NE1026: Weed Management Strategies for Sustainable Cropping Systems
Statement of Issues and JustificationWeed management is generally viewed as a major challenge in conventional, transitional and organic cropping systems. Control of weeds in agriculture costs the U.S. economy more than $15 billion annually, more than the cost of controlling insects and diseases combined (Bridges 1992). Although organic cropping systems are often highly profitable anyway, weed densities frequently boarder on or exceed tolerable levels (Mohler 2007), and surveys of organic growers and studies of organic farms indicate that weeds are a major production problem (Peacock 1990, OFRF 1999, Bond and Grundy 2001). Moreover, existing methods for controlling weeds on organic farms depend on excessive soil disturbance, resulting in loses in soil quality.
Currently, little research is directed toward the weed management needs of organic producers. New methods like organically certifiable herbicides and weed management with cover crops are needed. There is also a need to evaluate existing approaches like nutrient management for weed control and the mechanisms of cultivator action. Conversations with growers indicate that fear of uncontrolled weeds is frequently a factor inhibiting adoption of organic practices. Development of new weed management methods and improvement of traditional methods will speed adoption of organic practices, thereby reducing use of both herbicides and other pesticides. This will improve environmental quality and reduce expenses for farmers. Better weed management options will also improve yield and profits, thereby strengthening local communities.
All four objectives of the study are direct responses to growers' requests for information at talks and workshops. Interest in natural product herbicides has been growing rapidly, and is reflected in increasing sales of vinegar, clove oil, and citric acid based products. Such products have the potential of reducing organic growers' dependence on soil disturbance for weed management. Unfortunately, reliable information on the optimal use of these products has lagged behind. Organic growers also continue to express strong interest in the use of cover crops to balance goals of weed management and improvement in soil health. For example, at a 2005 needs-assessment workshop led by several organic growers (hosted by Cornell Universities' Organic Production and Marketing Project Work Team), cover crops for weed management were identified as a major research priority. Organic growers have long shown interest in nutrient effects on weed management. In particular, growers are interested in how cation ratios and micronutrient availability affect weed management. Unfortunately, most of the information currently available is anecdotal and contradictory. Organic growers throughout the U.S. are annually spreading thousands of tons of gypsum on circum-neutral soils to increase available calcium and control foxtail, with essentially no research data to support or refute the practice. Either growers are throwing away thousands of dollars per year on unnecessary supplements or other growers are suffering yield losses by not using them. Finally, improved information on cultivation is essential for successful control of weeds on organic farms. Cultivation is the primary means of weed management in organic systems. The whole thrust of objective 4, namely exploration of the different mechanisms whereby mechanical soil disturbance kills weeds and how weeds differ in their susceptibility to different kinds of disturbance, is directly relevant to questions and suggestions organic farmers Klaas and Mary Howell Martens raised in their recent article in The New Farm electronic journal (http://www.newfarm.org/ features/2005/0105/earlyweeds /index1.shtml). Such mechanistic information should facilitate more efficient use of cultivation tools, and help minimize their potentially destructive effect on soil health.
Even more than in conventional agriculture, the problems of organic farmers and approaches to their solution vary greatly in response to local soil and climatic conditions. Thus, a comparative approach that examines similar management methods across the U.S.A. and beyond will help identify common principles, and indicate how they have to be modified to fit local conditions. A multi-state approach is therefore ideal for addressing problems in organic weed management.
The research proposed here is intended to (i) increase the range of weed management options available to growers, (ii) improve overall weed management on a wide range of organic and transitional farms, (iii) encourage the transition to organic practices by reducing fear of unmanageable weed problems, (iv) improve soil health by substituting natural product herbicides and cover crops for tillage and cultivation, and (v) improve the overall profitability of transitional and established organic farms by decreasing labor and yield losses to weeds. The proposed research should also foster collaboration between weed scientists and help them leverage funding from other sources to pursue these topics in more depth. In particular, the proposed project will help leverage renewal of a long-term cropping system study funded by the USDA-Integrated Organic Program by providing some quick results through cultivation experiments nested within that study. The new project should also be helpful in leveraging funding proposals to the NE-IPM program, SARE and PMAP programs integrating buckwheat and mustard cover crops and natural product herbicides into weed management programs.
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