Herbicide-resistant crops (HRCs) have been used extensively during the past five decades, because crop tolerance is necessary for a selective herbicide. In the past, chemical company personnel screened a large number of organic compounds against a limited number of major crop and weed species to discover HRCs. Now a single herbicide can be evaluated for crop selectivity against a great number of biotypes of a single crop in tissue culture, or sometimes gene transfer can be used to produce tolerant genotypes. Thus, one can now choose an environmentally “benign” herbicide and search for or develop resistant crop cultivars. The advantages of these new HRCs are: (a) solutions may be more easily found for difficult weed management problems, (b) growers are more apt to use integrated weed management when they have effective backup weed control procedures if cultural or mechanical methods fail, (c) increased weed management options for growers of minor crops, (d) economic advantages to growers, and (e) increased use of more environmentally “benign” herbicides. Concerns about HRCs include: (a) these weed management procedures do not eliminate herbicides, (b) some believe biotechnology should not further herbicide use, (c) HRCs may become weeds, (d) this approach may facilitate less ecological diversity, (e) HRCs may increase herbicide use, (f) it could result in more herbicide carryover by facilitating the use of environmentally “harsh” herbicides, (g) HRCs may be less competitive to weeds, and (h) dependence on HRCs may decrease the weed control practices that a farmer uses. One needs to consider both the benefits and risks of HRCs to properly evaluate this technology.

Tolerance of barley to chlorsulfuron at various stages of crop development was studied in weed-free field and pot experiments. Five barley crops were sown between mid-May and mid-July in the field in 1988 and sprayed simultaneously with four rates of chlorsulfuron when the corresponding stages of crop development ranged from growth stage 7 (GS 7) to GS 31. Early-sown barley yielded more than late-sown barley, but percent grain yield reduction from chlorsulfuron was similar for all planting dates. In a field experiment in 1989, barley was sown at three dates (May, June, and July) and each was treated with chlorsulfuron at 0, 15, 30, and 60 g ai ha−1 at either GS 12 or GS 15. Grain yield of barley sown in May and treated with 15 g ha−1 chlorsulfuron at GS 12 was reduced 35%, compared with no effect when applied at GS 15; this yield reduction was related to spike size and number. Application of chlorsulfuron at GS 12 and GS 15 to barley sown in June caused yield reductions of 20 and 11%, respectively. In contrast, barley sown in mid-July was not affected by chlorsulfuron. Applications of chlorsulfuron at GS 12,13,14, and 15 led to reductions of 75,35,15, and 5% shoot dry matter (DM) of plants grown in pots and measured at GS 33. Root DM was more sensitive to chlorsulfuron than shoot DM. Tolerance of barley to chlorsulfuron increased with age of the plant at the time of application.

The regulation of transgenic plants is at the very early stages of dialog between the U.S. Environmental Protection Agency (EPA), the Food and Drug Administration (FDA), and the U.S. Department of Agriculture (USDA). Herbicide resistance is discussed in the broader terms of resistance management and of the cooperative efforts underway involving governments, industry, academia, and the environmental community on an international level. A new body, the International Organization for Resistant Pest Management (IOPRM) was formed to implement pesticide resistance management programs worldwide. The research base for integrated pest management programs which form the context for pesticide resistance management programs is in need of expansion. Public and private efforts to expand this base converge in an ambitious collaborative program between the U.S. EPA and USDA entitled the National Integrated Pest Management Forum. Finally, the potential role of EPA in the regulation of resistance management is discussed.

A total of 24 pre-and posttreatment plant frequency data sets were analyzed from 15 Wisconsin lakes treated with granular 2,4-D BEE herbicide for the control of Eurasian watermilfoil (Myriophyllum spicatum). Six data sets from four untreated control lakes were analyzed for comparison. The data sets included the results of line-transect aquatic plant surveys and point-intercept aquatic plant surveys. The results from these two survey methods were analyzed separately. Analysis of pre-and posttreatment changes in frequency of occurence for 46 species of aquatic plants indicated Eurasian watermilfoil was the only species to show significant declines in all the surveys. At application rates of 112 kg ha−1, Eurasian watermilfoil declined an average 65.9% among the line-transect surveys; and 58.0% among the point-intercept surveys. At application rates of 168 kg ha−1, Eurasian watermilfoil declined by 94.4% and 76.5% among line-transect and point-intercept surveys, respectively. Among the control lakes, Eurasian watermilfoil increased an average of 77% in year 1 and 24% in year 2. Northern watermilfoil (Myriophyllum sibiricum), a closely related native plant, underwent declines in frequency at the higher 2,4-D application rate (20.0%) but showed an increase (88.9%) at the lower rate among the line-transect surveys. Northern watermilfoil exhibited declines at both rates among the point-intercept surveys (48 and 50%, respectively); however, the plant also exhibited declines in the control lakes in year 2. Most other native aquatic plant species were unaffected or showed increases following treatment with 2,4-D BEE. The high degree of selectivity to Eurasian watermilfoil found in this survey of operational treatments with 2,4-D BEE suggests that this herbicide is an important tool for restoring plant communities that have been degraded by Eurasian watermilfoil.