Waterhemp (Amaranthus tuberculatus [Moq.] Sauer) escapes are common in midwestern U.S. soybean [Glycine max (L.) Merr.] fields due to the continued rise in herbicide-resistant (HR) populations. In a conventional harvesting system, weed seeds are harvested with the crop grain and spread back on to the field. Harvest weed seed control methods such as chaff lining concentrate weed seed-bearing crop and weed chaff into a narrow row (chaff line). These chaff lines (30- to 50-cm wide) are undisturbed the following growing seasons, under the assumption that the chaff line creates an environment less favorable for weed seed germination and survival. Field experiments were conducted in a soybean–corn (Zea mays L.) rotation in 2020 and 2021 in Ames, IA, and Roland, IA, to quantify the effectiveness of chaff lining for managing A. tuberculatus seeds. About 70% of the A. tuberculatus seeds were retained on the mother plant at soybean harvest in 2020. The chaff lining system concentrated more than 99% of the A. tuberculatus seeds exiting the combine into the chaff line. Although A. tuberculatus population density in 2021 was 76% higher inside the chaff line than outside the chaff line, A. tuberculatus aboveground biomass was 63% lower inside the chaff line than outside the chaff line at 12 wk after corn planting. Similarly, A. tuberculatus inside the chaff line had delayed emergence compared with A. tuberculatus outside the chaff line. Application of preemergence herbicides in corn inside the chaff line delayed A. tuberculatus emergence by more than 2 wk compared with A. tuberculatus outside the chaff line. Additionally, a follow-up postemergence herbicide application in corn was needed only inside the chaff line to manage A. tuberculatus, suggesting the possibility of lower overall herbicide use. These results support implementing chaff lining in soybean-based crop systems of the U.S. Midwest to help manage HR A. tuberculatus seedbanks.

Junglerice [Echinochloa colona (L.) Link] is increasing its prevalence in eastern Australia by adapting to Australia’s changing climatic conditions and conservation agricultural systems and by evolving resistance to glyphosate. Information is limited on the growth and seed production dynamics of E. colona when it interferes with mung bean [Vigna radiata (L). R. Wilczek], a major potential export crop for eastern Australia. This field study examined the interference of E. colona in mung bean for two summer seasons (2020 and 2021) at Gatton, QLD. Different infestation levels (0, 2, 4, 8, 16, and 32 plants m−2) of E. colona were assessed for their potential to cause yield reductions in mung bean. Seed yield of mung bean was highest in the weed-free plots (2,767 kg ha−1) and declined by 20%, 27%, 34%, and 43% at weed infestation levels of 4, 8, 16, and 32 plants m−2, respectively. Echinochloa colona biomass in mung bean varied from 11 to 137 g m−2 as weed density increased from 2 to 32 plants m−2. Based on a three-parameter hyperbolic rectangular decay model, crop yield loss was 52% and 57%, respectively, when weed density and weed biomass approached maximum. Echinochloa colona at the highest density (32 plants m−2) produced a maximum of 15,140 seeds m−2, and this seed production was reduced by 50% at a weed density of 10 plants m−2. Echinochloa colona plants retained 63% to 68% seeds at mung bean maturity, indicating a great opportunity for harvest weed seed control. This study suggests that a high infestation of E. colona in mung bean fields could cause a substantial yield loss and increase the weed seedbank.

Serotiny is a strategy in which the retention of mature seeds in parent structures allows plants to cope with environmental variability like heat, drought or fire. Although this phenomenon might be common in Cactaceae, and particularly in Melocactus, it has generally been scarcely addressed. The main goal of our work is to investigate if there are seeds hidden in the cephalium of Melocactus matanzanus and if there are, determine whether or not these seeds maintain their viability. We also discuss some advantages the cephalium may offer as diaspore after the death of individuals. Cephalia collected from dead individuals were divided into four slices and their seeds counted; we also assessed the viability and photoblastic response of the seeds by using growth chambers at 25/30°C, and by a cut test on the seeds that did not germinate. Our results showed retention of viable seeds of different ages in all slices of the cephalium. Seeds were photoblastic positive with germination between 11–22% and viability above 50% in the portion of the lots that did not germinate.

Prevalence of wild oat (Avena fatua L.) and sterile oat [Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne; referred to as A. sterilis hereafter], winter-season weeds, is increasing in the eastern grain region of Australia. Biological attributes of these weeds enable them to survive in a wide range of environments and under different weed infestation levels. The interference of A. fatua and A. sterilis in a wheat (Triticum aestivum L.) crop was examined in southeast Queensland, Australia, through field studies in 2019 and 2020. Different infestation levels (0, 3, 6, 12, 24, and 48 plants m−2) of A. fatua and A. sterilis were evaluated for their potential to cause yield losses in wheat. Based on a three-parameter logarithmic model, the A. fatua and A. sterilis infestation levels corresponding to 50% wheat yield loss were 15 and 16 plants m−2, respectively. The yield reduction was due to a reduced spike number per unit area because of an increased weed infestation level. At the highest weed infestation level (48 plants m−2), A. fatua and A. sterilis produced a maximum of 4,800 and 3,970 seeds m−2, respectively. Avena fatua exhibited lower seed retention (17% to 39%) than A. sterilis (64% to 80%) at wheat harvest, as most of the seeds of A. fatua had shattered at crop maturity. Our results implied that there is a good opportunity for harvest weed seed control if the paddock is infested with A. sterilis. This study suggests that in the absence of an integrated weed management strategy (using both chemical and nonchemical options), a high infestation of these weeds could cause a severe crop yield loss, increase weed seed production, and replenish the weed seedbank in the soil.

Before any late-season weed control operations are planned to manage herbicide-resistant weeds, it is essential to evaluate the plants’ maturity and shattering potential. Our goal was to assess the seed-shattering phenology of common ragweed (Ambrosia artemisiifolia L.) using pollination bags as seed traps. A secondary goal was to evaluate the efficiency of these traps. Trials were conducted from 2014 to 2017 at two locations in eastern Canada (Saint-Jean-sur-Richelieu, QC, and Harrow, ON). At each location, three adjacent fields were seeded with spring wheat (Triticum aestivum L.), soybean [Glycine max (L.) Merr.], or corn (Zea mays L.). Each field was divided into four replicate blocks that included two treatment plots with 5 weeds m−2 planted on the same date as the crop or when crop plants had two leaves (early or late emergence). To evaluate shattering in time, the experiment included up to 12 weekly collection dates (subplots). In each subplot, weeds were individually bagged at flowering (using mesh bags) until collection, when the number and viability of shattered and retained seeds per plant was recorded. Weather data as well as crop and weed stages were recorded. The effect of the pollen bags on seed retrieval and viability was evaluated by installing open and closed bags in corn and uncropped (bare) plots at a single location. Ambrosia artemisiifolia seed biomass was equivalent or higher in closed bags, and seed viability was equivalent or slightly reduced. No seeds were produced before harvest in spring wheat, as dispersal started in September. The percentage of seeds retained on the plant decreased linearly (1 site-year) or followed a logistic equation (4 site-years) with day of year or growing degree days. Dispersal in time was similar between early- and late-emerging weeds and similar in both corn and soybean. On average, more than 50% of A. artemisiifolia seeds were dispersed before harvest in corn and soybean.

Annual sowthistle (Sonchus oleraceus L.) is a broadleaf weed that is increasing in prevalence in the northern cropping regions of Australia. Being a member of Asteraceae family, this weed possesses many biological attributes needed to thrive in varying environments and under differing weed management pressures. Interference of this weed in a wheat (Triticum aestivum L.) crop was examined through field studies in 2016 and 2017. Different densities of S. oleraceus were evaluated for their potential to cause yield loss in wheat: 0.0 (weed-free), low (9 to 15 plants m−2), medium (29 to 38 plants m−2), and high (62 to 63 plants m−2). Based on the exponential decay model, 43 and 52 plants m−2 caused a yield reduction of 50% in 2016 and 2017, respectively. Yield components such as panicles per square meter and grains per panicle were affected by weed density. At the high weed infestation level, S. oleraceus produced a maximum of 182,940 and 192,657 seeds m−2 in 2016 and 2017, respectively. Sonchus oleraceus exhibited poor seed retention at harvest, as more than 95% of seeds were blown away by wind. Adverse effects on crop, high seed production, and wind-blown dispersal may lead to an increased prevalence of this weed in the absence of an integrated weed management strategy utilizing both herbicides and nonchemical options.

Turnipweed [Rapistrum rugosum (L.) All.] and Mexican pricklepoppy (Argemone mexicana L.) are increasingly prevalent in the northern cropping regions of Australia. The effect of different densities of these two weeds was examined for their potential to cause yield loss in wheat (Triticum aestivum L.) through field studies in 2016 and 2017. There was 72% to 78% yield reduction in wheat due to competition from R. rugosum. Based on the exponential decay model, 18.2 and 24.3 plants m−2 caused a yield reduction of 50% in 2016 and 2017, respectively. Rapistrum rugosum produced a maximum of 32,042 and 29,761 seeds m−2 in 2016 and 2017, respectively. There was 100% weed seed retention at crop harvest. Competition from A. mexicana resulted in a yield loss of 17% and 22% in 2016 and 2017, respectively; however, plants failed to set seeds due to intense competition from wheat. Among the yield components, panicles per square meter and grains per panicle were affected by weed competition. The studies indicate a superior competitiveness of R. rugosum in wheat and a suppressive effect of wheat on A. mexicana. The results indicate that a wheat crop can be included in crop rotation programs where crop fields are infested with A. mexicana. High seed retention in R. rugosum indicates the possibility to manage this weed through seed catching and harvest weed seed destruction.

Herbicide resistance is a major problem in United States and global agriculture, driving farmers to consider other methods of weed control. One of these methods is harvest weed seed control (HWSC), which has been demonstrated to be effective in Australia. HWSC studies were conducted across Virginia in 2017 and 2018, targeting Italian ryegrass in continuous winter wheat as well as common ragweed and Palmer amaranth in continuous soybean. These studies assessed the impact of HWSC (via weed seed removal) on weed populations in the next year’s crop compared with conventional harvest (weed seeds returned). HWSC reduced Italian ryegrass tillers compared with the conventional harvest at two locations in April (29% and 69%), but no difference was observed at a third location. At wheat harvest, HWSC at one location reduced Italian ryegrass seed heads (41 seed heads m−2) compared with conventional harvest (125 seed heads m−2). In soybean, before preplant herbicide applications and POST herbicide applications, HWSC reduced common ragweed densities by 22% and 26%, respectively, compared with the conventional harvest plots. By soybean harvest, no differences in common ragweed density, seed retention, or crop yield were observed, because of effectiveness of POST herbicides. No treatment differences were observed at any evaluation timing for Palmer amaranth, which is attributed to farmer weed management (i.e., effective herbicides) and low weed densities making any potential treatment differences difficult to detect. Across wheat and soybean, there were no differences observed in crop yield between treatments. Overall, HWSC was demonstrated to be a viable method to reduce Italian ryegrass and common ragweed populations.

As chemical management options for weeds become increasingly limited due to selection for herbicide resistance, investigation of additional nonchemical tools becomes necessary. Harvest weed seed control (HWSC) is a methodology of weed management that targets and destroys weed seeds that are otherwise dispersed by harvesters following threshing. It is not known whether problem weeds in western Canada retain their seeds in sufficient quantities until harvest at a height suitable for collection. A study was conducted at three sites over 2 yr to determine whether retention and height criteria were met by wild oat, false cleavers, and volunteer canola. Wild oat consistently shed seeds early, but seed retention was variable, averaging 56% at the time of wheat swathing, with continued losses until direct harvest of wheat and fababean. The majority of retained seeds were >45 cm above ground level, suitable for collection. Cleavers seed retention was highly variable by site-year, but generally greater than wild oat. The majority of seed was retained >15 cm above ground level and would be considered collectable. Canola seed typically had >95% retention, with the majority of seed retained >15 cm above ground level. The suitability ranking of the species for management with HWSC was canola>cleavers>wild oat. Efficacy of HWSC systems in western Canada will depend on the target species and site- and year-specific environmental conditions.

Broom snakeweed achene dispersal was monitored by placing surface-level traps outwards in the cardinal directions from 12 plants and collecting the achenes weekly or biweekly from September 1993 until seeds were no longer retained by the plants after 42 wk. About 50% of the achenes dispersed between October and December. Especially high numbers of achenes were dislodged during periods of intense winter winds and rains, with 78% of the seed placed into the east tray and 86% falling within 50 cm of the parent plant. Achene production averaged 3,928 (± 1,146) per plant in 1993 and 2,036 (± 987) per plant in 1994. Achenes collected over time directly from the inflorescence and achenes stored in nylon packets on the soil surface averaged 82% viability during fall and winter. Achene viability declined rapidly in late spring, and few remained viable before the next seed crop. Greenhouse experiments compared the influence of water application interval and water amount on broom snakeweed germination and seedling survival. Treatments consisted of 4 water intervals: daily, 5-d, 10-d, and 15-d intervals; and 4 water amounts: field capacity (1/1 fc), 3/4 fc, 1/2 fc, and 1/4 fc. Germination was 52% at daily 1/1 fc, and no seed germinated at daily 1/4 fc. Data suggest that optimum germination occurs when soils are maintained at a minimum soil matric potential (Ψm) > −180 kPa for at least 4 d. Optimum Ψm for seedling survival appears to range between −300 and −900 kPa, while seedling mortality would generally be expected with a Ψm of > −1800 kPa.

As herbicide-resistant weed populations become increasingly problematic in crop production, alternative strategies of weed control are necessary. Giant ragweed, one of the most competitive agricultural weeds in row crops, has evolved resistance to multiple herbicide biochemical sites of action within the plant, necessitating the development of new and integrated methods of weed control. This study assessed the quantity and duration of seed retention of giant ragweed grown in soybean fields and adjacent field margins. Seed retention of giant ragweed was monitored weekly during the 2012 to 2014 harvest seasons using seed collection traps. Giant ragweed plants produced an average of 1,818 seeds per plant, with 66% being potentially viable. Giant ragweed on average began shattering hard (potentially viable) and soft (nonviable) seeds September 12 and continued through October at an average rate of 0.75 and 0.44% of total seeds per day during September and October, respectively. Giant ragweed seeds remained on the plants well into the Minnesota soybean harvest season, with an average of 80% of the total seeds being retained on October 11, when Minnesota soybean harvest was approximately 75% completed in the years of the study. These results suggest that there is a sufficient amount of time to remove escaped giant ragweed from production fields and field margins before the seeds shatter by managing weed seed dispersal before or at crop harvest. Controlling weed seed dispersal has potential to manage herbicide-resistant giant ragweed by limiting replenishment of the weed seed bank.