Herbicide mixtures control glyphosate-resistant kochia (Bassia scoparia) in chemical fallow, but their longevity warrants careful stewardship

Glyphosate-resistant kochia [Bassia scoparia (L.) A.J. Scott], the first known glyphosate-resistant weed in western Canada, was confirmed initially in chemical fallow fields located in Warner County, Alberta in 2011. Further selection, lack of control, and rampant spread of this biotype contributed to its increased incidence, now present in about 50% of kochia populations sampled in Alberta. In 2014 and 2015, herbicide mixtures were evaluated based on control of glyphosate-resistant and susceptible kochia in chemical fallow fields near Lethbridge and Coalhurst, Alberta. The most consistent control (≥ 80% visual control in all environments with ≥ 80% biomass reduction in 2014) was observed with glyphosate + dicamba (450 + 580 g ae ha-1), glyphosate + dicamba/diflufenzopyr (450 + 150/50 g ai/ae ha-1), glyphosate + saflufenacil (450 + 50 g ai/ae ha-1), and glyphosate + carfentrazone + sulfentrazone (450 + 9 + 105 g ai/ae ha-1). Reduced efficacy was observed for several herbicide mixtures when they were applied to glyphosate-resistant compared with glyphosate-susceptible kochia accessions. Effective modes of action mixed with glyphosate include synthetic auxins (group 4), a combination of a synthetic auxin and an auxin transport inhibitor (group 19), or protoporphyrinogen oxidase inhibitors (group 14). In response to glyphosate-resistant kochia, many farmers in this region shifted their herbicide programs resulting in greater reliance on synthetic auxins; likely contributing to the recent discovery of auxinic herbicide-resistant kochia biotypes in Alberta in 2017. Careful herbicide stewardship is warranted to mitigate further selection of multiple herbicide-resistant kochia, suggesting an important role for integrated weed management.

Scouringrush (Equisetum spp.) control in dryland winter wheat

The adoption of chemical fallow rotations in Pacific Northwest dryland winter wheat production has caused a weed species composition shift in which scouringrush has established in production fields. Thus, there has been interest in identifying herbicides that effectively control scouringrush in winter wheat–chemical fallow cropping systems. Field experiments were established in growers’ fields near Reardan, WA, in 2014, and The Dalles, OR, in 2015. Ten herbicide treatments were applied to mowed and nonmowed plots during chemical fallow rotations. Scouringrush stem densities were quantified the following spring and after wheat harvest at both locations. Chlorsulfuron plus MCPA-ester resulted in nearly 100% control of scouringrush through wheat harvest. Before herbicide application, mowing had no effect on herbicide efficacy. We conclude chlorsulfuron plus MCPA-ester is a commercially acceptable treatment for smooth and intermediate scouringrush control in winter wheat–chemical fallow cropping systems; however, the lack of a positive yield response when scouringrushes were controlled should factor into management decisions.

Rational Way of Forming Stubble Coulisses under North Kazakhstan Conditions

The main limiting factor for increasing yields in the arid steppe conditions of Northern Kazakhstan is moisture. Shoots are usually uneven due to the lack of moisture at the initial stage of their growing. The main source of moisture in this period is winter precipitation. Currently, the following methods of winter precipitation moisture accumulation are used in North Kazakhstan: leaving high standing stubble, seeding coulisses on pure fallow fields, herbicide (chemical) fallow field, snow ridging, harvesting of crops with continuous combining; and forming stubble coulisses. The most preferable way of increasing snow moisture accumulation is the formation of stubble coulisses that can be done in two ways.Research purpose Efficiency evaluation of the ways of forming stubble coulisses.Materials and methods Agroengineering and technological evaluation is used as a main research method of different ways of forming stubble coulisses, which is followed by the selection of a more preferable way.Results and discussion It has been found that in snowy winter both ways of forming stubble coulisses – with alternative passes of a direct combining reaper and a stripping reaper and using a direct combining reaper with a stripper adapter – have shown the same results. However, when there is a little snow in winter, the second way provides more intensive snow accumulation.Conclusions It has been experimentally found that using the direct combining reaper with the stripper adapter decreases labour inputs by 17.8% and total costs by 23.8% as compared to the formation of coulisses by using sequential passes of the direct combining and the stripping reapers. It has been found that the formation of stubble coulisses every 5-9 meters along with in-line para-plowing at a depth of up to 35 cm provides the highest yield increase of in snowy winter as compared to the conventional ways of moisture accumulation.

Relay-cropping and Fallow Programs for Strawberry-based Production System: Effects on Crop Productivity and Weed Control

Many strawberry growers in Florida relay crop vegetables with strawberries or grow multiple crops on the same plastic mulch. The practice can reduce the overall input costs per crop but weed management can be problematic. Field experiments designed as a split plot were conducted in Balm and Dover, FL over two successive strawberry-growing seasons from Oct. 2014 to Mar. 2015 (year 1) and Oct. 2015 to Mar. 2016 (year 2) and two successive muskmelon-growing seasons from March to July 2015 (year 1) and March to July 2016 (year 2). The objectives were to examine the effect of summer fallow programs and the presence or absence of a relay-crop on weed density and strawberry (Fragaria ×ananassa Duchesne) and muskmelon (Cucumis melo L.) yields. Summer fallow programs included leaving the plastic mulch in place and reusing it in year 2, a sunn hemp (Crotalaria juncea L.) cover crop, or a conventional chemical fallow. Relay cropping muskmelon with strawberries had no effect on strawberry yield. Summer fallow programs had no effect on muskmelon growth and yield in Balm and Dover, as well as strawberry growth and yield in Balm. In Dover, the plastic mulch summer fallow had 22% to 34% lower berry yield in year 2 compared with cover crop and chemical fallow, respectively. In year 2, relay-cropping was more effective in reducing total weed density compared with strawberry monoculture in Dover but not in Balm. In year 2 in Dover, averaged overall summer fallow programs, the total weed density was ≈3-fold less in relay-cropping than strawberry monoculture. Of all the summer fallow programs evaluated, leaving the plastic mulch in place combined with glyphosate was the most effective summer fallow program, whereas the conventional chemical fallow was the least effective at weed suppression. We conclude that relay cropping or double use of plastic mulch for successive strawberry crops are viable options for Florida strawberry growers.

Can legumes provide greater benefits than millet as a spring cover crop in southern Queensland farming systems?

Cover crops grown during fallows can increase organic matter inputs, improve soil surface cover to reduce erosion risk, and enhance rainfall infiltration. An experiment compared a chemical fallow control with six different cover crops terminated at either 60 or 90 days after sowing. The commercial choice of millet (Echinochloa esculenta) was compared with two summer legumes (lablab (Lablab purpureus) and soybean (Glycine max)), and three winter legumes (field pea (Pisum sativum), faba bean (Vicia faba) and common vetch (Vicia sativa)). Cover crop biomass growth, atmospheric nitrogen (N) fixation, surface residue cover, and soil water and mineral N dynamics during the growth period and subsequent fallow were measured. Soil water and N availability and yield of wheat crops following the experimental treatments were simulated over a 100-year climate record using APSIM. Both experiments and simulations found the legumes inferior to millet as spring-sown cover crops, because they were slower to accumulate biomass, required later termination and provided groundcover that was less persistent, resulting in lower soil water at the end of the fallow. After 90 days of growth, the summer legumes, lablab and soybean, produced the most biomass and fixed more N (up to 25 kg N/ha) but also extracted the most soil water and mineral N. Legume N fixation was low because of high soil mineral N status (>100 kg N/ha) and occurred only when this had been depleted. At the end of the subsequent fallow in April, soil water was 30–60 mm less and soil mineral N 80–100 kg/ha less after both millet and 90-day terminated summer legume cover crops than the chemical fallow control. Simulations predicted soil-water deficits following legume cover crops to be >50 mm in the majority of years, but soil mineral N was predicted to be lower (median 80 kg N/ha) after millet cover crops. In conclusion, monoculture legume cover crops did not provide advantages over the current commercial standard of millet, owing to less effective provision of groundcover, low N fixation and possibly delayed release of N from residues. Further work could explore how legumes might be more effectively used as cover crops to provide N inputs and soil protection in subtropical farming systems.

Effective Preemergence and Postemergence Herbicide Programs for Kochia Control

Field experiments were conducted in 2011 through 2013 at the MSU Southern Agricultural Research Center near Huntley, MT, to evaluate the effectiveness of various PRE and POST herbicide programs for kochia control in the absence of a crop. PRE herbicides labeled for corn, grain sorghum, soybean, wheat/barley, and/or in chemical fallow were applied at recommended field-use rates. Acetochlor + atrazine,S-metolachlor + atrazine + mesotrione, and sulfentrazone applied PRE provided ≥91% control of kochia at 12 wk after treatment (WAT). Metribuzin, metribuzin + linuron, and pyroxasulfone + atrazine PRE provided 82% control at 12 WAT. PRE control with acetochlor + flumetsulam + clopyralid, pyroxasulfone alone, and saflufenacil + 2,4-D was ≤23% at 12 WAT. Paraquat + atrazine, paraquat + linuron, and paraquat + metribuzin controlled kochia ≥98% at 5 WAT. POST control with bromoxynil + fluroxypyr, paraquat, tembotrione + atrazine, and topramezone + atrazine treatments averaged 84% at 5 WAT, and did not differ from glyphosate. Control with POST-applied bromoxynil + pyrasulfotole, dicamba, diflufenzopyr + dicamba + 2,4-D, saflufenacil, saflufenacil + 2,4-D, saflufenacil + linuron was 67 to 78% at 5 WAT. Because of the presence of kochia resistant to acetolactate synthase-inhibiting herbicides at the test site, cloransulam-methyl was not a viable option for kochia control. In a separate greenhouse study, kochia accessions showed differential response to the POST herbicides (labeled for corn or soybean) tested. Tembotrione + atrazine, topramezone + atrazine, lactofen, or fomesafen effectively controlled the glyphosate-resistant kochia accession tested. Growers should utilize these effective PRE- or POST-applied herbicide premixes or tank mixtures (multiple modes of action) to control herbicide-resistant kochia accessions in the field. PRE herbicides with 8 wk of soil-residual activity on kochia would be acceptable if crop competition were present; however, a follow-up herbicide application may be needed to obtain season-long kochia control in the absence of crop competition.

Glyphosate-resistant kochia (Kochia scoparia L. Schrad.) in Saskatchewan and Manitoba

Beckie, H. J., Gulden, R. H., Shaikh, N., Johnson, E. N., Willenborg, C. J., Brenzil, C. A., Shirriff, S. W., Lozinski, C. and Ford, G. 2015. Glyphosate-resistant kochia (Kochia scoparia L. Schrad.) in Saskatchewan and Manitoba. Can. J. Plant Sci. 95: 345–349. Previous surveys have documented the occurrence of glyphosate-resistant (GR) kochia in Alberta in 2011 and 2012. To determine the incidence of GR kochia in Saskatchewan and Manitoba, a stratified-randomized survey of 342 sites (one population per site) in southern and central regions of Saskatchewan and a similar survey of 283 sites in southern Manitoba was conducted in the fall of 2013. Mature plants were collected, seed threshed, and progeny screened by spraying with a discriminating glyphosate dose of 900 g ae ha–1 under greenhouse conditions. Screening confirmed 17 GR kochia populations in nine municipalities in west-central or central Saskatchewan, but only two GR populations from different municipalities in the Red River Valley of Manitoba. While the majority of GR kochia populations in Saskatchewan originated in chemical-fallow fields, some populations were found in cropped fields (wheat, Triticum aestivum L.; lentil, Lens culinaris Medik.; GR canola, Brassica napus L.) and non-cropped areas (oil well, roadside ditch). In Manitoba, the two populations occurred in fields cropped to GR corn (Zea mays L.) and soybean (Glycine max L. Merr.). Agronomic and economic impact of this GR weed biotype is compounded because of consistent multiple resistance to acetolactate synthase-inhibiting herbicides. However, GR kochia is susceptible to dicamba, an increasingly important auxinic herbicide used for control of this multiple-resistant weed biotype.

Crop-sequence effects on productivity in a wheat-based cropping system at Wongan Hills, Western Australia

Western Australian grain production is dominated by wheat, but growing wheat continually in unbroken sequences leads to increasing problems with soil nutrient depletion, root and leaf disease build-up, high weed burdens, and possibly other less well-defined production constraints. These can adversely affect both production and grain quality. Including breaks in the crop sequence in the form of break crops, pasture, or fallow can reduce these problems, but these breaks can be expensive to implement, in terms of both direct cost and forgone revenue. It is therefore critical to predict the response of subsequent wheat crops to a break in order to choose crop sequences rationally. We conducted a 4-year experiment at Wongan Hills, Western Australia, evaluating how wheat productivity in a wheat-based cropping sequence is affected by including wheat, barley, lupins, triazine-tolerant and Roundup Ready® canola, oaten hay, volunteer pasture, serradella pasture, and chemical fallow. Wheat yield responded positively to fallow, lupins, oaten hay, volunteer pastures and serradella but not to barley or canola when compared with continuous wheat. Responses depended on seasonal conditions; in a dry year, a very large response occurred after fallow but not after lupin or serradella, whereas in a wetter year, there were large responses after these crops. Fallowing, cutting hay, crop-topping lupins, and spray-topping volunteer and serradella pasture all reduced seedset of annual ryegrass dramatically, and reduced weed competition was a major contributor to the observed break crop responses. Nitrogen fixation by lupins and serradella and water storage by fallow in a dry year were also important, but soilborne diseases did not contribute to wheat yield responses. Some yield responses persisted for at least 3 years, and the contribution of effects of weed competition to yield responses increased over this time. These results emphasise the importance of understanding which productivity constraints are present in a cropping system at a given time when deciding whether a break is necessary and which is the most appropriate break. The results also emphasise the importance of managing the wheat crop after a break to maximise the response and its longevity.

Response of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) to alternative herbicides

Burton, N., Shirriff, S. W. and Beckie, H. J. 2014. Response of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) to alternative herbicides. Can. J. Plant Sci. 94: 1407–1411. A greenhouse study was conducted to examine the response of glyphosate-resistant (GR) plus acetolactate synthase (ALS) inhibitor-resistant kochia to five post-emergence herbicide treatments commonly used to control the weed species in chemical fallow, cereals, or oilseed crops in western Canada. The treatments, which were applied to two GR kochia biotypes and one non-GR (susceptible) biotype, included the labeled rate of dicamba, dicamba/fluroxypyr, dicamba/diflufenzopyr, MCPA/bromoxynil, and glufosinate. Both GR and non-GR biotypes responded similarly to each of the herbicide treatments. Although both GR biotypes were sensitive to the herbicides, MCPA/bromoxynil was the most effective treatment in reducing shoot biomass 3 wk after application (99%), followed by glufosinate (91%) then the dicamba mixtures (82%). Dicamba alone only suppressed kochia biomass (76% reduction).

Occurrence and Characterization of Kochia (Kochia scoparia) Accessions with Resistance to Glyphosate in Montana

Herbicide-resistant kochia is an increasing concern for growers in the northwestern United States. Four suspected glyphosate-resistant (Gly-R) kochia accessions (referred to as GIL01, JOP01, CHES01, and CHES02) collected in fall 2012 from four different chemical-fallow fields in northern Montana were evaluated. The objectives were to confirm and characterize the level of glyphosate resistance in kochia accessions relative to a glyphosate-susceptible (Gly-S) accession and evaluate the effectiveness of various POST herbicides for Gly-R kochia control. Whole-plant dose–response experiments indicated that the four Gly-R kochia accessions had 7.1- to 11-fold levels of resistance relative to the Gly-S accession on the basis of percent control ratings (I50values). On the basis of shoot dry weight response (GR50values), the four Gly-R kochia accessions exhibited resistance index (R/S) ratios ranging from 4.6 to 8.1. In a separate study, the two tested Gly-R accessions (GIL01 and JOP01) showed differential response (control and shoot dry weight reduction) to various POST herbicides 21 d after application (DAA). Paraquat, paraquat + linuron, carfentrazone + 2,4-D, saflufenacil alone or with 2,4-D, and bromoxynil + fluroxypyr effectively controlled (99 to 100%) and reduced shoot dry weight (88 to 92%) of the GIL01 accession, consistent with the Gly-S kochia accession; however, bromoxynil + MCPA and bromoxynil + pyrasulfotole provided 76% control and 83% shoot dry weight reduction of the GIL01 accession and were lower compared with the Gly-S accession. The JOP01 accession exhibited lower control or shoot dry weight reduction to all herbicides tested, except dicamba, diflufenzopyr + dicamba + 2,4-D, paraquat + linuron, and bromoxynil + pyrasulfotole, compared with the Gly-S or GIL01 population. Furthermore, paraquat + linuron was the only treatment with ≥ 90% control and shoot dry weight reduction of the JOP01 kochia plants. Among all POST herbicides tested, glufosinate was the least effective on kochia. This research confirms the first evolution of Gly-R kochia in Montana. Future research will investigate the mechanism of glyphosate resistance, inheritance, ecological fitness, and alternative strategies for management of Gly-R kochia.