In an effort to find safe natural products to function in traditional agricultural chemical roles, short-chain fatty acids were evaluated as desiccants for dry beans. Desiccation was evaluated in greenhouse studies on three dry bean cultivars: ‘Montcalm’ kidney, ‘Midnight’ black turtle, and ‘Vista’ navy bean. Caprylic (C8) and pelargonic acid (C9) were the most effective in the C2 through C10 range. Effective emulsifiers with C8 were Henkel Emsorb 6900 and Henkel Emsorb 6915. Organosilicone, saponified, methylated, and ethylated seed oil activator adjuvants enhanced the efficacy of the caprylic acid. C8 was also phytotoxic to velvetleaf, giant foxtail, and common lambsquarters; esters of C6, C8, and C10 fatty acids were comparatively less effective than C8.

Growers from three counties in Virginia have recently experienced difficulty controlling shattercane in corn with acetolactate synthase (ALS)–inhibiting herbicides. Seed was collected from these locations and from a susceptible biotype and tested for resistance to imazethapyr, imazapyr, and nicosulfuron in greenhouse trials. Seedlings from these locations were also treated with glufosinate and glyphosate. Greenhouse experiments indicated that one of the four shattercane biotypes was resistant to ALS-inhibiting herbicides. Effective control of the resistant biotype was possible with glufosinate or glyphosate. Field experiments were conducted in 2003 and 2004 to determine the most effective herbicide program utilizing herbicide-tolerant/-resistant corn hybrids for the control of shattercane. Early postemergence (EP) and late postemergence (LP) applications of imazethapyr plus imazapyr or EP nicosulfuron did not control shattercane, and yield from the imidazolinone-tolerant (IT) hybrid was equivalent between these treatments and was equivalent to yield from the weedy control (WC). At 23 wk after planting (WAP), EP applications of glyphosate controlled shattercane 71 and 75% compared to only 21 and 66% with EP applications of glufosinate in 2003 and 2004, respectively. In both years, LP applications of glufosinate or glyphosate controlled shattercane better than did EP applications of glufosinate or glyphosate. Treatment timing with respect to corn yield within either the glufosinate-resistant (LL) or glyphosate-resistant (RR) corn hybrid was critical. EP treatments of glufosinate or glyphosate resulted in yields that were equivalent to yield from the weed-free control (WFC) of each hybrid. LP treatments of glufosinate or glyphosate, however, resulted in yields that were equivalent to only 90 and 91% of yield from the WFC of each hybrid, respectively.

Herbicide evaluation trials are typically conducted with the objective of rating herbicide efficacy and assessing crop yield loss. There is little if any attempt to quantify the economic risk associated with each treatment. The objective of this research was to use second-degree stochastic dominance to evaluate the economic stability of corn and soybean weed management systems between two contrasting environments. Weed management systems were evaluated in small-plot replicated trials over a 3-yr time period at two locations in southern Minnesota. One location (Waseca) had a slightly cooler and wetter environment than the second location (Lamberton). The Waseca location also had higher weed density and greater weed species diversity. Adjusted returns from weed management were calculated for each system by measuring economic returns, as determined by deducting weed management costs from the product of crop price and grain yield. Stochastic dominance is a technique that considers the entire distribution of net returns from weed management and compares these cumulative distributions as a basis for analyzing risk. Climate, soils, and weed diversity dictated differences in risk efficiency and effectiveness of the various weed management systems evaluated between the Waseca and Lamberton sites. Stochastic dominance testing is a useful tool for understanding long-term risk across environments. Results can be used to develop effective long-term weed management systems that minimize risk while maximizing profit potential.

Persian darnel control options are limited and unmanaged populations can cause substantial crop yield loss. Integrating crop diversification and higher crop seeding rates into a cropping system might improve Persian darnel management. Field experiments were conducted to determine the effect of different crops and increased crop seeding rates on Persian darnel fecundity. Persian darnel produced up to 2,800 seeds per plant and 53,000 seeds/m2 when grown without competition. Increasing crop density reduced Persian darnel tillers per plant, seed weight, and fecundity. Increasing crop density reduced Persian darnel fecundity 0.4 to 0.2% per spring wheat plant, 0.6 to 0.1% per canola plant, and 16 to 8% per sunflower plant. Persian darnel fecundity was impacted the greatest by reduced weed seedling establishment, which was caused by crop competition and seeding sunflower late in the spring preceded by a nonselective herbicide application. Results indicated delaying the seeding of spring crops or including a late-seeded warm season crop, like sunflower or safflower, in the cropping system is an effective weed management tool for reducing Persian darnel fecundity.

Experiments were conducted to investigate the effects of depth and duration of burial on seasonal germination, primary and secondary dormancy, viability, and seedling emergence of ivyleaf speedwell (Veronica hederifolia L.) seeds. The seeds were buried at 0, 5, 10, or 20 cm and retrieved from the field at monthly intervals. The exhumed seeds were germinated at 5 C. In the second experiment, seeds were stored in the laboratory after harvest and tested for germination at monthly intervals. In each experiment, nongerminated seeds were treated with triphenyltetrazolium chloride at monthly intervals to test their viability. The effects of stratification and burial depth on seedling emergence were observed for 1 yr. The seeds exhumed from the soil were dormant at the beginning of the experiment and exhibited dormancy/nondormancy/conditional dormancy cycling throughout the experiment. Depth of burial and time affected seed germination. Seeds retrieved from the soil surface germinated well initially, but germination decreased as depth of burial increased. In the dry storage experiment, seeds had a high level of primary dormancy, and viability decreased over time. Seedling emergence decreased when depth of burial increased. Seedlings emerged nonuniformly throughout the year and demonstrated typical winter annual characteristics.

In the Southern Great Plains, producers of hard red winter wheat seek sustainable methods for controlling cheat and improving economic returns. Experiments were conducted at two sites in north-central Oklahoma to determine the effect of cheat management programs, with various weed control strategies, on cheat densities and total net returns. The cheat management programs, initiated following harvest of winter wheat, included conventionally tilled, double-crop grain sorghum (Sorghum bicolor L.) followed by soybean (Glycine max L.); and continuous winter wheat. Rotating out of winter wheat for one growing season increased yield of succedent wheat up to 32% and 42% at Billings and Ponca City, respectively. Dockage due to cheat in the succedent wheat was reduced up to 78% and 87% by rotating out of winter wheat for one growing season at Billings and Ponca City, respectively. Cheat management programs including a crop rotation with herbicides applied to the grain sorghum, except for an application of atrazine + metolachlor at Ponca City, improved total net returns over the nontreated continuous wheat option. Cheat panicles in the succedent wheat were reduced up to 87% by rotation out of winter wheat for one growing season.

Experiments were conducted between 2002 and 2004 at multiple locations in Florida to determine the efficacy of aminopyralid and other herbicides on tropical soda apple (TSA) control. Aminopyralid applied at rates ≥0.08 kg ai/ha consistently provided >96% TSA control up to 335 d after treatment (DAT), while applications <0.06 kg/ha were less effective as well as inconsistent. Control of TSA with aminopyralid was often not statistically different from control with triclopyr, picloram, or dicamba. However, these responses were likely due to the variability in TSA control by triclopyr, picloram, or dicamba across several locations. For example, the standard error of the mean for TSA control with picloram at 335 DAT was 8, compared to 1 for aminopyralid. Herbicides were applied in April, January, and June, but time of year did not affect the efficacy of aminopyralid. Aminopyralid possesses soil residual activity and controlled 98% of germinating seedlings at 75 DAT, compared to 0% control for triclopyr or 2,4-D + dicamba. Therefore, aminopyralid controlled TSA from foliar applications and soil residual activity more consistently than any other herbicide evaluated in these experiments.

Corn inbreds are often more sensitive to herbicides than hybrids. Field experiments were conducted with three corn inbreds to (1) evaluate inbred sensitivity to the acetamide herbicides acetochlor, dimethenamid, flufenacet, and metolachlor, (2) compare the effects of various crop safeners in combination with acetochlor and metolachlor, and (3) measure the effect of herbicide microencapsulation on acetochlor injury. Herbicides were applied preemergence at the registered rate and at two, three, or four times the registered rate in corn. Injury ratings, plant population, and the percentage of plants showing acetamide injury symptoms were used to measure herbicide effect. The inbreds ‘Mo17’ and ‘Great Lakes 15’ (GL15) were sensitive to acetamide injury. Reductions in plant population and increases in the injury rating and the percentage of injured plants were caused by acetochlor, dimethenamid, flufenacet, metolachlor, and flufenacet + metribuzin when applied at three times the registered rate. The inbred ‘B73’ was not injured. The safeners benoxacor and dichlormid reduced injury caused by metolachlor. The percentage of plants injured by metolachlor 15 days after treatment (DAT) was lower when benoxacor was the safener compared to dichlormid. By 28 DAT, plants treated with safeners recovered from injury, and there were no differences between the treatments. The safeners dichlormid and furilazole reduced, but did not always eliminate, injury caused by acetochlor applied at three times the registered rate. Microencapsulation of acetochlor reduced injury to GL15. When the safeners dichlormid or furilazole were included in an acetochlor formulation, microencapsulation did not further reduce corn injury.

Putatively resistant (PR) and putatively susceptible (PS) common waterhemp populations were grown in the greenhouse and sprayed at the three- to four-leaf stage with glyphosate (0.63 kg ae/ha). Surviving plants from PR populations and randomly selected plants from PS populations were clonally propagated and the clones were sprayed with 0.1 to 10.0 kg/ha glyphosate. The glyphosate rates required to reduce growth by 50% (GR50) among the clones were relatively similar, but the concentration required to reduce growth by 90% (GR90) ranged from 1.5 to 16.3 kg/ha. The concentration of glyphosate required to kill 90% of plants (LD90) ranged from 2.3 kg/ha to over 10.0 kg/ ha. This range of responses to glyphosate in common waterhemp clones from different parts of the Midwestern United States indicates a risk of evolution of resistance in common waterhemp populations that are repeatedly selected by applications of glyphosate in the field.

Spring wheat competitive ability has recently been demonstrated to co-vary with seed size. The objective of this study was to determine if spring wheat seed size would influence the effects of variable tralkoxydim rates on wild oat control, wheat yield, and economic returns. The factorial treatment arrangement consisted of three spring wheat seed size classes and five tralkoxydim rates. Wild oat density, panicles, and biomass decreased as spring wheat seed size and tralkoxydim rate increased, with the combined effect being additive. Wild oat variables decreased in a log-logistic manner as tralkoxydim rate increased during both years. However, tralkoxydim was less effective in 2000 than 2002, as indicated by the higher dosage required to reduce the wild oat variables by 50% (greater I50 values). In contrast, the effect of large seeded wheat in suppressing wild oat was more consistently expressed, with wild oat variables decreasing linearly as seed size increased. Wheat yield and economic returns increased exponentially as tralkoxydim rate increased. At the same time, wheat yield and economic returns were greater for wheat plants derived from large seed compared to those derived from small seed. Averaged over all other factors, adjusted gross returns of 578, 657, and 703 $/ha were realized for the small, medium, and large seed size classes, respectively. The combined use of large seeded wheat plus tralkoxydim applications provided greater wild oat control than did either single tactic. The use of large seeded wheat had a stabilizing effect that increased the consistency and durability of the weed management system while simultaneously improving economic returns.

Decision support systems (DSSs) have been developed to assist producers and consultants with weed management decisions. WeedSOFT is a DSS currently used in several states in the north-central region of the United States. Accurate estimates of crop yield loss due to weed interference are required for cost-effective weed management recommendations. WeedSOFT uses competitive indices (CIs) to predict crop yield loss under multiple weed species, weed densities, and relative times of weed emergence. Performance of several WeedSOFT versions to predict soybean yield loss from weed competition was evaluated using CI values in WeedSOFT version 9.0 compared to new CI values calculated from weed dry matter, weed volume, and soybean yield loss in two soybean row spacings (19 and 76 cm) and two relative weed emergence times (at soybean emergence and first trifoliate leaf stage). Overall, new CI values improved predictions of soybean yield loss by as high as 63%. It was especially true with using new CI values based on yield loss compared to those based on weed dry matter or weed volume. However, there were inconsistencies in predictions for most weed species, suggesting that additional modifications are needed to further improve soybean yield loss predictions.

Phenoxy herbicides are frequently used to control volunteer canola populations. However, there have been claims that poor control could be due to cold acclimation of canola plants in the spring. The objective of this study was to determine whether cold acclimation or growth stage affected the response of canola volunteers to herbicides. In a growth room experiment, canola plants were prehardened and cold acclimated or were grown at 20/12 C and treated with one of six 2,4-D doses. Cold acclimation as achieved by this experiment affected upper and lower asymptotes of the dose–response curve but not the herbicide dose required to reduce canola weight by 50% relative to the nontreated control (GR50), indicating limited cold-related effects on canola tolerance to 2,4-D. Field experiments, conducted in the provinces of Québec and Saskatchewan, examined the effects of canola growth stage on the efficacy of 2,4-D, MCPA, and carfentrazone. Comparisons of the estimates from the dose–response curves confirmed that herbicide efficacy was consistently greater when canola plants were treated at an early growth stage, regardless of cultivar or herbicide used. The GR50 estimates for canola plants treated at a later growth stage exceeded the recommended rates. Some canola plants grown as volunteers in a wheat crop survived 2,4-D or MCPA treatments at 0.5× and 1× rates and produced up to 148 seeds/m2. Efficient control of canola volunteers will be obtained when plants are sprayed at an early growth stage, but near-total control will be highly desirable in order to restrict seedbank buildup, particularly when dealing with canola cultivars with different herbicide-resistant traits.

Herbicide-resistant cultivars account for over 90% of the canola grown in western Canada and cultivars resistant to glyphosate dominate the market. Field experiments were conducted at three locations in Alberta to compare the glyphosate system with more traditional herbicide regimes. Glyphosate applied before seeding in spring resulted in better weed control, lower dockage, and higher canola yield and net return than 2,4-D applied in the fall. Glyphosate applied once (two- to four-leaf canola) or twice (two- to four-leaf followed by five- to six-leaf canola) in-crop provided similar weed control, dockage, and canola yield as ethalfluralin applied PRE in the fall followed by an in-crop mixture of sethoxydim, ethametsulfuron, and clopyralid; and superior weed control and canola yield and lower dockage than ethalfluralin alone or an in-crop mixture of sethoxydim and ethametsulfuron. The in-crop glyphosate applications resulted in higher net revenues than the other treatments. There was little or no advantage to applying glyphosate twice compared with once in-crop. The amount of active ingredient entering the environment varied with the herbicide regime but was lower with the glyphosate system than with most of the traditional regimes, especially when glyphosate was applied only once in-crop.

Reduced-rate zone herbicide application (ZHA) consists of banding reduced herbicide rates between crop rows (≤ full broadcast registered rate, 1×) and banding much reduced herbicide rates over crop rows (≪ 1×). The objective of this research was to compare the mechanically complicated dual-boom ZHA sprayer with a much simpler, single-boom ZHA sprayer for controlling giant foxtail and common waterhemp in field corn in 2003 and 2004 in Missouri. The dual-boom ZHA sprayer employed two different herbicide solutions, which were propelled through two booms on separate sprayer systems to apply different herbicide rates over in-row and between-row areas while maintaining similar carrier volumes and coverage through two booms. In contrast, the single-boom ZHA sprayer is a mechanically simpler system in which both herbicide rates and carrier volumes were varied across one boom over in-row (IR) and between-row (BR) areas. In single-boom ZHA, two different nozzle tips were alternated on one boom over in-row and between-row areas, the number of nozzles per boom was doubled, and the distance between nozzles was halved compared with a conventional sprayer boom. In a 2-yr study, these different ZHA sprayers were used to apply preemergence atrazine + S-metolachlor between and over crop rows at various reduced rates (1× = 2,240 + 1,750 g ai/ha, respectively). Among all single- and dual-boom ZHA sprayer treatments and the weed-free checks, corn yields and in-row total weed cover were statistically indistinguishable for both years and for between-row total weed cover in 1 of 2 yr. In both years, a single-boom ZHA system prevented yield loss from competing weeds as effectively as the dual-boom ZHA system. The new single-boom ZHA system is a mechanically simple, inexpensive, generic alternative for reducing herbicide rates and lowering input costs.

Virginia buttonweed control in warm-season turfgrass species requires high application rates and/or repeated applications of herbicides (or both) with an auxin-type mode of action. These treatments often lead to unacceptable turfgrass injury. Diflufenzopyr functions as a synergist with auxin-type herbicides, and it has been suggested that it may do the same when combined with pyridine herbicides such as fluroxypyr. The objective of this field and laboratory research was to determine whether Virginia buttonweed control could be improved with admixtures of fluroxypyr and diflufenzopyr without unacceptable turf injury. Treatments consisted of fluroxypyr applied alone at 140 and 280 g ae/ha, diflufenzopyr alone at 70 and 140 g/ha, and all possible two-way admixtures. Treatments were applied to a hybrid bluegrass ‘Thermal blue’ infested with Virginia buttonweed. Sod of centipedegrass ‘common’, hybrid bermudagrass ‘Tifway’, hybrid zoysiagrass ‘Emerald’, and St. Augustinegrass ‘Raleigh’, which had been previously established in pots, were treated simultaneously and returned to a greenhouse. Fluroxypyr plus diflufenzopyr at 280 and 70 g/ha, respectively, controlled Virginia buttonweed nearly 40% more than fluroxypyr alone. Turfgrass injury was species-dependent, and was generally either equivalent to or less than that obtained with fluroxypyr alone. Radiotracer studies established that, depending upon the turfgrass species, fluroxypyr absorption was either not influenced or reduced by the addition of diflufenzopyr. Neither root nor foliar absorption of fluroxypyr by Virginia buttonweed was influenced by diflufenzopyr. Translocation of foliar-absorbed fluroxypyr was reduced, but translocation of root-absorbed fluroxypyr was increased by diflufenzopyr. The diflufenzopyr-induced synergism may indicate that a significant portion of the applied fluroxypyr was absorbed by roots or by other subsoil tissues, or both.

A laboratory study was conducted in 2003 at Louisiana State University in Baton Rouge, LA, to evaluate the interactive effects of bensulfuron or halosulfuron on clomazone in terms of rice foliar bleaching and chlorophyll content. Clomazone was applied alone at 0 and 1.227 μg/ml (672 g/ha) or in combination with bensulfuron at 0.0276 μg ai/ml (42 g ai/ha) or halosulfuron at 0.0345 μg ai/ml (53 g ai/ha) in a hydroponic solution. Bensulfuron and halosulfuron were also applied alone. Rice cultivars evaluated included short-grain ‘Pirogue’, medium-grain ‘Bengal’, and long-grain ‘Cocodrie’. Bensulfuron and halosulfuron, applied in a hydroponic solution, safened medium-grain Bengal, long-grain Cocodrie, and short-grain Pirogue at 21 d after treatment (DAT) from foliar bleaching caused by clomazone. Chlorophyll a and b and total chlorophyll content of all three rice cultivars decreased when treated with clomazone treatment. Only chlorophyll content of Cocodrie was increased by the addition of bensulfuron and halosulfuron compared with a single application of clomazone.

Field studies were conducted in 2002 and 2003 in New Jersey to determine the length of time after a bispyribac-sodium application at which creeping bentgrass, Kentucky bluegrass, and perennial ryegrass can be safely reseeded. Bispyribac at 148 or 296 g ai/ha was applied 6, 4, 2, or 1 week before seeding (WBS). Bispyribac at 148 g/ha applied 1 WBS reduced ground cover of creeping bentgrass and Kentucky bluegrass at 3 weeks after seeding (WAS) by 30 and 42% as compared to the nontreated check, respectively. Reductions in Kentucky bluegrass and creeping bentgrass ground cover from bispyribac at 296 g/ha applied 1 WBS were evident at 28 WAS, whereas perennial ryegrass recovered from initial reductions in ground cover by this time. Applications made 6 to 2 weeks before seeding did not adversely affect ground cover of any species at any evaluation date as compared to the nontreated check. These studies suggest creeping bentgrass, Kentucky bluegrass, and perennial ryegrass can be safely reseeded 2 weeks after a bispyribac application. However, ground cover may be reduced by bispyribac applied 1 WBS.

A laboratory bioassay was conducted to describe the effects of cold stratification and solid matrix priming (SMP®) on the germination response of common lambsquarters and Pennsylvania smartweed seeds. Treating seeds of common lambsquarters with a combination of cold stratification and SMP resulted in 78% germination compared with 13% in control seeds. Analogous treatments of Pennsylvania smartweed seeds resulted in 22% germination compared with 1% for control. Improved germination of common lambsquarters and Pennsylvania smartweed seeds suggested that the combination of cold stratification and SMP treatments have potential for improving seed germination in other weed species that exhibit high levels of seed dormancy.

Prescribed burning has primarily been used as a tool for the control of invasive late-season annual broadleaf and grass species, particularly yellow starthistle, medusahead, barb goatgrass, and several bromes. However, timely burning of a few invasive biennial broadleaves (e.g., sweetclover and garlic mustard), perennial grasses (e.g., bluegrasses and smooth brome), and woody species (e.g., brooms and Chinese tallow tree) also has been successful. In many cases, the effectiveness of prescribed burning can be enhanced when incorporated into an integrated vegetation management program. Although there are some excellent examples of successful use of prescribed burning for the control of invasive species, a limited number of species have been evaluated. In addition, few studies have measured the impact of prescribed burning on the long-term changes in plant communities, impacts to endangered plant species, effects on wildlife and insect populations, and alterations in soil biology, including nutrition, mycorrhizae, and hydrology. In this review, we evaluate the current state of knowledge on prescribed burning as a tool for invasive weed management.