The genus Lolium comprises many species, of which L. perenne ssp. multiflorum , L. perenne ssp. perenne , and L. rigidum are of worldwide agricultural importance as both pasture crops and as weeds. These three species are inter‐fertile, obligate out‐crossers with a self‐incompatible reproduction system. This combination contributes to high genetic diversity that supplies new variants during expansion to new natural areas and agricultural environments. Human dispersal, de‐domestication and crop‐weed hybridization events between Lolium spp., or with others such as Festuca spp., are likely associated with their distinct weediness abilities. Furthermore, new introductions followed by introgression may hasten adaptation to new environments. Most Lolium‐ related weed science studies have focused on adaptation leading to herbicide resistance, but other forms of adaptation may also occur. In this review, we explore how the wide genetic variation among Lolium species and hybridization with other species may contribute to range expansion, and adaptation to both new agricultural practices and future predicted climate change scenarios. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Herbicides are the most commonly used means of controlling weeds. Recently, there has been growing concern over the potential impacts of global climate change, specifically, increasing temperatures and elevated carbon dioxide (CO₂) concentrations, on the sensitivity of weeds to herbicides. Here, glyphosate response of both Conyza canadensis and Chenopodium album was evaluated under different environmental conditions. Reduced glyphosate sensitivity was observed in both species in response to increased temperature, elevated CO₂ level, and the combination of both factors. Increased temperature had greater effect on plant survival than elevated CO₂ level. In combination, high temperature and elevated CO₂ level resulted in loss of apical dominance and rapid necrosis in glyphosate-treated plants. To investigate the mechanistic basis of reduced glyphosate sensitivity, translocation was examined using ¹⁴C-glyphosate. In plants that were subjected to high temperatures and elevated CO₂ level, glyphosate was more rapidly translocated out of the treated leaf to shoot meristems and roots than in plants grown under control conditions. These results suggest that altered glyphosate translocation and tissue-specific sequestration may be the basis of reduced plant sensitivity. Therefore, overreliance on glyphosate for weed control under changing climatic conditions may result in more weed control failures.

There has been a longstanding and contentious debate about the future of glyphosate use in the European Union (EU). In November 2023, the European Commission approved the renewal of the use registration for glyphosate for a further 10 years. Nevertheless, the EU Farm to Fork strategy calls for a 50% reduction in pesticide use by 2030. In November 2022, the European Weed Research Society organised a 2 day workshop to identify critical glyphosate uses in current EU cropping systems and to review the availability of glyphosate alternatives. Workshop participants identified four current, critical uses in EU cropping systems; control and management of perennial weeds, weed control in conservation agriculture, vegetation management in tree and vine crops and herbicide resistance management. There are few herbicide alternatives that provide effective, economic, broad‐spectrum control of weeds, particularly perennial weeds. Mechanical weed control, and in particular, soil cultivation is the most obvious glyphosate alternative. However, this is not possible in conservation agriculture systems and, in general, increased soil cultivation has negative impacts for soil health. Emerging technologies for precision weed control can enable more targeted use of glyphosate, greatly reducing use rates. These technologies also facilitate the use and development of alternative targeted physical weed control (e.g. tillage, lasers, electricity), reducing the energy and environmental costs of these approaches. In tree crops, the use of organic and inorganic mulches can reduce the need for glyphosate use. In general, reduced use of glyphosate will require an even greater focus on integrated weed management to reduce weed establishment in agroecosystems, increase weed management diversity and limit the use of alternative resistance‐prone herbicides.

Multiple resistance to glyphosate, sethoxydim, and paraquat was previously confirmed in two Italian ryegrass [Lolium perenneL. ssp.multiflorum(Lam.) Husnot] populations,MR1andMR2, in northern California. Preliminary greenhouse studies revealed that both populations were also resistant to imazamox and mesosulfuron, both of which are acetolactate synthase (ALS)-inhibiting herbicides. In this study, three subpopulations,MR1-A(from seed ofMR1plants that survived a 16X rate of sethoxydim),MR1-P(from seed ofMR1plants that survived a 2X rate of paraquat), andMR2(from seed ofMR2plants that survived a 16X rate of sethoxydim), were investigated to determine the resistance level to imazamox and mesosulfuron, evaluate other herbicide options for the control of these multiple resistantL. perennessp.multiflorum, and characterize the underlying ALS-inhibitor resistance mechanism(s). Based on LD₅₀values, theMR1-A,MR1-P, andMR2subpopulations were 38-, 29-, 8-fold and 36-, 64-, and 3-fold less sensitive to imazamox and mesosulfuron, respectively, relative to the susceptible (Sus) population. OnlyMR1-P and MR2plants were cross-resistant to rimsulfuron, whereas bothMR1subpopulations were cross-resistant to imazethapyr. Pinoxaden (ACCase inhibitor [phenylpyrazoline 'DEN']) only controlledMR2andSusplants at the labeled field rate. However, all plants were effectively controlled (>99%) with the labeled field rate of glufosinate. Based on I₅₀values,MR1-A,MR-P, andMR2plants were 712-, 1,104-, and 3-fold and 10-, 18-, and 5-fold less responsive to mesosulfuron and imazamox, respectively, than theSusplants. Sequence alignment of theALSgene of resistant plants revealed a missense single-nucleotide polymorphism resulting in a Trp-574-Leu substitution inMR1-AandMR1-Pplants, heterozygous in both, but not in theMR2plants. An additional homozygous substitution, Asp-376-Glu, was identified in theMR1-Aplants. Addition of malathion or piperonyl butoxide did not alter the efficacy of mesosulfuron onMR2plants. In addition, the presence of 2,4-D had no effect on the response of mesosulfuron on theMR2andSus. These results suggest an altered target site is the mechanism of resistance to ALS inhibitors inMR1-AandMR1-Pplants, whereas a non–target site based resistance apparatus is present in theMR2plants.

Solanum rostratum Dunal is an invasive weed species that invaded Israel in the 1950s. The weed appears in several germination flashes, from early spring until late summer. Recently, an increase in its distribution range was observed, alongside the identification of new populations in the northern part of Israel. This study aimed to investigate the efficacy of herbicide application for the control of S. rostratum using two field populations originated from the Golan Heights and the Jezreel Valley. While minor differences in herbicide efficacy were recorded between populations, plant growth stage had a significant effect on herbicide response. Carfentrazone-ethyl was found to be highly effective in controlling plants at both early and late growth stages. Metribuzin, oxadiazon, oxyfluorfen and tembutrione showed reduced efficacy when applied at later growth stage (8–9 cm height), as compared to the application at an early growth stage (4–5 cm height). Tank mixes of oxadiazon and oxyfluorfen with different concentrations of surfactant improved later growth stage plant control. Taken together, our study highlights several herbicides that can improve weed control and may be used as chemical solutions alongside diversified crop rotation options. Thus, they may aid in preventing the spread and further buildup of S. rostratum field populations.