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Soil-applied herbicides are important for controlling weeds in many crops but risk damage to susceptible rotational crops if they persist. Field studies were conducted in Powell, Wyoming from 2015 through 2017 to evaluate the effect of reduced water availability on soil-applied herbicide dissipation. Eight soil-applied herbicides, applied to dry bean or corn, were exposed to three season-long irrigation treatments (100, 85, and 70% of estimated crop evapotranspiration [ETc]) by overhead sprinkler. Soil samples were collected to a depth of 10 cm from 0 to 140 d after application, and soil herbicide concentrations were quantified using gas or liquid chromatography and mass spectrometry. Herbicide concentrations were regressed over time to produce a soil half-life estimate for each herbicide and irrigation treatment. Reduced irrigation decreased dry bean yield by up to 77%, and corn yield by up to 50%. After adjusting for precipitation, the lowest irrigation treatment received 78% as much water as the full irrigation treatment in 2015 and 76% in 2016. This significantly increased the soil half-life of imazethapyr, but did not increase the soil half-life of atrazine, pyroxasulfone, saflufenacil, ethalfluralin, trifluralin, or pendimethalin. Reduced irrigation did not increase carryover injury to rotational crops from these herbicides one year after application. Instead, carryover response was determined by the inherent persistence of individual herbicides. Imazethapyr (0.1 kg ai ha-1) injured rotational sugar beet, and isoxaflutole (0.1 kg ai ha-1) injured rotational dry bean. Pyroxasulfone (0.2 kg ai ha-1), atrazine (2.0 kg ai ha-1), saflufenacil (0.1 kg ai ha-1) + dimethenamid-P (0.6 kg ai ha-1), ethalfluralin (0.8 kg ai ha-1), trifluralin (0.6 kg ai ha-1), and pendimethalin (1.1 kg ai ha-1) did not injure rotational crops regardless of irrigation treatment. Drought stress sufficient to cause up to 77% crop yield loss did not increase soil-applied herbicide carryover.
Development of integrated weed management strategies requires knowledge of weed emergence timing and patterns, which are regulated primarily by water and thermal requirements for seed germination. Laboratory experiments were conducted in fall 2017 to fall 2018 to quantify the effect of osmotic potential and temperature on germination of 44 kochia [Bassia scoparia (L.) A.J. Scott] populations under controlled conditions. Bassia scoparia populations were collected in fall 2016 from northern (near Huntley, MT, and Powell, WY) and southern (near Lingle, WY, and Scottsbluff, NE) regions of the U.S. Great Plains. Ten osmotic potentials from 0 to −2.1 MPa and eight constant temperatures from 4 to 26 C were evaluated. Response of B. scoparia populations to osmotic potential did not differ between the northern and southern regions. At an osmotic potential of 0 MPa, all B. scoparia populations had greater than 98% germination, and the time to achieve 50% germination (t50) was less than 1 d. At −1.6 MPa, 25% of seeds of all B. scoparia populations germinated. Osmotic potentials of −0.85 and −1.9 MPa reduced B. scoparia germination by 10% and 90%, respectively. Regardless of temperature regime, all populations exhibited greater than 88% germination. The germination rate was highest at temperatures between 15 to 26 C and did not differ between populations from northern versus southern regions. At this temperature range, all populations had a t50 of less than 1 d. However, at 4 C, B. scoparia populations from the northern region had a higher germination rate (5 h) and cumulative germination (7%) than populations from the southern region. Overall, these results indicate a wide range of optimum temperatures and osmotic potential requirements for B. scoparia germination.
Understanding the effects of crop management practices on weed survival and seed production is imperative in improving long-term weed management strategies, especially for herbicide-resistant weed populations. Kochia [Bassia scoparia (L.) A.J. Scott] is an economically important weed in western North American cropping systems for many reasons, including prolific seed production and evolved resistance to numerous herbicide sites of action. Field studies were conducted in 2014 in a total of four field sites in Wyoming, Montana, and Nebraska to quantify the impact of different crop canopies and herbicide applications on B. scoparia density and seed production. Crops used in this study were spring wheat (Triticum aestivum L.), dry bean (Phaseolus vulgaris L.), sugar beet (Beta vulgaris L.), and corn (Zea mays L.). Herbicide treatments included either acetolactate synthase (ALS) inhibitors effective on non-resistant B. scoparia or a non–ALS inhibiting herbicide effective for both ALS-resistant and ALS-susceptible B. scoparia. Bassia scoparia density midseason was affected more by herbicide choice than by crop canopy, whereas B. scoparia seed production per plant was affected more by crop canopy compared with herbicide treatment. Our results suggest that crop canopy and herbicide treatments were both influential on B. scoparia seed production per unit area, which is likely a key indicator of long-term management success for this annual weed species. The lowest germinable seed production per unit area was observed in spring wheat treated with non–ALS inhibiting herbicides, and the greatest germinable seed production was observed in sugar beet treated with ALS-inhibiting herbicides. The combined effects of crop canopy and herbicide treatment can minimize B. scoparia establishment and seed production.
Field studies were conducted from 2009 through 2011 at the Sustainable Agriculture Research and Extension Center near Lingle, Wyoming, to evaluate great northern bean response to PRE flumioxazin mixed with either trifluralin, pendimethalin, or ethalfluralin. Seven treatments were arranged in a randomized complete block with three or four replicates y−1. The soil texture of the study site was loam in 2009 and 2011, and sandy loam in 2010. Soil organic matter ranged from 1.4% to 1.8%. Treatments included flumioxazin plus trifluralin, flumioxazin plus pendimethalin, flumioxazin plus ethalfluralin, ethalfluralin plus EPTC, imazamox plus bentazon (POST), hand-weeded control, and nontreated control. Dry bean density 4 wk after planting differed among herbicide treatments (P < 0.001). Treatments that included flumioxazin reduced dry bean density 54% compared with treatments without flumioxazin. Dry bean yield was influenced by dry bean density; on average, yield in flumioxazin-containing herbicide treatments was 30% less than treatments not containing flumioxazin, even though weed control was generally greater in flumioxazin treatments.
Kochia is one of the most problematic weeds in the United States. Field studies were conducted in five states (Wyoming, Colorado, Kansas, Nebraska, and South Dakota) over 2 yr (2010 and 2011) to evaluate kochia control with selected herbicides registered in five common crop scenarios: winter wheat, fallow, corn, soybean, and sugar beet to provide insight for diversifying kochia management in crop rotations. Kochia control varied by experimental site such that more variation in kochia control and biomass production was explained by experimental site than herbicide choice within a crop. Kochia control with herbicides currently labeled for use in sugar beet averaged 32% across locations. Kochia control was greatest and most consistent from corn herbicide programs (99%), followed by soybean (96%) and fallow (97%) herbicide programs. Kochia control from wheat herbicide programs was 93%. With respect to the availability of effective herbicide options, glyphosate-resistant kochia control was easiest in corn, soybean, and fallow, followed by wheat; and difficult to manage with herbicides in sugar beet.
Field and greenhouse experiments were conducted from 2013 to 2015 at the University of Wyoming to evaluate the response of Beta vulgaris (L.) to reflected-light quality. Large-pail field studies included a factorial arrangement of three varieties of B. vulgaris (sugar beet, table beet, and Swiss chard) and reflected-light treatments (using either colored plastic mulch, grass, or bare-soil controls). Greenhouse studies included sugar beet as influenced by either grass or soil surroundings. In all studies, grass was grown in separate containers from B. vulgaris, so there was no root interaction. Grass was clipped regularly to prevent shading and competition for sunlight. Reflected light from different-colored plastic mulches (red, blue, green, black, clear) did not affect B. vulgaris growth. However, reflected light from the grass reduced the number of leaves in all B. vulgaris varieties such that there were 10 to 14 fewer leaves in B. vulgaris surrounded by grass compared with the soil treatment at 90 d after planting in the field study. Shade avoidance cues from surrounding grass reduced B. vulgaris total leaf area by 49% to 66%, leaf biomass by 21% to 30%, and root biomass by 70% to 72%. Similar results were observed in greenhouse experiments, where the grass treatment reduced sugar beet leaf biomass by 48% to 57% and root biomass by 35% to 64%. Shade avoidance cues have the potential to significantly reduce B. vulgaris yield, even in the absence of direct resource competition from weeds.
The objective of this WSSA Weed Loss Committee report is to provide quantitative data on the potential yield loss in sugar beet due to weed interference from the major sugar beet growing areas of the United States and Canada. Researchers and extension specialists who conducted research on weed control in sugar beet in the United States and Canada provided quantitative data on sugar beet yield loss due to weed interference in their regions. Specifically, data were requested from weed control studies in sugar beet from up to 10 individual studies per calendar year over a 15-yr period between 2002 and 2017. Data collected indicated that if weeds are left uncontrolled under optimal agronomic practices, growers in Idaho, Michigan, Minnesota, Montana, Nebraska, North Dakota, Ontario, Oregon, and Wyoming would potentially lose an average of 79%, 61%, 66%, 68%, 63%, 75%, 83%, 78%, and 77% of the sugar beet yield. The corresponding monetary loss would be approximately US$234, US$122, US$369, US$43, US$40, US$211, US$12, US$14, and US$32 million, respectively. The average yield loss due to weed interference for the primary sugar beet growing areas of North America was estimated to be 70%. Thus, if weeds are not controlled, growers in the United States would lose approximately 22.4 million tonnes of sugar beet yield valued at approximately US$1.25 billion, and growers in Canada would lose approximately 0.5 million tonnes of sugar beet yield valued at approximately US$25 million. The high return on investment in weed management highlights the importance of continued weed science research for sustaining high crop yield and profitability of sugar beet production in North America.
A meta-analysis of 11 previously published field studies was conducted with the objectives being to (1) estimate the no observable effects dose (NOED) for dicamba on susceptible soybean; (2) evaluate available evidence for hormesis, or increased soybean yield in response to low doses of dicamba; (3) estimate the dose of dicamba likely to cause measurable soybean yield loss under field conditions; and (4) quantify the relationship between visible injury symptoms and soybean yield loss. All studies that included visible injury data (N=7) reported injury symptoms at the lowest nonzero dicamba dose applied (as low as 0.03 g ae ha−1), and therefore a NOED could not be estimated from the existing peer-reviewed literature. Based on statistical tests for hormesis, there is insufficient evidence to support any claim of increased soybean yield at low dicamba doses. Future research should include a range of dicamba doses lower than 0.03 g ha−1 to estimate a NOED and determine whether a hormesis effect is possible at or below dicamba doses that cause visible injury symptoms. Soybean is more susceptible to dicamba when exposed at flowering (R1 to R2 stage) compared with vegetative stages (V1 to V7). A dicamba dose of 0.9 g ha−1 (95% CI=0.08 to 1.7) at the flowering stage was estimated to cause 5% soybean yield loss. When exposed at vegetative stages, dicamba doses that cause less than 30% visible injury symptoms (95% CI=23 to 49%) appear unlikely to cause greater than 5% soybean yield loss; however, if soybean is exposed at flowering, visible injury symptoms greater than 12% (95% CI=8 to 16%) are likely to be associated with at least 5% soybean yield loss.
Seven half-day regional listening sessions were held between December 2016 and April 2017 with groups of diverse stakeholders on the issues and potential solutions for herbicide-resistance management. The objective of the listening sessions was to connect with stakeholders and hear their challenges and recommendations for addressing herbicide resistance. The coordinating team hired Strategic Conservation Solutions, LLC, to facilitate all the sessions. They and the coordinating team used in-person meetings, teleconferences, and email to communicate and coordinate the activities leading up to each regional listening session. The agenda was the same across all sessions and included small-group discussions followed by reporting to the full group for discussion. The planning process was the same across all the sessions, although the selection of venue, time of day, and stakeholder participants differed to accommodate the differences among regions. The listening-session format required a great deal of work and flexibility on the part of the coordinating team and regional coordinators. Overall, the participant evaluations from the sessions were positive, with participants expressing appreciation that they were asked for their thoughts on the subject of herbicide resistance. This paper details the methods and processes used to conduct these regional listening sessions and provides an assessment of the strengths and limitations of those processes.
Herbicide resistance is ‘wicked’ in nature; therefore, results of the many educational efforts to encourage diversification of weed control practices in the United States have been mixed. It is clear that we do not sufficiently understand the totality of the grassroots obstacles, concerns, challenges, and specific solutions needed for varied crop production systems. Weed management issues and solutions vary with such variables as management styles, regions, cropping systems, and available or affordable technologies. Therefore, to help the weed science community better understand the needs and ideas of those directly dealing with herbicide resistance, seven half-day regional listening sessions were held across the United States between December 2016 and April 2017 with groups of diverse stakeholders on the issues and potential solutions for herbicide resistance management. The major goals of the sessions were to gain an understanding of stakeholders and their goals and concerns related to herbicide resistance management, to become familiar with regional differences, and to identify decision maker needs to address herbicide resistance. The messages shared by listening-session participants could be summarized by six themes: we need new herbicides; there is no need for more regulation; there is a need for more education, especially for others who were not present; diversity is hard; the agricultural economy makes it difficult to make changes; and we are aware of herbicide resistance but are managing it. The authors concluded that more work is needed to bring a community-wide, interdisciplinary approach to understanding the complexity of managing weeds within the context of the whole farm operation and for communicating the need to address herbicide resistance.
In 1994, the National Jointed Goatgrass Research Program was initiated with funding from a special USDA grant. The 15-yr program provided $4.1 million to support jointed goatgrass (Aegilops cylindrica Host.) research and technology transfer projects in 10 western states. These projects resulted in approximately 80 refereed manuscripts, including journal articles and extension publications. The research covered various topics related to the biology and ecology of jointed goatgrass as well as its management and control in wheat (Triticum aestivum L.) production systems. This review summarizes the research on jointed goatgrass published after Donald and Ogg’s 1991 review, most of which was conducted as part of the USDA-funded National Jointed Goatgrass Research Program. Specific topics that were studied and reviewed here include A. cylindrica genetics, especially as it relates to gene flow and hybridization rates with wheat and fertility of the resulting hybrids; vernalization requirements; seed dormancy, longevity, and germination requirements; competitiveness with wheat; and herbicide resistance acquired through evolution or gene flow from wheat. With respect to management, a wide variety of practices were evaluated, including various tillage types and frequencies; crop rotations, especially diversified wheat production systems that include spring-seeded annual crops; competitive wheat cultivars, seeding dates, seeding density, and row spacing; fertility management, including nitrogen application timing and placement; and field burning. Finally, many studies evaluated the use of herbicides, especially the introduction of imazamox in imidazolinone-resistant wheat cultivars, as well as comparison of adjuvant systems and application timings. In addition to the many management practices that were studied individually, several integrated management systems were evaluated that combined crop rotations, tillage, and herbicide programs. Between 1993 and 2013, weed scientists in 14 western states estimated that jointed goatgrass infestations decreased by 45% to 55% and attributed the reduction to the implementation of more diverse crop rotations, improved cultural practices, and use of imazamox-resistant wheat technology. This is evidence that the practical implications of the National Jointed Goatgrass Research Program have been successfully implemented by growers throughout the western United States.
Earlier reports have summarized crop yield losses throughout various North American regions if weeds were left uncontrolled. Offered here is a report from the current WSSA Weed Loss Committee on potential yield losses due to weeds based on data collected from various regions of the United States and Canada. Dry bean yield loss estimates were made by comparing dry bean yield in the weedy control with plots that had >95% weed control from research studies conducted in dry bean growing regions of the United States and Canada over a 10-year period (2007 to 2016). Results from these field studies showed that dry bean growers in Idaho, Michigan, Montana, Nebraska, North Dakota, South Dakota, Wyoming, Ontario, and Manitoba would potentially lose an average of 50%, 31%, 36%, 59%, 94%, 31%, 71%, 56%, and 71% of their dry bean yield, respectively. This equates to a monetary loss of US $36, 40, 6, 56, 421, 2, 18, 44, and 44 million, respectively, if the best agronomic practices are used without any weed management tactics. Based on 2016 census data, at an average yield loss of 71.4% for North America due to uncontrolled weeds, dry bean production in the United States and Canada would be reduced by 941,000,000 and 184,000,000 kg, valued at approximately US $622 and US $100 million, respectively. This study documents the dramatic yield and monetary losses in dry beans due to weed interference and the importance of continued funding for weed management research to minimize dry bean yield losses.
Genetically engineered (GE) herbicide-resistant crops have been widely adopted by farmers in the United States and other countries around the world, and these crops have caused significant changes in herbicide use patterns. GE crops have been blamed for increased problems with herbicide-resistant weeds (colloquially called by the misnomer “superweeds”); however, there has been no rigorous analysis of herbicide use or herbicide-resistant weed evolution to quantify the impact of GE crops on herbicide resistance. Here, I analyze data from the International Survey of Herbicide Resistant Weeds and the USDA and demonstrate that adoption of GE corn varieties did not reduce herbicide diversity, and therefore likely did not increase selection pressure for herbicide-resistant weeds in that crop. Adoption of GE herbicide-resistant varieties substantially reduced herbicide diversity in cotton and soybean. Increased glyphosate use in cotton and soybean largely displaced herbicides that are more likely to select for herbicide-resistant weeds, which at least partially mitigated the impact of reduced herbicide diversity. The overall rate of newly confirmed herbicide-resistant weed species to all herbicide sites of action (SOAs) has slowed in the United States since 2005. Although the number of glyphosate-resistant weeds has increased since 1998, the evolution of new glyphosate-resistant weed species as a function of area sprayed has remained relatively low compared with several other commonly used herbicide SOAs.
Timing of weed emergence and seed persistence in the soil influence the ability to implement timely and effective control practices. Emergence patterns and seed persistence of kochia populations were monitored in 2010 and 2011 at sites in Kansas, Colorado, Wyoming, Nebraska, and South Dakota. Weekly observations of emergence were initiated in March and continued until no new emergence occurred. Seed was harvested from each site, placed into 100-seed mesh packets, and buried at depths of 0, 2.5, and 10 cm in fall of 2010 and 2011. Packets were exhumed at 6-mo intervals over 2 yr. Viability of exhumed seeds was evaluated. Nonlinear mixed-effects Weibull models were fit to cumulative emergence (%) across growing degree days (GDD) and to viable seed (%) across burial time to describe their fixed and random effects across site-years. Final emergence densities varied among site-years and ranged from as few as 4 to almost 380,000 seedlings m−2. Across 11 site-years in Kansas, cumulative GDD needed for 10% emergence were 168, while across 6 site-years in Wyoming and Nebraska, only 90 GDD were needed; on the calendar, this date shifted from early to late March. The majority (>95%) of kochia seed did not persist for more than 2 yr. Remaining seed viability was generally >80% when seeds were exhumed within 6 mo after burial in March, and declined to <5% by October of the first year after burial. Burial did not appear to increase or decrease seed viability over time but placed seed in a position from which seedling emergence would not be possible. High seedling emergence that occurs very early in the spring emphasizes the need for fall or early spring PRE weed control such as tillage, herbicides, and cover crops, while continued emergence into midsummer emphasizes the need for extended periods of kochia management.
Volunteer corn can affect dry bean by reducing yields; expanding the life cycle of insects, mites, and pathogens; interfering with harvest; and contaminating bean seed. Field studies were conducted at Lingle, WY, and Scottsbluff, NE, to determine the relationship between volunteer corn density and dry bean yield, establish the proper time of volunteer corn removal, and determine whether dry bean yield was affected by the method used to remove volunteer corn. Volunteer corn reduced dry bean yields, as recorded in other crops. Growing conditions for each location were different, as indicated by the accumulated growing degree days (GDD): Lingle 2008 (990), Lingle 2009 (780), and Scottsbluff 2009 (957). No difference in dry bean yields was observed between hand removal of volunteer corn and herbicide application. Dry bean yield loss increased with longer periods of volunteer corn competition and ranged from 1.2 to 1.8% yield loss for every 100 GDD that control was delayed. Control measures should be implemented 15 to 20 d after planting when volunteer corn densities are close to 1 plant m−2. Dry bean yield losses also increased as volunteer corn densities increased, with losses from 6.5 to 19.3% for 1 volunteer corn plant m−2. Based on 2015 prices, the cost of controlling volunteer corn would be the equivalent of 102 kg ha−1 of dry bean, and potential losses above 4% would justify control and should not be delayed beyond 15 to 20 d after planting.
Diflufenzopyr is a synergist that improves broadleaf weed control when mixed with certain auxinic herbicides. In nonagricultural settings, it is only available in a premix with dicamba, which is labeled for noncrop sites, pasture, hay, and rangeland. Our objectives were to determine the influence of diflufenzopyr + dicamba when applied with auxinic herbicides for Russian knapweed control. Studies were conducted near Ethete, WY, from 2005 to 2008 in a pasture heavily infested with Russian knapweed. Treatments were applied in the fall (September) and included aminopyralid, clopyralid, clopyralid + 2,4-D, clopyralid + triclopyr, and picloram at standard and reduced rates, with and without diflufenzopyr + dicamba. At 12 and at 24 mo after treatment (MAT), diflufenzopyr + dicamba did not influence Russian knapweed control when applied with standard rates of aminopyralid, clopyralid, clopyralid + 2,4-D, clopyralid + triclopyr, or picloram. All of these treatments except clopyralid + 2,4-D consistently provided ≥ 80% control 24 MAT. Reduced-rate herbicide interactions with diflufenzopyr + dicamba were also not significant at 12 MAT. However, at 24 MAT, aminopyralid applied with diflufenzopyr + dicamba controlled Russian knapweed 83% compared with 59% when aminopyralid was applied alone. Russian knapweed control with all other reduced-rate treatments, except picloram, fell below 80%. These results indicate that diflufenzopyr + dicamba does not generally improve Russian knapweed control at 12 or 24 MAT with either standard or reduced rates of typical fall, auxinic herbicide treatments.
Glyphosate-resistant (GR) sugarbeet is commonly grown in rotation with GR corn, but there is limited information relating to volunteer GR corn interference or control in GR sugarbeet. Field studies were conducted near Lingle, WY and Scottsbluff, NE in 2009 and 2010 to quantify sugarbeet yield loss in response to volunteer corn density and duration of interference, and determine appropriate control practices for use in GR sugarbeet. Hybrid corn resulted in a similar competitive effect on sugarbeet sucrose yield as clumps of F2 volunteer corn. Clumps of volunteer corn were controlled 81% compared with 73% for individual plants. Linear regression indicated sucrose yield loss of 19% for each corn plant m−2 up to 1.7 plants m−2 at three of four experimental sites. Pearson correlation coefficients between percentage sucrose yield loss and proportion of sunlight reaching the top of the sugarbeet canopy ranged from −0.42 to −0.92. The duration of corn interference required to cause a 5% sucrose yield loss (YL5) ranged from 3.5 to 5.9 wk after sugarbeet emergence (WAE) for hand-weeding or herbicide removal, respectively, due to the length of time herbicide-treated volunteer corn continued to shade sugarbeet plants. Differences between herbicide and hand-removal methods were attributed to the time lag between when the treatments were applied and when the corn ceased to block light from the sugarbeet canopy. Sethoxydim generally provided less volunteer corn control compared with either quizalofop or clethodim, and control increased with the addition of an oil adjuvant. If a grower were to implement a volunteer corn control practice 3.5 WAE, economic sugarbeet yield loss would be avoided. In eastern Wyoming and western Nebraska, the sugarbeet crop will typically have between four to eight true leaves at 3.5 WAE, and therefore this would be an optimal time to control volunteer corn. If volunteer corn is being hand weeded, the YL5 estimate will also increase, and thus the window of time to control volunteer corn would be wider.
There are various reasons for using statistics, but perhaps the most important is that the biological sciences are empirical sciences. There is always an element of variability that can only be dealt with by applying statistics. Essentially, statistics is a way to summarize the variability of data so that we can confidently say whether there is a difference among treatments or among regression parameters and tell others about the variability of the results. To that end, we must use the most appropriate statistics to get a “correct” picture of the experimental variability, and the best way of doing that is to report the size of the parameters or the means and their associated standard errors or confidence intervals. Simply declaring that the yields were 1 or 2 ton ha−1 does not mean anything without associated standard errors for those yields. Another driving force is that no journal will accept publications without the data having been subjected to some kind of statistical analysis.
Redstem filaree is a troublesome weed for sugarbeet growers in northern Wyoming and southern Montana. Field studies were conducted in Powell, WY, in 2006 and 2008 to determine the influence of season-long interference of various redstem filaree densities and the duration of interference on sugarbeet. Root and sucrose yield decreased with increasing redstem filaree density. The rectangular hyperbola model with the asymptote (A) bounded at 100% maximum yield reduction characterized the relationship between redstem filaree density and sugarbeet yield reduction. The estimated parameter I (percent yield reduction per unit weed density as density approaches zero) was 5% for root and sucrose yield reduction. Sugarbeet root yield decreased as the duration of redstem filaree interference increased. The critical timing of redstem filaree removal to avoid 5 and 10% root yield reduction was estimated to be 25 and 32 d after sugarbeet emergence, respectively. Redstem filaree interference did not affect the sucrose content percentage. These results demonstrate that redstem filaree is competitive with sugarbeet and should be managed appropriately to reduce negative effects on yield.
Field experiments were conducted near Scottsbluff, NE, in 2001 and 2002 to compare economic aspects of glyphosate applied to different glyphosate-resistant sugar beet cultivars with that of conventional herbicide programs applied to near-equivalent, non–glyphosate-resistant conventional cultivars. Glyphosate applied two or three times at 2-wk intervals, beginning when weeds were 10 cm tall, provided excellent weed control, yield, and net economic return regardless of the glyphosate-resistant sugar beet cultivar. All conventional herbicide treatments resulted in similar net economic returns. Although the conventional sugar beet cultivars ‘HM 1640’ and ‘Beta 4546’ responded similarly to herbicide treatments with respect to sucrose content, ‘Beta 4546RR’ produced roots with 1% more sucrose than ‘HM 1640RR’. When averaged over herbicide treatments, a producer planting Beta 4546RR could afford to pay US $185/ha more for glyphosate-resistant technology as could a producer planting HM 1640RR. When averaged over cultivars and herbicide treatments, it is estimated that a producer could afford to pay an additional US $385/ha for glyphosate-resistant technology without decreasing net return.