Weed-free Control Research Articles

Effect of Halosulfuron Rate and Application Timing on Volunteer Azuki Bean Control in White Bean

Three field experiments were carried out during 2017-2019 at the University of Guelph Huron Research Station near Exeter, Ontario, Canada to determine the effect of halosulfuron rate (25, 37.5 or 50 g∙ai∙ha-1) and application timing (POST 1, POST 2 and POST 3) on volunteer azuki bean control in white bean. At POST 1, halosulfuron at 25, 37.5 and 50 g∙ai∙ha-1 controlled volunteer azuki bean 46% - 50% at 1 week after application (WAA), controlled decreased to 16% - 25% at 8 WAA. At POST 2, volunteer azuki bean controlled decreased from 34% - 39% at 1 WAA to 17% - 27% at 8 WAA. A similar trend was observed at POST 3. Halosulfuron applied POST 1 at 25, 37.5 and 50 g∙ai∙ha-1 reduced biomass 49%, 64% and 69%, respectively. Halosulfuron applied POST 2 did not reduce volunteer azuki bean biomass at 25 g∙ai∙ha-1, but decreased biomass 51% at 37.5 g∙ai∙ha-1 and 49% at 50 g∙ai∙ha-1. Similarly, halosulfuron applied POST 3 did not reduce volunteer azuki bean biomass at 25 g∙ai∙ha-1, but decreased biomass 40% at 37.5 g∙ai∙ha-1 and 44% at 50 g∙ai∙ha-1. There was as much as 19%, 22% and 25% dockage with halosulfuron applied POST 1, POST 2 and POST 3, respectively. Volunteer azuki bean interference reduced white bean yield 40%. Reduced volunteer azuki bean interference with halosulfuron applied POST 1 at 37.5 or 50 g∙ai∙ha-1 resulted in an increase in white bean yield relative to the weedy control; however white yield was less than the weed-free control. This study concludes that halosulfuron at rates and application timings evaluated does not provide adequate control of volunteer azuki bean in white bean.

Glyphosate-Resistant Canada Fleabane Control with Three-Way Herbicide Tankmixes in Soybean

Eight field trials (2 in 2016, 3 in 2017, 3 in 2018) were conducted in farmers’ fields with heavy infestations of GR Conyza canadensis (Canada fleabane, horseweed or marestail) to evaluate glyphosate (900 g ae ha-1) plus saflufenacil (25 g ai ha-1), 2,4-D ester (500 g ai ha-1) or paraquat (1100 g ai ha-1) applied preplant (PP) as 2-way tankmixes, or in 3-way tankmixes with sulfentrazone (140 g ai ha-1), flumioxazin (107 g ai ha-1) or metribuzin (400 g ai ha-1) for the glyphosate-resistant (GR) C. canadensis control in GR soybean. Glyphosate plus saflufenacil applied PP controlled GR C. canadensis as much as 90%. The addition of sulfentrazone, flumioxazin or metribuzin to the tankmix provided as much as 93%, 96% and 97% control of GR C. canadensis, respectively. Glyphosate plus 2,4-D ester applied PP provided as much as 59% control of GR C. canadensis. The addition of sulfentrazone, flumioxazin or metribuzin to the tankmix provided as much as 60%, 59% and 91% control of GR C. canadensis, respectively. Glyphosate plus paraquat applied PP provided as much as 85% control of GR C. canadensis. The addition of sulfentrazone, flumioxazin or metribuzin to the tankmix provided as much as 88%, 89% and 98% control of GR C. canadensis, respectively. Density and biomass reductions of GR C. canadensis with herbicides evaluated followed the same pattern as weed control evaluations. GR C. canadensis interference reduced soybean yield 66%. Reduced GR C. canadensis interference with the preplant herbicides evaluated provided soybean yield similar to the weed-free control. Results from this study show that glyphosate plus saflufenacil, glyphosate plus 2,4-D ester or glyphosate plus paraquat tankmixed with metribuzin can provide effective control of GR C. canadensis in GR soybean.

Efficacy of Trifluralin Compared to Ethalfluralin Applied Alone and Co-Applied with Halosulfuron for Weed Management in White Bean

There are a limited number of herbicides registered for weed management in white bean production in Ontario, Canada. Five field experiments were completed in Ontario from 2016 to 2018 to compare the efficacy of trifluralin and ethalfluralin applied alone and in combination with halosulfuron, applied preplant incorporated (PPI), for weed control efficacy and white bean tolerance and seed yield. At 2 and 4 WAE, there was no white bean injury from the herbicide treatments evaluated. Trifluralin applied PPI provided up to 32%, 99%, 13%, 99%, 27%, 99% and 99% control of velvetleaf, redroot pigweed, common ragweed, common lambsquarters, wild mustard, barnyardgrass and green foxtail, respectively. Trifluralin and ethalfluralin provide similar control of velvetleaf, redroot pigweed, barnyardgrass and green foxtail control, however, ethalfluralin is slightly more efficacious on common ragweed, common lambsquarters and wild mustard. Halosulfuron (35 g∙ai∙ha−1), applied PPI, provided as much as 76%, 98%, 96%, 96%, 100%, 19% and 23% control of velvetleaf, redroot pigweed, common ragweed, common lambsquarters, wild mustard, barnyardgrass and green foxtail, respectively. Trifluralin (600 or 1155 g∙ai∙ha−1) + halosulfuron (35 g∙ai∙ha−1), applied PPI, provided up to 88%, 100%, 98%, 100%, 100%, 99% and 98% control of velvetleaf, redroot pigweed, common ragweed, common lambsquarters, wild mustard, barnyardgrass and green foxtail, respectively. Ethalfluralin (810 or 1080 ai∙ha−1) + halosulfuron (35 g∙ai∙ha−1) provided similar control. Weed interference decreased white bean seed yield 44% - 45% with trifluralin, 30% - 41% with ethalfluralin and 34% with halosulfuron. However, decreased weed interference with trifluralin and ethalfluralin applied in combination with halosulfuron resulted white bean seed yield that was similar to the weed-free control. Trifluralin or ethalfluralin co-applied with halosulfuron can be safely used in white bean production for the control of common annual grass and broadleaf weeds in Ontario.

Weed Management in White Beans with Soil-Applied Grass Herbicides plus Halosulfuron

There are a limited number of soil-applied herbicides available for broad-spectrum weed control in dry bean production in Ontario, Canada. Four experiments were conducted from 2017 to 2019 in southwestern Ontario to compare the efficacy of six soil-applied grass herbicides [trifluralin (600 g ai ha-1), ethalfluralin (810 g ai ha-1), pendimethalin (1080 g ai ha-1), S-metolachlor (1050 g ai ha-1), dimethenamid-p (544 g ai ha-1) and EPTC (3400 g ai ha-1)] and halosulfuron (35 g ai ha-1) applied alone and in combination, applied preplant incorporated (PPI), on white bean tolerance and yield, and weed control efficacy. There was no white bean injury from the herbicide treatments evaluated. Grass herbicides (trifluralin, ethalfluralin, pendimethalin, S-metolachlor dimethenamid-P and EPTC) controlled velvetleaf 0% - 82%, pigweeds 87% - 99%, common ragweed 0% - 93%, common lambsquarters 81% - 99%, wild mustard 0% - 71%, barnyardgrass 98% - 100% and green foxtail 98% - 99%. Halosulfuron controlled velvetleaf 98%, pigweeds 94%, common ragweed 90% - 94%, common lambsquarters 97%, wild mustard 98% - 100%, barnyardgrass 19% - 24% and green foxtail 20% - 25%. Tankmixes of halosulfuron with soil-applied grass herbicides provided ≥93% control of the weed species evaluated. Reduction in density and biomass generally followed the same trend as visible control with herbicide treatments evaluated. Weed interference reduced white bean seed yield 70%. Seed yield was 53% - 66% of the weed-free control with trifluralin, ethalfluralin, pendimethalin, S-metolachlor and dimethenamid-P, 81% of the weed-free control with EPTC, 58% of the weed-free control with halosulfuron, and 87% - 95% of the weed-free control with halosulfuron tankmixes with the grass herbicides evaluated. Based on these results, halosulfuron in combination with trifluralin, ethalfluralin, pendimethalin, S-metolachlor, dimethenamid-p and EPTC, applied PPI at rates evaluated, can be used to effectively control common annual grass and broadleaf weeds in white beans.

Understanding the Competitive Effects of Blessed Milkthistle Densities on Wheat

ABSTRACT: Weed-induced yield loss in wheat crop is a great threat to food security in Pakistan. A comprehensive understanding of weed-crop competition is very important to develop sustainable and cost-effective weed management. For this purpose, two-year field studies were conducted to determine the effect of different blessed milkthistle densities on the phenology and yield of wheat crop in a rice-wheat cropping scheme in Sargodha, Pakistan during 2013-2014 and 2014-2015. The experiment comprised seven treatments: control (weed free), weedy check (weedy without any control) and blessed milkthistle densities of 5, 10, 15, 20 and 25 plants m-2. In response to increasing weed density, a gradual reduction in yield and yield-related traits of wheat was noted. Compared to the weed-free control, a significant reduction in number of productive tillers m-2 (20% and 18%), plant height (15% and 18%), spike length (19% and 26%), number of grains spike-1 (23% and 26%), 1000 grain weight (28% and 28%), grain (29% and 30%) and biological (20% and 24%) yields of wheat occurred at and beyond blessed milkthistle density of 5 plants m-2 during 2013-2014 and 2014-2015 respectively. It can be concluded that blessed milkthistle weed must be controlled if its population density reaches 5 plants m-2 in order to avoid significant grain yield losses in wheat.

Control of Glyphosate-Resistant Marestail in Identity-Preserved or Glyphosate-Resistant and Glyphosate/Dicamba-Resistant Soybean with Preplant Herbicides

Two studies, each consisting of six field experiments were conducted in growers’ fields in 2018 and 2019 to determine the optimal herbicide tankmixes, applied preplant (PP) for the control of glyphosate-resistant (GR) marestail in 1) identity-preserved and glyphosate-resistant soybean (Study 1) and, 2) glyphosate/dicamba-resistant soybean (Study 2). There was no significant injury in soybean with the PP herbicides evaluated in both studies. In Study 1, at 8 weeks after treatment (WAA), glyphosate + saflufenacil, glyphosate + 2,4-D ester, glyphosate + pyraflufen/2,4-D, glyphosate +, 4-D choline or glyphosate + halauxifen-methyl, applied PP, controlled GR marestail 93%, 58%, 60%, 67% and 71%, respectively. The addition of metribuzin to the tankmixes of glyphosate + saflufenacil, 2,4-D ester and pyraflufen/2,4-D increased the control to 98%, 91% and 95%, respectively. The addition of metribuzin + chlorimuron-ethyl to 2,4-D choline/glyphosate and glyphosate + halauxifen-methyl increased the control to 94% and 93%, respectively. In Study 2, at 8 WAA, glyphosate/dicamba, applied PP, controlled GR marestail 89% in glyphosate/dicamba-resistant soybean. The addition of metribuzin or saflufenacil to glyphosate/dicamba controlled GR marestail 86% and 97%, respectively. At 8 WAA, S-metolachlor/dicamba controlled GR marestail 83%. The addition of metribuzin or saflufenacil to the above premix controlled GR marestail 87% and 97%, respectively. Density and biomass reductions were similar to visible control. GR marestail interference reduced soybean yield 60% and 53% in Study 1 and 2, respectively. Reduced GR marestail interference with all the herbicide treatments evaluated in both studies resulted in soybean yield that was similar to the weed-free control.

Effect of weed control technologies on chickpeas (Cicer arietinum L.) and weeds

Purpose. In our experiment, effect of weed technologies on chickpeas (Cicer arietium L.) was set up in 2018 and 2019 at the Szeged-Othalom experimental area.Methods. In the first year we applied mechanical weed control in addition to pre-emergence herbicide (May 19, 2018) and 6–8 leaf chickpeas (June 20, 2018) in addition to post-emergence herbicide treatments. The year 2019 was different in that after the pre-emergence treatment (April 10, 2019), the post-emergence treatment of chickpeas with 6–8 leaf condition (May 15, 2019) was repeated in the budding state (June 18, 2019). The yield components one way analysis of variance was prepared using SPSS 22 software and graphic representation of the development of the plants was carried out Svab's cumulative yield analysis.Results. The effect of the treatments of 2018 and 2019 on the yield elements of chickpeas can be illustrated graphically in Figure 1 and Figure 2. For both years, the data are from plots of the ʻRealeʼ variety, where the 100% level is made up of the yield elements of the weed-free plots, and the yield elements of the other treatments are compared to this. Figure 1 shows that the number of shoots per unit area (1 m2) of weed-free plots that did not control weeds was 15%, the number of pods 45%, the number of seeds 58% and the weight of seeds 49% less than the weed-free control plots the same crop elements. Weeds were also significantly present in the plots treated only with pre-emergence treatment in the second half of the growing season, so the number of shoots per unit area was 3 %, the number of pods 23 %, the number of seeds 34% and the seed weight 35 % lower, as on weed-free plots. In the case of herbicide treatments, the decrease in yield elements was much smaller: the number of plants per unit area by 1%, the number of shoots by 3–10%, the number of pods by 5–12%, the number of seeds by 13–18%, the seed weight was by 1–5% less than on mechanically weed-controlled plots. Conclusions. Our two-year weed survey results show that the later sowing time of chickpeas favored warm-loving weeds. This is in complete agreement with the opinion of Nagy (2017), who found that sowing time determines the predominant weed species in a given area. At the same time, the statement of Kurnik (1970) was not confirmed, since in our experiment we proved in the case of ʻRealeʼ cultivar that the later sowing stock in 2018 gave higher yields than the plots with earlier sowing time in 2019. The changing weather caused by climate change makes the site characteristics of the given period much more unpredictable, so the yield is determined much more by the field factors developed during the growing season than by the calendar period.

Evidences of Allee Effect in Winter Crops: A Model Based Study

Plant species may be subject to Allee effect if individuals experience a reduction in fitness when population biomass is small. The instances of Allee effect are fewer in number for plants than the animals and the consequences are not substantially explored for the field crops. Here Allee effects on three winter crops, viz. Barley (Hordeum vulgare Sensulato), Wheat (Triticum aestivum L. emend. Fiori and Paol.) and Indian mustard [Brassica juncea (L.) Czernj. And Cosson] have been studied in sub-tropical sub-humid agro-ecosystem through field experiment and mathematical model formulation. The field experiment was conducted during the winter seasons of 2014–2015 and 2015–2016 at the Agricultural Experiment Farm of the Indian Statistical Institute, Giridih, Jharkhand under rainfed conditions. The underlying experimental design is a split-plot design with three replications for each winter crop. Two varieties of each winter crop were randomly allocated in the main plots. In sub-plots, four weed treatments are applied, viz. Weed-free control, other weeds except M. denticulata, M. denticulata alone, unweeded. We illustrate the mathematical models for the crop—weed interactive dynamics through the total biomass yield (in kg/ha) of the three winter crops. The existence of weak Allee effect in Barley and Wheat is established particularly in the presence of Medicago, but Indian mustard exhibits no such evidence. The importance of this dynamic process in plant ecology has been under appreciated and recent evidence suggests that it might have an impact on the population dynamics of many plants. A practical agro-economic benefit of M. denticulata has also been revealed.

Broccoli, cabbage, squash and watermelon response to halosulfuron preplant over plastic mulch

AbstractNutsedge species are problematic in plastic-mulched vegetable production because of the weed’s rapid reproduction and ability to penetrate the mulch. Vegetable growers rely heavily on halosulfuron to manage nutsedge species; however, the herbicide cannot be applied over mulch before vegetable transplanting due to potential crop injury. This can be problematic when multiple crops are produced on a single mulch installation. Field experiments were conducted to determine the response of broccoli, cabbage, squash, and watermelon to halosulfuron applied on top of mulch prior to transplanting. Halosulfuron at 80 g ai ha−1 was applied 21, 14, 7, and 1 d before planting (DBP), and 160 g ai ha−1 was applied 21 DBP. In all experiments, extending the interval between halosulfuron application and planting reduced crop injury. For squash and watermelon, visual injury, plant diameters/vine runner lengths, marketable fruit weights, and postharvest plant biomass resulted in similar values when applying 80 g ha−1 21 DBP and with the nontreated weed-free control. Reducing this interval increased injury for both crops. Visual crop injury and yield reductions up to 40% occurred, with halosulfuron applied 14, 7, or 1 DBP in squash and 1 DBP in watermelon. Broccoli and cabbage showed greater sensitivity, with injury and plant diameter reductions greater than 15%, even with halosulfuron applied at 80 g ha−1 21 DBP. Experimental results confirm that halosulfuron binds to plastic mulch, remains active, and is slowly released from the mulch over a substantial period, during rainfall or overhead irrigation events. Extending the plant-back interval to at least 21 d before transplanting did overcome squash and watermelon injury concerns with halosulfuron at 80 g ha−1, but not broccoli and cabbage. Applying halosulfuron over mulch to control emerged nutsedge before planting squash and watermelon would be beneficial if adequate rainfall or irrigation and appropriate intervals between application and planting are implemented.

Abrasive Grit Application in Organic Red Pepper: An Opportunity for Integrating Nitrogen and Weed Management

Weeds are a top management concern among organic vegetable growers. Abrasive weeding is a nonchemical tactic using air-propelled abrasive grit to destroy weed seedlings within crop rows. Many grit types are effective, but if organic fertilizers are used, this could integrate weed and nutrient management in a single field pass. Our objective was to quantify the effects of abrasive grit and mulch type on weed suppression, disease severity, soil nitrogen availability, and yield of pepper (Capsicum annuum L. ‘Carmen’). A 2-year experiment was conducted in organic red sweet pepper at Urbana, IL, with four replicates of five abrasive grit treatments (walnut shell grits, soybean meal fertilizer, composted turkey litter fertilizer, a weedy control, and a weed-free control) and four mulch treatments (straw mulch, bioplastic film, polyethylene plastic film, and a bare soil control). Abrasive weeding, regardless of grit type, paired with bioplastic or polyethylene plastic mulch reduced in-row weed density (67 and 87%, respectively) and biomass (81 and 84%); however there was no significant benefit when paired with straw mulch or bare ground. Despite the addition of 6 to 34 kg N/ha/yr through the application of soybean meal and composted turkey litter grits, simulated plant N uptake was most influenced by mulch composition (e.g., plastic vs. straw) and weed abundance. Nitrogen immobilization in straw mulch plots reduced leaf greenness, plant height, and yield. Bacterial spot (Xanthomonas campestris pv. Vesicatoria) was confirmed on peppers in both years, but abrasive weeding did not increase severity of the disease. Pepper yield was always greatest in the weed-free control and lowest in straw mulch and bare soil, but the combination of abrasive weeding (regardless of grit type) and bioplastic or polyethylene plastic mulch increased marketable yield by 47% and 21%, respectively, compared with the weedy control. Overall, results demonstrate that when abrasive weeding is paired with bioplastic or polyethylene mulch, growers can concurrently suppress weeds and increase crop N uptake for greater yields.

Weed Management Programs in Grain Sorghum (Sorghum bicolor)

A field study was conducted in Arkansas over three years to evaluate various herbicide treatments, including sequential and tank-mix applications for weed control in grain sorghum (Sorghum bicolor). The herbicide treatments used were quinclorac, atrazine + dimethenamid-p, S-metolachlor followed by (fb) atrazine + dicamba, dimethenamid-p fb atrazine, S-metolachlor + atrazine fb atrazine, S-metolachlor + mesotrione, and S-metolachlor fb prosulfuron. All herbicide treatments provided excellent (90% to 100%) control of Ipomoea lacunosa, Ipomoea hederacea var. integriuscula, and Sida spinosa by 12 weeks after emergence. Quinclorac and S-metolachlor fb prosulfuron provided the lowest control of Ipomoea lacunosa, Urochloa platyphylla, Amaranthus palmeri, and Ipomoea hederacea var. integriuscula. Weed interference in the non-treated control reduced grain sorghum yield by 50% as compared to the weed-free control. S-metolachlor + mesotrione and S-metolachlor fb prosulfuron reduced sorghum yields by 1009 to 1121 kg ha−1 compared to other herbicide treatments. The five best herbicide treatments in terms of weed control and grain sorghum yield were quinclorac, atrazine + dimethenamid-p, S-metolachlor fb atrazine + dicamba, dimethenamid-p fb atrazine, and the standard treatment of S-metolachlor + atrazine fb atrazine.

Broadleaf weed control in rain-fed chickpea

AbstractWeeds are among the main limitations on chickpea production in Iran. The efficacy of herbicide treatments including linuron PPI, imazethapyr PPI, PRE, and POST, pendimethalin PPI and POST, bentazon POST, pyridate POST, and oxadiazon POST along with one or two hand weedings were evaluated for weed control and yield response in rain-fed chickpea in Aleshtar, Lorestan, Iran in 2015 and 2016. Wild safflower, threehorn bedstraw, wild mustard, and hoary cress were the predominant weed species in both experimental years. Total weed dry biomass in weedy check plots averaged 187 and 238 g m−2 in 2015 and 2016, respectively, and weed density and biomass were reduced in all treatments compared to the weedy check in both years. Treatments composed of pyridate followed by one hand weeding or imazethapyr POST followed by two hand weedings resulted in the lowest weed biomass. The presence of weeds reduced yield by 74% and 66% in the weedy check plots compared to the weed-free control plots in 2015 and 2016, respectively. Application of oxadiazon, bentazon, and imazethapyr PPI, PRE, and POST resulted in lower chickpea yields. All herbicides tested injured chickpea slightly, with pyridate causing the least injury.

Preemergence herbicide delays the critical time of weed removal in popcorn

AbstractUnderstanding the critical time of weed removal (CTWR) is necessary for designing effective weed management programs in popcorn production that do not result in yield reduction. The objective of this study was to determine the CTWR in popcorn with and without a premix of atrazine and S-metolachlor applied PRE. Field experiments were conducted at the University of Nebraska–Lincoln, South Central Agricultural Laboratory near Clay Center, NE in 2017 and 2018. The experiment was laid out in a split-plot design with PRE herbicide as the main plot and weed removal timing as the subplot. Main plots included no herbicide or atrazine/S-metolachlor applied PRE. Subplot treatments included a weed-free control, a non-treated control, and weed removal timing at V3, V6, V9, V15, and R1 popcorn growth stages and then kept weed free throughout the season. A four-parameter log-logistic function was fitted to percentage popcorn yield loss and growing degree days separately to each main plot. The number of growing degree days, when 5% yield loss was achieved, was extracted from the model and compared between main plots. The CTWR was from the V4 to V5 popcorn growth stage in absence of PRE herbicide. With atrazine/S-metolachlor applied PRE, the CTWR was delayed until V10 to V15. It is concluded that, to avoid yield loss, weeds must be controlled before the V4 popcorn growth stage when no PRE herbicide is applied, and PRE herbicide, such as atrazine/S-metolachlor in this study, can delay the CTWR until the V10 growth stage.

Integrated weed management in direct-seeded rice: dynamics and economics

Weeds are often the most severe problem in direct-seeded rice (Oryza sativa L.) (DSR), causes reductions in yield and profitability. The traditional method of controlling rice weeds or manual weeding has several demerits as the practice is uneconomical and difficult. The effects of 10 different weed management practices were evaluated to identify the most effective and economical methods of managing weeds in DSR during in Nepal during the rainy season of 2010. Pendimethalin was applied pre-emergence where 2,4-D, bispyribac sodium, and oxadiargyl were applied post-emergence alone or combined with hand weeding. Sesbania (Sesbania aculeata Wild. Pers.) was co-cultured with rice and killed by 2,4-D. Weed emergence, density, and biomass per unit area of 3 weed types: broadleaf, sedges, and grasses were assessed during 20, 40, 60 days after seeding (DAS), and at harvest. Treatments were compared either to weedy check or weed-free control to determine weed control indices. A total of 42 weed species belonging to 27 genera and 11 families emerged across the growing season of rice. Most of the weeds were annual where broadleaf and sedges were dominant during the first two months, and grasses were dominant under flooding. Weeds reduced the rice yield by more than 80% in weedy-check with respect to weed-free control. A sequential application of pendimethalin as pre-emergence and bispyribac-sodium postemergence herbicides followed by a hand weeding at 45 DAS provided up to 85% weed control over weedy check than other weed control measures. However, that method found uneconomical when compared to the same without hand weeding because of the high cost of manual labor. Pendimethalin was effective in controlling early flush of weeds and bispyribac efficiently controlled weeds even after flooding turned out to be a less expensive method controlling in DSR. An integrated approach of weed management including both pre-emergence and post-emergence herbicides can provide season-long weed control greater economic return.

Efficacy of HPPD-inhibiting herbicides applied preemergence or postemergence for control of multiple herbicide resistant waterhemp [Amaranthus tuberculatus (Moq.) Sauer

Research was conducted in 2017 and 2018 to determine the relative efficacy of five HPPD-inhibitors, tank-mixed with atrazine, for the control of multiple herbicide resistant waterhemp. At 12 wk after application (WAA), isoxaflutole + atrazine, mesotrione + atrazine, and tembotrione + atrazine, applied preemergence (PRE), controlled waterhemp 90%, 87%, and 81%, respectively. None of the HPPD-inhibiting herbicides applied PRE controlled waterhemp similar to the weed-free control 12 WAA. Applied postemergence, topramezone + atrazine, mesotrione + atrazine, tolpyralate + atrazine, and tembotrione + atrazine controlled waterhemp 87%, 94%, 97%, and 98% 12 WAA, respectively, and were all similar to the weed-free control.

Control of multiple-resistant waterhemp [Amaranthus tuberculatus (Moq.) Sauer] with preemergence and postemergence herbicides in corn in Ontario

Waterhemp is a competitive, summer annual, broadleaf weed that poses a considerable threat to Ontario grain farmers. Populations with multiple resistance to Group 2 (ALS-inhibitors), Group 5 (photosystem II inhibitors), and Group 9 (EPSPS inhibitors) herbicides have been confirmed in Ontario. If left uncontrolled, waterhemp competition can result in corn yield losses of up to 74%. The objective of this research was to evaluate preemergence (PRE) and postemergence (POST) herbicides for control of multiple-herbicide resistant (MR) waterhemp. Two field studies at two locations (Cottam and Walpole Island) were conducted in 2016 and 2017. Fifteen PRE and 12 POST herbicides were evaluated for waterhemp control, density, and aboveground biomass and corn yield. At 8 wk after application (WAA), S-metolachlor/mesotrione/atrazine (1393/139/524 g a.i. ha−1) and S-metolachlor/mesotrione/bicyclopyrone/atrazine (1259/140/35/588 g a.i. ha−1) applied PRE were the most efficacious, controlling MR waterhemp 87% and 91%, respectively. At 8 WAA, the most efficacious POST herbicides were mesotrione + atrazine and dicamba/atrazine, controlling MR waterhemp 92% and 87%, respectively. Reduced waterhemp interference with the PRE herbicides evaluated resulted in corn yield that was similar to the weed-free control.

Carry-over effect of brown manuring supplemented with nitrogen on productivity and profitability in succeeding wheat (Triticum aestivum)

A field experiment was carried out on wheat (Triticum aestivum L.) (2017-18) in succession to maize (Zea mays L.) crop grown with several brown manuring (BM) practices (2017) at ICAR-Indian Agricultural Research Institute, New Delhi. The field layout was fixed for both maize and wheat. The 12 brown manuring/weed control treatments adopted in maize were taken as main plot treatments, and three levels of N, viz. 0, 60 and 120 kg N/ha were taken as sub-plot treatments. At 40 DAS, with respect to weed control, all BM/weed control treatments were inferior to weed-free control, which was freshly employed in both seasons, but was superior to un-weeded control. Among the BM treatments, the Sesbania + Crotalaria mixture (12.5+12.5 kg/ha) and 2,4-D applied at 35 DAS resulted in lowest total weed density (~31.8/m2), which was 46.5% lower than that in the un-weeded control. Total weed density was positively correlated with N level. Total weed density was highest at the highest dose of nitrogen at 120 kg/ha (~37.1/ m2) and was significantly higher than those in no nitrogen (~32.0/m2). Sesbania + Crotalaria mixture (12.5+12.5 kg/ha) and 2,4-D applied at 35 DAS was superior to others with respect to wheat’s ear bearing tillers (419.6), grains/ spike (49.1), 1000-grain weight (40.3 g), harvest index (38.5%), grain yield (4.41 t/ha) and biological yield (11.42 t/ ha), gross returns (111500 `/ha) and net returns (80600 `/ha). This treatment also resulted in higher grain yield (4.80 t/ha) and net returns (89400 `/ha) than other treatments at 60 kg N/ha, and was at par with weed-free control with 120 kg N/ha (5.19 t/ha and 92200 `/ha, respectively). Therefore, the carry-over effects of 1:1 mixture of Sesbania bispinosa and Crotalaria juncea (12.5+12.5 kg/ha) and 2,4-D 0.5 kg/ha applied at 35 DAS in combination with 60 kg N/ha can lead to higher wheat productivity and profitability.

Weed Control in Corn and Soybean with Group 15 (VLCFA Inhibitor) Herbicides Applied Preemergence

Limited information exists on the efficacy of pethoxamid for annual grass and broadleaf control in corn and soybean in Ontario. A total of 10 field experiments (5 with corn and 5 with soybean) were conducted during 2015 to 2017 in Ontario, Canada, to compare the weed control efficacy of dimethenamid-P at 544 g·ai·ha−1, pethoxamid at 840 g·ai·ha−1, pyroxasulfone at 100 g·ai·ha−1, and S-metolachlor at 1050 g·ai·ha−1 applied preemergence (PRE). Reduced weed interference with pyroxasulfone and dimethenamid-P resulted in corn yield that was similar to the weed-free control; however, weed interference with pethoxamid and S-metolachlor reduced corn yield 28 and 33%, respectively. Reduced weed interference with pyroxasulfone resulted in soybean yield that was similar to the weed-free control; however, weed interference with pethoxamid, dimethenamid-P, and S-metolachlor reduced soybean yield 27, 27, and 30%, respectively. At 4 and 8 weeks after application (WAA), all VLCFA inhibitor herbicides (Group 15) provided excellent redroot pigweed control (90 to 99%) in corn. There were no differences in common ragweed control, density, and dry weight among the VLCFA inhibitor herbicide evaluated; pyroxasulfone provided highest numeric common ragweed control and lowest numeric density and dry weight. At 4 and 8 WAA, pyroxasulfone provided the best common lambsquarters and wild mustard control and lowest numeric density and dry weight in corn and soybean. At 8 WAA, the VLCFA inhibitor herbicides controlled green foxtail 91 to 96% in corn; dimethenamid-P provided better control of green foxtail than pethoxamid in soybean. There were no differences in barnyard grass control among the VLCFA inhibitor herbicides evaluated.

Soybean and common ragweed (Ambrosia artemisiifolia) growth in monoculture and mixture

AbstractUnderstanding how plants alter their growth in response to interplant competition is an overlooked but complex problem. Previous studies have characterized the effect of light and water stress on soybean or common ragweed growth in monoculture, but no study has characterized soybean and common ragweed growth in mixture. A field study was conducted in 2015 and 2016 at the University of Nebraska-Lincoln to characterize the growth response of soybean and common ragweed with different irrigation levels and intraspecific and interspecific interference. The experiment was arranged in a split-plot design with irrigation level (0, 50%, 100% replacement of simulated evapotranspiration) as the main plot and common ragweed density (0, 2, 6, 12 plants m−1 row) as the subplot. Crop- and weed-free controls and three mixture treatments were included as subplots. Periodic destructive samples of leaf area and biomass of different organ groups were collected, and leaf area index (LAI), aboveground biomass partitioning, specific leaf area (SLA), and leaf area ratio (LAR) were calculated. Additionally, soybean and common ragweed yield were harvested, and 100-seed weight and seed production were determined. Soybean did not alter biomass partitioning, SLA, or LAR in mixture with common ragweed. Soybean LAI, biomass, and seed size were affected by increasing common ragweed density. Conversely, common ragweed partitioned less new biomass to leaves and increased SLA in response to increased interference. Common ragweed LAI, biomass, and seed number were reduced by the presence of soybean and increasing common ragweed density; however, seed weight was not affected. Results show that adjustment in biomass partitioning, SLA, and LAR is not the method that soybean uses to remain plastic under competition for light. Common ragweed demonstrated plasticity in both biomass partitioning and SLA, indicating an ability to maintain productivity under intra- and inter-specific competition for light or soil resources.

Interspecific Competition Between Sweet Sorghum and Weeds

ABSTRACT: While evidence is mounting that sweet sorghum [Sorghum bicolor (L.) Moench], an ethanol crop, may provide an alternative to sugarcane (Saccharum officinarum L.) on sugarcane lands under rehabilitation, little is known of its under production limiting factors (e.g., interspecific competition with weeds). Accordingly, the aim of the present study was to identify the initial mutual interspecific competition between sweet sorghum hybrids and weeds in high infestation situations. The experiment was carried out in pots, using a 5 × 6 factorial design: (i) a sorghum-free control and four sweet sorghum hybrids (CVSW 81198, CVSW 80007, CVSW 80147 and XBSW 82158), besides a control without sweet-sorghum, and (ii) five species of weeds [Cyperus rotundus L., Mucuna aterrima (Piper and Tracy) Holland, Brachiaria decumbens Stapf, Ipomoea hederifolia L. and Digitaria nuda Schumach.], besides a weed-free control. M. aterrima was the only weed whose dry mass was not reduced by the presence of sweet sorghum. The hybrids of sweet sorghum did not suffer developmental interference from C. rotundus, I. hederifolia or D. nuda. On the other hand, these weeds dry mass was reduced through competition with sweet sorghum. The sweet sorghum cohabiting with B. decumbens or M. aterrima has its aboveground and leaf dry mass reduced. Sweet sorghum is a high competitive and robust plant and, even when under a high weed density, suffers little interspecific interference from certain species of the weed community.