Editorial: Integrated weed management for reduced weed infestations in sustainable cropping systems

International audienceWeeds are a major biotic constraint of agricultural systems worldwide interfering with crop production and resource use efficiency (Oerke, 2006; Colbach et al., 2020). Chemical control is a cost-and time-effective weed management method and for that reason remains as the most widely and frequently used method to sustain agricultural productivity and food security in the current era. However, repeated use of a limited number of herbicide active ingredients in non-diversified crop rotations enhances the selection of herbicide-resistant weed biotypes. The over-reliance on chemical weed control has led to shifts in weed communities (Mahaut et al., 2019) which are now becoming dominated by highly competitive and herbicide-resistant prone species able to cause significant yield losses (Adeux et al., 2019b). Widespread herbicide resistance (Heap, 2023) accompanied by the increasing concern of herbicides entering the food chain and/or impacting the environment has created a tremendous demand for alternative weed management methods. Alternative weed management practices that reduce weed populations indirectly lowers selection pressure thus helping delay the evolution of further herbicide resistance. Controlling weeds during the critical period of weed removal is paramount for achieving the full yield potential of any crop (Zimdahl, 1988; Colbach et al., 2020). In conservation tillage with cover cropping, research on the critical period of weed removal is warranted to further elucidate cover crop weed suppressive attributes and efficient utilization of herbicides (Kumari et al.). Preventive weed control measures include all the possible means that restrict the entry and establishment of weeds in an area. Cultural control is an ecological method of weed control in which good crop management methods are followed to stimulate rapid crop growth and canopy closure (Petit et al., 2018). Cultivar selection, Frontiers in Agronomy frontiersin.org 0

Seed-shattering phenology at soybean harvest of economically important weeds in multiple regions of the United States. Part 3: Drivers of seed shatter

Seed retention, and ultimately seed shatter, are extremely important for the efficacy of harvest weed seed control (HWSC) and are likely influenced by various agroecological and environmental factors. Field studies investigated seed-shattering phenology of 22 weed species across three soybean [Glycine max (L.) Merr.]-producing regions in the United States. We further evaluated the potential drivers of seed shatter in terms of weather conditions, growing degree days, and plant biomass. Based on the results, weather conditions had no consistent impact on weed seed shatter. However, there was a positive correlation between individual weed plant biomass and delayed weed seed-shattering rates during harvest. This work demonstrates that HWSC can potentially reduce weed seedbank inputs of plants that have escaped early-season management practices and retained seed through harvest. However, smaller individuals of plants within the same population that shatter seed before harvest pose a risk of escaping early-season management and HWSC

Seed-shattering phenology at soybean harvest of economically important weeds in multiple regions of the United States. Part 1: Broadleaf species

Potential effectiveness of harvest weed seed control (HWSC) systems depends upon seed shatter of the target weed species at crop maturity, enabling its collection and processing at crop harvest. However, seed retention likely is influenced by agroecological and environmental factors. In 2016 and 2017, we assessed seed-shatter phenology in 13 economically important broadleaf weed species in soybean [Glycine max (L.) Merr.] from crop physiological maturity to 4 wk after physiological maturity at multiple sites spread across 14 states in the southern, northern, and mid-Atlantic United States. Greater proportions of seeds were retained by weeds in southern latitudes and shatter rate increased at northern latitudes. Amaranthus spp. seed shatter was low (0% to 2%), whereas shatter varied widely in common ragweed (Ambrosia artemisiifolia L.) (2% to 90%) over the weeks following soybean physiological maturity. Overall, the broadleaf species studied shattered less than 10% of their seeds by soybean harvest. Our results suggest that some of the broadleaf species with greater seed retention rates in the weeks following soybean physiological maturity may be good candidates for HWSC

Seed-shattering phenology at soybean harvest of economically important weeds in multiple regions of the United States. Part 2: Grass species

Seed shatter is an important weediness trait on which the efficacy of harvest weed seed control (HWSC) depends. The level of seed shatter in a species is likely influenced by agroecological and environmental factors. In 2016 and 2017, we assessed seed shatter of eight economically important grass weed species in soybean [Glycine max (L.) Merr.] from crop physiological maturity to 4 wk after maturity at multiple sites spread across 11 states in the southern, northern, and mid-Atlantic United States. From soybean maturity to 4 wk after maturity, cumulative percent seed shatter was lowest in the southern U.S. regions and increased moving north through the states. At soybean maturity, the percent of seed shatter ranged from 1% to 70%. That range had shifted to 5% to 100% (mean: 42%) by 25 d after soybean maturity. There were considerable differences in seed-shatter onset and rate of progression between sites and years in some species that could impact their susceptibility to HWSC. Our results suggest that many summer annual grass species are likely not ideal candidates for HWSC, although HWSC could substantially reduce their seed output during certain years

Comparison of Simulated Drift Rates of Common ALS-Inhibiting Rice Herbicides to Florpyrauxifen-Benzyl on Soybean

Acetolactate synthase- (ALS-) herbicides are among the most commonly used sites of action (SOA) in rice production. Many herbicides used in rice can cause carryover to soybean, which is commonly grown near to or rotated with rice. Florpyrauxifen-benzyl (Rinskor™ Active) brings an alternative SOA to rice production. The objective of this study was to compare the effects of simulated drift rates of florpyrauxifen-benzyl to commonly used ALS-inhibiting rice herbicides on soybean. A field study was conducted at two locations examining five ALS-inhibiting rice herbicides as well as florpyrauxifen-benzyl at a 1/20x and 1/80x simulated drift rate. Crop injury, height, and yield were evaluated at 14, 21, and 35 days after treatment (DAT). Florpyrauxifen-benzyl and bispyribac showed high injury levels at both drift rates. At 35 DAT florpyrauxifen-benzyl caused 76% and 17% visible damage to soybean whereas bispyribac caused 35 and 9% injury at 1/20x and 1/80x, respectively. These treatments resulted in a reduction in soybean height and yield. Although this alternative SOA herbicide in rice may be effective for weed control, our research demonstrates it to be injurious to soybean at both drift rates tested. Thus, proper precautions should be taken to avoid injury by ensuring that the label is followed

Quantifying Nutrient and Economic Consequences of Residue Loss from Harvest Weed Seed Control

Harvest weed seed control (HWSC) methods destroy, remove, or concentrate weed seeds collected during harvest. Depending on the method of HWSC, chaff and straw fractions may also be destroyed, removed, or concentrated. Observations at soybean (Glycine max (L.) Merr.) harvest in this study estimated the distribution of aboveground biomass between seed, straw, and chaff fractions and the nutrient composition of straw and chaff. Measurements were combined to predict nutrient consequences of HWSC, which have not been documented. The average harvest index of soybean was 0.57:1. Soybean biomass that enters the combine partitions into 7.25 ± 0.37% chaff, 36.05 ± 1.2% straw, and 56.7 ± 1.2% seed. Chaff and straw residues equal 13.4% and 68.5% of the seed weight, respectively. In a soybean crop yielding 3368 kg ha−1 (50 bu a−1), chaff yields 9.4, 0.8, 5.0, and 0.6 kg ha−1 and straw 31.6, 2.1, 1.1, and 2.0 kg ha−1 of N, P, K, and S, respectively. Using 5-year average fertilizer prices ending in 2021, the cost to replace chaff, straw, and the combination of both residues is USD 1.58, USD 5.88, and USD 7.46, respectively. These results give insight into the nutrient consequences and replacement costs of HWSC

Quantifying Nutrient and Economic Consequences of Residue Loss from Harvest Weed Seed Control

Harvest weed seed control (HWSC) methods destroy, remove, or concentrate weed seeds collected during harvest. Depending on the method of HWSC, chaff and straw fractions may also be destroyed, removed, or concentrated. Observations at soybean (Glycine max (L.) Merr.) harvest in this study estimated the distribution of aboveground biomass between seed, straw, and chaff fractions and the nutrient composition of straw and chaff. Measurements were combined to predict nutrient consequences of HWSC, which have not been documented. The average harvest index of soybean was 0.57:1. Soybean biomass that enters the combine partitions into 7.25 ± 0.37% chaff, 36.05 ± 1.2% straw, and 56.7 ± 1.2% seed. Chaff and straw residues equal 13.4% and 68.5% of the seed weight, respectively. In a soybean crop yielding 3368 kg ha−1 (50 bu a−1), chaff yields 9.4, 0.8, 5.0, and 0.6 kg ha−1 and straw 31.6, 2.1, 1.1, and 2.0 kg ha−1 of N, P, K, and S, respectively. Using 5-year average fertilizer prices ending in 2021, the cost to replace chaff, straw, and the combination of both residues is USD 1.58, USD 5.88, and USD 7.46, respectively. These results give insight into the nutrient consequences and replacement costs of HWSC

Risk of COVID-19 after natural infection or vaccinationResearch in context

Background: While vaccines have established utility against COVID-19, phase 3 efficacy studies have generally not comprehensively evaluated protection provided by previous infection or hybrid immunity (previous infection plus vaccination). Individual patient data from US government-supported harmonized vaccine trials provide an unprecedented sample population to address this issue. We characterized the protective efficacy of previous SARS-CoV-2 infection and hybrid immunity against COVID-19 early in the pandemic over three-to six-month follow-up and compared with vaccine-associated protection. Methods: In this post-hoc cross-protocol analysis of the Moderna, AstraZeneca, Janssen, and Novavax COVID-19 vaccine clinical trials, we allocated participants into four groups based on previous-infection status at enrolment and treatment: no previous infection/placebo; previous infection/placebo; no previous infection/vaccine; and previous infection/vaccine. The main outcome was RT-PCR-confirmed COVID-19 >7–15 days (per original protocols) after final study injection. We calculated crude and adjusted efficacy measures. Findings: Previous infection/placebo participants had a 92% decreased risk of future COVID-19 compared to no previous infection/placebo participants (overall hazard ratio [HR] ratio: 0.08; 95% CI: 0.05–0.13). Among single-dose Janssen participants, hybrid immunity conferred greater protection than vaccine alone (HR: 0.03; 95% CI: 0.01–0.10). Too few infections were observed to draw statistical inferences comparing hybrid immunity to vaccine alone for other trials. Vaccination, previous infection, and hybrid immunity all provided near-complete protection against severe disease. Interpretation: Previous infection, any hybrid immunity, and two-dose vaccination all provided substantial protection against symptomatic and severe COVID-19 through the early Delta period. Thus, as a surrogate for natural infection, vaccination remains the safest approach to protection. Funding: National Institutes of Health

Risk of COVID-19 after natural infection or vaccinationResearch in context

Summary: Background: While vaccines have established utility against COVID-19, phase 3 efficacy studies have generally not comprehensively evaluated protection provided by previous infection or hybrid immunity (previous infection plus vaccination). Individual patient data from US government-supported harmonized vaccine trials provide an unprecedented sample population to address this issue. We characterized the protective efficacy of previous SARS-CoV-2 infection and hybrid immunity against COVID-19 early in the pandemic over three-to six-month follow-up and compared with vaccine-associated protection. Methods: In this post-hoc cross-protocol analysis of the Moderna, AstraZeneca, Janssen, and Novavax COVID-19 vaccine clinical trials, we allocated participants into four groups based on previous-infection status at enrolment and treatment: no previous infection/placebo; previous infection/placebo; no previous infection/vaccine; and previous infection/vaccine. The main outcome was RT-PCR-confirmed COVID-19 >7–15 days (per original protocols) after final study injection. We calculated crude and adjusted efficacy measures. Findings: Previous infection/placebo participants had a 92% decreased risk of future COVID-19 compared to no previous infection/placebo participants (overall hazard ratio [HR] ratio: 0.08; 95% CI: 0.05–0.13). Among single-dose Janssen participants, hybrid immunity conferred greater protection than vaccine alone (HR: 0.03; 95% CI: 0.01–0.10). Too few infections were observed to draw statistical inferences comparing hybrid immunity to vaccine alone for other trials. Vaccination, previous infection, and hybrid immunity all provided near-complete protection against severe disease. Interpretation: Previous infection, any hybrid immunity, and two-dose vaccination all provided substantial protection against symptomatic and severe COVID-19 through the early Delta period. Thus, as a surrogate for natural infection, vaccination remains the safest approach to protection. Funding: National Institutes of Health