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The rice–wheat cropping system (RWCS) is the backbone of Indian farming, especially in the north-western region. But continuous adoption of the RWCS in northwest India has resulted in major challenges and stagnation in the productivity of this system. Additionally, the Indo-Gangetic Plains of Pakistan, Nepal, and Bangladesh are also facing similar challenges for sustainable production of the RWCS. Several emerging problems, such as the exhausting nutrient pool in soil, deteriorating soil health, groundwater depletion, escalating production cost, labor scarcity, environmental pollution due to crop residue burning and enhanced greenhouse gas emissions, climatic vulnerabilities, and herbicide resistance in weed species, are a few major threats to its sustainability. To address these challenges, a wide range of sustainable intensification technologies have been developed to reduce the irrigation and labor requirements, tillage intensity, and straw burning. Awareness and capacity building of the stakeholders and policy matching/advocacy need to be prioritized to adopt time- and need-based strategies at the ground level to combat these challenges. This review summarizes the current status and challenges of the RWCS in the northwest region of the country and also focuses on the precision management options for achieving high productivity, profitability, and sustainability.

Multiple herbicide classes–resistant (MHCR) kochia poses a serious concern for producers in the Central Great Plains, including western Kansas. Greenhouse and field experiments were conducted at Kansas State University Research and Extension Centers near Hays and Garden City, KS, to evaluate pyridate-based postemergence herbicide mixtures for controlling MHCR kochia. One previously confirmed MHCR population (resistant to atrazine, glyphosate, dicamba, and fluroxypyr) and a susceptible (SUS) kochia population were tested in a greenhouse study. The kochia population at Hays field site was resistant to atrazine, dicamba, and glyphosate, whereas the kochia population at the Garden City site was resistant to atrazine and glyphosate. Colby’s analysis revealed synergistic interactions when pyridate was mixed with atrazine, dicamba, dichlorprop-p, fluroxypyr, glyphosate, or halauxifen/fluroxypyr and resulted in ≥94% control and shoot dry-biomass reduction of MHCR kochia in a greenhouse study. Similarly, synergistic interactions were observed for MHCR kochia control in fallow field studies at both sites when pyridate was mixed with glyphosate or atrazine. Kochia control was increased from 26% to 90% with the application of glyphosate + pyridate and from 28% to 95% with atrazine + pyridate at both sites as compared to separate applications of glyphosate or atrazine. This is the first report for such a strong synergistic effect for both glyphosate and atrazine mixtures with pyridate on a weed resistant to both. All other pyridate-based herbicide mixtures showed an additive interaction and resulted in better control of MHCR kochia (87% to 100%) as compared to their individual applications (23% to 92%) across both sites except 2,4-D. These results suggest that pyridate can play a crucial role in various postemergence herbicide mixtures for effective control of MHCR kochia.

The authors would like to make the following correction to the published paper [...]

In February 2024, the United States Environmental Protection Agency (EPA) vacated the registrations of dicamba products for over-the-top applications on dicamba-resistant cotton and soybean following a court ruling. This decision has raised significant concerns among United States farmers, who now have limited chemical options to manage tough-to-control weeds. However, the risk of off-target dicamba movement to sensitive plants remains a critical issue. If permitted in the future, applying dicamba as a preemergence (PRE) treatment, tank-mixed with other soil residual herbicides, could help reduce off-target movement while preserving its utility for managing problem weeds. Field experiments were conducted in 2022 and 2023 in Minnesota and North Dakota, and in 2021 and 2022 in Wisconsin, to evaluate the effectiveness of dicamba-based PRE herbicide mixtures in soybean. Across all site-years, dicamba tank mixed with other soil residual herbicides provided better control of targeted weed species at 21 d after treatment (DAT) compared to applying the residual herbicides alone. In Minnesota, dicamba-based herbicide tank mixes provided an average waterhemp control of 72%, compared to 59% for treatments without dicamba at 21 DAT. Similarly, in North Dakota, waterhemp control at 21 DAT improved from 74% with residual herbicides alone to 97% when tank mixed with dicamba. In Wisconsin, dicamba-based tank mixes resulted in 96% control of common ragweed and 83% of velvetleaf, versus 83% and 73% for those species, respectively, without dicamba. At the Minnesota site, adding dicamba to residual herbicides improved common lambsquarters and giant ragweed control by 17% and 20%, respectively, and their densities were reduced by at least 50%. At the North Dakota site, kochia control was improved by 23% with dicamba PRE. The results from this research outlined the effectiveness of PRE application of dicamba tank mixed with other residual herbicides for effective weed management in the Upper Midwest.

Chenopodium album L. and Chenopodium murale L. are two principal weed species, causing substantial damage to numerous winter crops across the globe. For sustainable and resource-efficient management strategies, it is important to understand weeds’ germination behaviour under diverse conditions. For the germination investigations, seeds of both species were incubated for 15 days under different temperatures (10–30 °C), salinity (0–260 mM NaCl), osmotic stress (0–1 MPa), pH (4–10), and heating magnitudes (50–200 °C). The results indicate that the germination rates of C. album and C. murale were 54–95% and 63–97%, respectively, under a temperature range of 10 to 30 °C. The salinity levels for a 50% reduction in the maximum germination (GR50) for C. album and C. murale were 139.9 and 146.3 mM NaCl, respectively. Regarding osmotic stress levels, the GR50 values for C. album and C. murale were 0.44 and 0.43 MPa, respectively. The two species showed >95% germination with exposure to an initial temperature of 75 °C for 5 min; however, seeds exposed to 100 °C and higher temperatures did not show any germination. Furthermore, a drastic reduction in germination was observed when the pH was less than 6.0 and greater than 8.0. The study generated information on the germination biology of two major weed species under diverse ecological scenarios, which may be useful in developing efficient weed management tactics for similar species in future agri-food systems.

Two separate field experiments were conducted during the 2021 to 2022 and 2022 to 2023 growing seasons at Kansas State University Agricultural Research Center near Hays, KS, to understand the emergence dynamics of glyphosate-resistant (GR) kochia [Bassia scoparia (L.) A. J. Scott] as influenced by fall- and spring-planted cover crops (CC) and residual herbicide. Study sites were under winter wheat (Triticum aestivum L.)–sorghum [Sorghum bicolor (L.) Moench]–fallow rotation with a natural seedbank of GR B. scoparia. In Experiment 1, fall-planted CC mixture (triticale/winter peas/radish/canola) was planted after wheat harvest and terminated at triticale [×Triticosecale Wittm. ex A. Camus [Secale × Triticum] heading stage (next spring before sorghum planting). In Experiment 2, spring-planted CC mixture (oats/barley/spring peas) was planted in sorghum stubbles and terminated at oats (Avena sativa L.) heading stage. Four treatments were established in each experiment: (1) nontreated control (no CC and no herbicide), (2) chemical fallow (no CC but glyphosate + acetochlor/atrazine or flumioxazin/pyroxasulfone + dicamba were used to control weeds), (3) CC terminated with glyphosate, and (4) CC terminated with glyphosate plus residual herbicide (acetochlor/atrazine for fall-planted CC and flumioxazin/pyroxasulfone for spring-planted CC). Results indicated that fall-planted CC delayed GR B. scoparia emergence by 3 to 5 wk, whereas spring-planted CC delayed emergence by 0 to 2 wk compared with nontreated control. Fall-planted CC terminated with glyphosate plus acetochlor/atrazine reduced the cumulative emergence of GR B. scoparia by 90% to 95% compared with nontreated control across both years. Similarly, spring-planted CC terminated with glyphosate plus flumioxazin/pyroxasulfone reduced the cumulative emergence of GR B. scoparia by 83% to 90% compared with nontreated control. These results suggest that fall- or spring-planted CC in combination with residual herbicide at termination can be utilized for GR B. scoparia suppression. Results from this study will help in developing prediction models for GR B. scoparia emergence under different CC strategies.

Leucaena [Leucaena leucocephala (Lam.) de Wit] is a perennial weed in more than 25 countries, including Australia. Knowledge regarding the seed biology of L. leucocephala could help in making weed management decisions. Experiments were conducted to study the effect of hot water (scarification), alternating temperatures, heat stress, salt stress, water stress, and burial depth on seed germination of two populations of L. leucocephala collected from Toowoomba and Gatton, Australia. The optimum duration of hot water treatment to break the hard seed coat dormancy was 2 min for both populations. The highest germination (92% to 98%) was recorded at 35/25 C for both populations, and similar germination occurred at 30/20 C. The Toowoomba population recorded greater germination at low temperature (15/5 to 25/15 C) than the Gatton population. Additionally, the Gatton population had higher germination than the Toowoomba population after 5 min of exposure to temperatures of up to 100 C, suggesting that the Gatton population may be more tolerant to heat stress. Germination was completely inhibited at pretreatment (5 min) temperatures of 150 to 250 C. The Toowoomba population recorded 17% greater germination than the Gatton population at a high salt concentration (160 mM NaCl), indicating its greater salt tolerance. At low moisture stress (–0.1 and –0.2 MPa), higher germination was observed in the Toowoomba population than in the Gatton population, whereas germination was similar for both populations at higher water stress levels (–0.4 MPa or lower). Germination was similar for both populations at shallow depths (0 and 1 cm) but higher emergence was recorded for the Toowoomba population at 2 to 8 cm than the Gatton population. Differential germination behaviors of both populations suggest that they adapted differently in their respective local environments. Knowledge gained from this study will help in formulating integrated management practices for L. leucocephala.

The worldwide contamination of waters and food by herbicides is a major health issue, yet the toxic effects of herbicides to non-target organisms and ecosystems have been poorly summarized. Here we review the effects of herbicides belonging to the groups of chloroacetanilides, imidazolinones, sulfonylureas, and pyrimidinylcarboxylic, on small invertebrates, high vertebrates, plants, and the surrounding ecosystems. We describe toxicity in terms of behavioural changes, molecular biosynthesis, endocrine disruption, immunological responses, enzymatic alteration, and reproductive disorders. Strategies to decrease toxic effects are also presented. We observe widespread toxicity threats in amphibians and major aquatic species. Each herbicide group displays a different toxicity risk. For instance, chloroacetanilides display higher risks to soil, aquatic, algal, cyanobacteria, and terrestrial species, whereas alachlor, acetochlor, and metolachlor are highly carcinogenic to humans. Most imidazolinone herbicides cause phytotoxicity in non-target and succeeding crops. Sulfonyl-urea herbicides are severely toxic to soil microbes and succeeding crops. Pyrimidinylcarboxy herbicides are more toxic to soil microbes, aquatic species, and rats.

Vipergrass [Dinebra retroflexa (Vahl) Panzer] is an annual weed of the Poaceae family distributed in several parts of Australia, Asia, and Europe. Very limited information is available on its germination response to different environmental conditions. Knowledge of its seed ecology and biology could help in formulating better weed management decisions. Experiments were conducted to study the effect of alternating temperatures, light conditions, salt stress, water stress, seed burial depths, and wheat residue amounts on the germination or emergence of D. retroflexa. Also, different pre- and postemergence herbicides were evaluated to control D. retroflexa. The highest germination (98%) was recorded at 30/20 C followed by 35/25 C (95%). Light was required for the germination of D. retroflexa. Germination decreased with an increase in sodium chloride (NaCl) concentrations. Even at 80 mM NaCl, 81% of seeds germinated, indicating D. retroflexa's high salt tolerance. Seed germination gradually decreased with an increase in water stress, and no germination was recorded at –0.8 MPa osmotic potential. The emergence of D. retroflexa decreased with an increase in seed burial depths. The highest germination (83%) was recorded for surface-sown seeds, and emergence was reduced to 0 at a burial depth of 2 cm. Seedling emergence decreased from 82% to 2% when the crop residue load was increased from 0 to 800 kg ha–1. Applications of preemergence herbicides (at field rates), such as diuron, isoxaflutole, pendimethalin, pyroxasulfone, S-metolachlor, terbuthylazine, and triallate, and postemergence herbicides, such as clethodim, haloxyfop-methyl, glufosinate, glyphosate, imazamox plus imazapyr (a commercial mixture), and paraquat, resulted in complete control (100%) of D. retroflexa. Knowledge gained from this study will help us to understand the potential spread of D. retroflexa to other areas and to formulate integrated weed management strategies for its effective control.

Kochia [Bassia scoparia (L.) A. J. Scott] and Palmer amaranth (Amaranthus palmeri S. Watson) are the two most troublesome summer annual weeds in the Central Great Plains (CGP). The widespread evolution of herbicide resistance in both species warrants alternate weed management strategies in the region. The major objectives of this dissertation were to 1) determine the response of kochia populations from Kansas, Oklahoma, and Texas to commonly used herbicides and quantify the level of resistance in putative multiple herbicide-resistant (MHR) kochia populations, 2) determine the interactions of 2,4-D, dichlorprop-p, dicamba, and halauxifen/fluroxypyr applied in two- or three-way combinations for controlling MHR kochia, 3) evaluate pyridate-based tank mixtures for controlling MHR kochia, 4) determine the effect of fall-planted cover crop (CC) and soil residual herbicides on emergence pattern and emergence periodicity of glyphosate-resistant Palmer amaranth, and 5) determine the effect of fall-planted CC in combination with soil residual herbicides on weed suppression and on grain yield and net returns in no-till dryland grain sorghum. Greenhouse screening experiments showed that 23% of tested kochia populations (82 total) from Kansas, Oklahoma, and Texas were potentially four-way resistant (≥20% survival) to chlorsulfuron, dicamba, fluroxypyr, and glyphosate. Dose-response studies further revealed resistance to dicamba (5- to 13-fold), fluroxypyr (3- to 6-fold), and glyphosate (3- to 5-fold) in kochia populations from Kansas and Oklahoma and resistance to dicamba (2- to 4-fold) and glyphosate (5-fold) in Texas populations compared to susceptible population. Three-way tank-mixtures of 2,4-D, dicamba, dichlorprop-p, and halauxifen/fluroxypyr in various combinations had synergistic interactions and provided 85 to 97% control of MHR kochia. Results from greenhouse experiments also showed synergistic interactions when pyridate was tank-mixed with atrazine, dicamba, dichlorprop-p, fluroxypyr, glyphosate, or halauxifen/fluroxypyr and resulted in >94% control and shoot dry biomass reduction of MHR kochia. In a separate field study, a synergistic interaction was observed when pyridate was tank-mixed with glyphosate or atrazine. Results from a 3-year field study showed that fall-planted CC after winter wheat harvest and terminated before grain sorghum planting with glyphosate plus acetochlor/atrazine required 105 to 1257 more cumulative growing degree days for 90% emergence of glyphosate-resistant Palmer amaranth and reduced the cumulative emergence by 42 to 56% compared to chemical fallow. Furthermore, the same treatment reduced total weed density by 34 to 81% and total weed biomass by 45 to 73% compared to chemical fallow. Average grain sorghum yield was 790 to 1430 kg ha-1 and did not differ between chemical fallow and CC terminated with glyphosate plus acetochlor/atrazine. However, net returns were lower with both CC treatments (USD -$275 to $66 ha-1) in all three years than chemical fallow (USD -$111 to $120 ha-1). These results suggest that integrating a fall-planted CC after wheat harvest can help suppress glyphosate-resistant kochia and Palmer amaranth in the subsequent grain sorghum. This practice was not profitable most years but could be profitable during wet years with average yields (3800 to 5000 kg ha-1) of the region. Overall, the results confirm the widespread presence of MHR kochia populations in the southcentral Great Plains. Growers should adopt alternative herbicide tank-mixtures and CC strategies to manage herbicide-resistant kochia and Palmer amaranth populations in the region.