Goosegrass is considered one of the worst agricultural weeds worldwide. Understanding its life cycle will provide useful management information. Field experiments with six emergence times (April, May, June, July, August, and September) were conducted at Anyang, China in 2015 and 2017 to clarify the growth and reproduction of goosegrass emerging at different times within a season. The result showed that plant height, dry weight, average weight per inflorescence, total inflorescence weight, average seed number per inflorescence, and total number of seeds per plant were relatively low in the April cohort, peaked with the May or June emergence cohort, and decreased thereafter. However, the earliest emergence of goosegrass in April had the highest total number of inflorescences. The plants of the May cohort produced the greatest number of seeds: 225,954 and 322,501 seeds per plant in 2015 and 2017, respectively. Delayed emergence resulted in less seed production; most plants that emerged in September did not flower or set seed. The 1,000-seed weight did not vary among the emergence cohorts. The reproductive investment was lowest for plants of the May cohort and then increased as emergence time was delayed to June, July, and August. Fresh mature seed of all emergence cohorts was extremely dormant and had low germination only up to 6% from August to November, and high germination (44% to 93%) in December. The information gained from this study indicates that weed management strategies should focus on the early-emerged seedlings such as the April and May cohorts, so as to effectively prevent goosegrass seed production, minimize the weed seed replenishment into the soil seed bank, and reduce the infestation in subsequent seasons.

The WEEDSIM bioeconomic model was developed in Minnesota and was designed to support weed management decisions for both soil-applied and postemergence weed control programs in Zea mays and Glycine max. In this research, we adapted the WEEDSIM weed management model to Michigan by modifying the crop yield loss functions and herbicide efficacy ratings. We then validated the components of the model and determined whether WEEDSIM led to more profitable weed management than recommendations from SOYHERB or CORNHERB, computer decision aids based solely on herbicide efficacy and cost. The crop year significantly influenced the weed-free yield in Z. mays and G. max, but the weed—crop interference function did not change each year. Total weed seed increased in the untreated compared with the weed-free control over the 3-yr period. Weed seed did not increase significantly in WEEDSIM preemergence/postemergence (PRE/POST), WEEDSIM postemergence, or CORNHERB or SOYHERB treatments compared with the weed-free control, although annual grass seedling density at the time of postemergence herbicide application had increased by 1995 in the WEEDSIM postemergence treatment in G. max because of a 2,4-D amine application only in Z. mays in 1994. WEEDSIM PRE/POST and CORNHERB provided excellent weed control in all three years, and WEEDSIM PRE/POST resulted in gross margins over weed control costs equal to or greater than CORNHERB recommendations. In G. max, Chenopodium album and annual grass control was excellent in all three years for WEEDSIM PRE/POST, WEEDSIM postemergence, and SOYHERB treatments. The highest average gross margin for the 3-yr study was from mechanical weed control in 76-cm-wide rows of G. max ($806 ha−1) and from SOYHERB in 38- and 19-cm-wide rows of G. max ($776 and $808 ha−1, respectively). WEEDSIM recommendations controlled weeds and maintained crop yield in both Z. mays and G. max.

Weed control practices affected the weed seed content of the soil, weed seedling populations, and corn and soybean yields in two 4-yr field experiments. When the initial weed seed density was high, giant foxtail seed numbers in soil declined rapidly under weed-free conditions. Changes in seed densities when initial densities were low varied over years. Mechanical and chemical control treatments had variable effects on weed seed numbers over the course of the experiment. Weed seed numbers and weed densities were sometimes greater if herbicides were banded, but crop yields were similar to full-rate herbicides in both experiments in all years. When the initial density was low, giant foxtail seed numbers in soil increased over the course of the experiment regardless of the weed control treatment. Seed densities of broadleaf species decreased under the same conditions. Also, when initial weed densities were low, weed control and crop yields were less sensitive to weed control practices than at high weed densities. Weather factors that influenced treatment efficacy had a major affect on weed populations and crop yield responses to the weed control treatments over years. The interactions of weed control practices, weed populations, and crop yields were complex. Initial weed density and species composition interacted with weed control treatments and weather patterns to generate the results observed.

Cooperative research was initiated by a multidisciplinary team of weed scientists and agricultural economists in 1975 that laid the foundation for integrated weed management research in Colorado. Colorado's integrated weed management research has four phases: weed seed bank decline, systems approach to weed management, bioeconomic modeling, and multiple weed management tactics. Each phase considered weed seed bank, weed control efficacy, weed control costs, crop yield, and gross margin. All four phases emphasize the need for a weed management system that minimizes seed production in situations where a high soil weed seed bank exists. However, once the weed seed bank is reduced, a weed management program with less than 100% weed control can be employed without increasing the seed bank. Intensive weed management systems are seldom justified when economics, weed control, and weed seed bank are considered. Integrated weed management approaches require integrating crop and weed biology with management tactics. Integrated weed management requires advanced managerial skills and often more time than traditional approaches.

Changes in weed seedbank composition are often monitored by removing seeds from soil samples. One extraction method accomplishes this by creating a slurry of soil and a concentrated inorganic salt solution. Centrifugation is then used to separate constituents of differing densities. We have found that centrifugation of giant foxtail seeds in 3.2 M potassium carbonate solution as conducted in a centrifugation/flotation extraction method can reduce viability as measured by germination and tetrazolium tests. In one experiment, centrifugation/flotation separation reduced germination of giant foxtail seeds from 94 to 52%. The likely cause of seed damage was the high pH of the potassium carbonate solution in conjunction with the increased hydrostatic pressure due to centrifugation. While centrifugation affected quantitative measures of seed viability, it did not alter qualitative viability estimates using a pressure test.

Freshly collected redroot pigweed seeds were buried 5 cm deep in the field in November of 3 yr in succession. Treatments applied to the soil surface included KNO3 (400 kg ha-1) in midwinter, ethephon (11 kg ha-1) in late spring, and a soil cover (polyethylene sheet for 2 wk) in late spring. Seeds were recovered within 1 yr after treatment, examined for in situ germination, and tested for viability. The 3-yr averages for viable seeds remaining by October in the year after treatment with KNO3 or soil cover, either alone or in combination, did not differ from nontreated checks and averaged 47% of the original population. Viable seeds remaining in soil treated with ethephon either alone or combined with KNO3 were reduced to 21% of the beginning population. The most effective treatments were ethephon either combined with a soil cover or with a soil cover plus KNO3 which reduced the viable seeds to an average of 8% of the original. Ethephon plus a soil cover has the potential to reduce greatly redroot pigweed seed populations in the field.

Direct-seeding of cover crops is often promoted to reduce potential soil loss during the winter, enhance soil fertility, and reduce energy use and equipment traffic on fields. The impact of direct-seeding of cover crops on wild-proso millet seedling emergence in subsequent crops is unknown. In this study, a pulse–chase experiment determined the effect of five fall soil management strategies, two spring primary tillage levels, and two herbicide programs on wild-proso millet emergence in a subsequent crop of snap beans. Wild-proso millet seeds were sown following sweet corn harvest in two commercial production fields to simulate seed rain at a density of 500 and 1,000 seeds m−2 in the fall of 2004 and 2005, respectively. The experimental design was a split–split plot. Five fall treatments were applied to main plots and included direct drilling of cover crops, conventionally tilled and drilled cover crops, a winter fallow treatment, and two additional treatments that were direct-drilled and conventionally tilled in the fall but that were not seeded with cover crops to separate the effects of tillage and cover crops on wild-proso millet emergence. Main plots were split in the spring and snap beans planted without primary tillage or conventionally planted after the soil was tilled. Tillage and cover crop treatments applied in the fall influenced emergence in the spring but with slightly different outcomes at the two sites. Direct drilling without a cover crop produced more wild-proso millet seedlings in snap beans than the winter fallow plot; tillage before cover crop planting in the fall produced recruitment levels less than or equal to densities in the winter fallow plots, with one exception. At one site, cover crops increased emergence compared to plots without cover crops. Spring tillage did not alter the affect of the five fall management treatments on wild-proso millet emergence. Direct-seeding of cover crops should be done with equipment or methods that minimize soil disturbance to prevent movement of wild-proso millet seeds into protected and favorable zones of emergence in the soil.

Seeds of giant foxtail (Setaria faberi, 4,000 seeds/m2) or velvetleaf (Abutilon theophrasti, 3,000 seeds/m2) were added to the seed bank to determine the effect of increases in weed density on herbicide efficacy in corn (Zea mays). A herbicide program consisting of SAN 582 applied preemergence followed by a postemergence application of dicamba plus atrazine was evaluated at four levels (0.0, 0.3, 0.7 and 1.0 times the label rates). At a site with low initial weed densities, the addition of velvetleaf or giant foxtail seed to the seed bank did not influence herbicide efficacy at the 1.0× rate at 9 wk after planting (WAP). Giant foxtail densities were greater 9 WAP in augmented areas than in the native seed bank plots at both the 0.3× and 0.7× rates, whereas with velvetleaf, higher densities in augmented plots were seen only at the 0.3× rate. In areas with high native weed densities, addition of seed of either species resulted in an increase in final weed densities at all herbicide rates.

Weed control strategies based on conserving crop yields rather than preventing weed seed production may result in increased weed densities and management costs over the long-term, particularly in less competitive crops such as tomatoes. The effect of crop, tillage, and duration of weed control on weed seed bank size and composition was examined from spring 2001 to spring 2003 near Lafayette, IN. Main plots in 2001 and 2002 contained soybean or tomato planted in rotation (soybean-tomato, tomato-soybean). Subplots were managed with either conventional or no-till practices. Sub-subplots contrasted threshold strategies in which weeds were either controlled for four to six weeks (period threshold, PT) or throughout the growing season (no-seed-threshold, NST). Seed banks were sampled annually in the spring. Emergent weeds were counted` at four and twelve weeks after planting (WAP) in 2001 and 2002. Weed seed banks did not significantly change in the NST plots in any year. However, seed bank densities increased substantially following tomatoes in PT plots. In contrast, weed seed bank densities decreased following soybeans in PT plots. The difference in seed banks and emergent weeds between soybean and tomatoes could be attributed primarily to greater suppression of giant foxtail by the soybean canopy. Giant foxtail control was greater in PT soybeans than in PT tomatoes in both years and giant foxtail comprised most of the PT tomato seed bank in 2002 and 2003. Tillage did not affect weed seed banks in any year. This study highlights the need to control later emerging weeds in tomatoes to prevent large increases in the weed seed bank.

An experiment was conducted to determine the population dynamics of barnyardgrass under a range of weed management treatments in glyphosate-resistant (GR) cotton in Australia. These treatments consisted of glyphosate herbicide only (Glyphosate only), glyphosate herbicide plus a combination of conventional or integrated weed management practices (Glyphosate + IWM), glyphosate herbicide plus a reduced residual herbicide program (Glyphosate + Res.), glyphosate herbicide plus a grass herbicide (Glyphosate + Grass), and a combination of conventional weed management practices (IWM only). The experiment investigated the effects of weed management on the weed seed bank, weed emergence patterns, and weed populations. After three years, all treatments resulted in commercially acceptable control of barnyardgrass. However, treatments containing soil-applied residual herbicides proved more effective over the period of the experiment. Seed bank reductions were in the order of 100-fold over the period of the experiment for treatments that received residual herbicides compared to 10- to 20-fold reductions for treatments that did not. The experiment highlighted the importance of early-season weed control, as well as the importance of an integrated approach to weed management with residual herbicides to control later-emerging weeds in GR cotton.

Blackgrass is a common winter annual grass weed in autumn-sown crop rotations in Atlantic European countries. Control with a minimum amount of herbicides in integrated cropping systems would be facilitated by modeling the effect of cropping systems on its demography. To develop the submodel relating weed seed bank to emerged seedlings, laboratory experiments were conducted to analyze and quantify seed germination and shoot elongation. These processes were studied as a function of environmental conditions during seed production (nitrogen availability, water deficit, plant density, and crop) and of seed characteristics (seed weight, harvest date, storage length, and dry-stored/soil-buried). Nonlinear equations relating germination and shoot elongation to time calculated as cumulated degree-days were fitted to the observed germination and shoot elongation data. These were used to estimate parameters for germination proportion and rate, as well as final shoot length and elongation rate. Recently harvested seeds germinated best and fastest when they were collected in spring crops compared with winter crops. Germination proportion and rate increased with seed storage length, especially for seeds collected in winter crops. Midgermination time decreased with seed weight and water deficit during seed production; it increased with nitrogen amounts available to the mother plants. Maximum shoot length increased with seed weight and plant density during seed production. It decreased with nitrogen availability to mother plants and with storage length, irrespective of whether the seeds were dry-stored or buried in soil. Elongation rate was highest for early- and fast-germinating seeds. Time to midelongation increased with maximum shoot length. These germination and preemergence growth models can now be combined with other submodels to develop a blackgrass emergence model.

No-tillage offers potential for improved soil quality, reduced erosion, and equal or increased crop yields. We hypothesized that, compared with conservation tillage (CT), no-tillage (NT) offers conditions more conducive to microbial decay of weed seed. In NT systems seed remain at or near the soil surface where crop residues, moisture, and lack of disturbance create an environment with greater soil microbial diversity. In late fall of 1998 and 1999, dormant seed of wild oat, either individually glued to plastic toothpicks or mixed with soil and placed in mesh bags, were buried (mean seed depth of 2.5 cm) in replicated field plots managed by NT or CT since 1982. Treatments including fungicide seed treatment (thiram + metalaxyl + captan) and soil fumigation (propylene oxide) provided estimates of the contribution of microorganisms to observed mortality. Seed were retrieved in May and August, 1999 and 2000. Contrary to our original hypothesis, the proportion of dead seed was generally similar in NT and CT systems. Lack of tillage system by seed or soil treatments affecting the proportion of dead or decayed seed suggests that the contribution of microorganisms to seed fate is similar in these tillage environments. However, the proportion of dormant seed was consistently lower in the NT compared with CT treatments; there was a corresponding increase in the proportion of germinated seed. Overall, more than half of the wild oat seed bank losses could be directly attributed to germination whereas losses due to decay were relatively minor by comparison. Despite favorable distribution of seed and improved quality of the surface-strata of soil in NT systems, this study fails to provide evidence that enhanced microbial decay will contribute to a “weed-suppressive” capacity in such cropping systems.