Field studies were conducted to determine if varying carrier volume proportionally with herbicide dosage, thus maintaining constant herbicide concentration in the carrier, would change the response of sweet corn to glyphosate and of cotton to 2,4-D when compared with using a constant carrier volume where herbicide concentration would vary and be more dilute. For all the parameters measured, more sweet corn injury occurred if the concentration of glyphosate was constant in all volumes of spray. The glyphosate no-effect level for sweet corn was determined to be 0.046 kg/ha when using the variable carrier volume but was over four times greater (0.185 kg/ha) when applied at the constant carrier volume of 281 L/ha. Cotton response to 2,4-D was similar, with the constant herbicide concentration in the carrier at the lower volumes causing greater injury. The response of seed cotton yield was not different when comparing constant to variable carrier volume. The highly sensitive growth stage of cotton at the time of application (bud formation before blooming) may explain this result. These studies demonstrate the need to use carrier volumes that are proportional to the herbicide dosage, thus maintaining constant herbicide concentration in the carrier, when conducting simulated herbicide drift research. Failure to do so could underestimate the potential for injury.

Studies were conducted at Clayton, Lewiston, and Rocky Mount, NC, to evaluate weed and cotton response to herbicide systems in bromoxynil-resistant Stoneville BXN 47 cotton. Herbicide systems that included clomazone preemergence (PRE) controlled broadleaf signalgrass, common lambsquarters, common ragweed, goosegrass, large crabgrass, and prickly sida greater than 88%. Inconsistent Palmer amaranth control was observed with the addition of fomesafen PRE to clomazone PRE and pendimethalin preplant-incorporated (PPI) herbicide systems. Addition of bromoxynil early postemergence (EPOST) to clomazone and pendimethalin systems increased ivyleaf morningglory control to greater than 84% and provided higher yields than did the same systems without bromoxynil. Bromoxynil EPOST followed by (fb) cyanazine + MSMA late postemergence directed (LAYBY) improved weed control in clomazone and pendimethalin systems. Clomazone PRE and pendimethalin PPI with or without fomesafen PRE fb bromoxynil EPOST fb LAYBY herbicides controlled weeds and yielded equivalent to the standard herbicide system of pendimethalin PPI fb fluometuron PRE fb bromoxynil EPOST fb LAYBY.

In 1998, Indian regulatory agencies approved the registration of CGA 184927, MON 37500, and fenoxaprop for postemergence control of isoproturon-resistant littleseed canarygrass. Herbicides used in rice and wheat before 1998 were generally mixed with sand or urea and were applied by hand. Foliar pesticide spray applications consisted primarily of insecticides and fungicides that were applied to high-value crops. These pesticides were often sprayed to runoff with backpack sprayers that were equipped with single hollow-cone or flood nozzles. Applicators walked through the fields, swinging the wands in sweeping motions resulting in uneven pesticide distribution and overapplication. The newly registered postemergence herbicides were applied with the same equipment and in the same fashion. After these applications, control of littleseed canarygrass was strikingly inconsistent, and the growers blamed the lack of control on the manufacturers. It was later clear that basic understanding of the application techniques was lacking. In response to this, an application training workshop was organized and conducted in India and Nepal in 2000. The workshops focused on teaching the participants how to use and fabricate multiple-nozzle booms, the importance of flat-fan nozzles, calibration, drift avoidance, and applicator safety. To date, approximately 3,000 farmers, extension agents, scientists, and industry representatives have attended more than 30 workshops. The participants were unanimously enthusiastic about the value of the workshops. Although simplistic, the adoption of this technology will significantly decrease the amounts of herbicides applied and will increase efficacy and efficiency.

Glyphosate is the only herbicide used for controlling illicit coca (Erythroxylum coca and E. novogranatense), a source of cocaine. Because commercially available formulations of glyphosate were inconsistent in controlling coca, research was conducted in a large-scale aerial eradication program, greenhouse (in Maryland) and field (Hawaii), to develop more effective control systems. Sixteen surfactants (cationic, nonionic, or mixed) were tested with two commercial glyphosate herbicide formulations, in aqueous or oil-based carrier systems, for coca control. Ultimately, two glyphosate–surfactant systems (COC/OSI-U [a mixture of crop-oil concentrate, Agri-Dex® and organosilicone, Silwet L-77®] and CAT/ANA [cationic surfactant/anionic surfactant, Optima®]) were found that increased glyphosate phytotoxicity fourfold: 1.1 kg ae/ha of glyphosate + surfactant was equivalent to 4.4 kg ae/ha glyphosate without added surfactant, for both species. In consequence, the glyphosate mixture used in Colombia for coca eradication was modified with substantially improved results.

Studies were conducted from 1998 to 2001 in Tifton, GA, on weed management systems in transplanted cantaloupe and watermelon grown on polyethylene-covered seedbeds. Soil fumigants were metham (748 L/ha) and a nonfumigated control. All metham applications were sprayed in a 61-cm band and incorporated with a modified power tiller. Herbicide treatments were ethalfluralin (0.8 kg ai/ha) premergence (PRE), ethalfluralin plus halosulfuron (36 g ai/ha) PRE, ethalfluralin PRE followed by glyphosate (1.1 kg ai/ha) postemergence POST-SHIELDED, ethalfluralin plus halosulfuron PRE followed by glyphosate POST-SHIELDED, and a nontreated control. Premergence herbicides were directed to row middles not covered in polyethylene, without contacting the transplants. Glyphosate was applied to row middles using a hooded sprayer, just before vine running. Overall weed control was not improved with soil fumigation in either cantaloupe or watermelon, and there was no yield response in either crop. There may be minimal benefit in transplanted cantaloupe and watermelon on polyethylene-covered seedbeds from preplant soil fumigation for weed control, in the absence of other pests. Herbicide systems that included halosulfuron PRE or glyphosate applied POST-SHIELDED improved control of yellow nutsedge compared with ethalfluralin alone. Control of Texas panicum, southern crabgrass, Florida pusley, and smooth pigweed was not improved by halosulfuron or glyphosate. Polyethylene-covered seedbeds provide a mechanical barrier to weed infestation for many species. Integration of these weed control practices gives cantaloupe and watermelon growers effective options for weed management, particularly for a troublesome species such as yellow nutsedge.

Research was conducted to evaluate structure–function relationships of citric acid esters that varied in alkyl chain number (mono-, di-, and tri-), ethylene oxide number (EO 4,7,9,25,35,52), and alkyl chain length (C8, C12/14, C16/18). Adjuvant efficacy was evaluated on two weed species for each of the four herbicides. The experimental adjuvants were applied with glyphosate and glufosinate on giant foxtail and common lambsquarters, imazamox on velvetleaf and common lambsquarters, and nicosulfuron on giant foxtail and large crabgrass. Adjuvant efficacy was weed and herbicide specific. EO number and alkyl chain length and number influenced adjuvant efficacy with the effectiveness of various combinations dependent on both herbicide and weed species. EO numbers as high as 52 were shown to be effective for glyphosate, glufosinate, and imazamox.

Catchweed bedstraw, common hempnettle, wild buckwheat, and wild oat are serious competitors to arable crops in many parts of the world where cutting implements may be used to control weeds. After cutting, regrowth may become a problem. In greenhouse experiments, weed species were cut at different stages of development (wild oat had two or three leaves, and the dicot weed species were 10 or 15 cm high) and at different heights aboveground (5 and 8 cm). Three weeks after sowing, biomass was measured and compared with that of uncut plants. Cutting height had a significant effect on the regrowth of all species. Common hempnettle was the most sensitive to cutting height followed by wild oat, wild buckwheat, and catchweed bedstraw. Increasing cutting height from 5 to 8 cm above the soil surface increased biomass production by 100 to 400% for all species. Cutting catchweed bedstraw at 8 cm resulted in larger biomass production than that of uncut plants (about 30%). For this species, weed control by cutting once in the growing season, 8 cm aboveground, may result in increased weed biomass production when compared with no cutting. The stage of development when the plants were cut did not have a significant effect on the regrowth ability of any of the species, probably because the two growth stages were relatively close in time.

Field experiments were conducted from 1994 through 1996 to evaluate the effects of imazapic applied postemergence (POST) at 0.05 and 0.07 kg ai/ha, imazethapyr applied preplant incorporated (PPI) or POST at 0.07 kg ai/ha, and metolachlor applied PPI at 1.7 kg ai/ha on yellow nutsedge control, nutsedge tuber density, and peanut yield. All herbicides controlled yellow nutsedge at least 75% after 3 yr. Imazapic at 0.05 and 0.07 kg/ha controlled yellow nutsedge more consistently than did imazethapyr or metolachlor. Imazethapyr applied POST controlled yellow nutsedge more effectively than did imazethapyr applied PPI. Yellow nutsedge tuber densities in herbicide-treated plots were 51 to 75% less than in untreated control plots. Plots treated with imazapic, imazethapyr applied POST, and metolachlor resulted in higher peanut yields than did untreated control plots.

Glyphosate-resistant spring wheat is being developed and may soon be available to growers. Field experiments were conducted to examine the effect of various rates and application timings of glyphosate on the tolerance of glyphosate-resistant spring wheat and the level of weed control attained with glyphosate in wheat. Glyphosate-resistant wheat exhibited excellent tolerance to glyphosate applied at the one- to two- or four- to five-leaf stages at rates up to 1,780 g ae/ha, representing a fourfold safety margin to the proposed field use rate. Glyphosate at 445 g/ha reduced shoot biomass of green foxtail, wild oat, redroot pigweed, and wild mustard > 95% in glyphosate-resistant wheat in all years, but wild buckwheat biomass was only reduced 67 to 75% at doses up to 890 g/ha. Glyphosate applied in-crop at 667 g/ha reduced quackgrass biomass by 97 to 99%. Comparison of glyphosate with other spring wheat herbicides indicated that glyphosate provided similar or better in-crop control of several weed species. Yield of weed-infested glyphosate-resistant spring wheat responded positively to glyphosate in all years.

Sericea lespedeza is an invasive weed in the tallgrass prairies of the Southern Great Plains. Field experiments were initiated in 1995 at three locations in central Oklahoma to evaluate control of sericea lespedeza for several years after treatment with herbicide. Herbicide treatments included triclopyr at 560 and 840 g ae/ha, fluroxypyr at 210 and 560 g ae/ha, and metsulfuron at 13 and 21 g ai/ha applied at simple-stem (SS), branched-stem (BS), and flowering (FL) growth stages of sericea lespedeza. At all three locations, applications of triclopyr and fluroxypyr at the BS growth stage resulted in less than 4% of the pretreatment sericea lespedeza stem density remaining in the first growing season after treatment (GSAT). Metsulfuron applied at the FL growth stage resulted in 0 to 9% of the pretreatment stem density remaining in the first GSAT. Regardless of rate, triclopyr and fluroxypyr applied at the BS growth stage provided the most consistent long-term control of sericea lespedeza. Percentage of pretreatment stem density remaining with these treatments was 0 to 20% at two locations in the third GSAT, and 4 to 15% at one location in the fifth GSAT. Aboveground biomass yields of desirable grasses (bermudagrass, indiangrass, and little bluestem) at two locations were greater than that of the untreated check in the second and third GSAT in all herbicide treatments. But biomass yield of bermudagrass did not increase when sericea lespedeza was controlled at the location with eroded soil conditions.

No more the grassy brook reflects the day,

But, chocked with sedges, works its weedy way;

The Deserted Village, Oliver Goldsmith, 1770.

Yellow nutsedge (Cyperus esculentus L.) is a perennial herbaceous sedge native to the eastern Mediterranean (Mabberley 1997; Tutin et al. 1980; Zeven and Zhukovsky 1975). Cultivated in ancient Egypt for its tasty and oil-rich tubers, the wild type has spread as a weed to all the continents of the world and adapted to climates from tropical to subarctic. Adaptability to many agricultural habitats and the great reproductive capacity of yellow nutsedge have propelled it to rank as the 16th worst weed in the world (Holm et al. 1991a, 1991b; Negbi 1992).