Invasive weed managers are presented with a complicated and ever-enlarging set of management alternatives. Identifying the optimal weed management strategy for a given set of conditions requires predicting how candidate strategies will affect plant community composition. Although field experiments have advanced our ability to predict postmanagement composition, extrapolation problems limit the prediction accuracy achieved by interpreting treatment means as predictions. Examples of extrapolation problems include nonlinear relationships between competing plants, site-to-site variation in plant population growth rates, and the carrying capacities of desired species and weeds. Our objective was to develop a model that improves predictions of weed management outcomes by overcoming a subset of these problems. To develop the model, we used data from two field experiments in which four Kentucky bluegrass, six western wheatgrass, and six invasive plant (i.e., leafy spurge) densities were combined in field plots. Graphs of our model's predictions vs. observed field experiment data indicate that the model predicted the data accurately. Our model may improve predictions of plant community response to invasive weed management actions.

Two rapid, nondestructive assays were developed and tested for their potential in differentiating glyphosate-resistant from glyphosate-susceptible biotypes of horseweed. In one assay, leaves of glyphosate-resistant and -susceptible corn, cotton, and soybean plants, as well as glyphosate-resistant and -susceptible horseweed plants, were dipped in solutions of 0, 300, 600, and 1,200 mg ae L−1 glyphosate for 3 d, and subsequent injury was evaluated. In the second assay, plant sensitivity to glyphosate was evaluated in vivo by incubating excised leaf disc tissue from the same plants used in the first assay in 0.7, 1.3, 2.6, 5.3, 10.6, 21.1, 42.3, and 84.5 mg ae L−1 glyphosate solutions for 16 h and measuring shikimate levels with a spectrophotometer. The leaf dip assay differentiated between glyphosate-resistant and -susceptible crops and horseweed biotypes. The 600 mg L−1 rate of glyphosate was more consistent in differentiating resistant and susceptible plants compared with the 300 and 1,200 mg L−1 rates. The in vivo assay detected significant differences between susceptible and glyphosate-resistant plants of all species. Shikimate accumulated in a glyphosate dose–dependent manner in leaf discs from susceptible crops, but shikimate did not accumulate in leaf discs from resistant crops, and levels were similar to nontreated leaf discs. Shikimate accumulated at high (≥ 21.1 mg ae L−1) concentrations of glyphosate in leaf discs from all horseweed biotypes. Shikimate accumulated at low glyphosate concentrations (≤ 10.6 mg L−1) in leaf discs from susceptible horseweed biotypes but not in resistant biotypes. Both assays were able to differentiate resistant from susceptible biotypes of horseweed and could have utility for screening other weed populations for resistance to glyphosate.

It is difficult to quantify the mechanism(s) responsible for competition-induced yield loss using traditional experimental techniques. A technique using yield and 13C discrimination (Δ) for wheat, a C3 plant, has been developed to separate total yield loss (TYL) into yield loss due to N (YLNS) and water (YLWS) stresses. The objective of this research was to determine whether the Δ approach could be used in corn, a C4 plant, to separate TYL into YLNS and yield loss due to a combination of water and light stresses (YLWLS). The field study had a factorial design using five corn densities and five N rates and was conducted in western Nebraska in 1999 and 2000. Relationships for YLNS and YLWLS with TYL were derived from only a portion of the yield and Δ data collected in 1999 and validated based on the remaining data collected in 1999 and 2000. In 1999, 20 to 40% of TYL was due to YLWLS, whereas in 2000, a dry year, YLWLS accounted for 60 to 80% of the TYL. Results from using the Δ-based approach were consistent with analysis of variance results. For example, calculated YLWLS values were related to measured YLWLS by the equation: calculated YLWLS = 19 + 0.91 (measured YLWLS) (r2 = 0.95; P < 0.01). The Δ approach, based on a plant's physiological response to the environment, can be used to separate and quantify competition-induced YLNS and YLWLS in corn.

An in vivo shikimate accumulation assay with excised leaf tissue was developed to provide a fast and reliable method for identifying glyphosate-resistant plants. The assay is based on glyphosate-induced accumulation of shikimate. There was a linear accumulation of shikimate in excised leaf discs of soybean and canola treated with 250 μM glyphosate for 48 h. The IC50 for the accumulation of shikimate in soybean and corn leaf discs was 34 and 87 μM, respectively. Leaf discs excised from glyphosate-resistant corn or soybean did not accumulate shikimate when treated with 500 μM glyphosate. Leaf discs taken from a number of field-grown plants accumulated shikimate in a glyphosate dose–dependent manner. The accumulation of shikimate was dependent on light and the age of the leaf from which the disc was taken. The assay worked either in 96-well microtiter plates or in vials, and it clearly differentiated between glyphosate-resistant and -susceptible crops in which the resistance is due to an alteration of the target site for glyphosate. The assay was simple and robust and has the potential to be used as a high throughput assay to detect glyphosate resistance in weeds.

A better understanding of the persistence of jointed goatgrass seed in soil and its dormancy will lead to the development of more effective weed-management strategies. Three populations of jointed goatgrass were collected from winter wheat fields in Oregon, and grown together with the winter wheat variety ‘Madsen’ in nurseries at Moro and Pendleton, OR. Germination responses of jointed goatgrass and wheat seed were recorded over 14 d at 5/5, 15/10, 15/15, 25/15, 25/25, and 30/20 C day/night temperatures and a 12-h photoperiod. Because jointed goatgrass spikelets often contain two seed, primary and secondary seed germination values were recorded. Secondary seed germination was defined as 3-mm radicle protrusion, and primary seed germination was defined as 5-mm emergence of the second coleoptile. Jointed goatgrass secondary seed germinated when exposed to all temperature regimes. Jointed goatgrass secondary seed germination occurred 3 d earlier in temperature regimes involving 15 C compared to germination at 5/5, 25/25, and 30/20 C. Final germination values for jointed goatgrass secondary seed were greatest when seed were incubated at 25/15 C. Wheat seed germinated at all temperature regimes, although the onset of germination occurred 1 to 1.5 d later at 5/5 C compared to other temperature regimes. Jointed goatgrass primary seed germinated only at 15/10, 15/15, and 25/15 C, and maximum germination occurred at 25/15 C. Dormancy in jointed goatgrass might prevent germination of seed within freshly shattered spikelets until autumn when temperatures are low and moisture is available. Because final germination percentages in jointed goatgrass primary and secondary seed were less than 100%, additional research on factors regulating dormancy is needed.

A population of waterhemp was identified in Adams County, Illinois, that survived treatment of several acetolactate synthase (ALS) inhibitors and a postemergence (POST) application of lactofen, a protoporphyrinogen oxidase (PPO)–inhibiting herbicide. Greenhouse studies were conducted to quantify the responses of this waterhemp population, designated ACR, to multiple PPO inhibitors and various other herbicides with different sites of action. Resistance ratios were obtained by comparing herbicide dose–response curves between the ACR population and a herbicide-susceptible waterhemp population. The ACR population was resistant to lactofen (23-fold) and to five other PPO-inhibiting herbicides (ranging from 2.2- to 6.2-fold). Furthermore, the ACR waterhemp population was 17,000-fold and 18,000-fold resistant to imazamox and thifensulfuron, respectively, two ALS-inhibiting herbicides. In response to atrazine, a Photosystem II inhibitor, the ACR population was 38-fold resistant. Plants within the ACR waterhemp population survived treatment of a herbicide mixture containing lactofen at 175 g ai ha−1, imazamox at 44 g ae ha−1, and atrazine at 1,000 g ai ha−1. Thus, individual plants—not just the population as a whole—displayed multiple herbicide resistance. The ACR population was not resistant to glyphosate or paraquat. This is the first reported weed population from the United States with resistances to herbicides inhibiting three unique sites of action. Furthermore, this research identifies a significant reduction in the number of POST herbicide options available for waterhemp control in soybean production.

Resistance to imidazolinone (IMI) herbicides has been incorporated recently into domesticated sunflower through conventional breeding methods. However, there are concerns regarding gene flow of the IMI-resistance trait to wild species and possible accompanying ecological consequences. Hybrids of domesticated sunflower with both common sunflower and prairie sunflower were created, with and without the imazamox-resistance trait. The relative fitness of imazamox-resistant (IMI-R) hybrids was compared with their imazamox-susceptible (IMI-S) counterparts. Greenhouse experiments were conducted to study the growth of IMI-R and IMI-S common and prairie sunflower hybrids under noncompetitive conditions. The photosynthesis rate of IMI-S prairie sunflower was slightly higher than that of IMI-R plants. However, relative growth rate, net assimilation rate, leaf area, and total dry weight were similar in IMI-R and IMI-S common and prairie sunflower, whereas plant height of IMI-S hybrid was greater than that of IMI-R common sunflower hybrids. A replacement series study was conducted under field conditions in 2001 and 2002 to evaluate the relative competitiveness of IMI-R and IMI-S common and prairie sunflower. IMI-R and IMI-S hybrids of both sunflower species were equally competitive. The results suggest that, in the absence of IMI herbicides, genes controlling IMI-R do not reduce or increase the competitive ability of either common or prairie sunflower. Therefore, if the IMI-resistant trait is incorporated in these species, the frequency of IMI-resistance genes is unlikely to decrease, even in the absence of IMI selection pressure.

Developing ecological principles applicable to invasive plant management is central to implementing sustainable strategies. We tested portions of a potentially useful successional-based management framework to further our understanding of the relationship between disturbance and colonization during revegetation of invasive weed-dominated grasslands. We hypothesized (1) intermediate wheatgrass density and biomass would be greatest at highest seeding rates, (2) control and tillage procedures that increase the availability of safe sites would increase wheatgrass abundance, and (3) spotted knapweed density and biomass would be lowest in treatments with highest wheatgrass density and biomass. Treatments included three disturbance levels: (1) no disturbance, (2) application of glyphosate, and (3) fall tillage. Colonization treatments were seeding intermediate wheatgrass of 0, 500, 2,500, and 12,500 seeds m−2. Treatments were factorially applied in a randomized complete-block design with four replications at each of two sites located in Montana. Density and biomass of intermediate wheatgrass and spotted knapweed were sampled in 1997 and 2001. At both sites, seeding 2,500 or 12,500 seed m−2 increased wheatgrass density over that of the nonseeded control in 1997. The highest seeding rate produced almost three times as many wheatgrass plants as 2,500 seeds m−2 that year. By 2001, only the highest seeding rate produced wheatgrass densities greater than that of the nonseeded control at Bozeman. Seeding rates higher than 500 seeds m−2 yielded greater wheatgrass biomass than the nonseeded control with or without either tillage or glyphosate. At the highest seeding rate, tillage or glyphosate doubled intermediate wheatgrass biomass compared with no disturbance. Spotted knapweed generally had lower biomass where intermediate wheatgrass density and biomass was highest. One approach to rehabilitation is to design disturbances that favor desired species and then use high seeding rates that overwhelm the pool of available propagules and occupy a high percentage of safe sites.

Studies were conducted to evaluate uptake, translocation, and metabolism of root-absorbed 14C-sulfentrazone in peanut, prickly sida, and pitted morningglory. Peanut absorbed more than five and three times greater 14C-sulfentrazone than pitted morningglory and prickly sida, respectively. All plant species translocated appreciable amounts (≥ 39%) of radioactivity to the leaves. The three plant species had some capacity to metabolize 14C-sulfentrazone. At 3 h after treatment, 7, 29, and 71% of the radioactivity in the shoots of peanut, prickly sida, and pitted morningglory, respectively, was sulfentrazone. Sulfentrazone levels in the shoots at 3 and 6 h after treatment correspond to reported tolerance levels, with peanut being the most tolerant of the three species, whereas prickly sida and pitted morningglory are moderately tolerant and completely susceptible to sulfentrazone, respectively. Levels of metabolites varied among species, plant part, and harvest timing. On the basis of these data, tolerance in peanut is largely due to its ability to rapidly metabolize sulfentrazone.

A suspected glyphosate-resistant Italian ryegrass biotype was collected from a filbert orchard near Portland, OR, where glyphosate was applied multiple times per year for about 15 yr. Greenhouse studies were conducted to determine if this biotype was glyphosate resistant. The plants were sprayed with glyphosate (0.01 to 3.37 kg ae ha−1) 14 d after planting and shoot biomass was determined 3 wk after herbicide treatment. Based on the dose–response experiments conducted in the greenhouse, the suspected Italian ryegrass biotype was approximately fivefold more resistant to glyphosate than the susceptible biotype. Plants from both susceptible and resistant biotypes were treated with glyphosate (0.42 and 0.84 kg ha−1) and shikimic acid was extracted 12, 24, 48, and 96 h after treatment. The susceptible biotype accumulated between three and five times more shikimic acid than did the resistant biotype. Leaf segments from both susceptible and resistant biotypes were incubated with different glyphosate concentrations (0.5 to 3000 μM) for 14 h under continuous light. Shikimic acid was extracted from each leaf segment and quantified. At a concentration up to 100 μM, leaf segments from the susceptible biotype accumulated more shikimic acid than leaf segments from the resistant biotype. The epsps gene was amplified and sequenced in both susceptible and resistant biotypes; however, no amino acid change was found in the resistant biotype. The level of resistance in this biotype is similar to that reported for a glyphosate-resistant Italian ryegrass biotype from Chile.

Croftonweed is an invasive plant in southwest China. We examined the relationships between its invasion patterns and native plant diversity at different spatio-temporal scales. At the 25 m2 scale, invasion success was negatively correlated with native plant diversity, indicating that resource availability might be the dominant factor regulating community invasibility. At the 400-m2 scale, both negative and positive relationships were detected, possibly identifying a spatial scale threshold where extrinsic environmental factors became more important to community invasibility. At the vegetation province scale, variations in physical environment outweighed the importance of intrinsic biotic factors and positive relationships between diversity and invader success were found. Native plant diversity also inhibited croftonweed over the course of community succession and at the early stages of invasion at local spatial scales. However, the changing relationship might be an artifact of sampling at different spatial scales.

Weeds of the genus Orobanche parasitize many dicotyledonous species, causing severe damage to vegetable and field crops worldwide. In Oregon, the number of red clover fields contaminated with small broomrape has increased in recent years. Small broomrape parasitism in red clover is temperature related. In this study, the temperature-dependent relationship was developed into a predictive model based on growing degree-days (GDD) for small broomrape parasitism in red clover. The model was developed in greenhouse studies and validated in the field during three growing seasons. A strong relationship between GDD and parasite size allowed for the creation of a simple predictive model for tubercle number based on GDD. The proposed model is based on a temperature range realistic to western Oregon climatic conditions and predicts lag, log, and maximum phases for four parasitism sizes in relation to GDD. Small broomrape parasitism in red clover began at about 400 GDD, but red clover biomass accumulation was not affected by parasitism before 1,200 GDD. Small broomrape flower stalk emergence began at about 1,100 GDD. Field studies validated that GDD could be a predictive parameter for small broomrape parasitism and could be used to time detection surveys and herbicide applications.

Glyphosate-resistant (GR) crops are produced over large areas in North America. A study was conducted at six western Canada research sites to determine seed date and tillage system effects on weed populations in GR spring wheat and canola cropping systems from 2000 to 2003. Four-year wheat–canola–wheat–pea rotations were devised with varying levels of GR crops in the rotation. Weed populations were determined at pre– and post–in-crop herbicide application intervals in 2000 and 2003. Early seeding led to higher and more variable in-crop wild oat and wild buckwheat populations. High frequencies of in-crop glyphosate wheat in the rotation usually improved weed management and reduced weed density and variability. Canonical discriminant analysis (CDA) across all locations revealed that by 2003, green foxtail, redroot pigweed, sowthistle spp., wild buckwheat, and wild oat, all associated with the rotation lacking in-crop glyphosate. Similar CDA analyses for individual locations indicated specific weeds were associated with 3 yr of in-crop glyphosate (Canada thistle at Brandon, henbit at Lacombe, and volunteer wheat, volunteer canola, and round-leaved mallow at Lethbridge). However, only henbit at Lacombe and volunteer wheat at Lethbridge occurred at significant densities. Although excellent weed control was attained in rotations containing a high frequency of GR crops, the merits of more integrated approaches to weed management and crop production should also be considered. Overall, rotations including GR spring wheat did not significantly increase short-term weed management risks in conventional tillage or low soil-disturbance direct-seeding systems.

Characterizing the response of weeds to canopy shade is important for improved understanding of crop–weed competition and weed population dynamics. In 2000 and 2001, field studies were conducted in central New York state to examine the influence of three neighbor types (none, broccoli, or broccoli plus winter rye) and two locations (between or within rows of broccoli) on the morphology, phenology, and seed germination characteristics of Powell amaranth. Reductions in light availability and in the ratio of red-to-far red light were associated with increases in (1) partitioning of dry weight to stem tissue, (2) stem elongation, and (3) specific leaf area. Canopy shade also resulted in fewer main leaves at flowering and a reduced rate of leaf appearance but had no effect on the number of days to flowering. The relationship between Powell amaranth fecundity and aboveground dry weight was allometric, with both parameters declining significantly under competition. The weight of seeds produced did not vary significantly according to the competitive environment experienced by the maternal parent. However, the germination percentage of viable seeds was 40 to 50% lower for seeds maturing on plants grown under competition than without competition. Reductions in the number of main leaves at flowering and increased seed dormancy may be adaptive responses to canopy shade. Both mechanistic crop–weed competition models and population dynamic models would benefit from incorporation of data on the phenotypic plasticity of morphology, phenology, and seed germination characteristics of weeds.

A greenhouse experiment was conducted to determine the efficacy of glyphosate and acetyl-CoA carboxylase (ACCase)–inhibiting herbicides sethoxydim, clethodim, and quizalofop on prairie cupgrass and windmillgrass. Herbicides were applied at seedling, tillering, and heading growth stages. In addition, a study to determine glyphosate absorption and translocation in both species was conducted. Herbicide treatments were glyphosate at 541, 841, and 1121 g ha−1 and sethoxydim, clethodim, and quizalofop at 350, 210, and 70 g ha−1, respectively. In general, control of prairie cupgrass and windmillgrass increased as the rate of glyphosate increased. In addition, windmillgrass was less susceptible to glyphosate at heading and seedling stages than was prairie cupgrass. Efficacy of all ACCase-inhibiting herbicides applied at any growth stage was equal to or greater than efficacy of the highest rate of glyphosate applied at the same stage. Furthermore, all herbicide treatments were more phytotoxic to prairie cupgrass and windmillgrass at seedling stage than at tillering or heading. Differential response of prairie cupgrass and windmillgrass to glyphosate was attributed to differences in glyphosate translocation. Separate field experiments were conducted to evaluate preemergence (PRE) and postemergence (POST) herbicide treatments for prairie cupgrass and windmillgrass in no-till corn at Hays, KS, in 2001 and 2002. All PRE treatments provided at least 90% control of windmillgrass in both years 6 wk after treatment (WAT). Prairie cupgrass was controlled effectively by acetochlor plus atrazine, alachlor plus atrazine, and S-metolachlor plus atrazine in 2001. In 2002, the only PRE treatments that gave 90% control or greater of prairie cupgrass 6 WAT were alachlor plus atrazine and pendimethalin plus atrazine. Glyphosate sequential treatment was the only POST treatment that provided 100% control of prairie cupgrass and windmillgrass in both years.

Enhanced herbicide metabolism is less common than target site–based herbicide resistance in weeds and often confers resistance to chemically dissimilar herbicides. In a previous study, the mechanism of acetolactate synthase (ALS)-inhibitor resistance in a downy brome biotype was determined to be metabolism. Our research was aimed at determining the multiple resistance pattern in the downy brome biotype, establishing its physiological basis, and investigating its fitness. Dose–response experiments showed that the resistant biotype was also moderately resistant to ethofumesate, clethodim, fluazifop, diuron, and terbacil and highly resistant to the triazine herbicides, atrazine and metribuzin. DNA sequence analysis of the psbA gene, which is the target site of PSII inhibitors, demonstrated a single amino acid substitution from serine to glycine in the resistant biotype at residue 264 in the D1 protein. Thus, the resistant biotype contains two different resistance mechanisms, herbicide metabolism and an altered target site. The resistant biotype produced less shoot dry weight, leaf area, and seed and was shorter than the susceptible biotype. The resistant biotype was also less competitive than the susceptible biotype. Thus, in the absence of herbicides, the frequency of this resistant biotype is unlikely to increase in a population of mixed downy brome biotypes.

Combine harvesters have the potential to disperse weed seeds great distances. Reducing this dispersal may be important in an integrated weed management system. The objectives of this study were to determine the distance that wild oat seeds are dispersed by a combine harvester and the effect of chaff collection on combine harvester seed dispersal. This was measured by sampling wild oat seeds at varying distances behind a combine equipped with a removable chaff collection system after it passed through a wild oat patch. Chaff collection consistently reduced the amount and distance that wild oat seeds were dispersed. This occurred because more than 74% of the total wild oat seed that were ejected from the combine were in the chaff. Because most of the chaff falls in a row directly behind the combine, chaff collection only affected dispersal in this area. In 1996, chaff collection reduced wild oat seed dispersal past the wild oat patch to less than 10 seeds m−2 at 45 m, whereas without chaff collection, there was greater than 10 seeds m−2 up to 145 m. At distances beyond 145 m, chaff collection had no significant effect on seed dispersal. Chaff collection may be an important tool in an integrated weed management program because it may slow weed invasions and reduce the expansion of weed patches.

London rocket is hypothesized to be the most important overwintering host of the beet leafhopper in southern New Mexico. Knowledge of the environmental factors affecting the emergence of this plant is essential to developing a predictive model for London rocket and leafhopper populations. The temperature and moisture optima for London rocket germination and emergence were assessed using growth chamber studies. Temperatures of 5 to 35 C and soil water tension treatments of − 0.01 to − 1.5 MPa were tested. Optimal seed burial depth also was assessed. Optimal London rocket germination occurred at approximately 15 C and maximum emergence was achieved at 15 to 20 C with soil moisture tensions of − 0.01 to − 1.2 MPa. London rocket emergence occurred best at a seed burial depth of 2 mm.

Recent reports indicate that manganese (Mn), applied as a foliar fertilizer in tank mixtures with glyphosate, has the potential to antagonize glyphosate efficacy and reduce weed control. It was hypothesized that Mn2+ complexed with glyphosate in a similar manner to Ca2+, forming salts that were not readily absorbed and, thereby, reducing glyphosate efficacy. This study was conducted to confirm the interaction of Mn2+ and glyphosate and to measure the effect of Mn on glyphosate absorption and translocation in velvetleaf. In aqueous solutions, Mn2+ binds with solvent molecules and with chelating agents to form hexacoordinate complexes. The distribution of paramagnetic species, both the free manganous ion ([Mn{H2O}6]2+) and the Mn2+–glyphosate complex, in Mn–glyphosate solutions at various pH values were analyzed using electron paramagnetic resonance (EPR) spectroscopy. Glyphosate interaction with Mn appeared to increase as the pH was increased from spray solution levels (2.8 to 4.5) to levels common in the plant symplast (7.5). Growth chamber bioassays were conducted to measure absorption and translocation of 14C-labeled glyphosate in solution with four Mn fertilizers: Mn-ethylaminoacetate (Mn-EAA), Mn-ethylenediaminetetraacetate (Mn-EDTA), Mn-lignin sulfonate (Mn-LS), and Mn-sulfate (MnSO4). Mn-EDTA did not interfere with glyphosate efficacy, absorption, or translocation. However, both MnSO4 and Mn-LS reduced glyphosate efficacy, absorption, and translocation. Mn-EAA severely antagonized glyphosate efficacy, and although glyphosate in tank mixtures with Mn-EAA was absorbed rapidly, little was translocated from the treated leaf. The Mn-EAA fertilizer contained approximately 0.5% iron (Fe) not reported on the fertilizer label. Iron is presumed to be partially responsible for the very limited translocation of glyphosate from the treated leaf in Mn-EAA tank mixtures. Adding ammonium sulfate increased the efficacy, absorption, and translocation of glyphosate for each Mn fertilizer tank mixture.

Barnyardgrass (BYG) has been the most frequently reported troublesome weed in rice because it is an aggressive invader, is difficult to control, and reduces yields significantly. A replacement series study was conducted to determine how a naturally suppressive cultivar (T65∗2/TN 1; ‘PI 312777’), a nonsuppressive cultivar (‘Lemont’), and an F3 cross between the two (‘PI 312777 × Lemont’) would interfere with BYG in the southern United States. The rice cultivars did not differentially affect BYG height. The PI 312777 produced more tillers and greater shoot dry weight but was only moderately competitive (relative yield [RY]) or aggressive (relative crowding coefficient) against BYG. Competitiveness at 2:2 rice and BYG mixture proportion and replacement series illustrations on RYs for the number of tillers and shoot dry weights for the three rice cultivars indicated that PI 312777 suppressed BYG growth relatively better than the other two cultivars. Plant-for-plant, PI 312777 was more competitive than Lemont. PI 312777 × Lemont suppressed BYG relatively less than did PI 312777 and therefore would require significant genetic improvements before it is suitable for commercial use in a reduced herbicide production system.