide safety and herbicide resistance, weed management in herbicide-resistant crops and Nebraska noxious weeds

2007 Guide for Weed Management in Nebraska

2007 Guide for Weed Management in Nebraska. Includes special sections on weed control in corn, soybean, wheat, other small grains, sorghum, turfgrass and alternative crops. Also includes sections on integrated weed management, classification of herbicides by mode and site of action and chemical family, herbicide application and sprayer recommendations, weed response ratings to specific herbicides, herbicide hazards, herbicide safety and herbicide resistance, weed management in herbicide-resistant crops and Nebraska noxious weeds

EC08-708 Precision Agriculture : Weed Targeting Herbicide Management

Extension Circular 08-708 discusses weed targeting herbicide management as part of the precision agriculture series

Response of Nebraska Horseweed (\u3ci\u3eConyza canadensis\u3c/i\u3e) Populations to Dicamba

Dicamba-resistant soybeans are being developed to provide an additional herbicide mechanism-of-action for postemergence weed control in soybean. Numerous broadleaf species, including horseweed, have evolved resistance to glyphosate. It is anticipated that dicamba will be used by farmers as a primary tool to manage these weeds. Studying and understanding variability in horseweed response to dicamba will aid in developing appropriate risk management strategies to extend the utility of the dicamba-resistance technology. Horseweed plants from ten Nebraska populations were treated with one of nine doses of dicamba in greenhouse experiments. At 28 days after treatment (DAT) visual injury estimations were made and plants were harvested to determine dry weight. There was a three-fold difference in the I90 (90% visual injury estimate) between the least (638 g ha-1) and most (205 g ha-1) susceptible populations. Two plants from five populations were observed for an additional three months. No plants treated at doses above 280 g ha-1 survived to set seeds. These results suggest that maintaining use doses of 560 g ha-1 or greater may fully control horseweed populations from Nebraska and minimize the risk of plants surviving to set seed, in addition to practicing other proven herbicide-resistance management strategies

Optimizing Cover Crop Benefits with Diverse Mixtures and an Alternative Termination Method

Previous studies have demonstrated benefits of individual cover crop species, but the value of diverse cover crop mixtures has received less attention. The objectives of this research were to determine the effects of spring-sown cover crop mixture diversity and mechanical cover crop termination method on cover crop and/or cash crop productivity, soil moisture and N, and profitability in an organic cropping system. An experiment was conducted between 2009 and 2011 near Mead, Nebraska, where mixtures of two (2CC), four (4CC), six (6CC), and eight (8CC) cover crop species, or a summer annual weed mixture were included in a sunflower– soybean–corn rotation. Cover crops were terminated in late May using a field disk or sweep plow undercutter. Undercutting cover crops increased soil NO3–N (0–20 cm) by 1.0 and 1.8 mg NO3–N kg–1 relative to disk incorporation in 2010 and 2011, respectively. Cover crop mixtures often reduced soil moisture (0–8 cm) before main crop planting, though cover crop termination with the undercutter increased soil moisture content by as much as 0.024 cm3 cm–3 compared to termination with the disk during early main crop growth. Crop yields were not influenced by cover crop mixture, but termination with the undercutter increased corn and soybean yield by as much as 1.40 and 0.88 Mg ha–1, respectively. Despite differences in productivity between spring cover crop mixtures and weed communities, crop yield was not different among these treatments; thus, profitability of the weed mixture–undercutter treatment combination was greatest due to reduced input costs