Recipient Organization
TEXAS A&M UNIVERSITY
750 AGRONOMY RD STE 2701
COLLEGE STATION,TX 77843-0001
Performing Department
Soil & Crop Sciences
Non Technical Summary
Similar to any biological organism, weed communities have the potential to evolve resistance to selection pressure imposed on them (Gressel and Segel 1978; Harper 1956). Herbicides typically exert enormous selection pressures due to high control efficacies. Currently, herbicide-resistant weeds pose an immense threat to crop production efficiency worldwide. As of 2015, there are 449 unique cases of herbicide resistance in 245 weed species across the world (Heap 2015). A common phenomenon shared by these cases is that weed management practitioners relied heavily on few herbicide options without implementing sufficient management diversity (Norsworthy et al. 2012).In Texas, the evolution of herbicide-resistant weeds is an emerging problem in several cropping systems, tremendously affecting crop yields, quality and profitability. Currently, glyphosate-resistant Palmer amaranth and common waterhemp are two major weed issues in Texas causing serious economic damages in a number of row-crops, including cotton, sorghum, corn and soybean (Baumann 2013; McGinty et al. 2015). Herbicide-resistant annual ryegrass (resistance to ALS- and ACCase-inhibitors) is a serious threat to wheat production throughout the Blacklands of Texas (Swart 2012; Swart et al. 2012). The first ALS-inhibitor-resistant johnsongrass was reported in 2000 (Green 2000) and currently more resistant populations are suspected in Texas corn and sorghum. In Texas rice, ALS-inhibitor-resistant red rice (Avila et al. 2005) and barnyardgrass (Bradshaw, personal communication) are two of the important resistant weed problems. As a result of growing resistance issues, producers are forced to use more and more environmentally less-benign herbicides in their weed management programs, which has a direct impact on production costs and the environmental footprint of weed management practices. Surveys indicate that herbicide-resistant weed issues have tremendously increased herbicide use, hand-weeding, and mechanical tillage, tremendously increasing crop production costs (Sosnoskie and Culpepper 2014). In areas where conservation tillage practices have been adopted for long-time, returning to tillage as a means for controlling herbicide-resistant weeds has been jeopardizing all the soil conservation gains made over the past several years (Shaw et al. 2012). Overall, herbicide resistance issues have been threatening the sustainability of economical weed management in several cropping systems in Texas.Although herbicide resistance, particularly resistance to glyphosate, is a growing problem in Texas, it is still in its early stages in several parts of the state. There is a critical need to prevent further evolution and spread of resistant weeds and effectively manage already existing resistant populations. The key to preventing resistance is to be proactive, but a better understanding of the factors influencing the evolution of herbicide resistance can guide the deployment of robust and effective proactive tactics. Knowledge on weed biology, population genetics, management factors, and their interactions is vital to understand the evolutionary dynamics of herbicide resistance. However, research information is often limited in this regard.Developing a robust resistance management strategy begins with an understanding of the background levels of resistance at regional scales. A key consideration to herbicide resistance management is managing selection pressure (Norsworthy et al. 2012), which is achieved through diversifying management tools by integrating both chemical and non-chemical options. Diversified approaches will minimize selection pressure placed on a single management tool. Yet, the number of tools available for effective resistance prevention and management are limited. While there is a need to develop additional tools for integration, it is critical to protect and preserve all the management tools that are currently available. Additionally, research efforts are needed to develop stewardship practices to ensure sustainable deployment of herbicides and herbicide-resistant crop technologies in our cropping systems and minimize potential unintended impacts on the broader environment. Further, developing decision-support tools are necessary to facilitate extension and outreach activities geared towards promoting widespread adoption of sustainable resistance management practices.
Animal Health Component
40%
Research Effort Categories
Basic
50%
Applied
40%
Developmental
10%
Goals / Objectives
Evaluate and understand causes of herbicide failure on weeds of economic importance in various cropping systems in TexasDevelop and test alternative and sustainable weed management approaches (chemical and non-chemical tactics) for adoption by growers to tackle herbicide resistance issuesAssess the impact of herbicides and herbicide-resistant crops on the broader environment and develop stewardship protocols and mitigation strategies
Project Methods
Objective 1: The first objective focuses on conducting routine surveys and screening suspected samples for resistance. A semi-stratified sampling procedure will be followed in implementing the field survey. We will also solicit samples from growers and consultants who want their samples tested for herbicide resistance after reviewing their individual circumstances for non-control. The seed samples will be germinated and grown in a greenhouse and tested for survival after application of recommended field doses at standard application conditions. If survival is observed, then follow-up tests will be conducted to evaluate survival for other herbicides within the same mechanism of action (cross resistance) and also for some other herbicide mechanisms of action (multiple resistance). Dose-response assays will be conducted to confirm new cases of resistance.If a unique case of resistance is confirmed through greenhouse assays, then further studies will be conducted to understand the physiological and genetic mechanisms that facilitate resistance. In particular, experiments will be conducted using radio-labeled herbicides to understand differential uptake and translocation of herbicides. Enzyme assays will reveal the level of metabolic detoxification of a given herbicide prior to reaching the herbicide target site. If none of the above tests adequately explain resistance, then sequencing the target gene and looking for nucleotide changes (non-synonymous mutations) will help us determine the possible causes of resistance. These studies will allow for a better understanding of the resistance profile of the weed population in question, a knowledge that is critical for developing robust resistance management programs. Research will also be conducted to better understand the evolutionary biology and genetics of herbicide resistance evolution in weed communities using simulation modeling and population genetics tools.Objective 2: The second objective focuses on developing alternative, integrated weed management programs that help prevent/delay resistance in areas where herbicides are still effective and effectively manage resistance in fields where it is already a concern. The experiments conducted in objective 1 will greatly guide some of the management considerations. Within this objective, experiments will be conducted on a number of fronts to generate tools and knowledge that will aid the development of integrated weed/resistance management programs.A better understanding of the ecology and biology of the weed in question, with particular reference to fecundity and seedbank dynamics is key for targeting its population dynamics. While more research will be conducted on effective herbicide combinations and rotations, research will also focus on developing and testing additional weed management tools/practices for integration. Developing novel sources of herbicide resistance traits, evaluating non-chemical tactics such as harvest-time weed seed control and utilizing cover crops for weed suppression in conservation tillage systems are notable ones in this regard.Objective 3: The third objective focuses on the assessment of the impact of herbicides and novel herbicide-resistant crops on the broader environment, with a goal of developing sound stewardship protocols and risk mitigation strategies. Gene flow from herbicide-resistant crops to compatible wild relatives create challenges with agronomic management of the weedy relatives in addition to other ecological issues associated with hybrid fitness. In Texas, hybridization between sorghum-Johnsongrass, rice-red rice and sunflower-wild sunflower represents a significant concern. Studies will be conducted to understand gene flow, cytogenetics of hybridization, hybrid fitness and invasiveness. The knowledge generated from these experiments will be used to develop stewardship measures for improving the longevity of herbicide resistance technologies and minimizing any unintended impacts they may have on the broader environment. In addition, science-based stewardship measures are necessary to foster co-existence between genetically-engineered (GE) and non-GE production systems in agricultural landscapes, particularly in situations where identity preservation is vital for specific markets. An allied research focus is to monitor off-target movement of herbicides and develop strategies for preventing/mitigating any harmful impact of herbicides on sensitive ecosystems.