Problems associated with simplified weed management motivate efforts for diversification. Integrated weed management uses the fundamentals of weed biology and applied ecology to provide a framework for diversified weed management programs; the soil seed bank comprises a necessary part of this framework. By targeting seeds, growers can inhibit the propagule pressure on which annual weeds depend for agricultural invasion. Some current management practices affect weed seed banks, such as crop rotation and tillage, but these tools are often used without specific intention to manage weed seeds. Difficulties quantifying the weed seed bank, understanding seed bank phenology, and linking seed banks to emerged weed communities challenge existing soil seed bank management practices. Improved seed bank quantification methods could include DNA profiling of the soil seed bank, mark and recapture, or 3D LIDAR mapping. Successful and sustainable soil seed bank management must constrain functionally diverse and changing weed communities. Harvest weed seed controls represent a step forward, but over-reliance on this singular technique could make it short-lived. Researchers must explore tools inspired by other pest management disciplines, such as gene drives or habitat modification for predatory organisms. Future weed seed bank management will combine multiple complementary practices that enhance diverse agroecosystems. © 2018 Society of Chemical Industry.

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 thirteen economically important broadleaf weed species in soybean [Glycine max (L.) Merr.] from crop physiological maturity to four weeks after physiological maturity at multiple sites spread across fourteen states in the southern, northern, and mid-Atlantic U.S. Greater proportions of seeds were retained by weeds in southern latitudes and shatter rate increased at northern latitudes. Amaranthus species 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 ten percent 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.

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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 four weeks after maturity at multiple sites spread across eleven states in the southern, northern, and mid-Atlantic U.S. From soybean maturity to four weeks after maturity, cumulative percent seed shatter was lowest in the southern U.S. regions and increased as the states moved further north. 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 days 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 at during certain years.

Cover crops enhance the biodiversity of cropping systems and can support a variety of useful ecosystem services including weed suppression. In California orchards, cover crops are typically implemented as annual plants that can replace resident vegetation in orchard alleyways during the rainy winter season. Our research objective was to evaluate cover crop management factors that support a competitive, weed-suppressing cover crop in the unique orchard systems of Central California. We conducted two experiments, which included an experiment evaluating cover crop management intensification in walnuts and an experiment evaluating multispecies cover crop mixes and planting date in almonds. These experiments demonstrate that timely cover crop planting is important for producing an abundant cover crop, and a variety of cover crop management programs can produce weed-suppressing cover crops. However, cover crops do not result in weed-free orchards and should be considered within the context of integrated management programs. The apparent flexibility of orchard cover crop management provides opportunity to promote other agroecosystem services, with vegetation management and weed suppression as complementary management goals.

Grape growers are concerned about the potential impact of drift from commonly used auxinic herbicides. In California, this is frequently related to herbicides used in cereals and noncrop areas, whereas in other parts of the United States concerns are often related to dicamba- and 2,4-D-resistant cropping systems. Our objective was to compare the relative sensitivity of winegrapes to simulated auxinic herbicide drift, including grapevine symptomology, grape yield, and grape quality. In a small-plot herbicide evaluation, we applied 1/900×, 1/300×, 1/100×, and 1/33× rates of 2,4-D, aminopyralid, dicamba, and triclopyr based on 1× field rates of 1454, 122.5, 280, and 2240 g⋅ha–1 ae, respectively. Aminopyralid resulted in similar symptomology to 2,4-D and dicamba—namely, leaf cupping, leaf crinkling, excessive tendril twisting, and tendril death, although these symptoms were generally subtle. Triclopyr resulted in much greater levels of necrosis compared with the other herbicides. In our study, triclopyr was the only herbicide associated with grape yield loss, and greater triclopyr rates were also associated with increased grape sugar levels. This study demonstrates that grapes are sensitive to low rates of simulated herbicide drift, but symptoms do not necessarily indicate yield loss or quality effects. This study indicates that auxin-type herbicide simulated drift symptoms are not reliable markers for winegrape yield or quality reduction.

Seed retention, and ultimately seed shatter, are extremely important for the efficacy of harvest weed seed control (HWSC) and likely influenced by various agro-ecological and environmental factors. Field studies investigated seed shattering phenology of 22 weed species across three soybean [Glycine max (L.) Merr.] producing regions in the US. 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.

Developing cover crop systems for California almonds: Current knowledge and uncertainties A lmond (Prunus amygdalus) orchard systems are highly productive and widespread in Mediterranean climates and dominate the California agricultural landscape. However, current intensive monocultural bare soil production practices limit the potential to support nonproduction functions (i.e., multifunctionality) and long-term sustainability of the orchard system (Aizen et al. 2019;Fenster et al. 2021). Managing orchards for multifunctional benefits includes maintaining ecologically and economically viable yields while prioritizing water quality, soil health, reduced input use, and support for biodiversity. Recent studies in almond demonstrate that diversification, including planted or spontaneous (resident) vegetation in orchard alleys, can improve multifunctionality by enhancing nonproduction functions in the orchard without reducing crop yield, thereby providing opportunities to enhance sustainability and resilience (Fenster et al. 2021;Morugán-Coronado et al. 2020).Cover crops have been used in some Mediterranean orchards to accomplish a variety of goals for centuries (Proebsting 1958;Paine and Harrison 1993). In California, on-farm studies, such as the Biologically Integrated Orchard Systems (BIOS) for Almond program (Bugg et al. 1994; Bentley et al. 2001), developed valuable baseline information for cover crop implementation in modern almond orchard systems. Subsequent research suggests multiple avenues by which planted winter cover crops or resident vegetation can increase Mediterranean agroecosystem multifunctionality, though there is limited evidence from almonds. Synthesizing the information that exists could increase a shared understanding of expected benefits and trade-offs of integrating cover crops into almond orchards and clarify persistent knowledge gaps. Establishing this updated understanding can guide continued work