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A comprehensive, Wisconsin state-wide assessment of waterhemp response to a diverse group of herbicide sites of action has not been conducted. Our objective was to characterize the response of a state-wide collection of waterhemp accessions to postemergence (POST) and preemergence (PRE) herbicides commonly used in corn and soybean in Wisconsin. Greenhouse experiments were conducted with more than 80 accessions from 27 counties. POST treatments included 2,4-D, atrazine, dicamba, fomesafen, glufosinate, glyphosate, imazethapyr, and mesotrione at 1× and 3× label rates. PRE treatments included atrazine, fomesafen, mesotrione, metribuzin, and S-metolachlor at 0.5×, 1×, and 3× label rates. Ninety-eight percent and 88% of the accessions exhibited ≥50% plant survival after exposure to imazethapyr and glyphosate POST 3× rate, respectively. Seventeen percent, 16%, and 3% of the accessions exhibited ≥50% plant survival after exposure to 2,4-D, atrazine, and dicamba, respectively, applied POST at the 1× rate. Survival of all accessions was ≤25% after exposure to 2,4-D or dicamba applied POST at the 3× rate, or glufosinate, fomesafen, and mesotrione applied POST at either rate evaluated. No plant of any accession survived exposure to glufosinate at either rate. Forty-five percent and 3% of the accessions exhibited <90% plant density reduction after exposure to atrazine applied PRE at the 3× rate and fomesafen PRE at the 1× rate, respectively. Plant density reduction of all accessions was ≥96% after exposure to fomesafen applied PRE at the 3× rate, or metribuzin, S-metolachlor, and mesotrione applied PRE at the 1× rate. Our results suggest that waterhemp resistance to imazethapyr and glyphosate applied POST is widespread in Wisconsin, whereas resistance to 2,4-D, atrazine, and dicamba applied POST is present to a lower extent. One accession (A75, Fond du Lac County) exhibited multiple resistance to imazethapyr, atrazine, glyphosate, and 2,4-D when applied POST. Overall, atrazine applied PRE was ineffective for waterhemp control in Wisconsin. Proactive resistance management and the use of effective PRE and POST herbicides are fundamental for waterhemp management in Wisconsin.
The CoAXium® Production System includes a new herbicide-resistant wheat (AXigen®) that allows for fall and/or spring postemergence (POST) applications of quizalofop-P-ethyl (QPE) for control of winter annual grass weeds. As area planted with AXigen® wheat increases, so will the use of QPE herbicide, and with this comes an increased chance for physical drift, tank contamination, or misapplication to nearby sensitive plants. A total of eight field studies were conducted at four locations during the 2018–2019 and 2019–2020 growing seasons to understand the response of nonresistant wheat when exposed to various rates of QPE herbicide. Five rates of QPE were evaluated: 1× (92 g ai ha−1), 1/10×, 1/50×, 1/100×, and 1/200×. Treatments of QPE were applied in the fall (2- to 3-leaf wheat) or in the spring (3- to 4-tiller wheat). Results indicated an interaction between application timing and QPE rate on grain yield for half of the site-years. The 1× rate resulted in complete or near complete grain yield loss regardless of application timing. However, QPE at the 1/10× rate resulted in yield loss ranging from 0% to 41% when fall-applied, whereas spring application resulted in 80% to 100% yield loss. For site-years when only the main effect of QPE rate was significant, 86% to 100% yield loss was observed following exposure to QPE at the 1/10× and 1× rates. For all site-years, it was infrequent that significant yield reductions were observed following the three lowest rates of QPE. If the two highest QPE rates were considered to represent tank contamination or misapplication and the three lowest rates physical drift, we can assume that physical drift of QPE to non-AXigen® wheat is not of major concern if proper application guidelines are followed. Conversely, tank contamination and misapplication should be carefully considered by growers who have planted both AXigen® and non-AXigen® wheat varieties.
Pesticide regulations and application technologies are changing rapidly due to rising concerns around off-target movement of pesticides and increased focus on improving the efficiency of pesticide applications. In order to conduct relevant applied research and develop educational programs related to pesticide application, it is necessary to understand the common application practices and technologies that growers use. A survey was conducted to assess common pesticide application practices and technologies used by Georgia growers. Both online and printed survey copies were distributed by county agricultural extension agents to growers in all 159 counties. A total of 186 responses representing agronomic crops in 65 counties were received and analyzed for results. Main results of this survey indicated that 1) 72% of respondents produced ≥200 ha of crops; 2) 29% of respondents received their information from university Extension personnel; 3) 42% of respondents used a separate sprayer for applications of dicamba, 2,4-D, or 2,4-DB; 4) 46% of respondents used sprayers with boom lengths ≥18.3 m; 5) 65% of respondents used ≥121 L/ha to apply pesticides; 6) 53% of respondents used three or more different nozzles on their spray booms throughout the season; 7) 68% of respondents used TeeJet® nozzles; 8) 65% of respondents used global positioning systems and rate controllers on their application equipment; 9) 66% of respondents recorded their pesticide application data on a notepad or diary; and 10) 39% of respondents reported that application accuracy is the biggest advantage of new spray technologies. Respondents also reported that weather, timing, and pesticide drift/regulations were their biggest application challenges and that more research is needed on topics such as rates, carrier volumes, pest control, chemicals and adjuvants. Information from this survey provides useful insights into the current application practices, technologies, and research needs of Georgia growers and will be used for developing appropriate research and educational efforts.
Limited information exists on the global economic impact of glyphosate-resistant (GR) weeds. The objective of this manuscript was to estimate the potential yield and economic loss from uncontrolled GR weeds in the major field crops grown in Ontario, Canada. The impact of GR weed interference on field crop yield was determined using an extensive database of field trials completed on commercial farms in southwestern Ontario between 2010 and 2021. Crop yield loss was estimated by expert opinion (weed scientists and Ontario government crop specialists) when research data were unavailable. This manuscript assumes that crop producers adjust their weed management programs to control GR weeds, which increases weed management costs but reduces crop yield loss from GR weed interference by 95%. GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed would cause an annual monetary loss of (in millions of Can$) $172, $104, $11, $3, and $0.3, respectively, for a total annual loss of $290 million if Ontario farmers did not adjust their weed management programs to control GR biotypes. The increased herbicide cost to control GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed in the major field crops in Ontario is estimated to be (in millions of Can$) $17, $9, $2, $0.1, and $0.02, respectively, for a total increase in herbicide expenditures of $28 million annually. Reduced GR weed interference with the adjusted weed management programs would reduce farm-gate monetary crop loss by 95% from $290 million to $15 million. This study estimates that GR weeds would reduce the farm-gate value of the major field crops produced in Ontario by Can$290 million annually if Ontario farmers did not adjust their weed management programs, but with increased herbicide costs of Can$28 million and reduced crop yield loss of 95% the actual annual monetary loss in Ontario is estimated to be Can$43 million annually.
The use of different herbicide-resistant soybean technologies in proximity could lead to injury and yield loss due to an application error. Research was initiated to evaluate the effect of 6.25%, 12.5%, and 100% doses of isoxaflutole and mesotrione field use doses applied postemergence to 4-hyroxyphenylpyruvate (HPPD) inhibitor-susceptible soybean, representing physical drift or misapplication doses. Visible injury manifested as chlorosis with slight necrosis, progressing to necrosis and height reduction, with visible height reduction as the only symptom. Isoxaflutole at 6.25% and 12.5% injured V2 soybean more than V1 or V4 soybean at all evaluation dates. This is supported by soybean height data at 14, 28, and 42 d after treatment (DAT). Following the 100% dose, maximum injury occurred at 28 DAT with V1, V2, and V4 soybean injured 90%, 85%, and 72%, but injury declined over time. All isoxaflutole treatments reduced yield at least 310 kg ha−1, with no differences among application timings or between the two lowest doses for a revenue loss of US$147 ha−1 to US$623 ha−1. Visible injury following mesotrione manifested as chlorosis and necrosis advancing to visible height reduction. Following mesotrione at 6.25% and 12.5%, injury ranged from 20% to 36% among application timings and did not differ at 3 to 21 DAT. Soybean heights at 28 and 42 DAT do not support injury observations; therefore, the greater injury was due to chlorosis and necrosis. Following mesotrione at 100%, sensitivity decreased at 3 to 14 DAT when applied to later growth stages, with no differences at 42 DAT. Yields did not differ among application timings, but yield losses were at least 240 kg ha−1, with revenue losses of US$60 ha−1 and US$373 ha−1. Producers are cautioned to prevent off-target movement or errant application of isoxaflutole or mesotrione to HPPD inhibitor-susceptible soybean.
Little information is available on the relative efficacy of Group 4 herbicides for glyphosate-resistant (GR) horseweed management in soybean. Five field research experiments were conducted in growers’ fields from 2020 to 2021 to determine GR horseweed control with Group 4 herbicides applied preplant (PP) alone and in a mixture. There was minimal soybean injury (≤4%) with herbicides evaluated. Dicamba, 2,4-D, or halauxifen-methyl applied PP controlled GR horseweed 92% to 96%, 73% to 76%, and 85% to 89%, respectively. The mixtures of dicamba + 2,4-D, dicamba + halauxifen-methyl and dicamba + 2,4-D + halauxifen-methyl provided 97% to 99% control of GR horseweed, similar to dicamba applied alone. The mixture of 2,4-D + halauxifen-methyl provided 93% to 94% control of GR horseweed. Dicamba + saflufenacil controlled GR horseweed at 98%. Dicamba alone, dicamba + 2,4-D ester, dicamba + halauxifen-methyl, and dicamba + 2,4-D ester + halauxifen-methyl decreased GR horseweed density 97%, 99%, 99%, and 98%, respectively, similar to a 98% density reduction with dicamba + saflufenacil. Other herbicide treatments had no effect on GR horseweed density. Dicamba, 2,4-D, and halauxifen-methyl applied PP decreased GR horseweed dry biomass by 99%, 76%, and 72%, respectively. The mixtures of dicamba + 2,4-D, dicamba + halauxifen-methyl, and dicamba + 2,4-D + halauxifen-methyl decreased GR horseweed dry biomass by 99% to 100%, similar to a 99% dry biomass reduction with dicamba + saflufenacil. The mixture of 2,4-D + halauxifen-methyl decreased GR horseweed dry biomass by 94%. Soybean yield was decreased by 61% when GR horseweed was left uncontrolled. Results show that Group 4 herbicides that include dicamba applied PP can be very effective in managing GR horseweed in soybean.
Crop residue can intercept and adsorb residual herbicides, leading to reduced efficacy. However, adsorption can sometimes be reversed by rainfall or irrigation. Greenhouse experiments were conducted to evaluate the effect of differential overhead irrigation level on barnyardgrass response to acetochlor, pyroxasulfone, and pendimethalin applied to bare soil or wheat straw–covered soil. Acetochlor applied to wheat straw–covered soil resulted in 25% to 40% reduced control, 30 to 50 more plants 213 cm−2, and greater biomass than bare soil applications, regardless of irrigation amount. Barnyardgrass suppression by pyroxasulfone applications to wheat straw–covered soil improved with increased irrigation; however, weed control levels similar to bare soil applications were not observed after any irrigation amount. Barnyardgrass densities from pyroxasulfone applications to bare soil decreased with irrigation but did not change in applications to wheat straw–covered soil. Aboveground barnyardgrass biomass from pyroxasulfone decreased with greater irrigation amounts in both bare soil and wheat straw–covered soil applications; however, decreased efficacy in wheat straw–covered soil applications was not alleviated with irrigation. Pendimethalin was the only herbicide tested that displayed reduced efficacy when irrigation amounts increased in applications to both bare soil and wheat straw–covered soil. Barnyardgrass control from pendimethalin applied to wheat straw–covered soil was similar to bare soil applications when approximately 0.3 to 1.2 cm of irrigation was applied; however, irrigation amounts greater than 1.2 cm resulted in greater barnyardgrass control in bare soil applications. No differences between wheat straw–covered soil and bare soil applications of pendimethalin were observed for barnyardgrass densities. These data indicate that increased irrigation or rainfall level can increase efficacy of acetochlor and pyroxasulfone. Optimal rainfall or irrigation amounts required for efficacy similar to bare soil applications are herbicide specific, and some herbicides, such as pendimethalin, may be adversely affected by increased rainfall or irrigation.
Horseweed is a North American indigenous plant species commonly found in Nebraska cropping systems. Horseweed management is challenging because of horseweed’s prolific seed production, long-distance seed dispersal via wind, competitiveness, and rapid evolution of herbicide resistance. Understanding the horseweed emergence pattern across Nebraska can contribute to implementing effective and more sustainable tactics to minimize its impact on cropping systems. Field studies were conducted during fall and spring from 2016 to 2018 in Lincoln (corn and soybean), North Platte (wheat stubble and soybean), and Scottsbluff (corn and fallow) to investigate the emergence pattern of horseweed accessions from Lincoln, North Platte, and Scottsbluff, NE. Results show that most horseweed seedling emergence occurred in fall (99%) and only a few seedlings emerged in spring across locations, except in the wheat stubble experiment at North Platte, where higher spring emergence was detected (3% to 22%). In four out of six experiments, the density of total emerged seedlings of each accession was greatest when established in their site of origin. Our results suggest that late fall and/or early spring is likely the best timing for horseweed management across Nebraska.
Rigid ryegrass is a problematic weed species in winter crops and winter fallow; however, recently, this weed species has been observed in summer crops and fallow. These observations warrant the evaluation of different postemergence herbicides for its control. Outdoor pot studies were conducted during the spring and summer of 2021 to 2022 to determine the performance of POST herbicides on two summer-emerging (S3 and S6) and two winter-emerging (W3 and W8) accessions of rigid ryegrass. Across all accessions, butroxydim, clethodim, paraquat, and paraquat + amitrole at the field rate provided complete control of rigid ryegrass. Both summer-emerging accessions were found to be resistant to the field rates of glufosinate (750 g ai ha−1), glyphosate (454 g ae ha−1), haloxyfop (52 g ai ha−1), and pinoxaden (30 g ai ha−1). The S6 accession had the highest dose required for a 50% reduction in biomass for these herbicides (glufosinate 1,120 g ai ha−1, glyphosate 1,210 g ae ha−1, haloxyfop 140 g ai ha−1, and pinoxaden 55 g ai ha−1). This summer-emerging accession (S6) was also resistant to iodosulfuron. All four accessions were found susceptible to imazamox + imazapyr (a commercial mixture) and mesosulfuron. The study provides the first evidence of poor control of summer-emerging accessions of rigid ryegrass with different herbicides. Multiple-herbicide-resistant summer-emerging rigid ryegrass accessions would be a challenge to the production of summer crops (e.g., cotton and sorghum) as well as winter crops that rely on weed-free summer fallows for soil moisture retention; therefore these accessions warrant diversified management strategies.
The southern United States produces 90% of the nation’s cotton, and the Texas High Plains is the largest contiguous cotton producing region. Since 2011, glyphosate-resistant Palmer amaranth has complicated cotton production, and alternatives to glyphosate are needed. Integrating soil residual herbicides into a weed management program is a crucial step to control glyphosate resistant weeds before emergence. The recent development of p-hydroxyphenylpyruvate dioxygenase (HPPD)-resistant cotton by BASF Corporation may allow growers to use isoxaflutole in future weed management programs. In 2019 and 2020, field experiments were conducted in New Deal, Lubbock, and Halfway, Texas, to evaluate HPPD-resistant cotton response to isoxaflutole applied preemergence (PRE) or early postemergence (EPOST) and to determine the efficacy of isoxaflutole when used as part of a season-long weed management program. At the New Deal location, cotton response was observed following the EPOST application, but it never exceeded 10%. Cotton response was greatest following the PRE application in Lubbock in 2019 but did not exceed 14%. In 2020 in Lubbock, cotton was replanted due to severe weather. There was <1% cotton response following the PRE application, and maximum cotton response observed was 9% following EPOST and mid-postemergence (MPOST) applications. Cotton lint yields were not different from those of the nontreated, weed-free control at either location. In non-crop weed control studies in Halfway, all treatments controlled Palmer amaranth ≥94% 21 d after the EPOST application. Twenty-one days after the MPOST treatment, systems with isoxaflutole applied EPOST controlled Palmer amaranth by 88% to 93%, while systems with isoxaflutole PRE controlled Palmer amaranth by 94% to 98%. End-of-season Palmer amaranth control was lowest in the system without isoxaflutole (88%) and when isoxaflutole was used EPOST (88% to 91%). These studies suggest that the use of isoxaflutole in cotton weed management systems may improve season-long control of several troublesome weeds with no adverse effects on cotton yield and quality.
Fall panicum is a problematic weed in cropping systems including rice in southern Florida. There is limited information on growth and reproductive ability of fall panicum in water-stressed environments. The objective of this study was to determine the effect of 12.5%, 25%, 50%, 75%, and 100% pot soil water content (SWC) levels on fall panicum growth and panicle branch production under greenhouse conditions. Fall panicum height, number of leaves, and tillers decreased over time as SWC decreased. Fall panicum height decreased by 65% and 50% at 12.5% and 25% SWC, respectively, relative to height achieved at 100% SWC. Plants at 50% to 100% SWC were able to achieve 50% tiller production within 31 to 43 d compared with 28 d at 25% SWC. The 50% tiller production was not reached at 12.5% SWC during the duration of the study. Fall panicum shoot and root biomass, total leaf area, and number of panicle branches per plant at 56 d after SWC treatment initiation decreased as SWC decreased. Fall panicum biomass decreased 83% to 85% and 66% to 68% at 12.5% and 25% SWC, respectively, relative to 100% SWC. Leaf area declined 79% and 65% at 12.5% and 25% SWC levels, respectively, compared to the 100% SWC. Fall panicum was able to produce panicles at all SWC levels, although the plant produced significantly fewer panicle branches as SWC decreased. Plants at 12.5% and 25% SWC produced 82% and 59% fewer panicle branches, respectively, compared with plants at 100% SWC. This study shows that SWC influences the growth and reproductive capacity of fall panicum. Although fall panicum did not reach its full growth potential at low SWC levels, it was able to survive and develop panicles, showing its ability to adapt and reproduce under dry conditions.
Herbicide-resistant Palmer amaranth is a troublesome weed in several agronomic crops and is a relatively new challenge to dry bean production in western Nebraska. Objectives were to evaluate preemergence (PRE) and postemergence (POST) herbicides for control of acetolactate synthase–resistant Palmer amaranth and their effect on Palmer amaranth density and biomass as well as dry bean injury and yield in western Nebraska. Field experiments were conducted in 2017 and 2019 near Scottsbluff, NE. The experiments were arranged as a two-factor strip-plot design. The strip-plot factor consisted of no-PRE or pendimethalin (1,070 g ai ha–1) + dimethenamid-P (790 g ai h–1) applied PRE. The main-plot factor was POST herbicides, which consisted of various mixtures of imazamox, bentazon, or fomesafen applied in a single or sequential application at labeled rates, and reduced rates of imazamox (9 g ai ha–1) + bentazon (314 g ai ha–1) + fomesafen (70 g ai ha–1) applied in single or sequential (two or three) applications. PRE herbicides reduced Palmer amaranth density and biomass during both years and increased dry bean yield in 2017. POST treatments containing fomesafen improved Palmer amaranth control compared with treatments containing imazamox and bentazon only. The sequential-application reduced-rate POST system did not improve Palmer amaranth control compared to one POST application containing fomesafen at a labeled rate in either year. Using pendimethalin + dimethenamid-P PRE followed by POST treatments containing imazamox + bentazon + fomesafen at a labeled rate provided 86% and 99% Palmer amaranth control in 2017 and 2019, respectively.
The extensive and intensive use of herbicides has resulted in the spread of herbicide-resistant weeds in many crop production systems; therefore, it is imperative to devise new organic weed control methods. Recently, the application of spent coffee grounds (SCG) in agricultural fields has been found to inhibit plant growth and germination and is thus considered a potentially effective weed control measure. This study aimed to evaluate the effects of different amounts and methods of SCG application on weed growth through field experiments. The field experiments were conducted in an upland field converted from a paddy in western Japan. The results show that the plow-in application of over 10 kg m−2 of SCG and mulching application of 20 kg m−2 decreased the weed dry weight compared with the control. In addition, the growth of weed species of families other than Gramineae, such as wingleaf primrose-willow and horseweed, was not significantly affected by SCG application. Weed species of families other than Gramineae are dominant in some upland fields. Hence, the inhibitory effect of SCG on weeds may be lower in original upland fields than in the upland field converted from paddy field that was investigated in the present study. Overall, this study demonstrated that the plow-in application of 10 kg m−2 of SCG every 4 mo was effective for weed control in an upland field converted from a paddy field. Because SCG worked against grass weeds under the specific conditions in this study, it would be valuable to explore other potential applications of this novel means of weed control.
Smutgrass is an invasive weed species that can quickly outcompete bahiagrass because of its aggressive growth, prolific seed production, and rhizomatous nature. Total renovation of bahiagrass pastures or hayfields is generally not a feasible or economically viable option for most producers. Therefore, controlling the continual spread of smutgrass will require an integrated weed management (IWM) plan that incorporates multiple strategies. The objective of this study was to test the interactions of herbicides and fertilizers on smutgrass control in bahiagrass and determine the most efficacious and economical IWM plan for low-input bahiagrass systems. This research was conducted on a mixture of ‘Tifton 9’ and ‘Pensacola’ bahiagrass at the Alapaha Beef Station in Alapaha, GA. The study design was a randomized complete block with a three-by-four factorial treatment arrangement with six replications. Fertility treatments included 56 kg N ha–1 (ammonium nitrate, 34% N) + 56 kg K2O ha–1, 56 kg N ha–1, and an unfertilized control. Smutgrass was reduced to <15% ground coverage when a postemergent herbicide was applied. The addition of a preemergent herbicide and/or fertilizer further reduced the coverage of smutgrass (P < 0.01). As smutgrass declined, the bahiagrass ground coverage increased; other vegetation and dead material did not differ by treatment. Generally, herbage accumulation and crude protein were only affected following the second N application (P < 0.01). Treatments that included preemergent (indaziflam) and postemergent (hexazinone) herbicides in addition to N and K2O resulted in an improved bahiagrass stand as timely weed suppression removed competition, while fertilizer provided essential nutrients for optimum growth to fill in the gaps. Combining herbicide and fertilizer is a more economical option for producers when compared to a complete bahiagrass renovation.
The combination of florpyrauxifen-benzyl + 2,4-D is a new, pre-packaged herbicide mixture for use in pastures and hayfields in the United States. Unlike many other pasture herbicides, florpyrauxifen-benzyl + 2,4-D is reported to preserve white clover. However, limited research exists on the efficacy of florpyrauxifen-benzyl + 2,4-D on common weed species and on the level of tolerance of white clover to it. Field trials were conducted in Virginia in 2018 to 2020 to evaluate control of various broadleaf weeds with florpyrauxifen-benzyl + 2,4-D compared to other commonly used herbicides. Field and greenhouse studies were also carried out to assess white clover tolerance. Weed species evaluated included bulbous buttercup, Canada thistle, horsenettle, and broadleaf plantain. Florpyrauxifen-benzyl + 2,4-D provided 75% to 99% control of all weeds 90 d after application except for horsenettle (56%), while causing the least white clover injury of any herbicide treatment that was evaluated. Spring herbicide applications resulted in greater bulbous buttercup control compared to fall applications, but florpyrauxifen-benzyl + 2,4-D provided greater than 81% control from both application timings. There were no differences in aboveground biomass between white clover varieties; however, all herbicides reduced white clover biomass compared to a nontreated control. This research suggests that florpyrauxifen-benzyl + 2,4-D can improve overall forage quality by controlling broadleaf weeds in mixed grass-legume stands while preserving white clover.
Narrow-windrow burning (NWB) is a form of harvest weed seed control in which crop residues and weed seeds collected by the combine are concentrated into windrows and subsequently burned. The objectives of this study were to determine how NWB will 1) affect seed survival of Italian ryegrass in wheat and Palmer amaranth in soybean and 2) determine whether a relationship exists between NWB heat index (HI; the sum of temperatures above ambient) or effective burn time (EBT; the cumulative number of seconds temperatures exceed 200 C) and the post-NWB seed survival of both species. Average soybean and wheat windrow HI totaled 140,725 ± 14,370 and 66,196 ± 6224 C, and 259 ± 27 and 116 ± 12 s of EBT, respectively. Pre-NWB versus post-NWB germinability testing revealed an estimated seed kill rate of 79.7% for Italian ryegrass, and 86.3% for Palmer amaranth. Non-linear two-parameter exponential regressions between seed kill and HI or EBT indicated NWB at an HI of 146,000 C and 277 s of EBT potentially kills 99% of Palmer amaranth seed. Seventy-six percent of soybean windrow burning events resulted in estimated Palmer amaranth seed kill rates greater than 85%. Predicted Italian ryegrass seed kill was greater than 97% in all but two wheat NWB events; therefore, relationships were not calculated. These results validate the effectiveness of the ability of NWB to reduce seed survival, thereby improving weed management and combating herbicide resistance.
Branched broomrape, an obligate root parasitic weed, has recently re-emerged in tomato fields in several California counties. California produces more tomato than any other state, and the outbreak of this noxious weed could potentially wreak havoc on the industry’s economy. Preventive measures must be taken to stop or reduce the spread of branched broomrape seeds to other areas. Branched broomrape can produce thousands of tiny seeds, which can easily spread with farm machinery over short and long distances. To prevent branched broomrape seed dispersal, sanitation and disinfection of farm equipment are necessary before entering a new farm. We tested the effectiveness of various ammonium compounds, including didecyl dimethyl ammonium chloride (DDAC), alkyl dimethyl benzyl ammonium chloride (ADBC), didecyl dimethyl ammonium bromide (DDAB), ammonium bromide (AB), and ammonium chloride (AC) on prevention of branched broomrape seed germination. Dose-response analysis showed that three chemical products, ADBC, DDAB, and DDAC, could completely inhibit branched broomrape seeds (potentially making them nonviable) at 1%, 1%, and 10% wt/vol concentrations, respectively. These three compounds were further tested in an exposure duration experiment that additionally included Egyptian broomrape. Only 10 min of exposure to these compounds was needed to prevent germination of both branched and Egyptian broomrape seeds at 1% (ADBC, DDAB) and 10% wt/vol (DDAC). Lower concentrations can provide similar inhibition effects when combined with longer exposure times. Egyptian broomrape seeds were more sensitive than branched broomrape seeds. Findings suggest that quaternary ammonium compounds could be used as potential sanitation agents to disinfect agriculture machinery from branched and Egyptian broomrape seeds.
Trials were conducted in two experimental runs at the Purdue University Horticulture Greenhouses, West Lafayette, IN, to determine ‘Redefined Murray Mitcham’ peppermint tolerance to tiafenacil. Established peppermint in 20-cm-diameter polyethylene pots was subjected to a simulated harvest by removing aboveground biomass at the substrate surface; then, tiafenacil was applied at 0, 25, 50, 100, and 200 g ai ha−1. Visible crop injury, height, and aboveground dry biomass data were subjected to regression analysis to generate predictive models. At 2 wk after treatment (WAT), peppermint injury increased from 63% to 86% and from 25% to 76% in Experimental Run 1 and 2, respectively, as tiafenacil rate increased from 25 to 200 g ha−1. At 4 WAT, injury increased from 0% to 63% and from 4% to 37% in Experimental Run 1 and 2, respectively, as tiafenacil rate increased from 25 to 200 g ha−1. By 7 WAT (both experimental runs), injury increased from 0% to 17% as tiafenacil rate increased from 25 to 200 g ha−1. At 4 WAT, height decreased from 23.0 to 8.6 cm and from 17.6 to 10.3 cm in Experimental Run 1 and 2, respectively, as tiafenacil rate increased from 0 to 200 g ha−1. At 7 WAT, height decreased from 28.1 to 21.4 cm as tiafenacil rate increased from 0 to 200 g ha−1. Aboveground dry weight of the nontreated check was 20.3 g pot−1 and decreased from 19.3 to 7.0 g pot−1 as tiafenacil rate increased from 25 to 200 g ha−1. Despite acute necrosis, injury from tiafenacil at lower rates was not persistent. The proposed 1X rate of tiafenacil for peppermint, 25 g ha−1, resulted in ≤4% injury 4 and 7 WAT and in only a 3% reduction in plant height and a 4.7% reduction in aboveground dry weight compared to the nontreated check.
Dicamba and glufosinate are among the few effective postemergence herbicides to control multiple herbicide-resistant weeds in southeastern U.S. cotton and soybean production. Field studies were conducted to determine the effect of weed size and the application of dicamba and glufosinate individually, mixed, or sequentially on common ragweed, goosegrass, large crabgrass, ivyleaf morningglory, Palmer amaranth, and sicklepod control. Sequential herbicide treatments were applied 7 d after the initial treatment. The tested weeds sizes predominantly did not affect weed control. Control of broadleaf weed species with sequential herbicide applications never increased compared to the initial herbicide application. Two applications of glufosinate and/or dicamba + glufosinate controlled grasses better than one application. The order of the herbicides in the sequential applications did not affect broadleaf species control, whereas herbicide order was important for the control of grass weeds. Grass weed control was higher when glufosinate was applied before dicamba. Dicamba + glufosinate additively controlled the weeds, except for goosegrass, for which control was less for dicamba + glufosinate compared to glufosinate alone. The results of the experiment provide evidence that dicamba and glufosinate applied individually, mixed, and sequentially are effective on common row crop weeds found in the southeastern United States, but the species present may dictate how the herbicides are applied together.