Resistance to aryloxyphenoxypropionate and cyclohexanedione herbicides (ACCase inhibitors) was characterized in five green foxtail populations from western Canada. Field histories indicated that these populations were exposed to up to seven applications of diclofop-methyl and sethoxydim over the previous ten years. Major differences occurred among the populations in their levels of resistance and patterns of cross-resistance. With one exception, R/S ratios calculated from GR50 values derived from growth room experiments varied from 2 to 54 depending on the population and herbicide. The exception was UM131 which was at least 75 times more resistant to sethoxydim (R/S > 2981) than the other populations. UM59 was not resistant to sethoxydim. It was also the least resistant to the other herbicides with R/S ratios ranging from 2 for fenoxaprop-p-ethyl to 8 for diclofop-methyl. In comparison, UM8 was resistant to diclofop-methyl, fenoxaprop-p-ethyl, sethoxydim, and tralkoxydim with R/S ratios of 11, 5, > 39, and 27, respectively. In field experiments, shoot dry weights of UM8 treated at two times the recommended rates of these herbicides were reduced by 9, 45, 74, and 49%. In contrast, the susceptible population, UM7, was completely controlled. UM7 and UM8 did not differ in their response to trifluralin, ethalfluralin, quinclorac, propanil and TCA.

Velvetleaf control in sugarbeet by clomazone and commercially available sugarbeet herbicides was investigated in greenhouse and field studies. In greenhouse studies, clomazone at 0.07 and 0.04 kg ai ha-1 controlled 97 and 69% of velvetleaf, respectively, with little visible sugarbeet injury. Adding clomazone to pyrazon, TCA, ethofumesate, pyrazon plus TCA, or TCA plus ethofumesate increased velvetleaf control but increased visible sugarbeet injury. In field studies, clomazone at 0.07 kg ha-1 did not enhance sugarbeet injury. However, velvetleaf was not controlled by clomazone alone or clomazone plus pyrazon, ethofumesate, combinations of pyrazon plus TCA, pyrazon plus ethofumesate, or pyrazon plus TCA plus ethofumesate. Cycloate preplant incorporated plus pyrazon preemergence followed by postemergence herbicides controlled velvetleaf in all 3 yr of research. Postemergence herbicides increased velvetleaf control from soil-applied herbicides in 1987 and 1988.

In 1985, the Swedish government mandated a 50% reduction in agricultural pesticide use by 1990. The reference point was based on the average of total pesticide sales (kg ai) between 1981 and 1985. The goal was to halve the risks to users and to the environment. A two-pronged approach dealing with risk and with the actual reduction in agricultural pesticide use was developed. By 1991, 215 ‘unsafe’ or less effective pesticide products were withdrawn by producers or cancelled by the National Chemical Inspectorate, leaving only 322 registered. Additionally, the government was able to report a 47% reduction in agricultural pesticide use where 64, 54, and 2% reductions occurred in insecticides, herbicides, and fungicides, respectively. However, the treated area did not decrease. Pesticide reduction was achieved largely in cereal grain production by switching from high-dose to low-dose herbicides, reducing rates of herbicides, removal of inactive isomers from racemic mixtures, cancellation of TCA for quackgrass control, increased set-aside, and improved sprayer precision. During the same 5-yr period, Scotland achieved an equivalent reduction without government intervention, indicating that the reductions were largely due to changing herbicide technology. Determining the need for similar programs must take into account: 1. initial use rates (in 1987, average total pesticide use rates in the U.S. and in Sweden were 1.8 and 1.5 kg ai/ha, respectively, and following the mandate period, Swedish use has decreased to 0.8 kg ai/ha); 2. measurement criteria; and 3. the long-term effect of reducing herbicide rates on replenishing the soil weed seed bank reserves.