Industry, public-sector researchers and extension agents, and growers were surveyed in 1998 to determine their perspectives on how labeling herbicides with their site of action (group number) would affect the herbicide use practices of growers. The crop protection industry in Canada represented by the Crop Protection Institute (CPI) generally supports herbicide resistance labeling but has some concerns regarding the wording of the labels, including the identification symbol. Most researchers and extension agents believe that labeling herbicides with their site of action will facilitate herbicide group rotation by growers who frequently use herbicides from the same group. Of the two-thirds of the 126 surveyed growers who were familiar with herbicide groupings, 58% practiced herbicide group rotation. Those who did not tended to lack understanding of the basis and purpose of herbicide classification. Grower responses were similar to those from the research and extension community, although only 29% of the growers who currently do not rotate herbicides from different groups believed that resistance management labeling would influence them.

Following suggested guidelines developed by the Environmental Protection Agency (EPA), comparative snap bean herbicide performance field trials were conducted from 1993 to 1995 in New York. Data were obtained on crop injury, weed control, and weed biomass, and crop yield, quality, and losses during harvest. Trifluralin, EPTC, and pendimethalin applied preplant incorporated (PPI) and applications of metolachlor applied preemergence (PRE) provided less than adequate control of redroot pigweed, common lambsquarters, and hairy galinsoga. Cultivation improved weed control with PPI and PRE applications. Metolachlor + fomesafen PRE provided good control of hairy galinsoga, adequate redroot pigweed control, and marginal control of common lambsquarters. Fomesafen applied postemergence (POST), combinations of metolachlor applied PRE with fomesafen or bentazon applied POST, and fomesafen + bentazon applied POST adequately controlled the three weed species without cultivation. Herbicide treatments had little measurable impact on snap bean quality or losses during harvest. Information from product comparison trials may be useful in developing recommendations for growers but may prove less than adequate in providing data necessary for a thorough evaluation of the relative benefits of individual herbicides as intended by EPA guidelines. Difficulties were encountered in following the guidelines, and costs of conducting the product comparison trials for a single crop in one growing region exceeded $90,000 over 3 yr.

Characterization of herbicide dissipation under field conditions is an important component in determining the environmental impact of herbicides, and much information is available on this subject. However, this research area could be improved by standardizing and implementing several quality control procedures. The purpose of this review is to evaluate the recent literature on herbicide dissipation published in journals of the Weed Science Society of America. This review is not comprehensive with respect to all experimental parameters associated with field dissipation studies, but it is aimed at addressing specific areas of concern in the experimental approach to this research.

Potassium azide (PA) (112 kg/ha), oxadiazon + 1,3-dichloropropene (1,3-D) (168 kg/ha + 140 L/ha), dazomet (392 kg/ha), dazomet + chloropicrin (392 + 168 kg/ha), dazomet + 1,3-D (392 kg/ha + 140 L/ha), iodomethane (IM) (336 kg/ha), metam-sodium (MS) (748 L/ha), MS + chloropicrin (748 L/ha + 168 kg/ha), and MS + 1,3-D (748 + 140 L/ha) were evaluated at Jay and Arcadia, FL, in 1998 and 1999 as alternatives to methyl bromide (MeBr) fumigation for the management of common turfgrass weeds. Potassium azide was as effective as MeBr in controlling ‘Coastal’ bermudagrass, yellow and purple nutsedges, alexandergrass, broadleaf signalgrass, tall and sharppod morningglories, and various winter annual broadleaf weeds, but it failed to provide acceptable control of redroot pigweed. 1,3-Dichloropropene + oxadiazon did not control yellow nutsedge, purple nutsedge, or Coastal bermudagrass. Similarly, this combination treatment failed to control carpetweed but did provide 83% control of the winter annual weed species, 71% control of alexandergrass and broadleaf signalgrass, and ≥ 80% control of tall morningglory, sharppod morningglory, and redroot pigweed. Dazomet + combination treatments provided control of Coastal bermudagrass at Jay; however, control of common bermudagrass, alexandergrass, and broadleaf signalgrass was not acceptable at Arcadia. Sedge species control with dazomet + combinations was poor (< 63%) at both sites. Iodomethane, a treatment not yet registered by the U.S. Environmental Protection Agency (EPA), controlled weedy grass species, sedge species, and broadleaf weeds present at the two locations under different environmental conditions. Metam-sodium alone and MS + chloropicrin, tarped and untarped, and MS + 1,3-D provided acceptable weed control; however, MS + chloropicrin covered with a plastic tarp for 48 h was the best MS treatment. Metam-sodium + chloropicrin, with plastic tarp, controlled weedy grass and broadleaf species equal to MeBr; however, unacceptable sedge species control at Jay and Arcadia was 56 and 79%, respectively. Metam-sodium applied alone failed to control redroot pigweed; however, MS + combinations provided control. These studies confirm that no EPA-registered fumigant alternative to MeBr, applied alone or in combination for preplant turf soil fumigation, exists. Consequently, until such time that an effective alternative is identified, turf managers will be forced to forego fumigation, or they will have to choose a less-effective alternative and accept the consequences of contamination.

The classification of herbicides by site of action, published in 1997, has been revised. The classification system uses a numbering system for a herbicide's site of action, chemical family, and common name. Regulatory agencies in the United States and Canada have published labeling guidelines based on the classification to aid in herbicide resistance management.

Red rice has long been a troublesome, conspecific weed of cultivated rice. Rice varieties carrying certain herbicide-resistant traits acquired through genetic modification (herbicide-resistant varieties) now offer new options for red rice control. In concert with this innovation is the risk of gene flow, which can result in the transfer of that specific herbicide resistance to red rice and thus render this weed control measure ineffective. Gene flow in concept is simple, however, the parameters that determine the establishment of a new trait in a weed population are complex. Cross-pollination to make hybrid seed and the subsequent fate of those hybrid families in the general weed population are some of the biological factors that influence gene flow between red rice and cultivated rice. Natural outcrossing among rice plants is generally low. Most of the pollen dispersal studies published to date indicated that rice × rice outcrossing rates were less than 1.0%. Numerous reports summarized in this study suggest that outcrossing rates between rice and red rice can be highly variable but usually are similar to or lower than this level. However, once hybrids form, they may introgress into a red rice population within only a few generations. If hybrid seed families are to persist and establish herbicide-resistant red rice populations, they must successfully compete in the crop–weed complex. The ability to survive a herbicide applied to a herbicide-resistant rice variety would be a strong selective advantage for these hybrid families. Thus, the well-established principles of weed resistance management appear to be relevant for herbicide-resistant crop systems and should be used in combination with practices to minimize coincident flowering to mitigate the potential impact of gene flow from herbicide-resistant rice into red rice. For the rice–red rice crop–weed complex, there are both biological factors and agricultural practices that can work together to preserve these new weed control options.

Natural product herbicides for vegetation control are being considered as alternatives to synthetic herbicides by many public agencies. Studies were conducted along roadsides at the Hopland Research and Extension Center (HREC) in 2001 and 2002 and on California State Route 29 (SR29) in 2002 to evaluate acetic acid, pine oil, and plant essentials compared with glyphosate for control of herbaceous vegetation. In 2001, annual grass control after a single application of pine oil at HREC was 40% or less effective, whereas acetic acid was at least 79% effective. A second application of pine oil or acetic acid did not control regrowth or new plants. In 2002, plant essentials was the most effective (>80%) natural product at HREC for control of annual grasses, except slender oat. Pine oil often provided similar control of slender oat as plant essentials (71 and 69%, respectively). At SR29, five applications of acetic acid provided 83% or better control of slender oat, hare barley, medusahead, and broadleaf filaree. Plant essentials and pine oil controlled hairy vetch, broadleaf filaree, and hare barley at least 83%, but yellow starthistle, soft chess, buckhorn plantain, and medusahead control never exceeded 85%. Glyphosate controlled all vegetation in these experiments with one or two applications. The cost of one or more applications of the natural products was greater than 10 times the cost of using one or two applications of glyphosate. Natural products were neither efficaciously nor economically comparable with glyphosate for control of annual roadside vegetation.