Exploring the effect of region on diversity and composition of weed seedbanks in herbicide-resistant crop systems in the United States.

BACKGROUND: Soil seedbanks have been recognized as one of the crucial components of agricultural ecosystems. However, studies on the shift in structure and biodiversity of soil seedbanks in herbicide-resistant crop systems are limited, and a functional trait perspective of the soil seedbank is often overlooked. RESULTS: A 6 years experiment was conducted to investigate the roles of region, crop system, and weed management strategy on species richness, functional trait diversity, and composition of the weed seedbank. Species richness was different across the interaction of region and crop system, while functional trait diversity only showed difference across regions. Species and functional trait compositions were affected by the interaction of region and crop system. Specifically, the compositional difference among crop systems was mainly determined by the significant heterogeneity of group dispersion. CONCLUSION: Growers and practitioners should consider weed functional traits in developing lasting agricultural management strategies. Long-term weed research should draw attention to the impact of transgenic crop systems and specific management tactics on weed dispersal, functional composition, and resistance evolution of weed species in such agroecosystems. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Homeowner perceptions and responses to buffelgrass invasion risk in the Tucson, Arizona Wildland-Urban Interface.

In this study, we aimed to analyze homeowners' level of awareness and perceived risk about buffelgrass invasion in the Tucson, Arizona Wildland-Urban Interface (WUI), as well as the factors influencing their participation in buffelgrass control and fire risk mitigation efforts. Data for the study were generated through the administration of an online survey among 117 members of Home Owner Associations (HOAs) in the Tucson WUI. The results showed that the overwhelming majority of respondents were aware of buffelgrass, but their knowledge about buffelgrass control mechanisms appeared to be limited. Respondents also more frequently expressed concern about the risks posed by buffelgrass invasion to general targets, such as the Sonoran Desert ecosystem, native plants and wildlife than risks to their private property and neighborhoods. The results also showed that the level of involvement in HOAs, and leadership in HOAs had significant positive effects on homeowners' participation in buffelgrass control efforts. Homeowners' duration of residence also had a significant negative effect on participation in buffelgrass control efforts, suggesting that newcomers may be more involved than long-term residents. Similarly, the number of months respondents spent in Tucson per year had a negative effect on the number of hours spent on buffelgrass control efforts. Respondents' perceived risk about buffelgrass invasion also had a positive effect on the hours spent on buffelgrass control as well as their level of involvement in fire risk mitigation efforts. These results highlight the importance of local institutions and community heterogeneity in social responses to threats in WUI communities. Policies aimed at building the resilience of WUI communities need to account for their complexity as coupled social-ecological systems.

Efficacy of Cover Crops for Pollinator Habitat Provision and Weed Suppression.

Pollinator declines have been documented globally, but little information is available about native bee ecology in Midwestern U.S. agriculture. This project seeks to optimize pollinator support and weed suppression in a 3-yr crop rotation with a fallow growing season. During fallow, one of five cover crop treatments (T1: crimson, red, and ladino clover and Bob oats [Fabales: Fabaceae - Trifolium incarnatum L., Trifolium pratense L., Trifolium repens L., and Cyperales: Poaceae - Avena sativa]; T2: crimson clover and oats; T3: red clover and oats; T4: ladino clover and oats; T5: no cover crop; T6/control: winter wheat [Cyperales: Poaceae - Triticum aestivum] L.) was seeded in one-half of 25 agricultural fields, whereas wheat was left unharvested in the other half as a comparison. Treatments that provide season-long floral resources support the greatest bee diversity and abundance (T1), and treatments with red clover support declining (Hymenoptera: Apidae) Bombus species (T1 and T3). Late-season floral resources may be important, yet limited (T1 and T4), and some species of agricultural weeds provide floral resources. Floral diversity may be less important than flower abundance or timing for pollinator diversity (T1-T4). Weed diversity was greatest in the no cover crop treatment (T5), least in winter wheat (T6), and intermediate in cover crop treatments (T1-T4) with no differences in weeds of economic concern. Wheat suppresses weeds but does not provide floral resources for pollinators. These results may also be applicable to marginal lands taken out of cultivation or field margin pollinator plantings in a typical corn-soybean rotation. Floral resource availability across the landscape is critical to maintain pollinator diversity.

Syrphidae of Southern Illinois: Diversity, floral associations, and preliminary assessment of their efficacy as pollinators.

Syrphid flies (Diptera: Syrphidae) are a cosmopolitan group of flower-visiting insects, though their diversity and importance as pollinators is understudied and often unappreciated. Data on 1,477 Syrphid occurrences and floral associations from three years of pollinator collection (2017-2019) in the Southern Illinois region of Illinois, United States, are here compiled and analyzed. We collected 69 species in 36 genera off of the flowers of 157 plant species. While a richness of 69 species is greater than most other families of flower-visiting insects in our region, a species accumulation curve and regional species pool estimators suggest that at least 33 species are yet uncollected. In order to further the understanding of Syrphidae as pollinators in the Southern Illinois region, we produced a NMDS ordination of floral associations for the most common syrphid species. The NMDS did not sort syrphid species into discrete ecological guilds, and syrphid floral associations generally fit those predicted by traditional pollination syndromes. We also conducted a preliminary analysis of the pollen-carrying capacity of different syrphid taxa, which found several Eristalis species to carry pollen loads comparable to the European Honey Bee, Apis mellifera, and showed significant differences in the pollen-carrying capacity of various syrphid species. Notably, the extremely common genus Toxomerus and other small Syrphinae species carried very little pollen, while large and pilose Eristalinae species carried large pollen loads.

Benchmark study on glyphosate-resistant cropping systems in the United States. Part 7: Effects of weed management strategy (grower practices versus academic recommendations) on the weed soil seedbank over 6 years.

BACKGROUND: Shifts in weed species composition and richness resulting from near-exclusive reliance on herbicides in glyphosate-resistant (GR) cropping systems has necessitated the implementation of alternative weed management tactics to reduce selection pressures of herbicides. We contrasted the response of the weed soil seedbank to effects of weed management strategy, comparing grower practices with academic recommendations for best management practices (BMPs) over 6 years and across five weed hardiness zones in the US Midwest at sites subject to GR cropping systems. RESULTS: Total weed population density and species richness varied according to cropping system, location and prior year's crop, but less so to weed management strategy. The seedbank population density for 11 of the 14 most frequent weed species was affected by weed management strategy either alone or in an interaction with hardiness zone or year, or both. In only 29% of comparisons was weed population density lower following academic recommendations, and this depended upon prior crop and cropping system. The population density of high-risk weed species was reduced by academic recommendations, but only in two of six years and under continuous GR maize. Overall, the weed population density was decreasing in field halves subject to the BMPs in the academic recommendations relative to grower practices. CONCLUSION: The soil seedbank is slow to respond to academic recommendations to mitigate glyphosate-resistant weeds, but represents a biological legacy that growers need to keep in mind even when management practices reduce emerged field weed population densities.

Occurrence of an herbicide-resistant plant trait in agricultural field margins.

Agricultural environments allow study of evolutionary change in plants. An example of evolution within agroecological systems is the selection for resistance to the herbicide glyphosate within the weed, Conyza canadensis. Changes in survivorship and reproduction associated with the development of glyphosate resistance (GR) may impact fitness and influence the frequency of occurrence of the GR trait. We hypothesized that site characteristics and history would affect the occurrence of GR C. canadensis in field margins. We surveyed GR occurrence in field margins and asked whether there were correlations between GR occurrence and location, crop rotation, GR crop trait rotation, crop type, use of tillage, and the diversity of herbicides used. In a field experiment, we hypothesized that there would be no difference in fitness between GR and glyphosate-susceptible (GS) plants. We asked whether there were differences in survivorship, phenology, reproduction, and herbivory between 2 GR and 2 GS populations of C. canadensis in agrestal and ruderal habitats. We found that geographic location was an important factor in the occurrence of GR C. canadensis in field margins. Although not consistently associated with either glyphosate resistance or glyphosate susceptibility, there were differences in phenology, survivorship, and herbivory among biotypes of C. canadensis. We found equal or greater fitness in GR biotypes, compared to GS biotypes, and GR plants were present in field margins. Field margins or ruderal habitats may provide refugia for GR C. canadensis, allowing reproduction and further selection to occur as seeds recolonize the agrestal habitat. Agricultural practices may select for ecological changes that feed back into the evolution of plants in ruderal habitats.