Narrow-windrow burning (NWB) is a form of harvest weed seed control in which crop residues and weed seeds collected by the combine are concentrated into windrows and subsequently burned. The objectives of this study were to determine how NWB will 1) affect seed survival of Italian ryegrass in wheat and Palmer amaranth in soybean and 2) determine whether a relationship exists between NWB heat index (HI; the sum of temperatures above ambient) or effective burn time (EBT; the cumulative number of seconds temperatures exceed 200 C) and the post-NWB seed survival of both species. Average soybean and wheat windrow HI totaled 140,725 ± 14,370 and 66,196 ± 6224 C, and 259 ± 27 and 116 ± 12 s of EBT, respectively. Pre-NWB versus post-NWB germinability testing revealed an estimated seed kill rate of 79.7% for Italian ryegrass, and 86.3% for Palmer amaranth. Non-linear two-parameter exponential regressions between seed kill and HI or EBT indicated NWB at an HI of 146,000 C and 277 s of EBT potentially kills 99% of Palmer amaranth seed. Seventy-six percent of soybean windrow burning events resulted in estimated Palmer amaranth seed kill rates greater than 85%. Predicted Italian ryegrass seed kill was greater than 97% in all but two wheat NWB events; therefore, relationships were not calculated. These results validate the effectiveness of the ability of NWB to reduce seed survival, thereby improving weed management and combating herbicide resistance.

A 3-yr field study was conducted in Keiser, AR, to investigate the response of the naturally occurring weed flora, dominated by Palmer amaranth, under various combinations of 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide-based programs and crop rotation sequences. In the first year, corn plots were established with three corn HPPD-based herbicide programs designed to represent a range of efficacies and selection pressures for resistance. In the following two years, corn as monoculture or with soybean and/or cotton crops was included in the rotation sequence for selected herbicide programs. Weed emergence, weed biomass, and soil seedbank were assessed through the entire experimental period. The results show that crop rotation, especially a rotation sequence with corn followed by (fb) soybean fb cotton, and the lowest-risk herbicide program involving seven sites of action over the course of the entire crop rotation was effective in reducing the emergence of naturally occurring weeds, including Palmer amaranth, prickly sida, morningglory species, and grass weeds (broadleaf signalgrass, large crabgrass, barnyardgrass, and johnsongrass) by 88.3%, 57.5%, 28.7%, and 76.3%, respectively. Treatments without crop rotation (corn as monoculture for 3 consecutive years) and poor herbicide programs, with one site of action, increased weed emergence, notably of Palmer amaranth and prickly sida, by 73.5% and 74.1%, respectively. The soil seedbank showed a similar trend to weed emergence. This study highlights the fact that reducing the weed seedbank cannot rely on one management practice but requires a multitactic approach with various control methods. HPPD-inhibiting herbicide programs seem to be effective on Palmer amaranth when coupled with crop rotation and should be used with other best management practices.

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.

Nonnative plant invasions can have devastating effects on native plant communities; conversely, management efforts can have nontarget and deleterious impacts on desirable plants. In the arid sagebrush steppe rangelands of the western United States, nonnative winter annual species affect forage production and biodiversity. One method proposed to control these species is to suppress the soil seedbank using the preemergent herbicide indaziflam. Our goal was to evaluate the efficacy of indaziflam to control nonnative annual mustards (Alyssum spp.) and to understand potential nontarget effects of management on the diverse mountain sagebrush steppe plant communities within Yellowstone National Park. Six sites were established along an elevation gradient (1,615 to 2,437 m), each with high and low Alyssum spp. infestations. We applied 63g ai ha−1 of indaziflam in late summer of 2018 and evaluated plant community cover in situ for 2 yr after treatment and emergence of forb species from the soil seedbank ex situ. Indaziflam was highly effective at controlling emergence of Alyssum spp. for 2 yr. Richness and Shannon’s diversity of the nontarget plant community were significantly lower in sprayed plots than in the control, and both decreased along the elevation gradient. These reductions were due to a decrease in perennial forbs and native annual forbs in the sprayed plots; perennial graminoids were not affected. Overall, the aboveground and seedbank community composition was negatively impacted by indaziflam, and these effects were strongest for the native annual forbs that rely on annual regeneration from the seedbank. The effects of this herbicide to the nontarget community should be evaluated beyond the length of our study time; however, we conclude that indaziflam should likely be reserved for use in areas that are severely invaded and have seedbanks that are composed of nondesirable species rather than diverse, native mountain sagebrush communities.

The use of a corn–earthworm coculture (CE) system is an eco-agricultural technology that has been gradually extended due to its high economic output and diverse ecological benefits for urban agriculture in China. However, the effect of CE on weed occurrence has received little attention. A 5-yr successive experiment (2015 to 2019) was conducted to compare weed occurrence in CE and a corn (Zea mays L.) monoculture (CM). The results show that CE significantly decreased weed diversity, the dominance index, total weed density, and biomass, but increased the weed evenness index. The 5-yr mean number of weed species per plot was 8.4 in CE and 10.7 in CM. Compared with those in CM, the 5-yr mean density and biomass of total weeds in CE decreased by 59.2% and 66.6%, respectively. The effect of CE on weed occurrence was species specific. The mean density of large crabgrass [Digitaria sanguinalis (L.) Scop.], green foxtail [Setaria viridis (L.) P. Beauv.], goosegrass [Eleusine indica (L.) Gaertn.], and common purslane (Portulaca oleracea L.) in CE decreased by 94.5%, 78.1%, 75.0%, and 45.8%, whereas the mean biomass decreased by 96.2%, 80.8%, 76.9%, and 41.4%, respectively. Our study suggests that the use of CE could suppress weed occurrence and reduce herbicide inputs in agriculture.

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 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.

The soil weed seedbank is the source of future weed infestations. Seed predation can result in a large number of seed losses, thus contributing to weed biocontrol. Earthworms are important predators of seeds and seedlings and affect seeds and seedling survival after gut passage. A study was conducted to assess the ability of Pheretima guillelmi (Kinberg) to ingest and digest the seeds and seedlings of 15 main farmland weed species. Pheretima guillelmi ingested the seeds and seedlings of each weed species tested. The percentages of seeds and seedlings ingested were 96.7% to 100% and 21.7% to 94.2%, respectively. Pheretima guillelmi showed greater ingestion of seeds than seedlings for each species and digested the seeds and seedlings of each weed species tested to varying extents. The percentages of seeds and seedlings digested were less than 15% irrespective of the weed species. Passage through the gut of P. guillelmi affected the survival of seeds and seedlings. The germination of large crabgrass [Digitaria sanguinalis (L.) Scop.], green foxtail [Setaria viridis (L.) P. Beauv.], goosegrass [Eleusine indica (L.) Gaertn.], Chinese sprangletop [Leptochloa chinensis (L.) Nees], Malabar sprangletop [Leptochloa fusca (L.) Kunth], redroot pigweed (Amaranthus retroflexus L.), common purslane (Portulaca oleracea L.), barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], and ricefield flatsedge (Cyperus iria L.) seeds egested by P. guillelmi decreased by 46%, 49%, 47%, 25%, 38%, 26%, 32%, 13%, and 15%, respectively, compared with their respective controls. In contrast to seed ingestion, ingestion of seedlings by P. guillelmi was fatal to individuals of all weed species; no seedlings survived passage through the gut. Our results indicate that predation of weed seeds and seedlings by P. guillelmi probably depletes the soil weed seedbank and that the introduction of P. guillelmi into fields is a potential strategy for weed biocontrol in farmland.

Scotch broom [Cytisus scoparius (L.) Link] is a large nonnative, leguminous shrub that threatens native plant communities by rapidly invading recently disturbed sites, competing vigorously for soil water and nutrients, and imparting soil legacy effects that inhibit native plants. In the Pacific Northwest, logging debris retention after forest harvesting prevents or slows C. scoparius invasions. A series of studies were conducted to determine potential mechanisms by which logging debris modifies the light environment to limit germination and growth of C. scoparius. In laboratory studies, seed germination did not vary significantly (P > 0.05): (1) between presence and absence of light for several temperature regimes, (2) when exposed to red (660-nm wavelength) versus far-red (730-nm wavelength) light, and (3) across a range of red/far-red light (R/FR) ratios. These results indicate that modification of the light environment by logging debris or plant canopies has little or no influence on C. scoparius germination. In a study to simulate effects of variable mass of logging debris, “heavy” debris (2 kg m−2) caused biologically relevant reductions in photosynthetic photon flux density (PPFD) and R/FR relative to conditions under “light” debris (1 kg m−2). Cytisus scoparius germination did not differ significantly between simulated heavy and light debris; however, values of seedling root and shoot biomass under heavy debris were 16% and 71% of those observed under light debris, respectively. These results indicate that heavy debris limits biomass of C. scoparius seedlings, particularly roots, by reducing both PPFD and R/FR, which increases seedling vulnerability to summer drought or other stressors. Retention of heavy logging debris after forest harvesting has potential application on sites likely to be invaded by C. scoparius, as well as those sites with seedbanks containing C. scoparius.

Palmer amaranth, an annual weed, and Verticillium dahliae, a fungal pathogen, can substantially reduce chile pepper yield. On the basis of the results of this study, we clarified implementation strategies for a potential management tactic for Palmer amaranth and V. dahliae in chile pepper: mustard seed meal (MSM). The objectives were to (1) determine MSM effects on Palmer amaranth seedbanks under different moisture levels, (2) measure glucosinolate degradation in soil hydrated to saturation and field capacity, and (3) determine the effects of decreasing moisture availability on MSM control of Palmer amaranth and V. dahliae. To address objective 1, seedbanks with and without MSM were hydrated to levels expected to both inhibit and promote germination (flooded, saturated, −0.03, −0.6 MPa, respectively). For objective 2, soil columns with MSM were held at different moisture levels and sampled over time. For objective 3, Palmer amaranth seeds were incubated with and without MSM, and with polyethylene glycol (PEG) solutions comprising a range of water potentials (0, −0.03, −0.6, −1.0, and −2.0 MPa). These PEG solutions were also used to hydrate MSM in agar plates with plugs of V. dahliae. All experiments were performed in growth chambers with temperatures and light conditions conducive to Palmer amaranth germination and V. dahliae mycelial growth. MSM-induced mortality in Palmer amaranth seedbanks was greater in soil at field capacity than in saturated soil and flooded soil; however, rates of glucosinolate degradation were greatest in saturated soil. Decreasing water availability progressively decreased the efficacy of MSM on Palmer amaranth because MSM was ineffective on nongerminated seeds. When incubated with PEG solutions with water potentials of 0, −0.03, and −0.6 MPa, MSM stopped growth of V. dahliae; however, MSM-induced control of V. dahliae was reduced by water potentials of −1.0 and −2.0 MPa. The results of this study indicate soils hydrated to field capacity maximize MSM-induced control of Palmer amaranth and V. dahliae.

Blackgrass (Alopecurus myosuroides Huds.) and silky windgrass [Apera spica-venti (L.) P. Beauv.] are becoming a significant problem in Europe. Due to the development of herbicide-resistant biotypes and unwanted side effects of herbicides, there is a need for new integrated weed management strategies to control weeds. Therefore, reducing weed infestations by targeting seed production during crop harvest should be considered. In 2017 and 2018, we estimated the fraction of the total seed production of A. myosuroides and A. spica-venti in a field that potentially could be collected by a grain harvester during winter wheat (Triticum aestivum L.) harvest. Twenty plants of each species were surrounded by a porous net before flowering to trap shed seeds during reproductive development. Seeds were collected and counted weekly up until and immediately before wheat harvest, and the ratio of harvestable seeds to shed seeds during the growing season was determined. Alopecurus myosuroides produced on average 953 seeds plant−1 in 2017 and 3,337 seeds plant−1 in 2018. In 2017 and 2018, 29% and 37% of the total A. myosuroides seeds produced, respectively, were retained on plants at maturity. Apera spica-venti produced on average 1,192 seeds plant−1 in 2017 and 5,678 seeds plant−1 in 2018, and retained 53% and 16% of the seeds at harvest, respectively. If a grain harvester potentially collected approximately 30% of the total seed production of the two grass weeds and removed or killed them, it would reduce seed input to the soil seedbank. However, such methods cannot stand alone to reduce weed pressure.

Chinese tallowtree [Triadica sebifera (L.) Small] has reached unprecedented prevalence in coastal landscapes in the Gulf of Mexico, especially along edge habitat with low competition and abundant resource (e.g., light) availability. This study investigated the spatiotemporal patterns and mechanisms of T. sebifera spread along roadways and fire lines. Triadica sebifera individuals and landscape and community features were surveyed in equally spaced, spatially mapped plots. All T. sebifera individuals were felled to determine tree age and status (seed trees or non-seed bearing trees), and T. sebifera seed and seedling (≤2 yr old) densities and community and landscape features (over- and understory conditions, distance to seed trees) were measured. A zero-inflated negative binomial model was used to evaluate factors affecting T. sebifera seed dispersal and seedling recruitment contributing to the observed spatiotemporal patterns. Introduced into the Grand Bay National Wildlife Refuge around 30 yr ago, T. sebifera trees distribute in clustered patterns along roadways and fire lines and exhibit an exponential growth in density. High T. sebifera seed and seedling densities mainly occurred in sites that are ≤250 m from seed trees or have sparse overstory and high understory grass/herb coverage. With respect to the avian seed dispersal mechanism, the spatiotemporal patterns of T. sebifera spread along roadways and fire lines could be simply characterized by using landscape and community features that influence avian behaviors, including distance to seed trees, overstory tree density, and ground grass/herb coverage.

Depleting the soil weed seedbank is an important integrated weed management strategy that has the potential to foster lasting weed control. Long-term dormancy and decay resistance of weed seeds pose a challenge to weed eradication efforts. Select soil fungi have been shown to cause significant decay of weed seeds. The physical and chemical mechanisms by which seeds in the seedbank defend themselves against pathogens have been well researched. However, very few studies have purposefully investigated the biochemical defence response of seeds. Enzyme-based biochemical seed defences have been detected in dormant and non-dormant seeds, and research supports their function in pathogen defence. This review summarizes current knowledge of the seed defence enzymes polyphenol oxidase, peroxidase, chitinase and oxalate oxidase. The fungal enzymes chitinase, protease and xylanase that function in pathogenesis of seeds in the soil seedbank are also reviewed. Progress in the development and standardization of in situ enzyme analyses fosters our understanding of actual enzyme activity present in soils, while high-throughput microplate techniques promote efficiency and enable greater scope. Application of genomic, proteomic and transcriptomic techniques to glean a deeper and more holistic understanding of the enzymatic interactions of weed seeds and soil fungi in the soil seedbank will support the development of improved integrated weed management strategies.

Harvest weed seed control is an alternative non-chemical approach to weed management that targets escaped weed seeds at the time of crop harvest. Relatively little is known on how these methods will work on species in the US. Two of the most prominent weeds in soybean production in the midsouthern US are Palmer amaranth and barnyardgrass. Typically, when crop harvesting occurs the weed seed has already either shattered or is taken into the combine and may be redistributed in the soil seedbank. This causes further weed seed spread and may contribute to the addition of resistant seeds in the seedbank. There is little research on how much seed is retained on different weed species at or beyond harvest time. Thus, the objective of this study was to determine the percentage of total Palmer amaranth and barnyardgrass seed production that was retained on the plant during delayed soybean harvest. Retained seed over time was similar between 2015 and 2016, but was significantly different between years for only Palmer amaranth. Seed retention did not differ between years for either weed species. Palmer amaranth and barnyardgrass retained 98 and 41% of their seed at soybean maturity and 95 and 32% of their seed one month after soybean maturity, respectively. Thus, this research indicates that if there are escaped Palmer amaranth plants and soybean is harvested in a timely manner, most seed will enter the combine and offer potential for capture or destruction of these seeds using harvest weed seed control tactics. While there would be some benefit to using HWSC for barnyardgrass, the utility of this practice on mitigating herbicide resistance would be less pronounced than that of Palmer amaranth because of the reduced seed retention or early seed shatter.

Manure applied to cropland may serve as a source of weed introduction and dispersal. In 36 manure samples from 20 farms, apparently-viable seeds from 13 grasses and 35 broadleaf plants were found. Common lambsquarters was on more than half the farms, yellow foxtail on 35%, common chickweed and dandelion on 30%, and wild mustard, redroot pigweed, and barnyardgrass on 25%. Four farms had manure with no seeds at all; the remainder averaged 75 100 per 1000 kg manure. Twelve milking-cow and heifer barns on six farms with large velvetleaf infestations also were sampled with an average of 133 000 seeds per 1000 kg manure. Only one barn contained velvetleaf seeds. When compared to soil seedbank numbers, manure is not an important seed source for New York farms. However, problems may arise with imported feeds heavily infested with weed seed or which contain even small numbers of noxious weeds.

In laboratory experiments, we studied barnyardgrass, common lambsquarters, and redroot pigweed seed dormancy release by alternating temperatures under different soil water regimes, to determine whether that response serves as a mechanism for assuring seedling establishment. Alternating temperatures were important in breaking seed dormancy in the three weeds, but the species' response to alternating temperatures differed with soil water content. For redroot pigweed and newly dispersed seeds of barnyardgrass, dormancy breaking by alternating temperatures occurred only when soil water content was high enough for germination. Moreover, adverse incubation conditions (constant temperature and low water content) induced secondary dormancy in these seeds. Seventy percent of seeds incubated in open boxes emerged before the soil reached wilting point, when seeds were incubated at temperatures high enough for a high germination rate. A dormancy breaking mechanism that triggers a high rate of germination may be important in assuring success of seedling establishment where rainfall patterns result in wetting and drying cycles of the soil, especially in soil types that lose water rapidly from the surface layers.

In a semiarid Mediterranean site in central Spain, field experiments were conducted on a Calcic Haploxeralf (noncalcic brown soil), which had been managed with three crop rotations and two tillage systems (no-tillage and conventional tillage) since 1987. The crop rotations consisted of barley→vetch, barley→sunflower, and a barley monoculture. The study took place in two growing seasons (1992–1994) to assess the effects of management practices on the weed seedbank. During this period, spring weed control was not carried out in winter crops. In the no-tillage system, there was a significant increase in the number of seeds of different weed species: anacyclus, common purslane, corn poppy, knotted hedge-parsley, mouse-ear cress, spring whitlowgrass, tumble pigweed, venus-comb, and Veronica triphyllos. Conversely, the presence of prostrate knotweed and wild radish was highest in plots under conventional tillage. These results suggest large differences in the weed seedbank as a consequence of different soil conditions among tillage systems, but also the necessity of spring weed control when a no-tillage system is used. With regard to crop rotations, the number of seeds of knotted hedge-parsley, mouse-ear cress, and spring whitlowgrass was greater in the plots under the barley→vetch rotation. Common lambsquarters dominated in the plots under the barley→sunflower rotation, whereas venus-comb was the most frequent weed in the barley monoculture. Larger and more diverse weed populations developed in the barley→vetch rotation rather than in the barley→sunflower rotation or the barley monoculture.

Field studies were conducted at the Main Experiment Station, Fayetteville, AR, in 1994 and 1995 to evaluate the effect of postemergence herbicides applied at late-season timings on sicklepod seed production and viability. AC 263,222, dicamba, glyphosate, glufosinate, and paraquat were applied at five rates (zero; labeled rate; one-half, one-fourth, and one-eighth the labeled rate) to three sicklepod growth stages (bud formation, flowering to 9-cm pods, and 15- to 30-cm pods). The greatest reduction in seed production occurred when herbicides were applied at the flowering to 9-cm pod growth stage. All herbicides applied at one-half the labeled rate to sicklepod at bud formation and at the flowering to 9-cm pod growth stage reduced seed production greater than 80%, except glufosinate. Regardless of herbicide, rate, or application timing, viability of remaining seed was ≥ 90% with all treatments.

This research was conducted to determine the environmental conditions necessary for development and expression of very low fluence (VLFR) germination sensitivity, and to determine the roles of type I phytochrome, gibberellic acid (GA) biosynthesis, and nitrate in this process. Redroot pigweed seed was subjected to pregermination incubation regimes of 5, 12, and 23 C for up to 21 d in a −1.2 MPa polyethylene glycol solution in the dark. Development of VLFR sensitivity was most pronounced at 23 C, and induction of germination by the lowest fluence tested (3 μmol m–2) was greater at a germination temperature of 30 than 20 C. In dormant smooth pigweed seed, development of VLFR sensitivity occurred only when seed was subjected to a prechilling treatment to overcome primary dormancy. The instability of the fluence response of seed subjected to pregermination conditions favorable for development of VLFR was consistent with type I phytochrome accumulation and degradation after photoconversion. In redroot pigweed seed, inhibition of GA biosynthesis during pregermination incubation resulted in the partial attenuation of VLFR sensitivity. The addition of 75 ppm nitrate to pregermination and germination media enhanced VLFR sensitivity. Our results suggest that development of VLFR sensitivity is due to cooperative action between type I phytochrome and phytochrome-independent GA biosynthesis. In the soil seedbank, this sensitivity may be augmented in elevated soil nitrate environments.

This research presents a modified floatation method to extract weed seed from soil samples and an automated imaging technique to enumerate seed following extraction. Rapid floatation of weed seed from soil in a K2CO3 solution was facilitated by centrifugation. High recovery of seed from soil samples was accomplished in a relatively short time. Recovery of seed of giant foxtail and velvetleaf from a silt loam soil was near 100% and recovery of redroot pigweed was 86%. Germination of common lambsquarters, giant foxtail, and velvetleaf seed was reduced by exposure to K2CO3 under certain conditions. However, these reductions do not appear to reduce the utility of this extraction technique. The automated image capture technique for counting seed showed similar limitations as with manual counting. Seed count accuracy generally decreased with increased number of seed and smaller seed sizes. In general, the image capture technique compared favorably with manual seed counting and has the potential to further improve seedbank assessment methods.