Field studies were conducted at Dekalb, Urbana, and Brownstown, IL, in 1996 and 1997 to evaluate corn (Zea mays) injury and weed control from preemergence applications of RPA 201772 alone and tank-mixed with metolachlor, atrazine, or both. No significant corn injury from RPA 201772 was observed at any time for all experiments. Giant foxtail (Setaria faberi) control at 60 days after treatment (DAT) was variable and ranged from 47 to 93% for RPA 201772 applied alone at 105 g ai/ ha. Giant foxtail control of at least 90% was observed by applying metolachlor at 1,120 g ai/ha with 105 g/ha RPA 201772. The addition of atrazine at either 1,120 or 1,680 g ai/ha improved control of giant foxtail compared with RPA 201772 applied alone at 105 g/ha in two of the six studies. RPA 201772 applied at 105 g/ha controlled at least 88% of velvetleaf (Abutilon theophrasti), Pennsylvania smartweed (Polygonum pensylvanicum), and smooth pigweed (Amaranthus hybridus). RPA 201772 controlled 88% or less of common waterhemp (Amaranthus rudis), common ragweed (Ambrosia artemisiifolia), and common cocklebur (Xanthium strumarium). Control of these three species was 92% or greater with RPA 201772 plus atrazine. Control of common lambsquarters (Chenopodium album) was at least 96% with RPA 201772 applied alone at any rate in four of the six studies. However, common lambsquarters control was 68 and 77% for RPA 201772 applied alone at 105 g/ha at Urbana and Brownstown in 1997, respectively, where high common lambsquarters densities were prevalent. Under these conditions, the addition of atrazine to RPA 201772 at 105 g/ha improved control of common lambsquarters. RPA 201772 has excellent potential to provide consistent control of velvetleaf compared with atrazine. In contrast, these studies indicate RPA 201772 may provide inconsistent control of certain weed species in different environments. In order to achieve consistent control of a broad spectrum of weed species, RPA 201772 must be combined with other herbicides.

Field trials were conducted at two sites in 1996 and 1997 to evaluate weed control and crop response to herbicide programs in no-till soybean that include flumioxazin or sulfentrazone alone and each herbicide tank-mixed with either chlorimuron or imazaquin. A prepackaged mixture of metribuzin plus chlorimuron also was included for comparison. Cool, wet conditions after herbicide application in both years were conducive to soybean injury up to 21% at 3 wk after planting (WAP). Flumioxazin and sulfentrazone alone provided ≥ 89% control of velvetleaf, Pennsylvania smartweed, and common cocklebur. Sulfentrazone alone provided greater control of common waterhemp, common cocklebur, and ivyleaf and pitted morningglories than flumioxazin. Flumioxazin provided greater control of common ragweed than sulfentrazone. The addition of chlorimuron to flumioxazin or sulfentrazone provided greater control of velvetleaf than flumioxazin or sulfentrazone alone. The addition of imazaquin or chlorimuron to flumioxazin provided greater control of common cocklebur than flumioxazin alone. The addition of imazaquin or chlorimuron to sulfentrazone provided greater control of common ragweed than sulfentrazone alone. The addition of chlorimuron or imazaquin to sulfentrazone or flumioxazin provided little or no additional control of pitted morningglory, common waterhemp, or Pennsylvania smartweed. Metribuzin plus chlorimuron provided control of velvetleaf, Pennsylvania smartweed, common ragweed, and common cocklebur that was equal to or better than the control provided by sulfentrazone or flumioxazin plus chlorimuron or imazaquin.

Returns to land, management, and risk were compared where glyphosate and four graminicides (quizalofop-P, fluazifop-P, sethoxydim, and clethodim) were used for johnsongrass control in glyphosate-tolerant soybean. In 1994 and 1995, returns to land, management, and risk for glyphosate-tolerant soybean were highest using glyphosate and lowest using sethoxydim. Break-even analysis showed that yields needed for equivalent returns with any nontransgenic soybean cultivar treated with any of the graminicides could range from 67 kg/ha less to 202 kg/ha more than the yields achieved with glyphosate. Based on this methodology, farmers would increase their return to land, management, and risk by planting glyphosate-tolerant soybean if expected yield from a standard cultivar treated with a standard herbicide program were less than the break-even yield.

Preemergence herbicides were applied at recommended and three times the recommended rates during 1995, 1996, and 1997 to eight established zoysiagrass (Zoysia spp.) cultivars. Oxadiazon was the only herbicide that did not significantly reduce the quality of any zoysiagrass cultivar. The zoysiagrass cultivars had intermediate tolerance to prodiamine and pendimethalin, while oryzalin, dithiopyr, and benefin plus oryzalin caused the highest injury. ‘Emerald’ and ‘Meyer’ cultivars were least affected by herbicide application. ‘Diamond,’ ‘El Toro,’ ‘Cavalier,’ and ‘Crowne’ showed moderate injury, while ‘Royal' and ‘Palisades’ had the greatest injury. When the performance of zoysiagrass cultivars was averaged across herbicides, turf quality in May was best for Meyer, El Toro, and Crowne. The quality of the majority of cultivars except for Royal improved during the summer and was similar to that of Meyer by late August both years.

Experiments were conducted in 1996 and 1997 to determine the effects of postemergence (POST) application of rimsulfuron on quackgrass control. Rimsulfuron applied at 27 g ai/ ha to two-to four-leaf quackgrass controlled 100% of quackgrass 5 wk after treatment (WAT). Rimsulfuron applied to one- to two-leaf quackgrass was not as effective as the same rate applied to two- to four-or four- to six-leaf quackgrass. Stunting and leaf wrinkling of corn were observed 4 WAT when rimsulfuron was applied at 36 g/ha to four- to six-leaf quackgrass. The plants recovered from the stunting as the season progressed and by 12 WAT there was no appreciable stunting. Rimsulfuron (27 g/ha) applied to two- to four-leaf quackgrass increased grain and silage yield of corn by 36% and 45%, respectively, compared to the untreated check. The 27 g/ha rate of rimsulfuron applied to two- to four-leaf quackgrass resulted in 10% more grain yield than the same treatment applied to one- to two- leaf quackgrass. Rimsulfuron at 18 g/ha led to a 17% reduction of sitage yield when applied to the four- to six-leaf quackgrass. At all growth stages of quackgrass, rimsulfuron gave higher grain and silage yields than corn treated with the same rate and timing of nicosulfuron. Rimsulfuron reduced sprouting of quackgrass rhizome nodes, especially at higher rates.

Field experiments were conducted in 1996, 1997, and 1998 to evaluate weed control and corn tolerance from soil-applied RPA 201772. Treatments alone and in tank mixtures with other corn herbicides were applied preemergence (PRE) at two locations with conventional tillage and at early preplant (EPP) and PRE application timings in no-tillage corn. RPA 201772 was applied alone and in tank mixtures with one-half the typical field rates of other PRE corn herbicides. In conventional tillage experiments in 1996, 1997, and at one location in 1998, all treatments containing RPA 201772 provided > 90% control of common lambsquarters, redroot pigweed, common ragweed, and velvetleaf. In two no-tillage experiments, common lambsquarters and velvetleaf control was > 90%, regardless of application timing. However, control of redroot pigweed and common ragweed varied among years and application timings. Weed control was more variable from herbicide treatments applied EPP compared with the PRE application timing. Giant foxtail control in both tillage systems was rate, timing, and year dependent. RPA 201772 rates higher than 79 g/ha controlled giant foxtail > 85% at three of five locations. At one location, tank mixtures with RPA 201772 increased giant foxtail control. Corn injury occurred in one of two conventional tillage locations and at the no-tillage location in both 1996 and 1997. Injury was most commonly observed in coarse-textured soils with low clay and organic matter and was more severe with higher rates of RPA 201772. Increased corn injury was also observed when RPA 201772 was combined with acetochlor plus dicloramid or BAYFOE 5043 plus metribuzin. Corn injury from RPA 201772 occurred at application rates above the proposed rate for use on corn. In some cases, severe injury to corn reduced corn yield. Injury to corn from RPA 201772 was not unique to any tillage system and was site, year, and rate dependent.

Field studies were conducted at two locations in 1997 and 1998 to evaluate crop injury, weed control, yield, and net economic returns of single and sequential postemergence applications of labeled and reduced rates of glyphosate to no-till, glyphosate-resistant soybean planted in narrow rows. Sequential applications provided at least 91% control of giant foxtail, while single applications provided at least 86% control with labeled rates and 68–93% control with reduced rates. Common waterhemp control was slightly higher with sequential vs. single treatments and with labeled rates vs. reduced rates. Velvetleaf control was greater than 96% with all treatments. Common cocklebur control was 90% or higher with all treatments except a single application of glyphosate at 210 g/ha. Lower control of giant foxtail and common waterhemp with single-application, reduced-rate treatments in two of the four trials resulted in lower yields. Overall, sequential applications, regardless of rate, provided greater weed control, yield, and net income and lower coefficients of variation (C.V.s) of net income than reduced-rate single applications. Single-application treatments showed a trend of decreased weed control, yield, and net income and higher C.V.s of net income with reduced rates of glyphosate.

Canola (edible rapeseed) crops are often infested by related weed species. This paper addresses effects that seeds from various Brassicaceae weeds may have on canola oil and meal quality. Seeds of common Brassicaceae weeds were collected from canola fields throughout northern Idaho. These were wild mustard, black mustard, birdsrape mustard, shepherd's-purse, flixweed, tumble mustard, and field pennycress. Collected seeds were physically described by weight, size, and shape and were analyzed for oil concentration, fatty acid composition, and glucosinolate concentration. Seed weights ranged from 0.1 to 2 g/1,000 seed. Oil concentration in the weed seeds ranged from 25 to 38%, with erucic acid levels ranging from less than 1 to 47%. Glucosinolate concentration in the mustard weed seeds was over 100 μmol/g oil-free meal, except for shepherd's-purse, which had only 3.4 μmol/g. Using these data, a simple model predicts that both canola oil and seed meal quality can be adversely affected by contamination with weed seeds. Increased erucic acid concentration in modeled admixtures was the most likely oil quality problem associated with weed seed contamination. Glucosinolate concentration in modeled admixtures was higher than acceptable only in those admixtures that also had erucic acid levels that exceeded canola quality standards. Canola-quality oil and seed meal can be maintained with conspicuous weed seed mixtures up to the 2% maximum allowed in U.S. No. 1 canola. However, canola-quality oil and seed meal was not achieved when a 5% weed seed mixture allowed in No. 2 canola was evaluated with the model.

Field studies were conducted in 1992 and 1993 to evaluate AC 263,222 applied postemergence (POST) alone and as a mixture with atrazine or bentazon for weed control in imidazolinone-resistant corn. Nicosulfuron alone and nicosulfuron plus atrazine were also evaluated. Herbicide treatments were applied following surface-banded applications of two insecticides, carbofuran or terbufos at planting. Crop sensitivity to POST herbicides, corn yield, and weed control was not affected by insecticide treatments. AC 263,222 at 36 and 72 g ai/ha controlled rhizomatous johnsongrass 88 and 99%, respectively, which was equivalent to nicosulfuron applied alone or with atrazine. AC 263,222 at 72 g/ha controlled large crabgrass 99% and redroot pigweed 100%, and this level of control exceeded that obtained with nicosulfuron alone. AC 263,222 at 72 g/ha controlled sicklepod and morningglory species 99 and 98%, respectively. Nicosulfuron alone or with atrazine controlled these two species less than AC 263,222 at 72 g/ha. Addition of bentazon or atrazine to AC 263,222 did not improve control of any species compared with the higher rate of AC 263,222 at 72 g/ha applied alone. Corn yield increased over the untreated control when POST herbicide(s) were applied, but there were no differences in yield among herbicide treatments.

Green and yellow foxtail seed production following harvest of spring wheat is a concern of producers in the northern Great Plains of the United States and the Prairie Provinces of Canada. Experiments were conducted in 1996 and 1997 in three tillage systems, no till (NT), chisel plow (CP), and moldboard plow (MP), at the University of Minnesota West Central Experiment Station, Morris, MN, to determine whether time of glyphosate application or tillage after spring wheat harvest could reduce postharvest foxtail seed production. In both years, hard red spring wheat was planted in late April and a packaged mixture of fenoxaprop and 2,4-D ester and MCPA ester was applied at a rate of 53 g and 81 g and 246 g ai/ha for grass and broadleaf weed control. Following spring wheat harvest, each main plot was subdivided into seven subplots, including an untreated control. One subplot was disked twice at 4 to 6 d after harvest (DAH) of spring wheat, and five other subplots had glyphosate (0.25 kg ai/ ha) applied on different days (1 to 31 DAH). Foxtail seeds were collected from the soil surface following first frost, and the number of green and yellow foxtail seeds were determined. Tillage immediately after spring wheat harvest eliminated foxtail plants, and no new foxtail seedlings emerged in either tilled or glyphosate-treated plots despite ideal postharvest conditions for foxtail germination and emergence in 1997. Most viable green foxtail seeds were consistently obtained in NT plots, whereas yellow foxtail seed production varied among tillage systems. Either tillage soon after spring wheat harvest or glyphosate application within 16 DAH reduced green and yellow foxtail seed production by greater than 70%.

Growth chamber studies were conducted to investigate the effect of temperature, cultivar, and leaf wax content on the response of broccoli and collard to oxyfluorfen. Broccoli cultivars grown under cool temperatures (15/10 C) were more susceptible to preemergence (PRE) application of oxyfluorfen, and broccoli and collard cultivars grown at cool temperatures were more susceptible to postemergence (POST) application of oxyfluorfen than cultivars grown under warm temperatures (25/20 C). Differences between the tolerant cultivar ‘Pinnacle’ and the susceptible cultivar ‘Packman’ in response to PRE oxyfluorfen application were more distinct at warm temperatures than at cool temperatures. Although the broccoli and collard cultivars used in the POST study varied in leaf wax content, differences in wax content did not appear to be as important as other genetic factors in the differential response to POST oxyfluorfen application between cultivars.

Five cultivation implements (two flex-tine cultivators, brush hoe, and rolling and shovel cultivators) were evaluated for weed control and effect on broccoli, snap bean, and sweet corn yield. Each implement was used alone or in combination with flex-tine cultivators. Standard broadcast herbicide treatments were: broccoli, metolachlor at 2.3 kg ai/ha posttransplant; snap bean, metolachlor preemergence (PRE) at 2.3 kg ai/ha followed by fomesafen postemergence (POST) at 0.4 kg ai/ha; sweet corn, atrazine at 1.1 kg ai/ha plus metolachlor at 2.3 kg ai/ha PRE. In the snap bean trials, an additional treatment consisted of metolachlor at 2.3 kg ai/ha PRE applied in a 25-cm band over the crop row followed by fomesafen POST at 0.4 kg ai/ha directed at the crop row, with a subsequent shovel cultivation. In the sweet corn trials, all cultivation treatments received an application of atrazine at 1.1 kg ai/ha plus metolachlor at 2.3 kg ai/ha PRE in a 25-cm band over the crop row. In broccoli, weed control and yields with all cultivation treatments were comparable to those with broadcast herbicide. In snap bean, flex-tine cultivators failed to control weeds and prevent yield reductions compared to the broadcast herbicide treatment. When either the brush hoe or the shovel cultivator was preceded by flex-tine cultivation, weed control and snap bean yield were comparable to those with broadcast herbicides. Banded herbicides followed by shovel cultivation also controlled weeds and prevented yield reductions. In sweet corn, banded herbicides controlled in-row weeds, and despite variable between-row weed control, all cultivation treatments yielded as well as the broadcast herbicide treatment. Relative performance of the cultivators was influenced by soil type and rainfall as well as crop canopy characteristics.

There are limited options for controlling large crabgrass in spring-seeded cool-season turf. The objective of this experiment was to evaluate the safety and effectiveness of dithiopyr and quinclorac to control large crabgrass in spring-seeded Kentucky bluegrass and perennial ryegrass stands. Quinclorac at 0.84 kg/ha and dithiopyr at 0.56 kg/ha were applied separately at various times prior to seeding and after emergence of Kentucky bluegrass and perennial ryegrass. Quinclorac applied once at 2, 4, 8, or 12 weeks after emergence (WAE) or split-applied preplant incorporated (PPI) + 12 WAE will give season-long control of large crabgrass with no injury to spring-seeded Kentucky bluegrass or perennial ryegrass. Quinclorac applied PPI or 0 WAE is safe to use in spring seedings, but it will not provide season-long control of large crabgrass. Dithiopyr applied 2 or 4 WAE will control large crabgrass season-long while not injuring spring-seeded Kentucky bluegrass or perennial ryegrass. However, dithiopyr applied PPI or 0 WAE will severely limit germination of desirable turf, and dithiopyr applied 8 or 12 WAE will not control mature crabgrass.

The study was conducted to determine the cross-resistance of imazethapyr-resistant common sunflower (Helianthus annuus) to selected imidazolinone, sulfonylurea, and triazolopyrimidine herbicides. Whole-plant herbicide dose–response curves and in vitro enzyme studies showed that imazethapyr-resistant common sunflower was highly resistant to imazamox, slightly resistant to thifensulfuron and chlorimuron, and not resistant to cloransulam. Resistance ratios of herbicide concentrations required to inhibit growth by 25% were 310, 3.3, 2.0, and 1.4 times greater in the resistant biotype than in the susceptible biotype for imazamox, thifensulfuron, chlorimuron, and cloransulam, respectively. Similarly, herbicide concentrations required to inhibit ALS activity in vitro by 25% were 332.0, 18.6, 8.3, and 1.2 times greater in the resistant biotype than in the sensitive biotype for imazamox, chlorimuron, thifensulfuron, and cloransulam, respectively.

Field studies were conducted in Colorado, Kansas, and Wyoming to compare the use of quinclorac plus 2,4-D with picloram plus 2,4-D, dicamba plus 2,4-D, a glyphosate plus 2,4-D premix, and 2,4-D alone for control of field bindweed (Convolvulus arvensis) in a winter wheat (Triticum aestivum)-fallow rotation. Treatments were applied in late summer or fall each year for two, three, or four consecutive years at the beginning and end of each fallow period. Evaluations were taken 10 to 12 mo after treatment each year. Quinclorac plus 2,4-D and picloram plus 2,4-D consistently performed as well as or better than 2,4-D, dicamba plus 2,4-D, and glyphosate plus 2,4-D. Wheat yields increased when field bindweed was controlled during the fallow period. Strong correlations (r > −0.85) were obtained among visual field bindweed evaluation, biomass, and stand count data.

Field experiments were conducted at three Mississippi locations to evaluate potential antagonism when postemergence graminicides were tank-mixed with CGA-277476 and to determine if the antagonism could be overcome with an increase in graminicide rate. At all locations when the 1X rate of clethodim, fluazifop-P, or quizalofop was tank-mixed with 79 g ai/ ha CGA-277476, johnsongrass, broadleaf signalgrass, and barnyardgrass control was reduced 5 to 30%. When the graminicide rates were increased to 1.5X, antagonism was still present for fluazifop-P and quizalofop. However, 156 g ai/ha clethodim overcame the antagonism when tank-mixed with 79 g/ha CGA-277476 compared to 105 g/ha clethodim. CGA-277476 alone controlled barnyardgrass and broadleaf signalgrass 38 to 63% and johnsongrass 60 to 85%. There were no differences in soybean yields with graminicides applied alone or tank-mixed with CGA-277476.

Certain linear alcohol ethoxylate surfactants with large hydrophobes enhanced nicosulfuron activity on giant foxtail (Setaria faberi) more effectively at low doses than surfactants with small hydrophobes and commercial standards. The most effective surfactants had a C16–18 hydrophobe and 12 to 30 moles of ethoxylation or a C24 hydrophobe with 13 moles of ethoxylation. Response curve analysis showed these linear alcohol ethoxylate surfactants were five- to 20-fold more active on a dose basis than currently used commercial surfactants.

Field experiments were conducted in North Carolina from 1994 through 1998 to evaluate the effects of five weed management strategies and four corn (Zea mays)–peanut (Arachis hypogaea) rotation sequences on purple nutsedge (Cyperus rotundus) population development. Effects of these weed management programs on cotton (Gossypium hirsutum) and peanut production in following years were also investigated. Herbicide programs included a nontreated control, a carbamothioate preplant incorporated (PPI) combination treatment utilizing vernolate in peanut and butylate in corn, an early postemergence (EPOST) acetolactate synthase (ALS) inhibitor combination treatment utilizing imazapic in peanut and halosulfuron in corn, and EPOST treatments of imazapic and imazethapyr in both peanut and imidazolinone-resistant corn. Crop rotation sequences for the 3 yr included continuous corn (CCC), corn–peanut–corn (CPC), peanut–corn–peanut (PCP), and continuous peanut (PPP). The imazapic and ALS inhibitor combination treatments both provided excellent shoot and tuber control. After 3 yr, imazapic and the ALS inhibitor combination treatment reduced shoot and tuber population densities to less than 10% of the nontreated control. Imazethapyr provided variable but better control than the carbamothioate treatment with tuber densities (measured from 0 to 15 cm soil depth) and shoot densities increasing from 733 to 2,901 tubers/m3 of soil and 16 to 43 shoots/m2, respectively, after 3 yr. Tuber densities increased in the nontreated control from 626 to 9,145 tubers/m3 of soil and from 962 to 5,466 tubers/m3 of soil in the carbamothioate treatment during this same period. Also, shoot densities increased in the nontreated control from 22 to 159 shoots/m2 and from 8 to 92 shoots/m2 in the carbamothioate treatment. There was a 31% peanut yield reduction from 1994 to 1996 when peanut was continuously planted or rotated to corn for only 1 yr. Herbicide carryover effects were not observed in cotton during 1997.

Control of two perennial weeds, quackgrass and Canada thistle, and the differential sensitivities of three imidazolinone-resistant (IMI) corn hybrids and their sensitive isolines to various acetolactate synthase (ALS)-inhibiting herbicides were evaluated in greenhouse studies. The postemergence sulfonylurea herbicides nicosulfuron and primisulfuron controlled quackgrass > 80%. The imidazolinone herbicides imazapyr and imazamox applied postemergence controlled quackgrass 70 and 74%, respectively. Canada thistle control was 89% with the sulfonylurea herbicide metsulfuron. Primisulfuron, chlorsulfuron, and tribenuron controlled Canada thistle > 70%. The imidazolinonesensitive corn hybrids did not tolerate the imidazolinone herbicides imazethapyr, imazaquin, imazapyr, AC 263,222, and imazamox; the sulfonylurea herbicides chlorimuron, chlorsulfuron, metsulfuron, tribenuron, and triflusulfuron; and the pyrimidinylthiobenzoate herbicide pyrithiobac applied postemergence. The ‘Ciba 4393 IMR’ corn hybrid, homozygous for an unknown allele, was resistant to all of the various ALS-inhibiting herbicides that injured its sensitive isoline. The magnitude of resistance for this hybrid was greater than the other IR corn hybrids. The ‘Pioneer 3751 IR’ corn hybrid, homozygous for the XA-17 ALS allele, was also resistant to a number of ALS-inhibiting herbicides. The ‘ICI 8692 IT’ corn hybrid, heterozygous for the Mut2 allele, was only resistant to the imidazolinone herbicides.

A new biotype of common cocklebur, called multiple-seeded cocklebur (MSC), was found in Bell County, TX, in 1994. MSC has up to 25 seeds per bur, usually producing up to nine seedlings, whereas normal common cocklebur (NCC) has two seeds per bur which usually produce only one seedling. MSC burs are large, round, covered with hairy spines or prickles, and flattened on one end, with each seed terminated by a beak. Leaf morphology differs among the biotypes, and stems of MSC are straighter and smoother than NCC. Apomixis occurred with MSC but not with NCC. Both biotypes have potential dormancy with germination occurring in the second growing season. MSC produces increased numbers of seedlings which increases the difficulty in controlling common cocklebur.