Recently, roundleaved mallow, redroot pigweed, and annual smartweed species have become problems for flax producers in the Canadian prairies. The use of thifensulfuron to enhance weed control with commonly used herbicide mixtures was tested at Indian Head, SK and Morden, MB. Visible crop injury and reduced height, yield, and quality occurred at rates as low as 0.5–1.0 g/ha. Improved control of broadleaf weeds was not consistent and antagonism of grassy weed control with sethoxydim occurred.

Crambe has gained interest as an alternative crop for industrial oil production. No herbicides are currently registered in crambe and weed control strategies need to be identified if crambe is to become a viable crop. Field experiments were conducted to determine crambe tolerance to several herbicides. Crambe was tolerant to soil-applied trifluralin, pendimethalin, and cinmethylin, or DPX-A7881 applied postemergence. Postemergence applications of chlorimuron or imazethapyr were injurious to crambe.

The Office of Pesticide Programs (OPP) within the United States Environmental Protection Agency (EPA) has initiated several programs to reduce risks associated with the use of pesticides. Examples include accelerated registration of new products (including biological pesticides) that offer reduced risk to human health and the environment, and regulatory relief for products posing virtually no risk to provide replacement for more problematic pesticides. In addition, efforts are being undertaken to reduce pesticide resistance in target pests, develop joint “Environmental Stewardship” efforts between the EPA, United States Department of Agriculture (USDA), and the United States Food and Drug Administration (FDA). The new Biopesticides and Pollution Prevention Division (BPPD), established as a pilot in October 1994, has responsibility for many above functions, with special emphasis on registration of biological pesticides and development of the new Pesticide Environmental Stewardship Program (PESP). This program is designed to recognize achievements already made by farmers to reduce conventional pesticide use and to find further improvements through cooperative efforts with growers.

The agricultural-chemical industry has been offering solutions in plant protection for several decades. The primary role of Industry in weed control has mainly been to provide chemicals with increasingly attractive profiles regarding safe handling, ecological acceptance, and economical attractiveness. These objectives have been reached by significant developments, e.g. in rates, persistence, and specificity for non-target organisms. It is therefore safe to assume that in the year 2015 and beyond chemicals will continue to maintain a major role in weed control. However, as cropping systems and criteria for desirable control levels change, industry will have to change from a re-active to a pro-active participant in the development of integrated systems. Chemical solutions will be complemented by biological and agronomical methods and will be further supported by biotechnological successes in the crop area. In addition, it is anticipated that sophisticated computer models now in development will help exploit the potential of products as well as of integrated systems. Thus, fully integrated companies active in chemical, biological, and molecular-biological research and having branches in the agro-chemical as well as in the seed business will be especially suited to be driving forces in the changing world of modern weed control. The practice will ask for services much more than for single products. Industry will not only have to offer those services but at the same time assist in the education of growers to enable efficient use of the increasingly intricate methods of future weed control.

Texasweed is an annual broadleaf plant belonging to the Euphorbiaceae family and is an emerging problem in southern U.S. rice fields. Field studies were conducted in 2008 and 2009 to study the effect of flood depth on Texasweed survival and growth. The trearments were five flood depths: 0, 10, 15, 20, and 30 cm and two Texasweed growth stages: two- to three-leaf stage and four- to five-leaf stage. The experiment was conducted in a completely randomized split-plot design with three replications. Flooding conditions were created by placing potted plants in 1.3 m by 0.7 m by 0.7 m polyvinyl chloride troughs. The effect of flood depth on Texasweed growth and fruit production was evaluated using ANOVA and regression analysis. Texasweed plants were able to survive in floods up to 30 cm; however, growth and fruit production were reduced. Increasing flood depths resulted in increased plant height and greater biomass allocation to stem. Texasweed plants produced adventitious roots and a thick spongy tissue, secondary aerenchyma, in the submerged roots and stem, which may play a role in its survival under flooded conditions. The recommended flood depth for rice in Louisiana is 5 to 10 cm. A 10-cm flood in the present study caused about 30 and 15% biomass reduction in two- to three-leaf and four- to five-leaf stage Texasweed, respectively. The results, thus, suggest that flooding alone may not be a viable option for Texasweed management in drill-seeded rice. However, appropriate manipulation of flooding could enhance the effectiveness of POST herbicides. This aspect needs further investigation.

The productivity of riparian sites in managed forests can be focused to provide productive fish and wildlife habitat while yielding most of its productive capacity for other than amenity values. Establishment of habitat protection goals and measures of achievement permit flexible approaches for meeting them. Once the protection standards are set, intensive management of the woody cover is logically dependent on minimum disturbance methods, in general, for both vegetation management and harvest. Several currently registered chemical products and non-chemical methods are helpful and safe in achieving both yield and protection goals.

BAY MKH 6561, a sulfonylaminocarbonyl-triazolinone herbicide for postemergence control of annual grasses and selected broadleaf weeds in wheat, was evaluated for weed control and rotational crop (barley, pea, lentil, and mustard) injury in the Pacific Northwest. BAY MKH 6561 was applied postemergence in winter wheat at 22, 45, and 90 g ai/ha during fall 1997 and spring 1998 near Moscow, ID, Pendleton, OR, and Wilcox, WA, to determine its effect on barley, pea, lentil, and mustard planted during spring 1999. At Pendleton, BAY MKH 6561 reduced barley height 6% and grain yield 11%, when applied in the spring at 90 g/ha, and visibly injured mustard 4 to 19% when applied at 45 or 90 g/ha. All BAY MKH 6561 treatments reduced mustard seed yield 47 to 54% at Moscow and 38 to 48% at Wilcox. Pea and lentil seed yields were not affected by herbicide treatments at all locations, whereas barley was not affected at Moscow and Wilcox. In growth chamber soil bioassay experiments, fall-applied BAY MKH 6561 dissipated 10 to 48% faster at Moscow compared to Pendleton, and the predicted half-life ranged from about 68 (Moscow) to 79 d (Pendleton). Dissipation of spring-applied BAY MKH 6561 at 45 and 90 g/ha was 17 to 21% slower at Moscow than Wilcox, and the predicted half-life ranged from 60 (Wilcox) to 69 d (Moscow).

Field studies were conducted over 2 yr and two locations per year in soft red winter wheat to determine the efficacy of thifensulfuron and thifensulfuron plus DPX-L5300 (2:1 ratio) on all wild garlic reproductive bulbs. The herbicide formulations controlled wild garlic equally. Aerial bulblet control was excellent (>90%) with either herbicide regardless of application timing (March 21, April 8, and April 29) and significantly better than the standard treatment of the butoxyethanol ester of 2,4-D. Control of developing underground offset bulbs was less complete compared to aerial bulblets, and was found to depend on application time. Offset bulbs were controlled better when herbicides were applied in late March or early April compared to the April 29 treatment date. The rate response (9 to 70 g ha-1) was positive for the control offset bulb production at the two earlier dates but not at April 29. These herbicides also adversely affected the germination and viability of the bulbs that were produced.

Information on jointed goatgrass caryopsis development is currently lacking in published literature. It is hoped that through a better understanding of jointed goatgrass caryopsis ontogeny more effective weed-management strategies will be developed. Greenhouse experiments were initiated in fall 2002 and 2003 and completed the following spring seasons. Jointed goatgrass plants were started from spikelets, vernalized for 8 wk at 4 C, and grown in a greenhouse. Treatments were the number of days after anthesis (DAA) that a spike was allowed to remain on the plant before harvesting and ranged from 2 to 34 DAA, in increments of 1 (2002) or 2 (2003) d. Individual spikes were divided at harvest into three sections: top, middle, and bottom, disarticulated from the rachis, placed into a germinator, and germination recorded each day. Goatgrass spikelets germinated as early as 2 DAA, although spikelets harvested <7 DAA had <3% germination for all spike sections and were extremely variable, especially for the middle and bottom sections. Time to germination was similar for all sections of the spike. Maximum average germination of the top section was 72% compared with 86% for the bottom and middle sections. Our data suggest that factors other than developmental rate (i.e., dormancy) may affect germination in sections of the spike. A second year of the experiment was conducted for validation. Model validation suggested that although trends were similar in both years, variation in germination response might be too great for accurate, predictive model construction. The early germination shown in this research demonstrates that control measures must be implemented earlier than previously prescribed to prevent jointed goatgrass reproduction.

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.

Seedling emergence and seed bank longevity were followed in field experiments with natural populations of common crupina for 4 yr. Emergence the first fall after dissemination was 90 to 98% of all seedlings eventually to emerge from the seedbank. Seedling emergence over time did not differ between plots which either were treated with the potassium salt of picloram or were hand weeded. No viable seed remained in the soil 25 to 26 months after seed production stopped. Five locations in a common crupina infestation undergoing eradication were sampled for seed in the soil. No viable seeds were found during the first year of the eradication, and no intact seeds were found after 4 yr.

The pH of deionized water, initially adjusted to a pH of 6 to 9, all decreased to near pH 5 upon pressurization with CO2 in a backpack spray system. When deionized water contained bicarbonate (NaHCO3 or KHCO3) at 0 to 800 mg/L to buffer against a pH decrease from CO2 pressurization the return to their initial pH was more rapid than deionized water alone regardless of bicarbonate source. Acidification of spray solution following CO2 pressurization of 138, 276, or 414 kPa was similar and bicarbonate had a greater effect than spray pressure. Addition of acidifying buffer and bicarbonate to the solution resulted in an initial and post-CO2 pressurization pH range of less than one pH unit. All spray solution pH levels returned to near their initial pH following depressurization, indicating that the pH decrease was not permanent. Rate of recovery from acidification with CO2 increased with initial pH and bicarbonate concentration.

The allelopathic influence of sweet potato cultivar ‘Regal’ on purple nutsedge was compared to the influence on yellow nutsedge under controlled conditions. Purple nutsedge shoot dry weight, total shoot length and tuber numbers were significantly lower than the controls (47, 36, and 19% inhibition, respectively). The influence on the same parameters for yellow nutsedge (35, 21, and 43% inhibition, respectively) were not significantly different from purple nutsedge. Sweet potato shoot dry weight was inhibited by purple and yellow nutsedge by 42% and 45%, respectively. The major allelopathic substance from ‘Regal’ root periderm tissue was isolated and tested in vitro on the two sedges. The I50's for shoot growth, root number, and root length were 118, 62, and 44 μg/ml, respectively, for yellow nutsedge. The I50's for root number and root length were 91 and 85 μg/ml, respectively, for purple nutsedge and the I50 for shoot growth could not be calculated.

Studies were conducted in the summer and fall of 2001 in North Brunswick, NJ, and Marion County, Oregon, to evaluate the response of glyphosate-resistant and glyphosate-susceptible creeping bentgrass hybrids, colonial bentgrass, redtop, and dryland bentgrass grown as individual plants to postemergence (POST) herbicides. Glyphosate at 1.7 kg ae/ha, glufosinate at 1.7 kg ai/ha, fluazifop-P at 0.3 and 0.4 kg ai/ha, clethodim at 0.3 kg ai/ha, sethoxydim at 0.5 kg ai/ha, and a combination of glyphosate and fluazifop-P were applied 6 wk after planting. Glyphosate provided almost complete control of all susceptible bentgrass species at 4 weeks after treatment (WAT). Glufosinate provided 95% or greater control of all bentgrass species at 4 WAT, but regrowth was observed on all species in the summer experiment in Oregon. Fluazifop-P, clethodim, and sethoxydim provided slower control of bentgrass species, which ranged from 38 to 94% at 4 WAT, depending on species, herbicide, and experimental location. By 8 WAT, fluazifop-P at 0.4 kg/ha applied alone or in combination with glyphosate showed the highest levels of control (>90%) across all bentgrass species. Studies were also conducted in 2002 in the spring and summer in North Carolina to evaluate the response of a mature stand of glyphosate-susceptible ‘Penncross’ creeping bentgrass to POST herbicides. Two applications of glyphosate at 1.7 kg/ha were required to achieve 98% bentgrass control at 8 WAT. Fluazifop-P at 0.4 kg/ha, clethodim at 0.3 kg/ha, and sethoxydim at 0.4 kg/ha exhibited herbicidal activity, but two applications were required to reach (>82%) control of bentgrass at 8 WAT. Two sequential applications of clethodim or the combination of glyphosate and fluazifop-P provided 98% control of bentgrass at 8 WAT. Of the other herbicide treatments evaluated, only atrazine and sulfosulfuron provided (>80%) control at 8 WAT. The results of these studies demonstrate that fluazifop-P, clethodim, and sethoxydim have substantial herbicide activity on bentgrass species and may be viable alternatives to glyphosate for control of glyphosate-resistant creeping bentgrass and related bentgrass species in areas where they are not wanted. Glufosinate, atrazine, and sulfosulfuron also exhibited substantial herbicidal activity on bentgrass, and further research with these herbicides is warranted.

Students studying weed science would expand their knowledge by conducting targeted experiments on invasive weeds. Tamarix spp., some of the most problematic weeds known in the United States, have value for weed science education. Tamarix was used in an undergraduate laboratory course to demonstrate weed science principles for a minimal cost and with great potential for academic enhancement. The laboratory exercise was designed to teach weed science students about the difficulty associated with controlling invasive weeds even at a relatively young age in a region where plants have been detected but large-scale invasion has not occurred to emphasize the importance of early detection and rapid response. The successful execution of this exercise and the positive student response suggests that Tamarix and other weeds with similar reproductive capacities could be valuable additions to weed science curricula. Innovative approaches to teaching weed science facilitate greater learning of this complex subject by students from diverse backgrounds and academic disciplines.

Field studies were conducted to determine the effects of synthetic auxin herbicides at simulated exposure rates applied to ‘Covington’ sweetpotato propagation beds on the quality of nonrooted stem cuttings (slips). Treatments included diglycolamine salt of dicamba, 2,4-D choline plus nonionic surfactant (NIS), and 2,4-D choline plus glyphosate at 1/10, 1/33, or 1/66 of a 1X application rate (560 g ae ha−1 dicamba, 1,065 g ae ha−1 2,4-D choline, 1,130 g ae ha−1 glyphosate) applied at 2 or 4 wk after first slip harvest (WASH). Injury to sweetpotato 2 wk after treatment was greatest when herbicides were applied 2 WASH (21%) compared to 4 WASH (16%). More slip injury was caused by 2,4-D choline than by dicamba, and the addition of glyphosate did not increase injury over 2,4-D choline alone. Two weeks after the second application, sweetpotato slips were cut 2 cm above the soil surface and transplanted into production fields. In 2019, sweetpotato ground coverage 8 wk after transplanting was reduced 37% and 26% by the 1/10X rates of dicamba and 2,4-D choline plus NIS, respectively. Though dicamba caused less injury to propagation beds than 2,4-D choline with or without glyphosate, after transplanting, slips treated with 1/10X dicamba did not recover as quickly as those treated with 2,4-D choline. In 2020, sweetpotato ground coverage was 90% or greater for all treatments. Dicamba applied 2 WASH decreased marketable sweetpotato storage root yield by 59% compared to the nontreated check, whereas treatments including 2,4-D choline reduced marketable yield 22% to 29%. All herbicides applied at 4 WASH reduced marketable yield 31% to 36%. The addition of glyphosate to 2,4-D choline did not increase sweetpotato yield. Results indicate that caution should be taken when deciding whether to transplant sweetpotato slips that are suspected to have been exposed to dicamba or 2,4-D choline.

Knowledge of weed control practices and farmers’ awareness of herbicide resistance could be a basis for improving weed management programs with respect to herbicide resistance, but research on this topic is limited. This study reports current weed control practices and levels of awareness of herbicide resistance among cereal farmers of northern Greece. Face-to-face interviews were conducted with 250 cereal farmers of Evros district, based on a structured questionnaire. Most farmers (82.8%) used herbicides in cereal production, with one application per growing season. Farmers appeared divided with respect to using the same herbicide each year; the majority of the farmers (90.8%) applied crop rotation. Almost half of the farmers (47.2%) did not know what herbicide resistance is, but most farmers (75.1%) felt herbicide resistance would be a problem for them. According to their answers on nine knowledge questions about herbicide resistance, 66.8% of the farmers had good knowledge, and 33.2% had poor knowledge. Almost seven in 10 farmers (69.8%) did not consider herbicide resistance when purchasing an herbicide for use, and only 40.4% were willing to change common weed control practices to prevent herbicide resistance. Awareness of herbicide resistance did not differ by sex; poor awareness levels increased with advanced age, low education levels, and small farm size. Farmers who used chemical weed control had higher awareness levels of herbicide resistance than farmers who never used herbicides. Farmers who were keeping records of herbicide applications, those who observed low efficacy of herbicides in their field, and those who applied crop rotation had high awareness levels of herbicide resistance, whereas farmers who used the same herbicide each year had poor awareness. Findings shed light on inter-relationships between farmers’ awareness of herbicide resistance and current weed control practices that could be useful for targeted extension education.

Knotroot foxtail has become more prevalent and problematic in pastures and hayfields in the southeastern United States. Gaps exist in our knowledge of which herbicide practices are best for managing this species in bermudagrass forage production. This study was conducted to determine the efficacy of various ways to control knotroot foxtail in bermudagrass with herbicide applications in autumn, postemergence (POST), with and without also applying a herbicide in preemergence (PRE), in spring. The study was a randomized complete block with a factorial arrangement of treatments and included a nontreated control for both fall and spring timings. Glyphosate at two rates (0.35 or 0.7 kg ae ha−1), nicosulfuron (0.07 kg ai ha−1) + metsulfuron (0.012 kg ai ha−1), and hexazinone (1.3 kg ai ha−1) were applied alone in the fall or followed by indaziflam (0.067 kg ai ha−1) or pendimethalin (4.46 kg ai ha−1) in the spring. Three harvests were conducted throughout the growing season to evaluate weed species (knotroot foxtail, large crabgrass, and horsenettle) and bermudagrass biomass as well as overall species composition. The combination of fall and spring treatments did not affect weed species or bermudagrass biomass. Therefore, treatment main effects were analyzed by fall or spring application timing. A spring application of either pendimethalin or indaziflam increased bermudagrass biomass compared with that of the nontreated control. However, neither PRE herbicide effectively reduced knotroot foxtail biomass compared with the nontreated control, although pendimethalin did reduce season-long knotroot foxtail composition. Spring PRE herbicides are an effective tool for forage producers, but further research is needed to identify effective herbicides and additional approaches for the control of knotroot foxtail.

Glyphosate and paraquat are effective preplant burndown herbicide options for multicrop vegetable production that uses plastic mulch, but problematic weeds such as wild radish, cutleaf evening primrose, annual morningglory, or horseweed may not be adequately controlled with these herbicides alone. The herbicides 2,4-D and dicamba could help control these troublesome weeds prior to planting if they can be removed from plastic mulch and thus avoid crop damage. Treatments included 2,4-D (1,065 and 2,130 g ae ha−1) and dicamba (560 and 1,120 g ae ha−1) applied broadcast over plastic mulch a day before transplanting. Just before transplanting, treatments received either 0.76 cm of water via overhead irrigation or no irrigation. Plastic mulch samples were collected at application and planting to determine herbicide presence using analytical techniques, and cantaloupe and zucchini squash were subsequently transplanted on the plastic beds. Analytical ultra-high performance liquid chromatography revealed that 88% to 99% of the initial herbicide concentration was present at crop planting when irrigation was not implemented. At most, a 1/50 rate of dicamba and a 1/500 rate of 2,4-D was present at planting when overhead irrigation was applied prior to transplanting. Maximum cantaloupe and squash injury from 2,4-D with irrigation was 10% and did not influence plant growth, biomass, or yield. For dicamba with overhead irrigation, cantaloupe injury was 35%, vine lengths were reduced by 24%, and maturity was delayed, whereas squash injury ranged from 9% to 12%, with no influence on growth or yield. Without irrigation to wash herbicides from the mulch prior to planting, 60% to 100% injury of both crops occurred with both herbicides. Zucchini squash was more tolerant to dicamba than cantaloupe. Results demonstrated that 2,4-D can be adequately removed from the surface of plastic mulch with irrigation, whereas a single irrigation event was not sufficient to remove dicamba.