Summer Annual Weed Research Articles

Development of arable weed seedbanks during the 6 years after the change from conventional to organic farming

SummaryAll of the arable land of a farm in southern Germany was investigated during an 8‐year period, starting 2 years before and ending 6 years after the change to organic farming. The first 3 years after the conversion, the total seed number in the soil increased from 4050 to 17 320 m−2. From the fourth to the sixth year, it dropped back to 10 220 m−2. The number of seeds increased particularly at sites with a low crop cover and a high density of weed plants at the soil surface. The increase predominantly occurring on the more fertile soils may have been caused by the rotation commencing with less competitive crops. Crops which increased the seedbank by 30–40% were winter cereals, sunflowers and lupins. Potatoes and sown fallow caused no significant change and grass–clover mixtures even reduced the number of seeds by 39%. Among 44 species occurring frequently enough for statistical analysis, 31 increased and only 3 decreased. The change of management particularly increased summer annual, perennial and dicotyledonous weeds. This can be attributed to both operations which are characteristic of organic farming (e.g. replacing herbicide applications by mechanical weed control) and to general modifications of the management practice which may also occur in non‐organic farming systems (increasing the percentage of broad leaved and spring sown crops in crop rotation). The present study confirms investigations into the aboveground vegetation that indicate that arable organic farming favours plant species diversity and provides evidence that the conversion need not encourage the dominance of a few noxious weeds.

Weeding Efficacy of Sulfonylurea Resistance Weed, Monochoria (Monochoria vaginalis) with Brown Leaf Blight Caused by BWC01-54

A summer annual weed of monochoria (Monochoria vaginalis) grows in the edges of rice paddies, ditches, and moist upland throughout Korea. It is very difficult to control with herbicide because of its sulfonylurea resistance. It is very competitive with fast growing pattern, that can cause reducing yields of rice. Brown leaf blight of monochoria (Monochoria vaginalis) occurred naturally in rice paddy, is first reported in Korea. The fungal isolate BWC01-54 was successfully isolated from the diseased leaves of monochoria. The fungus BWC 01-54 was grown well at , conidia of the greysh black brown mycelia were abundant produced on PDA at 15 days. The fungus was grown well in potato dextrose broth at and fully grown within 10 days in 250 ml of flask. In host and pathogenicity test, conidia suspension of BWC01-54 was the most effective to control of monochoria compare to others isolates. Typical symptoms having pin point brown lesions were formed on stem and leaf and which severely affected the whole plants ware blighted within two weeks, respectively. Under paddies field condition, conidial suspension of the fungus BWC01-54 gave around 90% control. Therefore, we conclude that the fungus may have a potential as a biological control agent against sulfonylurea resistance weed in rice paddy.

地表面で越冬した夏畑雑草種子の発芽に対する温度と光条件の影響

地表面で越冬した夏畑雑草種子の発芽に対する温度と光条件の影響

Winter Wheat Cultivar Characteristics Affect Annual Weed Suppression

Thirteen hard red winter wheat cultivars were evaluated for their ability to suppress summer annual weeds in grain production systems near North Platte, NE, from 1993 through 1997. ‘Turkey’, a 125-yr-old landrace selection, suppressed both broadleaf and grass weeds more than other cultivars. Some relatively new cultivars, such as ‘Arapahoe’, ‘Jules’, ‘Pronghorn’, and ‘Vista’ suppressed summer annual grasses almost as well as Turkey. Total weed density was negatively correlated with number of winter wheat stems/m2, mature winter wheat height, and lodging. Weed density after wheat harvest was positively correlated with delay in winter wheat seeding date and was negatively correlated with precipitation 0 to 30 d after winter wheat seeding, during tillering, tillering to boot stage, and heading to maturity stage. Mean air temperature 0 to 30 d after wheat seeding was positively correlated with weed density. In the spring, weed density was positively correlated with temperatures during the tillering stage, tillering to boot stage, and heading to maturity stage. Stinkgrass and witchgrass densities were positively correlated with severity of wheat leaf rust. The highest grain-producing cultivars included three medium height cultivars ‘Alliance’, Arapahoe, and ‘Niobrara’. Alliance wheat produced 53% more grain than Turkey, and the other two produced 43% more grain.

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 winter barley as a cover crop on the weed vegetation in a no‐tillage soybean

The present study clarified the effects of winter barley as a cover crop on the weed vegetation, expressed as a multiplied dominance ratio (MDR), and emergence of summer annual weeds in a no‐tillage soybean system. A 3 year field study with treatments consisting of six systems was conducted: no‐tillage single cropping, no‐tillage cropping following winter barley and tillage single cropping, respectively with and without herbicide application. The MDR of perennial weeds increased annually in the no‐tillage fields in spring, but summer annual weeds were abundant in all fields, including the no‐tillage fields in summer. Grasses, for example Digitaria ciliaris (Retz.) Koeler, were especially abundant in the no‐tillage fields. The MDR of summer annual weeds, especially grasses in the barley and soybean fields, were much lower than for the no‐tillage single soybean fields. Densities of D. ciliaris and Echinochloa crus‐galli (L.) Beauv. var. crus‐galli in the no‐tillage single soybean fields were much greater than in the tilled fields, with few exceptions. In contrast, broad‐leaved weeds emerged more in tilled fields than in the no‐tillage fields. Winter barley suppressed emergence of summer annual weeds, especially during the first 3 years. The MDR for grasses in summer showed a good correlation with the frequency of emergence for grasses every year. These results showed that the increase in the volume of grasses in summer resulted mainly from an increase in the frequency of emergence, and that the suppression of grasses by winter barley resulted mainly from suppression of the emergence frequency. Soybean yields were higher in the barley and soybean fields for the first 2 years.

Zone herbicide application controls annual weeds and reduces residual herbicide use in corn

Abstract To minimize the chance of surface water contamination by herbicides, farmers need alternative ways to manage weeds in field crops, such as field corn, that reduce herbicide use. Zone herbicide application (ZHA) reduces herbicide use compared with conventional broadcast herbicide application by (1) banding low herbicide rates between corn rows (≤ 1× normal broadcast registered rate), (2) managing crops to favor crop competition, and (3) banding very low herbicide rates over crop rows (≪ 1× normal rate). The research goal was to compare the relative effectiveness of reduced-rate ZHA with broadcast herbicide application on in-row (IR) and between-row (BR) summer annual weed cover (chiefly giant foxtail and waterhemp species), grain yields, and net returns resulting from herbicide application in field corn. Preemergence ZHA of atrazine + metolachlor + clopyralid + flumesulam was made in zones (i.e., even width bands) at different rates between and over crop rows for three site-years in Missouri, and ...

Orchard Floor Management Influence on Summer Annual Weeds and Young Peach Tree Performance

This study compared the effect of weed control and orchard floor management (OFMA) options including organic mulch on summer annual weed interference in a newly established peach orchard. Weed interference where no preemergence (PRE) herbicides were applied, including vole damage, caused 29% peach tree mortality, reduced tree trunk cross-sectional area (TCSA) 62% by the fourth year of orchard establishment, and reduced fruit yield and fruit number in 1999 by 73 and 75%, respectively, but had no effect on fruit size. Compared with a no-till or conventionally tilled orchard floor, the population of grassy weeds within the tree row was greater in killed perennial ryegrass sod (PRS) plus hard fescue residue mulch treatments but was less in killed PRS plus tall fescue residue mulch treatments. Among the no-PRE treatments, the tree row broadleaf weed populations were suppressed in killed PRS with or without the addition of fescue residue mulch to the tree row when compared with the no-till or conventionally tilled orchard floor treatments. PRE herbicide treatments strongly affected peach fruit yield and TCSA but not average fruit size. There was no effect among the killed PRS, with or without hard or tall fescue residue mulch treatments, on peach fruit yield, TCSA, or average fruit size when compared with the no-till or conventionally tilled orchard floor treatment options. All treatments with herbicide had higher yields in 1999 than those without herbicides.

Weed Management in a Glyphosate Resistant Soybean System: Weed Species Shifts

With increased reliance on glyphosate for weed control, weed species composition shifts are likely. Changes in relative abundance could arise from differential tolerance or resistance to, or avoidance of, glyphosate. This study characterized the potential changes in seedbank composition of a mixed population of summer annual weeds due to glyphosate application timing. Seven weeds common in soybean fields in the Midwest were introduced at known densities and treated with glyphosate at several treatment timings. Common lambsquarters, common sunflower, common waterhemp, eastern black nightshade, ivyleaf morningglory, shattercane, and woolly cupgrass were selected to represent a range of emergence patterns and tolerances to glyphosate. Seedling emergence and seed production were monitored. Differences in herbicide tolerance and avoidance, through markedly different weed emergence patterns, were strong contributors to projected changes in weed species composition. Lessened sensitivity to glyphosate allowed some emerged species, such as ivyleaf morningglory, to better survive the herbicide. Late emergence allowed others, such as shattercane and ivyleaf morningglory, to avoid glyphosate applications. Such mechanisms may allow specific species to increase in a continuous glyphosate system.

Tillage index predicts weed seedling recruitment depth

The influence of tillage on the depth of weed seedling recruitment has implications for species competitive ability, weed management strategy development, and the modeling of weed emergence; characterization of this relationship could aid in the creation of field-specific models of weed seedling recruitment. A tillage index based on the percentage of residue cover remaining on the soil surface after tillage events was assessed for 44 zero-tillage and 44 conventional-tillage fields across Manitoba, Canada. This index was related to in situ measurements of seedling recruitment depth from the same fields for five annual weed species. The modeled relationship was linear and unique for each species (R2 values ranged from 0.38 to 0.71). The relationship did not differ between pre- and post-seeding measurements, or between years, except for green foxtail. Slopes of the regression lines were greater for species such as volunteer wheat, which can recruit from a great range of depths. The results of this study show that recent tillage strongly influences mean weed seedling recruitment depth, and that the recruitment depth of summer annual weed seedlings is related in a continuous and reliable manner to a simple estimation of the relative level of tillage (including seeding) applied in one season. Key words: Recruitment depth, tillage index, weed emergence, weed seedlings

Conventional- and conservation-tillage systems influence emergence periodicity of annual weed species in canola

Variation in spring emergence periodicity (both before and after crop seeding) of summer annual weeds is a potentially exploitable attribute that may be applied to weed management in canola. Tillage intensity, which is decreasing in the Great Plains of North America, may influence emergence periodicity of summer annual weeds. Emergence periodicity of common lambsquarters, field pennycress, green foxtail, redroot pigweed, wild buckwheat, wild mustard, and wild oat were monitored during the spring of 2000 in 17 producers' canola fields across southern Manitoba, Canada. The fields represented a region of approximately 2 million ha and included a broad range of soil types, agronomic practices, environmental conditions, and seedbank distributions. Fields were grouped into one of two broad tillage classifications (conventional or conservation). For most species, except redroot pigweed and wild mustard, conservation tillage promoted earlier emergence than conventional tillage in terms of both thermal and chronological time. The differences were significant even though there was only a limited range of tillage intensity for the two tillage classes within this region. Onset of canola crop emergence preceded that of all but one weed species in the conservation-tillage fields and five weed species in the conventional-tillage fields. This suggests that canola seeded in conservation- vs. conventional-tillage systems may have a competitive advantage by way of an earlier relative time of crop emergence. The influence of tillage system on weed emergence periodicity is likely due to the influence of tillage on the vertical origin of weed seedling recruitment because measurements of soil temperature and soil moisture did not help to fully explain the differences in emergence periodicity between tillage systems. The results from this study will facilitate weed control timing decisions in canola and provide validation data for weed emergence models.

The biology of Canadian weeds. 120. Neslia paniculata (L.) Desv.

A review of biological information is provided for Neslia paniculata. Native to central Eurasia, this species is naturalized in other temperate regions of the northern hemisphere. In North America it is most abundant in Canada’s prairie provinces, but has spread west and north to British Columbia, Alaska, Yukon and the Northwest Territories, and to scattered locations in eastern Canada and the northern United States. It is typically a summer annual weed of disturbed soils. Its growth habit and persistence in the seed bank have enabled it to spread as an adventive and to maintain its presence in cultivated areas. While it is present in relatively low frequency as a weed in most crops, its indehiscent seed pods can contaminate harvested crops and spread in seed commodities. The small size of its seed pods and the similarity of its seeds to those of canola and condiment mustard have led to its regulation as a significant contaminant of commercial seed. It is generally well controlled by herbicides (e.g., sulfonylureas, glyphosate, MCPA, bromoxynil, and 2, 4-D); however, a population resistant to metsulfuron-methyl, one of the Group 2 herbicides that inhibit acetolactate synthase (ALS), was found at a site in Alberta in 1998. Key words: Ball mustard, Neslia paniculata, weed biology, herbicide resistance, seed contaminant

Solaria Help Predict In-Crop Weed Densities1

At locations in Argentina and the United States, solaria (miniature, portable, plastic green- houses or a plastic sheet approximately 1 m 2 ) were placed on field soils in autumn or late winter in an attempt to predict summer annual weed densities. Initial emergence of summer annual weeds covered by solaria commenced weeks before that of weeds in exposed seedbeds. Cumulative emer- gence of many species in solaria reached asymptotes before crops were sown. At asymptotic cu- mulative emergence, densities of dominant weeds in solaria (common lambsquarters, green foxtail, and large crabgrass) were correlated with weed densities occurring 4 wk after sowing, the typical time for making postemergence weed control decisions. These results indicate that solaria may sup- plement seedbank-sampling techniques for predicting weed densities in crops. Nomenclature: Common lambsquarters, Chenopodium albumL. # 3 CHEAL; green foxtail, Setaria viridis (L.) Beauv. # SETVI; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA. Additional index words: Decision making, emergence, postemergence control, seedlings, solariza- tion. Abbreviations: CWD, in-crop weed density; OM, organic matter; PPI, preplant incorporated; PRE, preemergence; SWD, weeds inside solaria; TWD; threshold weed density.

不耕起大豆作での冬作緑肥導入による夏生一年生雑草の防除

不耕起大豆作での冬作緑肥導入による夏生一年生雑草の防除

Eliminating soil disturbance reduces post-alfalfa summer annual weed populations

The influence of method (tillage vs. no-till) and time of year of alfalfa (Medicago sativa L.) termination on the population of naturally occurring weeds was assessed over three site-years in southern Manitoba. Termination method was found to be more important than timing. Populations of weeds such as green foxtail [Setaria viridis (L.) Beauv.], redroot pigweed (Amaranthus retroflexus L.), wild mustard [Brassica kaber (DC) L.C. Wheeler] and lamb’s quarters (Chenopodium album L.) were usually lower (P < 0.05) in the undisturbed (i.e., no-till) system, compared to where tillage was used. It was concluded that the combination of alfalfa in rotation and no-till management can provide significant weed control benefits to cropping systems. Key words: Weed ecology, no-till cropping, forages

Between-Row Mowing + Banded Herbicide to Control Annual Weeds and Reduce Herbicide Use in No-till Soybean (Glycine max) and Corn (Zea mays)1

Abstract: Alternative methods are needed to control weeds in no-till corn and soybean which minimize herbicide contamination of surface or ground water. The objective of this research was to determine whether between-row (BR) mowing + band-applied herbicide could help reduce herbicide use, without sacrificing summer annual weed control or yield, in no-till soybean and field corn. Glyphosate was applied shortly before or at planting to control emerged winter annual weeds in all treatments. In the BR mowing weed management system, the band-applied soil residual herbicides imazaquin + alachlor in soybean or atrazine + alachlor in corn were applied shortly before or after planting followed by two or more between-row mowings to control summer annual weeds. Annual weeds were first mowed when they were about 8 cm tall and again just before crop canopy closure. Between-row mowing weeds very close to the soil surface two or three times killed or suppressed summer annual grass and broadleaf weeds, chiefly giant fox...

Weed Suppression by Annual Legume Cover Crops in No‐Tillage Corn

Cover crops often reduce density and biomass of annual weeds in no‐till cropping systems. However, cover crops that over‐winter also have the potential to reduce crop yield. Currently, there is an interest in annual medics (Medicago spp.) and other annual legumes that winter‐kill for use as cover crops in midwestern grain cropping systems. A 2‐yr study was conducted at East Lansing and the Kellogg Biological Station, Michigan, to investigate the influence of annual legume cover crops on weed populations. Two annual medic species [burr medic (M. polymorpha cv. Santiago) and barrel medic (M. truncatula Gaertn. cv. Mogul)], berseem clover (Trifolium alexandrinum L. cv. Bigbee), and medium red clover (Trifolium pratense L.) were no‐till seeded as cover crops into winter wheat (Triticum aestivum L.) stubble in a winter wheat/corn (Zea mays L.) rotation system. Density of winter annual weeds were between 41 and 78% lower following most cover crops when compared with no cover control in 2 out of 4 site years, while dry weight was between 26 and 80% lower in all 4 site years. Impact of cover crops on the density of summer annual weeds was infrequent; however, weed dry weights were reduced by 70% in 1995 following burr medic and barrel medic. Dry weight of perennial weeds before corn planting were 35 to 75% lower following annual legumes compared with the control, while weed density was not affected. This study indicated a potential for annual legumes to reduce weed density and growth in no‐till corn grain systems.

Vegetation Management Options in Almond Orchards

A well maintained orchard floor is critical for insuring year-round orchard access and a clean almond harvest operation. This study compared three methods of orchard floor vegetation management over a 4-year period. The objective of this study was to evaluate cost effective vegetation management programs for difficult to control summer annual weeds while maintaining the population of desirable winter annual species. Common purslane (Portulaca oleracea) can be a major summer weed problem that interferes with almond harvesting operations. A low rate residual herbicide program controlled purslane more consistently than mechanical or chemical mowing programs. Desirable winter weed cover was preserved in all three management systems. The costs for each program were similar; however, there was a reduction in the number of operations required for both chemical mowing and low rate residual programs compared to the mechanical mowing program.

183 Influence of Cover Crops on Weed Control and Plant Growth in Strawberry (Fragaria × ananassa Duch.)

Fall-planted cover crops killed in spring is practiced in strawberry cultivation in different regions of the North America. These systems have shown significant weed suppression and conservation of soil without significant yield reduction in strawberry. During the establishment season, this study was initiated to assess weed suppression with cover crops (`Wheeler' rye and `Micah' and `Steptoe' barley) along with perlite, an artificial plant medium. Strawberry (`Selva' and `Totem') plant growth and weed biomass were measured during 1995-96 season. Small-seeded summer annual weeds were suppressed in cover crop treatments compared to control treatment. `Micah' barley in growth phase suppressed more than 81% of the total weed biomass compared to control plots with no cover crop in early spring. However, in early summer, cover crop residues failed to suppress different types of weeds 60 days after killing of cereal with herbicide (2% glyphosate). Distinct differences in strawberry plant growth were evident between the cover crop treatments and non-cover crop treatments including `Micah' applied on surface. Strawberry growth was doubled during 10 July to 15 Aug. in both cultivars. `Micah' barley applied on surface produced better growth in both strawberry varieties than the growth in other treatments. `Micah' barley applied on soil surface produced 50% more strawberry shoot biomass may indicate the root competition between cover crops and strawberry.

Tolerance of Seashore Paspalum Cultivars to Preemergence Herbicides

Abstract The efficacy of preemergence herbicides among seashore paspalum (Paspalum vaginatum Swartz) cultivars used for summer annual weed control is limited. No differences were found in turfgrass tolerance among four paspalum cultivars from preemergence herbicides during 1996 and 1997 at Griffin, GA. The tolerance of paspalum turfgrass was good when treated with Ronstar (oxadiazon) at rates ≤ 10.1 kg/ha (9.0 lb/A), pendimethalin (various trade names, water-dispersible granules) or Barricade (prodiamine) at recommended rates [3.4 kg/ha (3.0 lb/A) and 0.8 kg/ha (0.7 lb/A), respectively]. When rates of these herbicides were increased to three times recommended, 15% injury was noted. During May 1996, Dimension (dithiopyr) injured the turf 12% when applied at the normal rate [0.6 kg/ha (0.5 lb/A)], but the injury was 35% in plots treated with three times recommended. Dimension did not cause any injury in 1997. Surflan (oryzalin) at 3.4 kg/ha (3.0 lb/A) and XL (benefin + oryzalin) at 3.4 kg/ha (3.0 lb/A) caused a maximum of 26% and 20% injury, respectively, when applied at the recommended rates. Maximum injury ranged from 48% for Surflan and 38% for XL when applied to plots at the three times recommended. The quality of PI 509018-1, SIPV-2, and AP-10 was generally higher than Adalayd from early spring until late August both years.