Homozygous, sethoxydim-tolerant corn was field tested at two locations in 1989 and 1990. Sethoxydim at 0.22, 0.44, and 0.88 kg ha−1 was applied to sethoxydimtolerant corn in the 3- and 7-leaf stages. None of the sethoxydim treatments caused visible injury to the sethoxydim-tolerant corn, but all treatments were lethal to a parental corn line used as a control. Sethoxydim applied at either stage of corn development had no effect on number of days to 50% silk emergence, plant height, or grain yield, compared to nontreated plants. Sethoxydim-tolerant corn was also tolerant to mixtures of sethoxydim plus other postemergence herbicides that control dicotyledonous weeds. Sethoxydim mixed with atrazine or sethoxydim applied in sequential applications with dicamba or 2,4-D gave annual grass control similar to sethoxydim applied alone. However, the sethoxydim plus bentazon treatment resulted in reduced grass control in comparison to sethoxydim alone. When the broadleaf herbicides were mixed with sethoxydim or applied as sequential treatments, broadleaf weed control was the same as when the broadleaf herbicides were applied alone. The high level of corn tolerance to sethoxydim and the broad spectrum of weed control resulting from combinations of sethoxydim plus other postemergence herbicides indicates that sethoxydim-tolerant corn hybrids could increase the options available for weed control in corn.

Harvest weed seed control (HWSC) techniques have been implemented in Australian cropping systems to target and reduce the number of weed seeds entering the seedbank and thereby reduce the number of problematic weeds emerging in subsequent years to infest subsequent crops. However, the influence of HWSC on ameliorating herbicide-resistance (HR) evolution has not been investigated. This research used integrated spatial modeling to examine how the frequency and efficacy of HWSC affected the evolution of resistance to initially effective herbicides. Herbicides were, in all cases, better protected from future resistance evolution when their use was combined with annual HWSC. Outbreaks of multiple HR were very unlikely to occur and were nearly always eliminated by adding annual, efficient HWSC. The efficacy of the HWSC was important, with greater reductions in the number of resistance genes achieved with higher-efficacy HWSC. Annual HWSC was necessary to protect sequences of lower-efficacy herbicides, but HWSC could still protect herbicides if it was used less often than once per year, when the HWSC and the herbicides were highly effective. Our results highlight the potential benefits of combining HWSC with effective herbicides for controlling weed populations and reducing the future evolution of HR.

Since its initial introduction in the late 1950s, chemical control has dominated weed management practices in China. Not surprisingly, the development of herbicide resistance has become the biggest threat to long-term, sustainable weed management in China. Given that China has followed the same laissez-faire approach toward resistance management that has been practiced in developed countries such as the United States, herbicide resistance has evolved rapidly and increased steadily over the years. Previously, we carried out a systematic review to quantitatively assess herbicide-resistance issues in China. In this review, our main objective is to focus on mechanistic studies and management practices to document the (1) history of herbicide application in China; (2) resistance mechanisms governing the eight most resistance-prone herbicide groups, including acetolactate synthase inhibitors, acetyl-CoA carboxylase inhibitors, synthetic auxin herbicides, 5-enolpyruvylshikimate-3-phosphate synthase inhibitors, protoporphyrinogen oxidase inhibitors, photosystem I electron diverters, photosystem II inhibitors, and long-chain fatty-acid inhibitors; and (3) herbicide-resistance management strategies commonly used in China, including chemical, cultural, biological, physical, and integrated approaches. At the end, perspectives and future research are discussed to address the pressing need for the development of integrated herbicide-resistance management in China.

Field and greenhouse experiments in 1981 and 1982 determined the potential interactions of three preemergence and three postemergence herbicides with four granular insecticides in soybeans [Glycine max (L.) Merr.]. Generally, metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] increased soybean injury and lowered yields when applied to plots treated with an organophosphate insecticide at planting. Soybean injury from these treatments and from aldicarb [2-methyl-2-(methylthio)-propionaldehyde-o-(methylcarbamoyl)oxime] plus metribuzin applied in the field was greater in 1982 than 1981 due to excessive rainfall immediately after planting. Oryzalin (3,5-dinitro-N4,N4 -dipropylsulfanilamide) plus several of the in-furrow insecticide treatments in the greenhouse increased injury to soybeans. Other than this, the method of insecticide application, banded or in-furrow, had no effect on that caused by each pesticide combination.

Experiments were conducted in the greenhouse and growth chamber to evaluate competitive mechanisms of soybean and common cocklebur during seedling growth. Soybean was approximately 1.5 to 2 times taller and was more competitive aboveground than common cocklebur during the first few weeks of growth. Common cocklebur had an approximate 20 to 50% finer root system and was more competitive belowground than soybean during early growth.

In replacement experiments in the greenhouse, plant relative yield (PRY) of both eastern black nightshade and tomato increased as the proportion of nightshade plants increased in the pots, indicating that nightshade is less competitive than tomato. In field studies tomato yield was reduced by two-thirds if three nightshade plants m–1 of row were allowed to grow with tomato more than 6 weeks following tomato establishment The percent marketable fruit decreased linearly from 73% with no nightshade to 49% when nightshade were present for 12 weeks. When nightshade and tomato were transplanted together, tomato yield was 9000 kg ha–1 and 49% of the fruit was marketable, while tomato yields were 30 000 kg ha–1 and 70% of the fruit was marketable when nightshade was established 9 weeks after tomato planting.

Patterns of weed emergence in upland and lowland soils were observed for several months after tillage by counting all emerged species. Forty to 50% of weed emergence occurred within 6 weeks of tillage on both sites. Significant emergence occurred within 3 weeks on both sites, but very little emergence occurred within 1 week in lowland soil. The data confirm the strong influence of soil tillage on weed emergence. They also suggest an influence of radiant energy on weed emergence. Peaks of weed emergence 6 or more weeks after tillage often occurred coincident with or soon after peaks of radiant energy.

The fate of 2,4-dichlorophenyl p-nitrophenyl ether (nitrofen) in the foliage of rape (Brassica campestris L. ‘Echo’), redroot pigweed (Amaranthus retroflexus L.), and green foxtail (Setaria viridis (L.) Beauv.) was investigated with the aid of 14C-nitrofen. Only limited amounts of the label were translocated in these species. Plants treated with 14C-nitrofen under high light conditions produced several labelled compounds of different molecular size and chromatographic properties. The time at which these compounds were first detectable depended on light intensity. At least two of these compounds are lipid-nitrofen conjugates or nitrofen polymers and others may be formed by cleavage of nitrofen at the ether linkage.

We surveyed soils that produce rice (Oryza Sativa L.) at the University of Arkansas Rice Branch Experiment Station at Stuttgart, Arkansas, to determine whether residues of 3, 3′,4,4′-tetrachloroazobenzene (hereinafter referred to as TCAB) accumulated with repeated applications of 3′,4′-dichloropropionanilide (propanil). We sampled Crowley silt loam with known histories of propanil application to determine the effect of depth, rate, and time on TCAB formation. Propanil and TCAB were measured by electron capture gas chromatography. Low concentrations of TCAB (<0.2 ppm) generally were detected in the surface 0 to 10.1-cm layer of soil receiving applications of propanil at rates of 6.7 kg/ha. Concentration and occurrence of TCAB decreased with increasing time and depth in soil.

The effects of herbicide concentration, soil water content, and temperature on the fate and degradation of the monosodium salt of methylarsonic acid (MSMA) were evaluated in four soils. Available arsenicals were extracted, purified, and separated using reversed-phase high-performance liquid chromatography (HPLC). Residual MSMA was determined with a graphite furnace atomic absorption spectrophotometer at 193.7 nm. Initial loss of MSMA was rapid, and degradation followed first-order kinetics. The rate of change of the rate constant was temperature dependent only at soil water contents less than field capacity. MSMA dissipation was significantly faster in finer textured soils with continuous flooding and under controlled laboratory conditions (<180 days) than under field (ca. 350 days) conditions. Also, in finer textured soils, degradation of MSMA resulted in significant increases in arsenate and cacodylic acid (dimethyl arsinic acid) over native levels under flooded conditions. However, MSMA treatments contributed only a small fraction to total soil arsenic which dissipated to original concentrations by 120 days. The results indicate that under present recommended use patterns it is highly unlikely that MSMA will accumulate in the environment or carry over from one growing season to the next.

Effects of wild proso millet interference with irrigated corn were evaluated in Nebraska and Colorado over a 2-yr period. Corn yield reductions ranged from 13 to 22% from a wild proso millet density of 10 plants m–2. As density increased, corn yield reduction could be predicted with a rectangular hyperbola regression model. Ten wild proso millet plants m–2 growing with corn produced 4200 to 6200 seed m–2. Corn yields were reduced 10% at one location if wild proso millet removal was delayed 2 weeks after corn planting. If removal was further delayed until 6 weeks after corn planting, corn yield reductions at the two locations ranged from 16 to 28%.

The effects of weed control measures in established alfalfa (Medicago sativa L.) on forage yield and quality were investigated at three sites with varying alfalfa densities and weed populations. Herbicide treatments were 0.56 and 1.12 kg/ha metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] applied in fall or spring, respectively, 1.68 kg/ha pronamide [3,5-dichloro (N-1,1-dimethyl-2-propynyl)benzamide] applied in fall, and combinations of these treatments. First-harvest forage yields (weeds plus alfalfa) were either reduced or unchanged by herbicide treatments. Total forage yield was not altered by the herbicide treatments, but first-harvest and total alfalfa yield as well as first-harvest forage protein content were increased by several treatments, depending on stand density and weed pressure. Little effect was observed on in vitro digestible dry matter or acid detergent fiber content.

Field research was conducted at two locations in 1982 and 1983 to evaluate the competitiveness of coffee senna (Cassia occidentalis L. # CASOC) with cotton (Gossypium hirsutum L.). With season-long competition, each increase of 1 coffee senna plant/7.5 m of row reduced seed cotton by 9 to 117 kg/ha. Each additional week of competition from a dense stand (40 plants/m of row) of coffee senna reduced seed cotton yield by 118 kg/ha and cotton main stem height by 1.25 cm. Neither cotton stand density nor fiber properties were affected by coffee senna density or duration of competition. Seed cotton yields and main stem heights obtained when cotton was kept weed free for 6 weeks after cotton emergence were not significantly different from those kept weed free for 8, 10, or 14 weeks. Coffee senna dry-matter production was essentially zero when cotton was maintained weed free for 8 or more weeks.

Ryegrass (Lolium multiflorum Lam. # LOLMU) control in wheat (Triticum aestivum L.) using chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino] carbonyl] benzenesulfonamide} at 35 g ai/ha was significantly higher when applied preemergence (pre) than early postemergence (poe) to ryegrass with two to four leaves and wheat with three to five tillers. Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] applied at 420 g ai/ha early poe controlled more than 95% of the ryegrass, but control was unacceptable when the same rate was applied late poe when the ryegrass was at midtiller and wheat at full tiller. Wheat leaf burn, stunting, and stand reduction occurred where metribuzin was applied early poe but yields were not affected. Ryegrass control was excellent where diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} was applied early poe at 560 g ai/ha. Wheat yields, averaged over years, for early poe applications of chlorsulfuron at 35 g/ha, metribuzin at 280 and 420 g/ha, and diclofop at 560 g/ha were 22, 22, 24, and 20% higher, respectively, than the untreated stands. Injury associated with the herbicide treatments was not observed on soybeans [Glycine max (L.) Merr.] planted following wheat.

Rates of trifluralin (α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and vernolate (S-propyl dipropylthiocarbamate) were compared with and without 45 kg/ha of nitrogen for 2 yr on soybeans [Glycine max (L.) Merr.]. Nodulation was the only factor affected significantly by nitrogen. Nodule weight was 65% greater where nitrogen was not applied. Nodulation was suppressed by trifluralin, but not by vernolate. Delays in emergence, stunting, plant injury, and yield reduction were associated with preplant incorporated treatments of trifluralin at 1.12 kg/ha and with incorporated vernolate at 2.24 and 4.48 kg/ha. Trifluralin incorporated at 0.56 kg/ha and vernolate injected at 2.24 and 4.48 kg/ha had essentially no effect on plant injury and did not reduce yields significantly. Soybeans were injured more by incorporated vernolate than by trifluralin. Average yields of weed-free soybeans for 2 yr were reduced 10.5, 8.6, and 14.0%, respectively, by (a) trifluralin at 1.12 kg/ha and (b) incorporated vernolate at 2.24 and 4.48 kg/ha. However, injected vernolate (compared to other treatments) significantly increased soybean emergence, reduced plant injury, and increased yields.

Absorption, translocation, and metabolism of 14C-labeled 2,4-bis (isopropylamino)-6-methylmercapto-s-triazine (prometryne) from solution cultures by cotton (Gossypium hirsutum L., var. DPL smoothleaf) and soybean (Glycine max Merr., var. Lee) were investigated. Cotton (moderately tolerant) and soybean (sensitive) absorbed essentially equal amounts of prometryne. Whereas 14C was uniformly distributed in soybean, it was concentrated in the lysigenous glands and in the root primordia of cotton. Soybean had a considerably higher concentration of radioactivity in shoots than in roots, whereas the reverse was true in cotton. The major methanol extractable 14C-labeled component in the roots and shoots of both species was prometryne. Both species converted some prometryne to the derivative, 2,4-bis(isopropylamino)-6-hydroxy-s-triazine (hereinafter referred to as hydroxypropazine), but cotton shoots had a slightly higher percentage of the latter than the soybean shoots. The concentration of prometryne in soybean shoots was about four times greater than in cotton shoots. Differential translocation of prometryne appeared to be a major factor contributing to the difference in susceptibility between cotton and soybean.

To investigate the mode of action of a grass-specific herbicide, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} was added to corn and soybean cell suspension cultures containing metabolic intermediates such as sucrose [14C-U], sodium acetate [14C-1,2], or L-leucine [14C-U]. Death of the corn suspension cells occurred within 3 days after haloxyfop was added at a concentration of 1.0 μM to supplemented Murashige and Skoog's medium. At 0.1 μM haloxyfop, 14C-sucrose uptake and 14C loss due to respiration of the corn cells declined without a significant reduction in cell fresh weight, cell viability, cellular ATP level, free sugar content, cell wall materials, or level of glycolytic intermediates. The proportions of sucrose, glucose, and fructose in the free sugar fraction were not affected. However, the 14C-labeled free amino acid level was increased. During a 24-h incubation period, incorporation of leucine [14C] as a precursor revealed that haloxyfop did not inhibit protein synthesis. Incorporation of acetate [14C-1,2] showed that total lipid synthesis was inhibited by 42% at 0.1 μM haloxyfop (sublethal). Similar responses were observed in the soybean suspension cells; however, the calculated 50% lethal concentration (LC50) was 47 times higher than for corn cells. The results of this study suggest that the site of action of haloxyfop is located where metabolic intermediates enter the Kreb's cycle and lipid synthesis. Glycolysis is not inhibited.

Soil solarization has been proposed as an alternative to methyl bromide for controlling nutsedges. Little is known, however, about the relationship between soil solarization and nutsedge tuber viability. Combinations of elevated temperatures and durations of exposure were evaluated for their effect on purple nutsedge and yellow nutsedge tuber viability and new tuber production in growth chamber studies. Estimates of the duration of exposure at each temperature that reduced nutsedge growth parameters 50% (TT50) were supplied by log-logistic regression analysis. Nutsedge tuber viability was reduced when temperatures were ≥ 45 C. Relative to purple nutsedge, yellow nutsedge tuber viability had smaller TT50 values for 45, 50, and 55 C. Tuber viability TT50 at 60 C was similar for both nutsedges. The TT50 for production of new purple nutsedge tubers at 50 C was larger than that for yellow nutsedge. However, there were no differences between species in TT50 values for new tuber production at higher temperatures. With sufficient durations of exposure, both purple and yellow nutsedge tubers were killed at temperatures ≥ 50 C. However, application of these data to field situations in Georgia may be limited using present technology because the soil temperature cannot be raised to high enough levels for acceptable solarization effects.

Inheritance of resistance to diclofop was studied in three wild oat biotypes (designated B, C., and H) from the Willamette Valley of Oregon. Cultivated oat (cultivar ‘Monida’) was crossed, including reciprocals, to three wild oat biotypes. Leaves of each F1 plant were spotted with diclofop as a nondestructive test for resistance or susceptibility. All F1 hybrids were resistant, indicating that resistance is dominant and is under nuclear control. The F2 plants where Monida was the maternal parent were screened with diclofop, and F2 plants of the Monida/C cross were screened with fenoxaprop because the parent C biotype was resistant to fenoxaprop. At lower doses, a 3:1 (R:S) segregation ratio in F2 was observed and at higher doses a 1:3 (R:S) segregation ratio was often observed. The F2:3 families segregated in a 1:2:1 (all resistant : segregating resistant and susceptible all susceptible) ratio when treated with a 1.1-kg ae ha−1 dose of diclofop. This confirms that resistance to diclofop in the B, C, and H biotypes is primarily under monogenic control, with resistance being dominant to susceptibility at lower herbicide doses. At increased doses, susceptibility becomes dominant. Knowledge of the inheritance of resistance may help in the development of containment measures to prevent the spread of herbicide-resistance genes.

Fenoxaprop-P-ethyl, a phenoxy herbicide of the aryloxy–phenoxy–propionic acid group, had a strong control effect when applied POST to weedy rice in this study, with the effective concentrations of 294 μM and 218 μM of herbicide causing 50% inhibition (IC50) in plant height and fresh weight values, respectively. However, fenoxaprop-P-ethyl caused phytotoxicity in cultivated rice. Isoxadifen-ethyl, a widely used herbicide safener in rice, can decrease the phytotoxicity caused by fenoxaprop-P-ethyl. Owing to the extremely similar morphological features and physiological properties of weedy and cultivated rice, it is not practical to spray isoxadifen-ethyl directly on cultivated rice plants to safen them. Applying the safener directly to cultivated rice seeds may be a practical alternative method. To improve the biological activity of isoxadifen-ethyl seed treatments, novel compounds were designed by splicing other groups, including amines, amino acids, and 2- methoxy-5-nitrophenol sodium salt, to the parental structure of isoxadifen-ethyl. Through hydrolysis, acyl chlorination, acyl amination, and esterification, a series of isoxadifen-ethyl derivatives were synthesized and their structures were determined by mass spectrometry and 1H nuclear magnetic resonance spectroscopy. The biological activities of five of the isoxadifen-ethyl derivatives, which possessed recovery effects similar to isoxadifen-ethyl, were able to relieve herbicide phytotoxicity. In pot experiments, isoxadifen-ethyl showed almost no activity as a seed treatment, while three derivative compounds, when used independently as seed treatments, were able to prevent the damage caused by fenoxaprop-P-ethyl. The results will help to develop a new control method for weedy rice, thereby decreasing production costs and increasing farmers’ incomes.