Summer Annual Weed Species Research Articles

Looking beyond Glyphosate for Site-Specific Fallow Weed Control in Australian Grain Production

Summer annual weed species in northern Australian summer fallows are frequently present at low densities and, increasingly, are glyphosate-resistant, creating the need for alternative herbicides for site-specific weed control. Alternative non-selective herbicide treatments are effective on problematic summer fallow weeds; however, many are yet to be evaluated as site-specific (spot spraying) treatments. This study aimed to identify herbicides that could be used in place of glyphosate to control larger/mature Chloris virgata and Sonchus oleraceus plants. The response of these weed species to 12 herbicide treatments was evaluated in pot experiments conducted over summer/autumn 2022. Despite herbicide treatments not being consistently effective across both species, there were instances where control was achieved by some herbicide treatments. S. oleraceus was controlled (i.e., ≤10% plant survival) by glufosinate-ammonium, paraquat and also with protoporphyrinogen-oxidase (PPO)-inhibiting herbicides saflufenacil, tiafenacil and trifludimoxazin. However, these results were not consistent in repeated studies or for C. virgata. Glyphosate was the only herbicide that controlled C. virgata. A glyphosate replacement as a spot-spraying treatment was not identified, and until further studies are more successful, alternative approaches are needed to preserve the ongoing effectiveness of this herbicide.

Assessment of Cover Crop Management Strategies in Nebraska, US

Adoption of cover crops has the potential to increase agricultural sustainability in the US and beyond. In 2017, a survey was conducted with Nebraska stakeholders in an attempt to evaluate current cover crop management strategies adopted in soybean (Glycine max [L.] Merr.), field corn (Zea mays L.), and seed corn production. Eighty-two Nebraska stakeholders answered the survey, of which 80% identified themselves as growers. Eighty-seven percent of respondents manage cover crops, and the average cover crop ha planted on a per farm basis is 32%. The primary method of establishing cover crops following soybeans and field corn is drilling. In seed corn, interseeding is the main seeding strategy for cover crop establishment. Cereal rye (Secale cereale L.) appeared as the most adopted cover crop species (either alone or in mixtures with radish [Raphanus sativus L.] or hairy vetch [Vicia villosa Roth]). Over 95% of respondents utilize herbicides for cover crop termination in the spring before crop planting. Glyphosate is used by 100% of survey respondents that use herbicides for cover crop termination. The major observed impacts of incorporating cover crops into a production system according to survey respondents are reduced soil erosion and weed suppression. According to 93% of respondents, cover crops improve weed control by suppressing winter and/or summer annual weed species. The biggest challenge reported by cover crop adopters is planting and establishing a decent stand before winter. According to the results of this survey, there are different management strategies, positive outcomes, and challenges that accompany cover crop adoption in Nebraska. These results will help growers, agronomists, and researchers better guide cover crop adoption, management, and future research and education needs in Nebraska and beyond.

Control of Photosystem II– and 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor–Resistant Palmer Amaranth (Amaranthus palmeri) in Conventional Corn

AbstractPalmer amaranth, a dioecious summer annual weed species, is the most troublesome weed in agronomic crop production systems in the United States. Palmer amaranth resistant to photosystem (PS) II- and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors is of particular concern in south central Nebraska. The objectives of this study were to determine the effect of PRE followed by POST herbicide programs on PS II- and HPPD-inhibitor-resistant Palmer amaranth control, crop yield, and net economic return in conventional corn. A field study was conducted in 2014, 2015, and 2016 in a grower’s field infested with PS II- and HPPD-inhibitor-resistant Palmer amaranth near Shickley in Fillmore County, Nebraska. A contrast analysis suggested that mesotrione+S-metolachlor+atrazine applied PRE provided 83% Palmer amaranth control at 21 d after application compared to 78 and 72% control with pyroxasulfone+fluthiacet-ethyl+atrazine and saflufenacil+dimethenamid-P, respectively. Most of the PRE followed by POST herbicide programs provided ≥85% Palmer amaranth control. Based on contrast analysis, POST application of dicamba+diflufenzopyr provided 93% Palmer amaranth control compared to 87, 79, and 42% control with dicamba, dicamba+halosulfuron, and acetochlor, respectively, at 28 d after POST. All PRE followed by POST herbicide programs, aside from mesotrione+S-metolachlor+atrazine followed by acetochlor (2,530 to 7,809 kg ha−1), provided 9,550 to 10,500 kg ha−1corn yield compared with 2,713 to 6,110 kg ha−1from nontreated control. Similarly, PRE followed by POST herbicide programs, except for mesotrione+S-metolachlor+atrazine followed by acetochlor ($191 and $897 ha−1), provided similar net return of $427 to $707 ha−1and $1,127 to $1,727 ha−1in 2014 and 2015-16, respectively. It is concluded that herbicide programs based on multiple sites of action are available for control of PS II- and HPPD-inhibitor-resistant Palmer amaranth in conventional corn.

Timing of Soil-Residual Herbicide Applications for Control of Giant Ragweed (Ambrosia trifida)

Fall-applied residual and spring preplant burn-down herbicide applications are typically used to control winter annual weeds and may also provide early-season residual control of summer annual weed species such as giant ragweed. Field experiments were conducted from 2006 to 2008 in southern Illinois to (1) assess the emergence pattern of giant ragweed, (2) evaluate the efficacy of several herbicides commonly used for soil-residual control of giant ragweed, and (3) investigate the optimal application timing of soil-residual herbicides for control of giant ragweed. Six herbicide treatments were applied at four application timings: early fall, late fall, early spring, and late spring. Giant ragweed first emerged in mid- and late-March in 2007 and 2008, respectively. The duration of emergence varied by year, with 95% of emergence complete in late May of 2008, but not until early July in 2007. Giant ragweed emergence occurred more quickly in plots that received a fall application of glyphosate + 2,4-D compared with the nontreated. Fall-applied residual herbicides did not reduce giant ragweed emergence in 2007 when compared with the nontreated, with the exception of chlorimuron + tribenuron applied in late fall. Giant ragweed control from early- and late-spring herbicide applications was variable by year. In 2007, saflufenacil (50 and 100 g ai ha−1) and simazine applied in early spring reduced giant ragweed densities by 95% or greater through mid-May; however, in 2008, early-spring applications failed to reduce giant ragweed emergence in mid-April. The only treatments that reduced giant ragweed densities by > 80% through early July were late-spring applications of chlorimuron + tribenuron or saflufenacil at 100 g ha−1. Thus, the emergence patterns of giant ragweed in southern Illinois dictates that best management with herbicides would include late-spring applications of soil-residual herbicides just before crop planting and most likely requires subsequent control with foliar or soil-residual herbicides after crop emergence.

Predicting Emergence of 23 Summer Annual Weed Species

First- and second-year seedbank emergence of 23 summer annual weed species common to U.S. corn production systems was studied. Field experiments were conducted between 1996 and 1999 at the Iowa State University Johnson Farm in Story County, Iowa. In the fall of 1996 and again in 1997, 1,000 seeds for most species were planted in plastic crates. Seedling emergence was counted weekly for a 2-yr period following seed burial (starting in early spring). Soil temperature at 2 cm depth was estimated using soil temperature and moisture model software (STM2). The Weibull function was fit to cumulative emergence (%) on cumulative thermal time (TT), hydrothermal time (HTT), and day of year (DOY). To identify optimum base temperature (Tbase) and base matric potential (ψbase) for calculating TT or HTT, Tbaseand ψbasevalues ranging from 2 to 17 C and −33 to −1,500 kPa, respectively, were evaluated for each species. The search for the optimal model for each species was based on the Akaike's Information Criterion (AIC), whereas an extra penalty cost was added to HTT models. In general, fewer seedlings emerged during the first year of the first experimental run (approximately 18% across all species) than during the second experimental run (approximately 30%). However, second-year seedbank emergence was similar for both experimental runs (approximately 6%). Environmental effects may be the cause of differences in total seedling emergence among years. Based on the AIC criterion, for 17 species, the best fit of the model occurred using Tbaseranging from 2 to 15 C with four species also responding to ψbase= −750 kPa. For six species, a simple model using DOY resulted in the best fit. Adding penalty costs to AIC calculation allowed us to compare TT and HTT when both models behaved similarly. Using a constant Tbase, species were plotted and classified as early-, middle-, and late-emerging species, resulting in a practical tool for forecasting time of emergence. The results of this research provide robust information on the prediction of the time of summer annual weed emergence, which can be used to schedule weed and crop management.

Weed vegetation of arable land in the Czech Republic: environmental a management factors determining weed species composition

This paper reports on the current situation in weed vegetation composition on arable land in selected areas of the Czech Republic, assessment of influence of selected variables: applied management systems (conventional, organic), crops (winter cereals, root crops) and altitude and ranking of the importance of these particular factors. A phytocoenological survey was conducted from 2006 to 2008 during a vegetation period using releves that were 100 m 2 in size, placed in the central part of fields. In total, 202 releves of agricultural vegetation were recorded. The combined environmental variables explained 10.6% of the variability. Based on the pCCAs, the highest effect was found at altitude, which explains 5.1% of the species composition variability. The second and third most significant factors are crop and management system, which explain 3.3% and 1.8% of the variability, respectively. The lowlands were generally characterised by the thermophilous summer annual weed species. The higher altitudes were populated by species that are typical for colder areas and poor, humid, and acidic soil types, such as cambisoil.

Response of Four Summer Annual Weed Species to Mowing Frequency and Height

Greenhouse experiments were conducted in 2011 to evaluate the effect of mowing frequency and mowing height on four summer annual weed species (large crabgrass, barnyardgrass, giant ragweed, and common lambsquarters). Plants were clipped at three heights (5, 10, or 20 cm) and at two frequencies (single clipping or repeated clippings at the same height) to simulate mowing. A nonclipped control was also grown for each species. When clipped once, large crabgrass, barnyardgrass, and giant ragweed produced at least 90% of the total dry weight (DW) of the nonclipped plants, and common lambsquarters produced at least 75%. A single cut was generally not sufficient to prevent weed seed production or kill any of the weeds in this study. Repeated clipping reduced large crabgrass, giant ragweed, and common lambsquarters reproductive DW to 46, 27, and 10% respectively, of the nonclipped control. Barnyardgrass plants that were repeatedly clipped produced between 0 and 8% of the seed DW of nonclipped plants, depending on clipping height. Repeated clipping reduced weed total DW to below 40% for all species compared to nonclipped plants. Our results suggest that, unless combined with other weed management practices, repeated mowing may be necessary to limit the growth and seed production of these weed species.

Seasonal emergence of selected summer annual weed species in dependence on soil temperature

This study aimed to describe emergence cycles of selected weed species under Central European conditions in relation to cumulative soil temperatures from the start of the vegetation season. Emergence of Chenopodium album, Echinochloa crus-galli, Galinsoga ciliata, and Abutilon theophrasti was observed from March to October during the period 2001–2006 at two locations. The beginning of main field emergence was determined as the day when the sum of effective hour temperatures was achieved, and was detected from the second decade of April to early May for C. album, in the second decade of May for E. crus-galli, from late April to the beginning of May for G. ciliata, and from the end of April to mid-May for A. theophrasti. The relationship between cumulative soil surface layer temperature and weed mass field emergence at the beginning of the growing season is very direct (differences ±7 days) – but only when soil moisture is sufficient. In a drier spring, the beginning of mass field emergence occurs with 1–4 weeks of delay and field emergence is usually slower and protracted.

Influence of Fall and Early Spring Herbicide Applications on Winter and Summer Annual Weed Populations in No-Till Corn

Field trials were initiated at three Missouri locations in the fall of 2004 and 2005 to compare the efficacy of fall and early spring herbicide applications on winter and summer annual weed populations in no-till soybean. All three experiments received applications of chlorimuron plus sulfentrazone plus 2,4-D; chlorimuron plus tribenuron plus 2,4-D; and glyphosate plus 2,4-D in the fall, 60 d prior to planting (60 PP), 30 days prior to planting (30 PP), and 7 d prior to planting (7 PP). Good control of all winter annual weeds, except for common chickweed, was observed at planting from fall applications of chlorimuron plus sulfentrazone plus 2,4-D and chlorimuron plus tribenuron plus 2,4-D. Fall, 60 PP, and 30 PP applications of chlorimuron plus sulfentrazone plus 2,4-D provided relatively poor control of common chickweed. Glyphosate plus 2,4-D applied in the fall and 60 PP provided adequate control of early fall germinating winter annuals, such as common chickweed and henbit. However, these treatments provided poor control of winter annual species that exhibited some degree of spring germination. Control of summer annual weed species 7 wk after planting (WAP) was highly variable. Relatively poor control of common waterhemp was obtained from all treatments except chlorimuron plus sulfentrazone plus 2,4-D applied at all three spring timings. Giant foxtail control was highly variable ranging from 0 to 95%. Measurements of weed biomass collected 7 WAP revealed larger amounts of biomass present in the fall application timing of each herbicide treatment. Emergence of winter and summer annual weed species from early March to 7 WAP varied by herbicide treatment. Emergence of total winter and summer annual weed species was reduced with both residual herbicide treatments when compared with glyphosate plus 2,4-D and the untreated control. Nomenclature: Chlorimuron; 2,4-D; glyphosate; sulfentrazone; tribenuron; common chickweed, Stellaria media (L.) Vill. STEME; common waterhemp, Amaranthus rudis Sauer AMATA; giant foxtail, Setaria faberi Herrm. SETFA; henbit, Lamium amplexicaule L. LAMAM; soybean, Glycine max (L.) Merr. ‘Dekalb 38-52’.

Influence of Fall and Early Spring Herbicide Applications on Winter and Summer Annual Weed Populations in No-till Soybean

Field trials were initiated at three Missouri locations in the fall of 2004 and 2005 to compare the efficacy of fall and early spring herbicide applications on winter and summer annual weed populations in no-till soybean. All three experiments received applications of chlorimuron plus sulfentrazone plus 2,4-D; chlorimuron plus tribenuron plus 2,4-D; and glyphosate plus 2,4-D in the fall, 60 d prior to planting (60 PP), 30 days prior to planting (30 PP), and 7 d prior to planting (7 PP). Good control of all winter annual weeds, except for common chickweed, was observed at planting from fall applications of chlorimuron plus sulfentrazone plus 2,4-D and chlorimuron plus tribenuron plus 2,4-D. Fall, 60 PP, and 30 PP applications of chlorimuron plus sulfentrazone plus 2,4-D provided relatively poor control of common chickweed. Glyphosate plus 2,4-D applied in the fall and 60 PP provided adequate control of early fall germinating winter annuals, such as common chickweed and henbit. However, these treatments provided poor control of winter annual species that exhibited some degree of spring germination. Control of summer annual weed species 7 wk after planting (WAP) was highly variable. Relatively poor control of common waterhemp was obtained from all treatments except chlorimuron plus sulfentrazone plus 2,4-D applied at all three spring timings. Giant foxtail control was highly variable ranging from 0 to 95%. Measurements of weed biomass collected 7 WAP revealed larger amounts of biomass present in the fall application timing of each herbicide treatment. Emergence of winter and summer annual weed species from early March to 7 WAP varied by herbicide treatment. Emergence of total winter and summer annual weed species was reduced with both residual herbicide treatments when compared with glyphosate plus 2,4-D and the untreated control.Nomenclature: Chlorimuron, 2,4-D, glyphosate, sulfentrazone, tribenuron, common chickweed, Stellaria media (L.) Vill. STEME, common waterhemp, Amaranthus rudis Sauer AMATA, giant foxtail, Setaria faberi Herrm. SETFA, henbit, Lamium amplexicaule L. LAMAM, soybean, Glycine max (L.) Merr. ‘Dekalb 38-52’

Predicting changes in dormancy level in weed seed soil banks: Implications for weed management

The development of models that allow the prediction of timing and extent of weed emergence is essential for planning more effective weed control strategies in agricultural systems. Dormancy is a common attribute of many weed seed populations and this hampers the task of predicting emergence from weed seed banks under field conditions. In this paper, we present a conceptual framework as an attempt to understand how the different environmental factors affect dormancy in weed seed banks in soil. We also present examples showing how these concepts could be used to develop quantitative models to predict dormancy loss in summer annual weed species and discuss how predictions derived from these models could be used to maximise the effect of weed control techniques.

Environmental factors affecting seed persistence of annual weeds across the U.S. corn belt

Weed seedbanks have been studied intensively at local scales, but to date, there have been no regional-scale studies of weed seedbank persistence. Empirical and modeling studies indicate that reducing weed seedbank persistence can play an important role in integrated weed management. Annual seedbank persistence of 13 summer annual weed species was studied from 2001 through 2003 at eight locations in the north central United States and one location in the northwestern United States. Effects of seed depth placement, tillage, and abiotic environmental factors on seedbank persistence were examined through regression and multivariate ordinations. All species examined showed a negative relationship between hydrothermal time and seedbank persistence. Seedbank persistence was very similar between the two years of the study for common lambsquarters, giant foxtail, and velvetleaf when data were pooled over location, depth, and tillage. Seedbank persistence of common lambsquarters, giant foxtail, and velvetleaf from October 2001 through 2002 and October 2002 through 2003 was, respectively, 52.3% and 60.0%, 21.3% and 21.8%, and 57.5% and 57.2%. These results demonstrate that robust estimates of seedbank persistence are possible when many observations are averaged over numerous locations. Future studies are needed to develop methods of reducing seedbank persistence, especially for weed species with particularly long-lived seeds.

Weed Control with Fall and Early-Preplant Herbicide Applications in No-Till Soybean

Field studies were conducted during 1999 and 2000 to compare weed control after fall and early-preplant (EPP) herbicide applications in no-till soybean. Three residual treatments (chlorimuron plus metribuzin, chlorimuron plus sulfentrazone, and metribuzin) were applied at two rates and timings (fall and 30 d EPP) either alone or in combination with glyphosate and 2,4-D. The addition of glyphosate and 2,4-D to fall-applied residual herbicides significantly increased control of common chickweed, annual bluegrass, cressleaf groundsel, and shepherd's-purse. The effect of application rate on weed control was species dependent. Fall-applied residual herbicides were comparable with EPP treatments with respect to winter annual weed control; however, at planting control of summer annual weed species with fall treatments was less consistent compared with EPP residual herbicides.

Effects of Tillage and Light Environment on Emergence of 13 Annual Weeds

Seeds of many plant species require a brief exposure to light to induce germination. Modifying the light environment during soil tillage may alter weed emergence in agricultural systems. The objective of this research was to evaluate the effect of secondary tillage conducted during daylight and at night on the emergence of 13 summer annual weed species under the same soil and environmental conditions. Annual grass and large-seeded broadleaf species showed little response to light environment during tillage. However, emergence was often less when no tillage was conducted than with any tillage by light environment combination. Emergence of small-seeded broadleaf species often was lower when tillage was conducted during darkness than with tillage during the light. Reductions varied by experiment and species and ranged from 70% for common lambsquarters to less than 30% for Pennsylvania smartweed. Large variations in response also occurred within species.

Emergence Periodicity of Six Summer Annual Weed Species

Emergence periodicity of common purslane, hemp sesbania, horse purslane, prickly sida, spurred anoda, and velvetleaf was determined from March to October during 5 yr at Stoneville, MS, in the absence of reseeding. In early March of each year prior to emergence determinations, plots were not tilled or tilled to depths of 0, 5, 10, or 15 cm. Yearly emergence periodicity of the six weed species was not affected by tillage. In each year, weeds of all species emerged in identifiable flushes and very few emerged at other times during the growing season. Velvetleaf emerged mainly during the early growing season from March through May. Peak periods of emergence for the other species varied slightly over the 5 yr, but conformed generally to the early or the midseason peak period (June, July, and August) or both. In most years, common purslane, horse purslane, hemp sesbania, prickly sida, and spurred anoda emerged during the midseason period. Annual patterns of temperature fluctuations were similar during the 5 yr, but relatively warm soil temperatures during the early growing season of 1977 may have caused earlier emergence of velvetleaf, prickly sida, and hemp sesbania. Weekly water balance (rainfall minus open-pan evaporation) varied during March through May of each year but was negative during each June, July, and August. Apparently the main effect of a positive water balance during most of the year was to cause merger of the early and midseason peak emergence periods in 1979. Early and midseason emergence peaks were possibly due to different populations of seeds able to germinate in cooler soil temperatures of the early season and warmer soil temperatures of the midseason, respectively.