Sulfometuron at 17 g ai/ha in the planting furrow (13% of the anticipated fallow-field application rate) inhibited sugarcane emergence and development and ultimately reduced sugar yields in the initial production year by 13% when compared to a weed-free control that contained no herbicide in the planting furrow. Residual levels of metribuzin in the planting furrow representing 100% of the standard fallow-field application rate of 1,680 g ai/ha had no adverse effect on sugarcane development or sugar yield. When applied only to the soil surface immediately after planting, sulfometuron did not injure sugarcane, and sugar yields were equivalent to standard, at-planting, preemergence (PRE) applications of either metribuzin at 2,020 g/ha or a mixture of pendimethalin plus atrazine each at 2,240 g ai/ha. To minimize sugarcane injury, sulfometuron should be kept out of the germinating zone of lateral buds along planted sugarcane stalks.

Asynchronous flowering was noted in a recently discovered infestation of siam weed in north Queensland. This may indicate some genetic diversity in the infestation, increasing concerns about the origin of the infestation. Internal transcribed spacer 1 (ITS1) sequence data were obtained for siam weed individuals from north Queensland, Indonesia, Thailand, South Africa, Ivory Coast, Brazil, Colombia, and the U.S. The ITS1 region is 258 base pairs long, and the populations that flower at different times in north Queensland differ by four base substitutions. The genotype common in north Queensland is also reported throughout the native and introduced ranges. The other genotype is reported only in north Queensland and southern Brazil. These data, in conjunction with prior investigations into possible origins, indicate that Brazil is the most likely source of the infestation in Australia.

Leafy spurge is an exotic perennial weed that infests more than 1 million ha in North America and reduces rangeland carrying capacity. Experiments were initiated on range sites in Nebraska and North Dakota in 1994 and 1995 to determine the response of leafy spurge and other vegetation to AC 263,222. Herbicide treatments evaluated included AC 263,222 at 0 to 280 g ai/ha, picloram at 560 g ai/ha plus 2,4-D at 1,120 g ae/ha, and quinclorac at 1,120 g ai/ha. In Nebraska, a single application of AC 263,222 in the fall at 140 g/ha provided ≥ 90% leafy spurge control 11 to 12 mo after treatment. At Jamestown, ND, leafy spurge control increased to almost 90% and stem density declined to two shoots/m2 12 mo after the second consecutive fall application of AC 263,222 at 140 g/ha. At Hankinson, ND, leafy spurge control was ≤ 50% when AC 263,222 was applied in the fall only, but increased to > 80% when AC 263,222 was applied in the fall and again at 70 or 140 g/ha in the spring. There were no differences in herbage biomass of established cool- and warm-season grasses where AC 263,222 at 140 g/ha, picloram plus 2,4-D, quinclorac, or no herbicide was applied in the fall. In contrast, application of AC 263,222 in the fall and again in the spring usually reduced cool-season grass biomass.

Chlorimuron, clomazone, imazaquin, imazethapyr, and pendimethalin were each applied at five rates to soils at 10 different sites each year for three years to determine which soil properties influenced their bioactivity. Six soils in the U.S. (NC) and four in Zimbabwe were characterized for their plow-layer contents of organic matter (OM), humic matter (HM), clay mineral (CM), and silt and for pH and cation exchange capacity (CEC). At each site, the rate of each herbicide yielding 80% weed control (I80) was determined by visually evaluating the treated plots. The I80 values were then regressed with the various soil properties to determine which of them contributed to this rate. In the U.S. soils, the I80 was highly correlated with % OM (r 2 = 0.64–0.72) and % HM (r 2 = 0.55–0.69) for chlorimuron, imazaquin, and pendimethalin but was less correlated with % OM (r 2 = 0.30) and pH (r 2 = 0.31) for imazethapyr. Equations relating the herbicide rate for 100% weed control to soil properties were derived for chlorimuron, imazaquin, imazethapyr, and pendimethalin then compared with registered recommended rates for each chemical from the label. Herbicide rate equations based on similar soil parameters were taken from the literature to compare with our rate equations and with registered rate recommendations for comparison purposes and to add validity to the use of soil parameters for making herbicide rate recommendations. The rate equations, based on selected soil parameters, produced rates comparable with registered rates for chlorimuron, pendimethalin, and metribuzin and lower rates of application than registered rates for imazaquin, imazethapyr, alachlor, and metolachlor for soils with OM levels below 3.5%.

Field studies were conducted at three locations in 1993 and 1994 to evaluate weed control and crop response to combinations of glyphosate, metolachlor, 0.5 X and 1 X label rates of chlorimuron plus metribuzin applied prior to planting (PP), and 0.5 X and 1 X label rates of imazethapyr applied early postemergence (EPOST) or postemergence (POST) in no-till narrow-row soybean production. Giant foxtail densities were reduced with sequential PP followed by (fb) EPOST or POST treatments. Large crabgrass was reduced equivalently with all herbicide combinations involving chlorimuron plus metribuzin PP fb imazethapyr. Common cocklebur control was variable but was usually greater with treatments that included imazethapyr. Ivyleaf morningglory densities were not reduced with any herbicide combinations. Sequential PP fb EPOST or POST treatments tended to provide slightly better weed suppression than PP-only treatments, but the difference was rarely significant. Soybean yields with treatments utilizing 0.5 X rates were usually equal to 1 X rates.

Fifty irrigated cornfields in five eastern Colorado counties were sampled for their seedbanks and annual weed seedlings and mature populations between 1988 and 1992. Fourteen annual broadleaf species and seven annual grass species were identified in the 50 seedbanks sampled after the fields were tilled in the fall. Redroot pigweed and a mixture of green and yellow foxtail were the weed species encountered most, occurring in 90 and 54% of the fields, respectively. The single-plant populations of broadleaf and grass species in June and September were similar to those observed in the seedbanks. The number of weed species as seeds in the seedbank, June seedlings, and September plants per field ranged from zero to five grass species and zero to eight broadleaf species.

Field experiments were conducted to identify herbicides for selectively controlling foxtail barley seedlings in spring wheat and flax. ICIA0604, fenoxaprop-P/safener, CGA184927/safener, metribuzin, and MON37500 in wheat and sethoxydim, clethodim, quizalofop, fluazifop-P, and the mixture of fluazifop-P/fenoxaprop-P in flax were applied at the three- to four-leaf and one- to three-tiller stages of foxtail barley. MON37500 was the only herbicide tested in wheat that provided excellent control of foxtail barley and a high degree of crop tolerance. MON37500 at 13 to 19 g/ha applied at the early growth stage controlled foxtail barley but rates of 25 to 30 g/ha were needed at the later growth stage. In flax, quizalofop was the most efficacious herbicide on foxtail barley. Sethoxydim and clethodim sometimes provided weed control similar to that of quizalofop when applied at the three- to four-leaf stage, but quizalofop was always more effective at the one- to three-tiller stage of foxtail barley. Wheat and flax yields were greater when effective herbicides were applied at the early than at the late stage, indicating the need for early control of foxtail barley to minimize weed competition. MON37500 in wheat and quizalofop in flax provide growers with highly efficacious herbicide options for in-crop control of foxtail barley in conservation tillage systems.

In field studies, in 1993, 1994, and 1995, clomazone at 390 g ai/ha and rimsulfuron at 35 g ai/ha were evaluated preplant incorporated (PPI) and postemergence (POST), respectively, for weed control and crop response in transplanted ‘Keystone RG3’ bell pepper. Clomazone did not injure bell pepper. Common lambsquarters and jimsonweed control was 77 to 95% by clomazone treatments but was variable by rimsulfuron treatments at 41 to 93% common lambsquarters control and 42 to 68% jimsonweed control; common ragweed control by both herbicides was unacceptable. Injury by rimsulfuron to bell pepper in the field was 19 to 47% at 21 DAT. In the greenhouse, injury to Keystone RG3 and three additional bell pepper varieties, ‘Camelot,’ ‘Jupiter,’ and ‘Memphis’ was similar at 44 to 62% by rimsulfuron at 17 to 35 g/ha POST, and bell pepper had lower height and dry weight than untreated controls. In the greenhouse, jimsonweed control was below 49% and black nightshade control was below 23% by 17 to 35 g/ha rimsulfuron. In these studies, clomazone controlled common lambsquarters and jimsonweed without injury to bell pepper. The solanaceous weeds treated in this study were not well controlled by rimsulfuron, and bell pepper was not sufficiently tolerant to rimsulfuron to permit its use in this crop.

In preliminary field trials, a reduction in grass control was observed when flumetsulam or MON 12037 with and without the safener MON 13900 was applied with metolachlor compared to metolachlor alone. Greenhouse studies were initiated to study potential interactions between acetolactate synthase (ALS)-inhibiting herbicides and metolachlor. Metolachlor at 0.14, 0.28, and 0.56 kg ai/ha was applied alone and in combination with flumetsulam at 0.0073 and 0.015 kg ai/ha and MON 12037 with safener at 0.011 and 0.021 kg ai/ha. Flumetsulam and MON 12037 with safener alone provided 13 to 23% visible barnyardgrass control and metolachlor at 0.14 kg/ha provided 82% control. Combining flumetsulam and MON 12037 with metolachlor did not increase herbicide activity beyond that observed from metolachlor alone, regardless of the parameter evaluated. Combinations of 0.14 kg/ha of metolachlor with 0.011 and 0.021 kg/ha of MON 12037 with safener or 0.015 kg/ha of flumetsulam resulted in antagonism of barnyardgrass according to Colby's multiplicative interactive model. Visible control and plant dry weight were also antagonized when 0.28 kg/ha of metolachlor was applied with 0.021 kg/ha of MON 12037 with safener. Field studies were conducted in corn and soybean to evaluate giant foxtail control from metolachlor alone and in tank mixtures with flumetsulam, chlorimuron and MON 12037 with and without safener. Although isolated incidences of antagonism were noted, there was no consistent effect on grass control when these ALS-inhibiting herbicides were applied in combination with metolachlor in 3 years of field trials.

The effect of adding a spray adjuvant to SAN 582H tank mixtures with fluazifop-P, imazethapyr, and sethoxydim was evaluated. SAN 582H synergistically increased broadleaf signalgrass control with reduced rates of all three postemergence (POST) herbicides when no spray adjuvant was used and when crop oil concentrate was added. For example, broadleaf signalgrass control increased from 50% to 83% when SAN 582H was tank-mixed with 52 g ai/ha sethoxydim and crop oil concentrate. In another experiment, several formulations of SAN 582H, including blank solvent-only formulations (no SAN 582H), were evaluated in combination with a reduced rate of sethoxydim to determine the source of synergism from tank mixtures. The SAN 582H molecule, not the carrier solvents in formulated product, was determined to be the source of synergism. The synergistic properties of SAN 582H were compared to other chloroacetamides. Synergism from acetochlor was similar to SAN 582H when applied POST with a reduced rate of either fluazifop-P, imazethapyr, or sethoxydim for grass control. Metolachlor also synergistically increased the control of grasses with the POST herbicides; however, metolachlor caused considerable phytotoxicity when applied alone and synergistic interactions were detected less frequently. The efficacy of sethoxydim mixed with SAN 582H was evaluated under different soil moisture conditions. Broadleaf signalgrass control increased from 81% to 93% under dry, moisture-stressed conditions when 210 g/ha sethoxydim was tank- mixed with SAN 582H.

The interactions of two fungal biocontrol agents, Alternaria cassiae and Pseudocercospora nigricans, and soybean planting density on sicklepod mortality and dry weight were studied in the field over 2 yr. The experimental field was divided into three equal areas: one without soybean and two where the soybean was sown in densities of 20 and 36 seeds per meter row with a 0.95-m row spacing. The fungi were sprayed alone or in a mixture at three growth stages of sicklepod plants grown at three levels of crop interference resulting from the three soybean planting densities. The fungal treatments were: an untreated control, A. cassiae (105 spores/m2), P. nigricans (3.3 g mycelium/m2), and the mixture of these two fungi. Sicklepod was at the cotyledonary leaf, two-leaf, and four-leaf stages when treated. Alternaria cassiae was most effective in reducing both sicklepod survival and dry weight. The mixture of P. nigricans and A. cassiae was generally comparable to but not better than A. cassiae alone in killing the weed (mortality) and reducing its growth (dry weight). Soybean density did not have significant effects on the mortality or the dry weight of sicklepod. Thus, there is no advantage to combining the highly effective biocontrol agent A. cassiae with the less effective P. nigricans or with soybean interference to control sicklepod. However, the results validate the efficacy of A. cassiae by itself as a bioherbicide.

Glyphosate and adjuvant combinations were applied to rhizome johnsongrass at vegetative and reproductive growth stages to evaluate control and rainfastness in field studies. Using a rainfall simulator delivering 1.3 cm of water in 15 min, plots received either no rainfall or rainfall 15 or 60 min after glyphosate was applied at 2.1 kg ai/ha in combination with the nonionic surfactants Kinetic® HV at 0.25% (v/v) or Induce® at 1.0% (v/v) or the silicone surfactant Break-Thru® at 0.125% (v/v). Regardless of adjuvant, rainfall 15 or 60 min after application reduced johnsongrass control compared with no rainfall. Johnsongrass control 14 d after treatment at the reproductive stage was at least 89% with no rainfall, but no more than 53 and 65% with rainfall at 15 and 60 min, respectively. Based on initial weed control, adjuvants did not consistently improve rainfastness. Johnsongrass regrowth did not occur when glyphosate was applied with either adjuvant. In contrast, for glyphosate applied to johnsongrass in the vegetative stage, addition of Break-Thru improved control over Induce at both 15- and 60-min rainfall timings in one of two experiments. With no rainfall, addition of Kinetic HV and Break-Thru increased johnsongrass control in only one experiment. For application at the vegetative stage, johnsongrass regrowth averaged across rainfall timings was no more than 10%. In other field experiments, glyphosate at 1.4 kg/ha plus nonionic surfactants, silicone surfactant, crop oil concentrate, methylated seed oil, or a blend of silicone surfactant and methylated seed oil were equally effective in reducing johnsongrass regrowth when applied after seedhead emergence. Improved control of vegetative johnsongrass with some adjuvants was not reflected in decreased regrowth.

Field studies to evaluate the response of cotton to flame cultivation were conducted in 1994, 1995, and 1996. Flame cultivation at different liquid propane-gas (LP-gas) pressure settings (100 and 175 kPa) with or without watershield protection was applied to cotton at two stages of growth (20 to 25 cm and 40 to 45 cm tall). In 1994, younger cotton was more susceptible to flame cultivation than older cotton, and flaming at an LP-gas pressure of 175 kPa without watershield protection increased plant injury regardless of growth stage, whereas injury was not evident in 1995 and 1996. Injury caused by flame cultivation was a transient browning of lower leaf margins. The use of a watershield sprayed above the burner reduced injury. Flame cultivation applied to cotton 20 to 25 cm tall slightly elevated the first fruiting node, but no effects were noted on other vegetative and reproductive growth parameters or yield regardless of pressure setting or watershield protection. Flame cultivation applied to cotton 40 to 45 cm tall did not affect the position of the first fruiting node. Although flame cultivation caused some injury one year, total seed cotton and cotton lint yields were not reduced.

Experiments were conducted from 1994 through 1996 to determine the response of the rice cultivars ‘Bengal,’ ‘Cypress,’ ‘Jodon,’ and ‘Kaybonnet’ to triclopyr at 0.42 (standard rate) and 0.84 kg ai/ha applied postemergence at the four-leaf and panicle initiation stages of growth. Applications at the four-leaf stage were made in close association with fertilization and flood establishment, which often increases the potential for triclopyr to injure rice. Visible injury from triclopyr was slightly higher for the cultivar Jodon than for the cultivars Bengal, Cypress, or Kaybonnet. Injury was 3% or less when triclopyr at 0.42 kg/ha was applied at panicle initiation regardless of the cultivar. Triclopyr at 0.42 and 0.84 kg/ha applied at the four-leaf growth stage injured rice 7% and 22%, respectively. Triclopyr at 0.84 kg/ha applied at the four-leaf stage of growth delayed days from seedling emergence to seed head emergence and rice grain yield, irrespective of cultivar.

The effect of DPX-79406 was evaluated on eight corn hybrids in 1993 and on 18 hybrids in 1994. Experiments were conducted each year at Charlottetown, Prince Edward Island, and Stewiacke, Nova Scotia. Corn tolerance was similiar between sites but varied from year to year with certain hybrids. Generally, tolerance was hybrid dependent. Most hybrids displayed chlorosis and stunting 7 days after treatment (DAT) but recovered quickly. Injury at 7 DAT ranged from 8 to 64%. Grain yield indicated that ‘Pickseed 2444,’ ‘Pioneer 3921,’ ‘Pioneer 3979,’ and ‘DK 302’ were tolerant to 25 g ai/ha of DPX-79406. Pioneer 3979 and Pickseed 2444 grain yields were reduced with DPX-79406 at 50 g/ha in 1 yr. ‘DK 291’ and ‘DK 235’ were severely injured both years and did not recover appreciably from early injury. Responses of ‘Pioneer 3984’ and ‘Pickseed 2477’ varied from year to year, and they were considered sensitive to DPX-79406. ‘Pioneer 3947,’ ‘Pioneer 3962,’ ‘Pickseed 2290,’ ‘Pickseed 2299,’ ‘DK 220,’ ‘G-4011,’ and ‘N0565’ were tested only 1 yr and were tolerant to both rates of DPX-79406.

Johnsongrass control systems that included commercially available corn herbicides applied to crop sequences of continuous corn or corn–cotton–corn rotation were evaluated over a 3-yr period at the Texas Agricultural Experiment Station in Burleson County. Herbicide treatments evaluated were EPTC + R-25788 applied preplant incorporated (PPI); metolachlor applied preemergence (PRE); nicosulfuron applied postemergence (POST); and the combination of metolachlor PRE and glyphosate POST applied after corn harvest. Weed control practices applied to plots planted to cotton in the second growing season provided excellent johnsongrass control (≈ 95%). Visual control ratings indicated that nicosulfuron provided the best johnsongrass control (> 80%) among the herbicides evaluated all three years. Metolachlor and glyphosate combinations provided acceptable johnsongrass control the third year of the experiment in both cropping sequences. Corn grain yield and johnsongrass control were best in cotton-rotated plots. The highest returns observed in continuous corn were from either nicosulfuron or the combination of metolachlor and glyphosate. Net returns for all control systems in corn–cotton–corn rotated plots were greater than the weedy check and were equivalent to the lead systems in continuous corn.

Field studies were conducted in 1993 and 1994 to evaluate the tolerance of 16 sweet corn cultivars, representing a range of genotypes, to rimsulfuron applied postemergence (POST) at 12.5 and 25 g ai/ha. There was a significant cultivar by herbicide interaction for visual plant injury, plant height, and yield. ‘Merit’ and ‘Silver Extra Sweet’ were the most sensitive cultivars, with rimsulfuron resulting in complete plant mortality regardless of application dose. ‘Golden Jubilee,’ ‘King Arthur,’ ‘Ivanhoe,’ and ‘Zenith’ were less sensitive. Ten cultivars were tolerant to applications of rimsulfuron at 12.5 g/ha. Sensitivity to rimsulfuron increased as application dose increased.

Field studies were conducted in 1992 and 1993 to determine the effect of atrazine and pendimethalin on velvetleaf competitiveness in corn. The three factors included in this research were herbicide, velvetleaf density (zero or nine plants per meter of row), and treatment (treated with herbicide or untreated). Herbicide treatments consisted of atrazine (0.6 and 1.1 kg/ha) or pendimethalin (0.6 and 1.1 kg/ha) applied preemergence. In 1992 and 1993, both atrazine and pendimethalin applied at 1.1 kg/ha greatly reduced velvetleaf growth and seed production and prevented velvetleaf from reducing corn yield. Both atrazine and pendimethalin applied at 0.6 kg/ha reduced velvetleaf growth and seed production in 1993, but only atrazine prevented yield loss in 1992. In the absence of velvetleaf, corn yield was not affected by either herbicide. These results indicate that sublethal exposure to atrazine or pendimethalin can significantly reduce velvetleaf competitiveness in corn.

Field studies were conducted from 1994 to 1996 in Michigan to evaluate postemergence (POST) herbicides for hemp dogbane control in corn. Studies were initiated at no-tillage and chisel-plowed sites each of the three years. Nicosulfuron and primisulfuron were evaluated alone and in combination with 2,4-D amine or dicamba. In 1995 and 1996, CGA-152005 plus primisulfuron was also applied alone and in combination with 2,4-D or dicamba. Control varied among years and sites. Nicosulfuron, primisulfuron, and CGA-152005 plus primisulfuron applied alone controlled 30% of the hemp dogbane, and dicamba or 2,4-D alone controlled 42 and 66%, respectively. Tank mixtures of nicosulfuron, primisulfuron, or CGA-152005 plus primisulfuron with dicamba were more effective and more consistent than dicamba alone. Combinations of nicosulfuron, primisulfuron, or CGA-152005 plus primisulfuron with 2,4-D gave the most effective and consistent control across sites, with an average of 93% control. In general, treatments controlled only shoots that had emerged at the time of application. New shoots emerged following herbicide application at the chisel-tillage sites in 1994 and 1995 but not at the no-tillage sites. However, in 1996, shoot emergence following treatment occurred in both no-tillage and chisel-tillage sites.

Nine corn inbreds were selected from a test on 250 inbreds based on distinctly different response to herbicides. These inbreds showed up to 50,000-fold differences, which varied by inbred and herbicide. Only the inbred GA209 was sensitive to bentazon and the four sulfonylurea herbicides. GA209 and B90 were the most sensitive inbreds to the sulfonylurea herbicides. F2R was generally the most tolerant inbred. The pattern of herbicide tolerance varied greatly. For example, the relative tolerance of F2 to thifensulfuron was 12-fold more than to rimsulfuron while Mo17 was 56-fold more tolerant to rimsulfuron than thifensulfuron. F2 was fivefold more tolerant of chlorsulfuron than chlorimuron, whereas B80 was 100-fold the reverse. These inbreds provide a small subset of varieties to evaluate the large and inherent differences in herbicide tolerance of corn.