Over 175 growers in each of six states (Illinois, Indiana, Iowa, Mississippi, Nebraska, and North Carolina) were surveyed by telephone to assess their perceptions of the benefits of utilizing the glyphosate-resistant (GR) crop trait in corn, cotton, and soybean. The survey was also used to determine the weed management challenges growers were facing after using this trait for a minimum of 4 yr. This survey allowed the development of baseline information on how weed management and crop production practices have changed since the introduction of the trait. It provided useful information on common weed management issues that should be addressed through applied research and extension efforts. The survey also allowed an assessment of the perceived levels of concern among growers about glyphosate resistance in weeds and whether they believed they had experienced glyphosate resistance on their farms. Across the six states surveyed, producers reported 38, 97, and 96% of their corn, cotton, and soybean hectarage planted in a GR cultivar. The most widely adopted GR cropping system was a GR soybean/non-GR crop rotation system; second most common was a GR soybean/GR corn crop rotation system. The non-GR crop component varied widely, with the most common crops being non-GR corn or rice. A large range in farm size for the respondents was observed, with North Carolina having the smallest farms in all three crops. A large majority of corn and soybean growers reported using some type of crop rotation system, whereas very few cotton growers rotated out of cotton. Overall, rotations were much more common in Midwestern states than in Southern states. This is important information as weed scientists assist growers in developing and using best management practices to minimize the development of glyphosate resistance.

Container-grown nursery crops in the southeastern United States are typically grown in a rooting substrate comprised primarily of the ground bark of pine trees. However, pine bark is becoming less available and more costly because of changes in production and marketing practices within southeastern pine forestry. This shortage has resulted in the economic incentive to seek pine bark alternatives. Two possible alternatives are clean chip residual and whole tree. These alternatives are like pine bark, because both are products of southern pine forestry. Unlike pine bark, which is a single part of the tree, these alternatives contain all parts of the tree, including wood and foliage in various portions. Registration of preemergence-active herbicides has been based solely upon data obtained from pine bark–based nursery production. Research was conducted to determine if the control of (1) large crabgrass with prodiamine, (2) eclipta with flumioxazin, and (3) spotted spurge with isoxaben would be comparable in these alternatives to what has been established in pine bark. Seed germination of all three weed species in no-herbicide controls was approximately 10% and equivalent between pine bark and the alternatives. Foliage fresh weight production of large crabgrass and spotted spurge was less in the alternatives compared to pine bark; eclipta was not affected. For all three weed species–herbicide combinations, weed control was nearly identical between pine bark and the alternative substrates, provided the herbicide had been applied at its registered rate. For all three herbicides, rates that are effective in pine bark substrates will be equally effective in the pine bark alternatives.

A survey of farmers from six U.S. states (Indiana, Illinois, Iowa, Nebraska, Mississippi, and North Carolina) was conducted to assess the farmers' views on glyphosate-resistant (GR) weeds and tactics used to prevent or manage GR weed populations in genetically engineered (GE) GR crops. Only 30% of farmers thought GR weeds were a serious issue. Few farmers thought field tillage and/or using a non-GR crop in rotation with GR crops would be an effective strategy. Most farmers did not recognize the role that the recurrent use of an herbicide plays in evolution of resistance. A substantial number of farmers underestimated the potential for GR weed populations to evolve in an agroecosystem dominated by glyphosate as the weed control tactic. These results indicate there are major challenges that the agriculture and weed science communities must face to implement long-term sustainable GE GR-based cropping systems within the agroecosystem.

Greenhouse experiments were conducted to evaluate the response to halosulfuron of several smooth pigweed populations that had been shown to be resistant to acetolactate synthase (ALS, EC 2.2.1.6)-inihibiting herbicides. Five ALS-resistant smooth pigweed populations (R1, R2, R3, R4, and R5) and one susceptible (S) population were treated with halosulfuron POST at 0.27, 2.7, 27, 270, and 2,700 g ai/ha. Percentage injury and dry weight were used to determine resistance of smooth pigweed populations to halosulfuron. Populations of smooth pigweed with previous reports of resistance to ALS-inhibiting herbicides showed varying degrees of resistance to halosulfuron compared with the susceptible population. Concentrations of halosulfuron required to reduce ALS-resistant smooth pigweed dry weights 50% were 2 to 12-fold higher than that of the susceptible population. One population, designated R2, had increased resistance to halosulfuron applications, requiring 97 g/ha halosulfuron to reduce shoot dry weight 50% compared with only 8 g/ha for S. Our results show that populations of smooth pigweed with a history of ALS-inhibiting resistance can have differing degrees of resistance to halosulfuron.

Greenhouse dose–response studies were conducted to determine the effectiveness of PRE and POST applications of saflufenacil on blue mustard, flixweed, Palmer amaranth, redroot pigweed, and tumble pigweed. Weed species did not differ in their responses to saflufenacil applied PRE. Averaged across species, PRE application of saflufenacil at 6 to 30 g/ha reduced weed biomass 82 to 98%, but biomass did not differ among rates of 12 g/ha or higher. POST application of saflufenacil reduced weed biomass by 92%, averaged across species and rates. On the basis of regression analysis, the 90% plant biomass reduction for saflufenacil applied PRE and POST was 9 and 6 g/ha, respectively. Saflufenacil applied PRE reduced population density by 77 to 98%, averaged across weed species; a rate of 9 g/ha reduced population density 90% (DR90) on the basis of regression analysis. Averaged across species, POST application of 6 to 30 g/ha reduced population density by 63 to 93%, but regression analysis indicated that the DR90 value was greater than 30 g/ha. Averaged across rates, saflufenacil reduced the population density of flixweed, Palmer amaranth, redroot pigweed, tumble pigweed, and blue mustard by 49, 64, 67, 73, and 78%, respectively.

A phone survey was administered to 1,195 growers in six states (Illinois, Indiana, Iowa, Mississippi, Nebraska, and North Carolina). The survey measured producers' crop history, perception of glyphosate-resistant (GR) weeds, past and present weed pressure, tillage practices, and herbicide use as affected by the adoption of GR crops. This article describes the changes in tillage practice reported in the survey. The adoption of a GR cropping system resulted in a large increase in the percentage of growers using no-till and reduced-till systems. Tillage intensity declined more in continuous GR cotton and GR soybean (45 and 23%, respectively) than in rotations that included GR corn or non-GR crops. Tillage intensity declined more in the states of Mississippi and North Carolina than in the other states, with 33% of the growers in these states shifting to more conservative tillage practices after the adoption of a GR crop. This was primarily due to the lower amount of conservation tillage adoption in these states before GR crop availability. Adoption rates of no-till and reduced-till systems increased as farm size decreased. Overall, producers in a crop rotation that included a GR crop shifted from a relatively more tillage-intense system to reduced-till or no-till systems after implementing a GR crop into their production system.

A telephone survey was conducted with growers in Iowa, Illinois, Indiana, Nebraska, Mississippi, and North Carolina to discern the utilization of the glyphosate-resistant (GR) trait in crop rotations, weed pressure, tillage practices, herbicide use, and perception of GR weeds. This paper focuses on survey results regarding herbicide decisions made during the 2005 cropping season. Less than 20% of the respondents made fall herbicide applications. The most frequently used herbicides for fall applications were 2,4-D and glyphosate, and these herbicides were also the most frequently used for preplant burndown weed control in the spring. Atrazine and acetochlor were frequently used in rotations containing GR corn. As expected, crop rotations using a GR crop had a high percentage of respondents that made one to three POST applications of glyphosate per year. GR corn, GR cotton, and non-GR crops had the highest percentage of growers applying non-glyphosate herbicides during the 2005 growing season. A crop rotation containing GR soybean had the greatest negative impact on non-glyphosate use. Overall, glyphosate use has continued to increase, with concomitant decreases in utilization of other herbicides.

Novel forms of selective weed control are needed by many types of growers, but especially by organic growers who are restricted from using synthetic herbicides. Abrasive grit made from corn cobs was expelled from a sand blaster at 517 kPa pressure and aimed at plants of common lambsquarters and corn positioned 300 mm distant. Most small weed plants were killed by one split-second blast of grit, but corn plants suffered little damage by the same treatment. Air-propelled grit made from agricultural residues possibly could be used for selective nonchemical weed control without the need for soil tillage.

A botanical survey conducted from 2003 to 2007 showed the occurrence of the acacia strap flower and the Oriental mistletoe plant in different regions in Jordan. Acacia strap flower was found parasitizing 26 plant species belonging to 12 families. Oriental mistletoe attacked 14 plant species from eight families. Parasitized species ranged from wild shrubs to fruit and forest trees. Eleven Fabaceae species were parasitized by acacia strap flower, whereas Oriental mistletoe parasitized six Rosaceae species. Caper, pomegranate, white weeping broom, and white willow were attacked by both parasites. Infection by both parasites resulted in mortality of host plants in many cases. Hosts severely attacked by acacia strap flower were African jujube, Australian pine, chinaberry, Christ thorn jujube, common jujube, oleander, poinciana, sumac, tamarisk, terebinth, and white weeping broom. Oriental mistletoe heavily parasitized almond, mosphilla, olive, Palestine buckthorn, pomegranate, and white weeping broom. Results indicated the high potential of both parasites to spread and attack new hosts in the absence of control measures.

A johnsongrass population from a cotton field in northern Greece along with a population from the university farm (“Control”) were evaluated for resistance to the herbicide quizalofop; cross-resistance to cycloxydim, propaquizafop, and fluazifop (acetyl coenzyme A [CoA] carboxylase [ACCase]-inhibiting herbicides), and multiple resistance to nicosulfuron (acetolactate synthase [ALS]-inhibiting herbicides). In greenhouse experiments, the application of four times the recommended rates of quizalofop and propaquizafop to suspected resistant rhizomatous plants resulted in 4 and 5% growth reduction, respectively. However, the growth of suspected resistant seedlings was reduced by 54 and 28% after the application of two times the recommended rate of the same herbicides. In contrast, the application of quizalofop and propaquizafop at recommended rates on rhizomatous plants and seedlings of the Control population reduced their growth by 97 to 100%. Also, the growth reduction of both populations by the application of cycloxydim, fluazifop, and nicosulfuron at recommended rates ranged from 93 to 100%. In the field experiment, quizalofop and propaquizafop applied at four times the recommended rate reduced growth of the suspected resistant population by 9 and 18%, respectively, whereas the recommended rate of fluazifop gave a 94% growth reduction of this weed. The herbicide rate required for 50% growth reduction (GR50) values for rhizomatous plants of the suspected resistant population were 0.90 and 2.465 kg ai/ha for quizalofop and propaquizafop, respectively, whereas the corresponding GR50 values for the seedlings were 0.074 and 0.185 kg ai/ha. These results indicate that a johnsongrass population developed cross-resistance to quizalofop and propaquizafop, but did not evolve cross-resistance to cycloxydim and fluazifop or multiple resistance to nicosulfuron.

Soft rush is a perennial, tussock-forming plant that often infests low-lying grazing areas in Florida. Experiments were conducted to determine the most effective herbicides for control of soft rush. Herbicide treatments included triclopyr + fluroxypyr at 0.43 + 0.15 and 0.86 + 0.30 kg/ha, 2,4-D amine at 1.12 and 2.24 kg/ha, 2,4-D amine + carfentrazone at 1.12 + 0.02 and 2.24 + 0.02 kg/ha, aminopyralid at 0.12 kg/ha, and 2,4-D amine + dicamba at 1.61 + 0.56 kg/ha and were applied to soft rush with and without mowing to a 15-cm stubble height. Aminopyralid and triclopyr + fluroxypyr did not control soft rush with or without mowing 1 and 12 mo after treatment (MAT). When mowing occurred prior to application, treatments containing 2,4-D provided at least 81% control of soft rush 1 MAT. In contrast, control was no greater than 59% when treatments were applied without mowing soft rush. Mowing had no impact on soft-rush control with herbicides 12 MAT. Applications of 2.24 kg/ha 2,4-D provided at least 90% control 12 MAT, but this was not significantly different from the premix of 2,4-D + dicamba or 2.24 + 0.02 kg/ha 2,4-D + carfentrazone treatments. Therefore, effective control of soft rush can be obtained with the use of 2,4-D amine or products that contain 2,4-D amine.

Corn and soybean growers in Illinois, Indiana, Iowa, Mississippi, Nebraska, and North Carolina, as well as cotton growers in Mississippi and North Carolina, were surveyed about their views on changes in problematic weeds and weed pressure in cropping systems based on a glyphosate-resistant (GR) crop. No growers using a GR cropping system for more than 5 yr reported heavy weed pressure. Over all cropping systems investigated (continuous GR soybean, continuous GR cotton, GR corn/GR soybean, GR soybean/non-GR crop, and GR corn/non-GR crop), 0 to 7% of survey respondents reported greater weed pressure after implementing rotations using GR crops, whereas 31 to 57% felt weed pressure was similar and 36 to 70% indicated that weed pressure was less. Pigweed, morningglory, johnsongrass, ragweed, foxtail, and velvetleaf were mentioned as their most problematic weeds, depending on the state and cropping system. Systems using GR crops improved weed management compared with the technologies used before the adoption of GR crops. However, the long-term success of managing problematic weeds in GR cropping systems will require the development of multifaceted integrated weed management programs that include glyphosate as well as other weed management tactics.

The interactive effects of nitrogen rate (0, 28, 56, and 112 kg/ha), vine density (0, 1.8, 3.6, and 5.4 t/ha of the cultivar ‘Stevens’), and weed management (preemergence herbicide, postemergence control, inoculation with weed seeds, and untreated) were determined on the recolonization of open spaces caused by localized biomass removal in a newly planted commercial cranberry bed. To assess the effect of the 64 treatment combinations on initial colonization, all cranberry and weed biomass was removed from a randomly selected 930-cm2 area in each plot in Year 1. To quantify recolonization of the disturbed area, the same quadrat was resampled and all plant biomass was collected in Year 2. Cranberry biomass production in the disturbed area increased in a quadratic fashion with increasing N rates for all vine densities except zero. Cranberry biomass in the year after disturbance was positively correlated with cranberry biomass present in the previous year. Weed stem biomass in the year after disturbance was positively correlated with weed stem biomass from Year 1 and negatively correlated with percentage cranberry biomass from Year 1 and Year 2. Less than one-third of the treatment combinations recovered enough to produce at least 200 g/m2 1 yr postdisturbance (a reasonable expectation of biomass production). Growers who have low weed pressure and extensive cranberry cover on their farms can expect that disturbed areas will be recolonized by cranberry vines when they utilize adequate, but not excessive, nitrogen regimes.

WeedSOFT is a state-of-the-art decision support system for weed management in the north central region of the United States, but its accuracy to predict corn yield loss associated with later-emerging weed communities has not been adequately assessed. We conducted experiments in 2004 and 2005 to compare observed and predicted corn yield related to four establishment times of mixed-species weed communities for validation of competitive index modifier (CIM) values in WeedSOFT. Weed communities were established at VE, V2, V4, and V6 corn (emergence, second-leaf, fourth-leaf, and sixth-leaf stages, respectively), and consisted largely of annual grass and moderately competitive annual broadleaf species. Compared to weed-free corn, yield loss occurred in each of seven site-years for weed communities established at VE corn, but in only one site-year for communities established at V2 corn. No corn yield loss was associated with weed communities established at V4 or V6 corn. For communities established at VE corn, predicted corn yield differed from observed yield in all but one site year, with predicted yield less than observed yield in three site-years, and greater than observed yield in two site-years; however, nonlinear regression analyses of yield data pooled over site-years showed that fitted values were similar between predicted and observed yield. For communities established at V2 and V4 corn, predicted yield was less than observed yield in six and five site-years, respectively. For communities established at V6 corn, predicted yield was less than observed yield in three of six site-years, but was similar to observed yield in three of six site-years. These results indicated that the CIM values in WeedSOFT tended to overestimate the competitiveness of late-emerging weed communities. Corn yield data from a pooled analysis of all site-years were used to generate a revised set of growth stage CIM values, which improved the accuracy of predicted corn yield. These results should improve weed management decisions and reduce the need for herbicide applications to late-emerging weeds.

Field studies were conducted from 2005 through 2007 to determine the response of three rice cultivars (‘Cocodrie’, ‘Wells’, and ‘Lemont’) to three application timings and two formulations of pendimethalin in a stale seedbed rice production system. Pendimethalin formulated as an emulsifiable concentrate and capsule suspension was applied to rice 0, 3, and 7 d after planting. No visual injury was detected for any cultivar. Seedling density, days to 50% heading, and rice yield were not affected by pendimethalin formulation or application timing. The practice of planting cultivars with excellent seedling vigor into nondisturbed soils with greater available moisture could provide an opportunity to use pendimethalin as a preemergence herbicide for rice production.

Field trials were conducted during 2006 and 2007 and a container study was performed twice in 2007 at the Dean Lee Research and Extension Center in Alexandria, LA to evaluate the interaction of glyphosate and zinc coapplied to selected weeds. Across all experiments, no differences in either visible weed control or weed fresh weight were detected among glyphosate formulations. In the field studies, weed control was greatest when glyphosate was applied alone, in which case control of barnyardgrass, browntop millet, and Palmer amaranth ranged between 93 and 95%. When glyphosate was coapplied with formulations of zinc, control of the aforementioned weed species was reduced to 39, 39, and 45%, respectively. Visual estimates of weed control in the container studies showed glyphosate performance to be the highest (82 to 98%) in the absence of zinc for control of barnyardgrass, browntop millet, johnsongrass, ivyleaf morningglory, and redroot pigweed. Across all weed species, control was reduced 43 to 59% when zinc was coapplied with glyphosate. Similar results were noted in reduction of weed fresh weights. Results indicate that glyphosate-based weed control is reduced when coapplied with the zinc products at their current use rates. Producers should be aware of this antagonism and these coapplications should not be recommended.

Sulfentrazone is a phenyl triazolinone herbicide used for control of certain broadleaf and grass weed species. Sulfentrazone persists in soil and has residual activity beyond the season of application. A laboratory bioassay was developed for the detection of sulfentrazone in soil using root and shoot response of several crops. Shoot length inhibition of sugar beet was found to be the most sensitive and reproducible parameter for measurement of soil-incorporated sulfentrazone. The sugar beet bioassay was then used to examine the effect of soil properties on sulfentrazone phytotoxicity using 10 different Canadian prairie soils. Concentrations corresponding to 50% inhibition (I50 values) were obtained from the dose–response curves constructed for the soils. Sulfentrazone phytotoxicity was strongly correlated to the percentage organic carbon (P = 0.01) and also to percentage clay content (P = 0.05), whereas correlation with soil pH was nonsignificant (P = 0.21). Because sulfentrazone phytotoxicity was found to be soil dependent, the efficacy of sulfentrazone for weed control and sulfentrazone potential carryover injury will vary with soil type in the Canadian prairies.

Glyphosate-resistant crops will be grown for the first time in Western Australia in 2009. A survey was conducted across 150,000 km2 of the southeastern part of the Western Australian grain belt in 2007 to determine whether glyphosate-resistant Conyza populations were present. Sixty-eight Conyza populations were collected from various fields and roadside locations. These populations were collected from areas where Conyza was known to exist. Populations were screened with glyphosate and all populations were found to be glyphosate-susceptible. While no glyphosate-resistant Conyza populations were found in the southeastern grain belt of Western Australia, it provides baseline data prior to the introduction of glyphosate-resistant crops in this region. It is important to monitor the efficacy of glyphosate as resistance becomes more prevalent in weeds of various cropping systems worldwide.