Weed seeds with mechanical damage are more susceptible to mortality in soil than nondamaged seeds. In this study we introduce a colorimetric assay to distinguish mechanically damaged weed seeds from nondamaged weed seeds. Our objectives were to 1) compare steepates from mechanically damaged seeds against steepates from nondamaged seeds for their capacities to reduce resazurin—a nontoxic, water-soluble dye that changes color and light absorbance properties in response to pH; and 2) use light absorbance data from steepate-resazurin solutions to create classification trees for distinguishing damaged from nondamaged weed seeds. Species in this study included barnyardgrass, curly dock, junglerice, kochia, oakleaf datura, Palmer amaranth, spurred anoda, stinkgrass, tall morningglory, and yellow foxtail. Seeds of each species were subjected to mechanical damage treatments that collectively represented a range of damage severities. Damaged and nondamaged seeds were individually soaked in water to produce steepates that were combined with resazurin. Light absorbance properties of steepate-resazurin solutions indicated that for all species except kochia, damaged seeds reduced resazurin to greater extents than nondamaged seeds. Prediction accuracy rates for classification trees that used absorbance values as predictor variables were conditioned by species and damage type. Prediction accuracy rates were relatively low (66% to 86% accurate) for lightly damaged seeds, especially grass weed seeds. Prediction accuracy rates were high (91% to 99% accurate) for severely damaged seeds of specific broadleaf and grass weeds. Steepate-resazurin solutions that successfully separated seeds took no more than 32 h to produce. The results of this study indicate that the resazurin assay is a method for quickly distinguishing damaged from nondamaged weed seeds. Because rapid assessments of seed intactness may accelerate the development of tactics for reducing the number of weed seeds in soil, we advocate further development of resazurin assays by laboratories studying methods for weed seedbank depletion.

Downy brome, feral rye, and jointed goatgrass are problematic winter annual grasses in central Great Plains winter wheat production. Integrated control strategies are needed to manage winter annual grasses and reduce selection pressure exerted on these weed populations by the limited herbicide options currently available. Harvest weed-seed control (HWSC) methods aim to remove or destroy weed seeds, thereby reducing seed-bank enrichment at crop harvest. An added advantage is the potential to reduce herbicide-resistant weed seeds that are more likely to be present at harvest, thereby providing a nonchemical resistance-management strategy. Our objective was to assess the potential for HWSC of winter annual grass weeds in winter wheat by measuring seed retention at harvest and destruction percentage in an impact mill. During 2015 and 2016, 40 wheat fields in eastern Colorado were sampled. Seed retention was quantified and compared per weed species by counting seed retained above the harvested fraction of the wheat upper canopy (15 cm and above), seed retained below 15 cm, and shattered seed on the soil surface at wheat harvest. A stand-mounted impact mill device was used to determine the percent seed destruction of grass weed species in processed wheat chaff. Averaged across both years, seed retention (±SE) was 75% ± 2.9%, 90% ± 1.7%, and 76% ± 4.3% for downy brome, feral rye, and jointed goatgrass, respectively. Seed retention was most variable for downy brome, because 59% of the samples had at least 75% seed retention, whereas the proportions for feral rye and jointed goatgrass samples with at least 75% seed retention were 93% and 70%, respectively. Weed seed destruction percentages were at least 98% for all three species. These results suggest HWSC could be implemented as an integrated strategy for winter annual grass management in central Great Plains winter wheat cropping systems.

Feral rye and jointed goatgrass are winter annual grasses that infest winter wheat in the western United States. Currently, no herbicides are available that selectively control these weeds in wheat. Because of this constraint, producers need cultural practices that reduce the seed densities of these two grasses in the soil seedbank. This research shows that applying nitrogen 5 mo before wheat planting and increasing the seeding rate with a tall wheat cultivar reduces seed production per plant of either species by > 40%. However, tall wheat cultivars usually yield less grain than semidwarf cultivars. Producers can avoid this yield loss by combining narrow rows with time of N application and increased seeding rate of semidwarf cultivars. This combination reduces weed seed production similarly to cultural systems with tall cultivars.

Tactics that target seedbanks are important components of weed management systems; however, such tactics can be difficult to adopt because consequences of seedbank reduction are often unclear. This study developed model-based software to provide insights on the economic outcomes, in the context of chile pepper production, of additions to tall morningglory seedbanks. Data for the model were derived from this and previous studies. In this study, field experiments were conducted to determine chile pepper yield and harvest efficiency responses to mid-season tall morningglory infestations. The experimental treatments were factorial combinations of herbicide (pendimethalin-treated, nontreated) and tall morningglory density (0, 4, 8, 12, 16, 20 plants 10-m row–1). Treatments were installed 9.5 weeks after crop seeding. Data collected included fresh weight of marketable chile peppers and time required for one individual to harvest 10-m of crop row, which was used to calculate the amount of chile pepper harvested in 1 min (harvest efficiency). Results indicated that crop yield was not influenced by tall morningglory density, pendimethalin treatment and interactions between tall morningglory density and pendimethalin. Harvest efficiency was influenced by tall morningglory density but was not influenced by herbicide treatment or interactions between herbicide treatment and tall morningglory density. Each additional tall morningglory plant decreased the amount of chile pepper harvested in 1 min by 9.7 g. The results of this and previous studies were used to develop model-based software that presents tall morningglory seedbank density effects on: (1) tall morningglory seedling densities after pendimethalin, (2) time requirements for hand-hoeing after pendimethalin, and (3) time requirements for hand-harvesting to acquire yield goals. The model-based software is intended to be used in the instruction of weed seedbank management strategies. By presenting seedbank density effects on weed control outcomes and crop production expenses, the model-based software might promote adoption of seedbank reduction strategies.

Pendimethalin control failures on tall morningglory are critical shortcomings in weed-control programs for chile pepper in New Mexico. Using weed seedbank augmentation, we conducted a field study to (1) determine if pendimethalin control of tall morningglory is affected by tall morningglory seedbank density, and (2) identify weed community factors that influence labor for removing the tall morningglory plants that escape pendimethalin. The field study was complemented with a growth chamber study conducted to clarify the effects of pendimethalin rate on the putative association between tall morningglory seedbank density and pendimethalin control outcomes. Under field conditions and after square-root transformation of the dependent variable, the effects of seedbank density on seedling escape density were described with natural logarithmic functions. Although pendimethalin control of tall morningglory decreased with increasing seedbank density, seedbank additions increased labor requirements for removing tall morningglory at only a site-year characterized by low population densities in the indigenous weed community. In growth chambers, increasing pendimethalin rate negatively influenced the effects of increasing seedbank density on pendimethalin control failures. This study shows that pendimethalin control of tall morningglory is reduced when seedbank densities of this species are high. Knowledge of seedbank density effects on specific control outcomes may influence grower attitudes on management strategies that target weed seedbanks.

Because herbicide and cultivation efficacy is generally density independent, seedling density following these weed control practices will be proportional to the density of germinable seeds in the seedbank. Most farmers would therefore benefit from management practices that reduce seed inputs, increase seed losses, and reduce the probability that remaining seeds establish. Germination, predation, and decay are the primary sources of loss to the seedbank that may respond to management. Farmers have long prepared stale seedbeds in which shallow soil disturbance encourages germination losses. Postdispersal seed predation by vertebrate and invertebrate granivores may cause high rates of seed mortality in a wide range of cropping systems, but seed dispersal asynchronous with predator activity, and seed burial, may limit the overall effect on the seedbank. Although seeds would seem to be an ideal carbon source for soil microorganisms, limited evidence from a study of wild oat suggests that decay may be less responsive to management than germination, and likely predation. A final management objective, supporting a program that aims to reduce seedbank inputs and increase losses, is to reduce the size of the effective seedbank through manipulation of residues and disturbance to reduce the probability of establishment. Incorporation of green manures generally reduces weed establishment, whereas larger-seeded or transplanted crops may better tolerate the residue-mediated changes in the chemical, biological, and physical properties of the soil surface environment. Evidence from no-till systems further support the hypothesis that changes in soil surface conditions may regulate the abundance of “safe sites” for weed establishment, thereby modulating the size of the effective seedbank.

Weeds are a major challenge for organic farmers, yet we know little about the factors influencing organic farmers’ weed management decisions. We hypothesized that farmers and scientist ‘experts’ differ in fundamental areas of knowledge and perceptions regarding weeds and weed management. Moreover, these differences prevent effective communication, outreach programming and research prioritization. An expert mental model, constructed primarily from interviews with research scientists and extension professionals, revealed expert emphasis on knowledge of ecological weed management as crucial for successfully implementing such strategies. We interviewed 23 organic farmers in northern New England, yielding an aggregate farmer mental model to compare with the expert model. Farmers demonstrated knowledge of the major concepts discussed by experts, but differed in emphasis. Farmers placed less emphasis on ecological complexity than experts. One-third of farmers interviewed discussed the potential role of weeds as indicators of soil nutrient status, a concept of which experts were skeptical. Farmer beliefs about the weed seedbank highlighted potential misconceptions regarding seed persistence, with one-fourth of farmers focusing on the concept that seeds can live for an exceptionally long time in the soil, while experts focused on the concept of the seed half-life. Farmers emphasized the role of experience, both their own and that of other farmers, rather than knowledge derived from scientific research. Farmers considered yield and the cost of time and labor as equally at risk because of weeds, whereas experts predominantly discussed yield loss. During discussions of management, both farmers and experts most emphasized risks associated with cultivation and benefits associated with cover cropping. These results have prompted us, first, to develop new educational materials focused on weed seed longevity and management of the weed seedbank, and, second, to conduct regional focus groups with farmers who prioritize fertility management in their efforts to control weeds, especially manipulations of soil calcium and magnesium.