The Future of Herbicides in Weed Control Systems of the Great Plains

Herbicides have played a vital role in dryland agriculture in the Great Plains since their introduction in the late 1940s. Herbicides have reduced the amount of tillage required for crop production. Reduced‐tillage leaves crop residues at the soil surface, which results in greater soil water capture and retention, and reduces soil loss to wind and water erosion. Despite the benefits provided by herbicides, their future role in agriculture is uncertain. Trends including a decline in the introduction of new herbicides, the potential loss of older herbicides, a rapid increase in the number of cases of herbicide resistance in weeds, a dramatic increase in the capability to detect pesticides in the environment, and rising public concern about the effects of pesticides in the environment may indicate a reduction in herbicide use in the future. In order to retain herbicides as effective tools in sustainable crop production, strategies to maximize the efficiency of herbicide use must be developed and implemented. These strategies should include the use of crop rotation, competitive crops and cultivars, fertilizer placement technology, residue conserving tillage, biological control agents, and precision application technology. Introduction Herbicide use in the Great Plains has allowed producers to reduce the amount of tillage required to raise a crop. This reduction in tillage has resulted in better management of crop residues for soil erosion control and increased soil water storage efficiency. Herbicides have increased farmer profitability and improved their soil stewardship. Despite these benefits, the future role of herbicides in agriculture is uncertain. Economic, social, and regulatory pressures may force a reduction in herbicide use that could erase the efficiency and environmental gains achieved over the last 40 yr. Literature Summary Herbicides may be used to replace tillage operations for weed control. Eliminating or reducing tillage helps to retain crop residues on the soil surface where they serve to reduce wind arld water erosion. No‐till can reduce soil erosion by 90% compared with cleanly tilled fields. Crop residues also improve soil water storage in the semiarid Great Plains, and thereby stabilize crop production. The extra soil water resulting from greater crop residue retention allows for more intensive crop rotations such as winter wheat‐sorghum or cornfallow rather than the traditional winter wheat‐fallow. Reducing or eliminating fallow can improve profitability and reduce erosion hazards while increasing the water use efficiency of the cropping system. Several current trends, including a decline in the introduction of new herbicides, the potential loss of older herbicides, a rapid increase in the number of cases of herbicide resistance in weeds, a dramatic increase in the capability of detecting pesticides in the environment, and rising public concern with pesticide use in food production, suggest that herbicide use probably will be reduced in the future. Weed control with herbicides may be supplemented by strategies that include crop rotation, the use of competitive crops and cultivars, fertilizer placement technology, residue conserving tillage, biological control agents, and precision application technology. Study Description We do not know the future of herbicide use in agriculture, but this paper presents some of the trends that may have an influence on the role herbicides play in Great Plains agriculture. It also suggests several strategies that may be used to supplement herbicides for weed control. Applied Questions Will herbicides continue to be a valuable tool for weed control in the Great Plains? Herbicides will continue to be a valuable tool in agricultural production in the Great Plains for many years, but their role probably will be reduced in scope from their current status. Rapidly increasing developmental costs for pesticides have reduced the number of new pesticides introduced. New pesticides often are expensive and not labeled in minor crops. Older chemical products also are being removed from the marketplace as a result of the EPA's reregistration and special review processes. The rapid development of herbicide resistance in several of the newer herbicide classes also will limit the efficacy of many of the most recently introduced products. Add to these factors the ability to detect chemicals in the environment at exceedingly low levels and its consequent effect on the public's anxiety with pesticides, and a scenario of reduced herbicide use is easy to envision. It should be stated, however, that much of this anxiety has arisen from herbicide use in more humid environments, where off‐site movement of chemicals through runoff and leaching have been better documented than in the Great Plains. What strategies can be used to supplement herbicides for weed control? Cropping sequence has a major influence on weed species composition. Well designed crop rotations can reduce the amount of herbicide required to successfully produce crops. Choosing cultivars based on their competitive ability with weeds is another option. Any crop can be manipulated to improve its competitive ability with weeds through optimum plant arrangement and appropriate seeding dates. Placement and timing of fertilization can be manipulated to optimize crop competitiveness. Residue conserving tillage can be used along with herbicides and crop rotation to manage the weed seedbank. Biological control methods, including the use of livestock, can also be integrated into some of our cropping systems. Precision application technology may allow producers in the near future to use herbicides in a much more efficient manner than is possible today. The new technology will allow herbicides to be applied only to portions of a field where weed pressures are sufficiently high to warrant their use. This has the potential to reduce herbicide use by as much as 90% in any given field.