Yellow Foxtail Research Articles

Evaluation of Glyphosate-Resistant Hard Red Spring Wheat (Triticum aestivum)

The potential for future commercialization of glyphosate-resistant wheat necessitates evaluation of agronomic merits of this technology. Experiments were established to evaluate glyphosate-resistant wheat and weed responses to glyphosate rate, application timing, and tank mixtures. Glyphosate at 1,680 g/ha did not injure wheat. Wheat response to glyphosate applied to one- to three- or three- to five-leaf wheat was not different from that of untreated wheat. Wheat was injured more from glyphosate plus thifensulfuron or glyphosate plus dicamba than from individual herbicides at one of six locations, but grain yield was not affected by glyphosate tank mixtures. Glyphosate application timing did not affect control of wild oat or common lambsquarters 56 d after treatment. Glyphosate when applied to one- to three-leaf wheat provided better control of wild buckwheat than later glyphosate application, whereas glyphosate applied to three- to five-leaf wheat provided the best control of green and yellow foxtail, redroot pigweed, and Canada thistle. Weed control with glyphosate tended to be better than with conventional herbicides, and wheat treated with glyphosate produced approximately 10% more grain than wheat treated with conventional herbicide tank mixes.

Influence of Yellow Foxtail on Corn Growth and Yield

Yellow foxtail [Setaria pumila syn. Setaria glauca (L.) Beauv.] competitive influence on corn (Zea mays L.) growth and yield was investigated at Brookings, South Dakota, and Morris, Minnesota, in 1995 and 1996. Yellow foxtail was seeded at different densities, and at Morris, two levels of nitrogen (N) were applied. Corn biomass measured at V‐6 or V‐8, silking, and harvest and grain yield were correlated negatively to foxtail biomass and density, but the loss differed between years and sites. Nitrogen increased corn growth and decreased yield loss. Defining a single foxtail density or biomass that resulted in a maximum yield loss of 10% was not possible. The most conservative estimate was 3 yellow foxtail plants m−2 or 24 g m−2 of yellow foxtail biomass, but ranged up to 55 plants m−2 and 256 g m−2 when weather conditions and N were optimal.

Tillage effect on reproductive output by foxtail cohorts in corn and soybean

Reliable estimates of weed fecundity require determination under ranges of management practices such as differing crops and tillage systems. We measured components of reproductive output per plant (numbers of primary tillers, panicles, and seeds; and sizes of panicles) in three emergence cohorts of green foxtail and yellow foxtail growing among corn and soybean in moldboard plow (MP), chisel plow (CP), ridge till (RT), spring disk (SD), and no till (NT). Differences in emergence between crops and foxtail Cohorts 1, 2, and 3 were 5, 0, and −7 d, respectively. In MP, Cohort 1 of green foxtail produced 2.3 primary tillers and 5.6 panicles per plant, and Cohort 1 of yellow foxtail produced 4.6 primary tillers and 9.0 panicles per plant. Panicle size was variable for both species across tillage systems, crops, and cohorts both years. Green foxtail plants produced the most seeds per plant (3,811) in NT corn, and cohorts did not vary greatly, whereas fecundity was highly variable across tillage systems and cohorts in soybean, where it averaged 3,240 (± 388) seeds per plant. Green foxtail seed number per plant were closely related to panicle numbers per plant for each year in corn (r2 = 0.90) and soybean (r2 = 0.78), and the relationship did not vary among tillage systems. Yellow foxtail seed number per plant was closely related to panicle number per plant, and it was specific for each tillage system in corn (r2 = 0.60 to 0.85) and soybean (r2 = 0.65 to 0.92). Estimates for vegetative and reproductive growth were more reliable for green foxtail than for yellow foxtail across tillage systems, crops, cohorts, and years.

Johnsongrass, Yellow Foxtail, and Broadleaf Signalgrass as New Hosts for Six Species of Bipolaris, Curvularia, and Exserohilum Pathogenic to Bermudagrass.

Johnsongrass (Sorghum halepense (L.) Pers.), broadleaf signalgrass (Brachiaria platyphylla (L.) Beauv.), and yellow foxtail (Setaria glauca L.) are common volunteer grasses in bermudagrass (Cynodon dactylon (L.) Pers.) pastures in the southeastern United States. Johnsongrass and broadleaf signalgrass are potential forages whereas yellow foxtail is a noxious weed. In 1999 and subsequent years, necrosis and dieback of leaves, stems, and roots, stunting, and plant death were observed on all three species in bermudagrass pastures in north Mississippi (3). Symptoms on johnsongrass and yellow foxtail were most severe where bermudagrass exhibited severe symptoms of infection caused by dematiaceous hyphomycetes (2,3); symptoms on broadleaf signalgrass often occurred independently. Symptomatic leaf tissues from 15 to 33 plants of each species and stem and root tissues from 4 to 14 plants of johnsongrass and yellow foxtail were surface disinfested, plated on water agar, and examined for sporulation after 5 to 10 days (2,3). Pathogens were identified by specific morphological features of spores and sporulation as on bermudagrass (3), and axenic cultures were established by spore transfers to cornmeal agar. Bipolaris cynodontis (Marig.) Shoemaker, Curvularia lunata (Wakk.) Boedijn, C. geniculata (Tracy & Earle) Boedijn, and Exserohilum rostratum (Drechs.) Leonard & Suggs were isolated from symptomatic leaves of all three grasses and frequently also observed on stems and roots. B. stenospila (Drechs.) Shoemaker was observed only on broadleaf signalgrass (19 of 33 plants) and B. spicifera (Banier) Subr. on johnsongrass and yellow foxtail. Species most frequent on leaves (58 to 100%) were B. spicifera, C. lunata, and E. rostratum on johnsongrass and yellow foxtail and B. cynodontis, B. stenospila, and E. rostratum on broadleaf signalgrass. The three grasses were grown from seed in potting mix in the greenhouse (one plant per 375-cm3 container), and five replicates 31 to 60 days old were inoculated with a mixture of three isolates of each pathogen observed on them in two experiments. Conidia produced from infested wheat and oat grain were atomized onto foliage (1.2 to 4 × 104 conidia per ml, 20 ml per plant) as described (2). All pathogens incited similar necrotic lesions and streaks on the three grasses after 12 to 15 days, and B. stenospila also caused extensive golden yellow chlorosis on broadleaf signalgrass. All pathogens caused significant (P = 0.05) necrosis (means = 5 to 35% of foliage necrotic based on visual estimates, controls = 1 to 3%), and all were reisolated and grown in pure culture by spore transfers to cornmeal agar from surface-disinfested, symptomatic leaf tissue of each grass. When bermudagrass grown from seed was inoculated at similar spore concentrations, isolates of E. rostratum, B. cynodontis, and B. spicifera from two or all three grasses caused symptoms as severe as did isolates from bermudagrass. Results document new North American or worldwide records of occurrence and pathogenicity for B. cynodontis, C. geniculata, and C. lunata on all three grasses, B. stenospila and E. rostratum on broadleaf signalgrass, and B. spicifera on johnsongrass and yellow foxtail (1). These volunteer grasses, bermudagrass, and the six fungi all appear to represent large, interacting complexes of multiple hosts and potentially cross-infecting pathogens. Reference: (1) D. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory. Online publication. USDA, ARS, 2005. (2) R. Pratt, Agron. J. 92:512, 2000. (3) R. Pratt. Phytopathology 95:1183, 2005.

Weed Management withS-Metolachlor and Glyphosate Mixtures in Glyphosate-Resistant Strip- and Conventional-Tillage Cotton (Gossypium hirsutumL.)

Five studies were conducted at Clayton, Rocky Mount, and Lewiston-Woodville, NC, in 2001 and 2002, to evaluate weed management, crop tolerance, and yield in strip- and conventional-tillage glyphosate-resistant cotton. Cotton was treated with two glyphosate formulations; glyphosate-IP (isopropylamine salt) or glyphosate-TM (trimethylsulfonium salt), early postemergence (EPOST) alone or in a mixture withS-metolachlor. Early season cotton injury was minimal (3%) with either glyphosate formulation alone or in mixture withS-metolachlor. Weed control and cotton yields were similar for both glyphosate formulations. The addition ofS-metolachlor to either glyphosate formulation increased control of broadleaf signalgrass, goosegrass, large crabgrass, and yellow foxtail 14 to 43 percentage points compared with control by glyphosate alone.S-metolachlor was not beneficial for late-season control of entireleaf morningglory, jimsonweed, pitted morningglory, or yellow nutsedge. The addition ofS-metolachlor to either glyphosate formulation increased control of common lambsquarters, common ragweed, Palmer amaranth, smooth pigweed, and velvetleaf 6 to 46 percentage points. The addition of a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA increased control to greater than 95% for all weed species regardless of EPOST treatment, and control was similar with or withoutS-metolachlor EPOST. Cotton lint yield was increased 220 kg/ha with the addition ofS-metolachlor to either glyphosate formulation compared with yield from glyphosate alone. The addition of the LAYBY treatment increased yields 250 and 380 kg/ha for glyphosate plusS-metolachlor and glyphosate systems, respectively.S-metolachlor residual activity allowed for an extended window for more effective LAYBY application to smaller weed seedlings instead of weeds that were possibly larger and harder to control.

Management in a modified no-tillage corn–soybean–wheat rotation influences weed population and community dynamics

Conservation tillage systems, such as no-tillage, are ecologically advantageous because they reduce soil erosion; however, they rely heavily on herbicide use. Our goal was to determine how weed communities of no-tillage systems are affected when the system is modified to reduce herbicide use through a combination of banded herbicides and interrow cultivation. To this end, we conducted a 9-yr study in a no-tillage corn–soybean–winter wheat rotation. All management systems had a preplant application of glyphosate, followed by either broadcast PRE herbicides (conventional no-tillage), interrow cultivation with banded PRE herbicides, or interrow cultivation alone. Aboveground weed densities were assessed each year and data were grouped into early (1991 to 1993) and late (1996 to 1998) time periods. Over time, weed communities became more distinct, showing a strong response to management and crop. In the early years, weed communities separated more in response to management than crop. In the late years, this was reversed. Weed communities in systems with interrow cultivation were more diverse than those in conventional no-tillage. The response to weed management system and crop was species specific. For example, the abundance of yellow foxtail was higher when interrow cultivation was employed, but abundance was equal in all crops. Dandelion was more abundant in conventional no-tillage of corn and soybean; however, it was equally abundant in all management systems in wheat. Seed bank species richness increased over time and was highest in systems with interrow cultivation. Herbicide use can be reduced in a modified no-tillage corn–soybean–wheat rotation by incorporating interrow cultivation, with or without banded herbicides, into the management plan. The weed community trajectory changes, and the weed community becomes more diverse. A more diverse weed community will not necessarily alter how we manage weeds.

Phytotreatment of propellant contamination

Nitroglycerine (NG) and 2,4-dinitrotoluene (2,4-DNT) are propellants often found in soil and groundwater at military firing ranges. Because of the need for training with live ammunition, control or cleanup of these contaminants may be necessary for the continued use of these firing ranges. One inexpensive approach for managing sites exposed to these contaminants is the use phytoremedation, particularly using common or native grasses. In this study, the uptake of NG and 2,4-DNT from water by three common grasses, yellow nutsedge ( Cyperus escalantus), yellow foxtail ( Setaria glauca), and common rush ( Juncus effusus), was investigated using hydroponic reactors. Rapid removal from solution by all grasses was observed, with yellow nutsedge removal rates being the highest. NG or 2,4-DNT accumulated in the tissues in all of the plants, except yellow foxtail did not accumulate NG. Higher concentrations were observed in killed roots, demonstrating the presence of plant-based enzymes actively transforming the contaminants. Yellow nutsedge was also grown in 2,4-DNT spiked soil. Significant uptake into the plants roots and leaves was observed and concentrations in the soil decreased rapidly, although 2,4-DNT concentration also decreased in the unplanted controls. In summary, the three grasses tested appear to be good candidates for phytoremediation of propellant contamination.

Long-term effects of spring wheat–soybean cropping systems on weed populations

A long-term cropping systems experiment was conducted near Fargo, North Dakota, from 1994 to 2001, to examine the effect of tillage systems and crop rotations on weed populations over time. The cropping systems were a conventional spring wheat–soybean rotation, a no-till spring wheat–soybean rotation, and a mulch-till system with a spring wheat–yellow sweetclover–winter-annual rye–soybean rotation. Emerged weeds were sampled three times each year in wheat and soybean at pre-plant, before post-emergence herbicide treatment, and post-harvest. Soil seed banks were determined at initiation and termination of the experiment. Thirty-nine weed species were identified during the experiment and annual broadleaf weeds were most prevalent. Canada thistle, common lambsquarters, dandelion, green and yellow foxtail, kochia, redroot pigweed, wild buckwheat, and wild mustard were dominant weeds in each cropping system over the 8-year experiment. Between 1994 and 2001, total weed density decreased in the mulch-till system based on weeds sampled in wheat ( r = −0.93) and soybean ( r = −0.68), primarily due to a decrease in annual broadleaf weeds. Total density of weeds sampled in wheat increased in the no-till system ( r = 0.63), primarily due to an increase in common lambsquarters. The mulch-till system in combination with reduced amounts of herbicide, which were used to control Canada thistle, kept weed densities similar to conventional and no-tillage systems. Final soil seed bank densities were lower in the conventional system than either the no-till or mulch-till systems. Common lambsquarters and redroot pigweed seed banks were greater in no-till than the conventional or mulch-till systems in 2001, whereas green and yellow foxtail seed banks were greatest in the mulch-till system. In 2001, no-till and conventional system soil seed banks consisted of about 87% broadleaf and 13% grass species, whereas the mulch-till system soil seed bank consisted of 68% broadleaf and 32% grass species.

Carfentrazone-Ethyl Injury to Spring Wheat (Triticum aestivum) Is Minimized by Some ALS-Inhibiting Herbicides1

Many herbicides that control broadleaf weeds in wheat can antagonize grass herbicide efficacy, resulting in less grain yield due to competition. Also, the broadleaf herbicide carfentrazone-ethyl can injure wheat, leading to less grain yield because of physiological response. Experiments were conducted to evaluate carfentrazone-ethyl antagonism of fenoxaprop-ethyl, tralkoxydim, clodinafop-propargyl, imazamethabenz, and flucarbazone-sodium and injury to wheat with tank mixes of carfentrazone-ethyl plus each grass herbicide or thifensulfuron, tribenuron, metsulfuron, or imazamox. Carfentrazone-ethyl did not adversely affect control of wild oat or yellow foxtail by grass herbicides in wheat. Carfentrazone-ethyl alone caused 21% wheat injury 3 d after treatment. Adding flucarbazone-sodium to carfentrazone-ethyl resulted in the least wheat injury among treatments that included carfentrazone-ethyl. Fenoxaprop-P-ethyl or clodinafop-propargyl with carfentrazone-ethyl also resulted in less wheat injury compared with carfentrazone-ethyl alone, which was attributed to formulation safeners. Sulfonylurea herbicides provided safening of carfentrazone-ethyl similar to flucarbazone-sodium, while imidazolinones did not alleviate injury. Tralkoxydim plus carfentrazone-ethyl gave 28% wheat injury compared with 21% from carfentrazone-ethyl alone. Wheat injury was no longer visible by 20 d after treatment, and wheat yield was not affected by carfentrazone-ethyl injury when wild oat and yellow foxtail were present or controlled with herbicide.Nomenclature: Carfentrazone-ethyl; clodinafop-propargyl; fenoxaprop-P-ethyl; flucarbazone-sodium; tralkoxydim; yellow foxtail, Setaria glauca (L.) Beauv. #3 SETLU; wild oat, Avena fatua L. # AVEFA; wheat, Triticum aestivum L. ‘Alsen’, ‘ND722’, ‘Oxen’.Additional index words: Antagonism, crop injury, safening with herbicides, imazamethabenz, imazamox, thifensulfuron, tribenuron, metsulfuron.Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); COC, crop oil concentrate; DAT, days after treatment; MSO, methylated seed oil; NIS, nonionic surfactant; PO, petroleum oil; UAN, urea and ammonium nitrate solution.

A Screening of Weed Control Options During Juneberry (Amelanchier alnifolia) Establishment

Few weed management options are available for juneberry, which has limited the potential for this new crop. Field trials were initiated at three locations in North Dakota to evaluate efficacy and crop safety associated with chemical and physical weed control treatments applied just before or immediately after transplanting. All treatments except norflurazon and trifluralin provided at least 85% control of redroot pigweed, common lambsquarters, common purslane, and yellow foxtail for the duration of the trial at Absaraka, ND, during 2001. Stinkgrass weed control 8 wk after treatment (WAT) dropped to unacceptable levels (<85%) with all treatments except azafenidin at 0.5 kg ai/ ha, norflurazon, and oxyfluorfen at 1.1 kg ai/ha at Dawson, ND, during 2001. However, juneberry injury 4 WAT by azafenidin at 0.5 kg/ha, flumioxazin at both locations, or azafenidin at 0.34 kg/ha and oxyfluorfen at 1.1 kg ai/ha at Absaraka, ND, was greater than observed for plants within the physical treatments. Juneberry injury generally decreased with time, yet remained >20% at 8 WAT for azafenidin and flumioxazin at Absaraka, ND, and for all treatments except the mulches at Dawson, ND. Plant injury 8 WAT at Absaraka in 2002 was 10% or less for all treatments and was lower compared with 2001. All physical treatments—azafenidin at 0.34 and 0.5 kg/ha, flumioxazin at 0.29 kg/ha, and oryzalin at 4.5 kg/ha—provided at least 85% control of all weed species at Carrington and Absaraka, ND, during 2002.

Effect of Soil Disturbance on Annual Weed Emergence in the Northeastern United States

A 2-yr experiment evaluated the effect of spring soil disturbance on the periodicity of weed emergence. At four locations across the northeastern United States, emerged weeds, by species, were monitored every 2 wk in both undisturbed plots and plots tilled in the spring with a rotary cultivator. Eight weed species including large crabgrass, giant and yellow foxtail, common lambsquarters, smooth pigweed, eastern black nightshade, common ragweed, and velvetleaf occurred at three or more site-years. Spring soil disturbance either had no effect or reduced total seedling emergence compared with undisturbed soils. Total seedling emergence for large crabgrass, giant foxtail, smooth pigweed, and common ragweed were on average, 1.4 to 2.6 times less with spring soil disturbance, whereas eastern black nightshade and velvetleaf were mostly unaffected by the soil disturbance. The influence of soil disturbance on yellow foxtail and common lambsquarters emergence varied between seasons and locations. Although the total number of emerged seedlings was often affected by the soil disturbance, with the exception of yellow foxtail and common ragweed, the periodicity of emergence was similar across disturbed and undisturbed treatments.

Experimental Substrate Affects Rate of Seed Removal in Assays of Invertebrate Seed Predation

Postdispersal seed predation by ground beetles may be an important form of biological weed control. Field experiments conducted in 2002 and 2003 determined invertebrate seed predators' ability to detect and remove seeds from different experimental substrates. Predation of wild mustard and common lambsquarters was greater when seeds were presented on sand compared with the two types of synthetic finishing pads; however, predation of velvetleaf, redroot pigweed, and hairy galinsoga was unaffected by substrate. Predation rates were not consistent across all experimental substrates. Estimates of invertebrate predation of common lambsquarters, yellow foxtail, and velvetleaf were greater for seeds offered on sand or synthetic pads than for seeds offered on soil or double-sided tape covered with soil. Although each substrate would be useful to estimate treatment effects on relative predation rates, the weed species by substrate interaction should be considered when comparing predation rates across experiments or when the absolute rate predation is of critical importance.

Interactions Among Western Corn Rootworm (Coleoptera: Chrysomelidae), Yellow Foxtail, and Corn

Field studies at sites with two contrasting soil types investigated effects from the presence of yellow foxtail [Setaria pumila (Poir.) Roem. and Schult.], established in bands parallel to corn rows, on western corn rootworm (Diabrotica virgifera virgifera LeConte) survival, corn root injury, lodging, biomass production, and yield. Results suggested that the presence of foxtail as an alternate host influenced the degree and progression of corn rootworm damage and adult emergence in a given locality. Rootworm adults emerged later from foxtail band areas and had smaller head capsule size than did individuals from areas without foxtail, consistent with earlier findings that foxtail in the diet of western corn rootworm was a poor nutritional substitute for corn. Lodging was reduced in the presence of yellow foxtail in some cases, but corn stover biomass and yield also were lower. Influences, if any, of soil type on rootworm survival were unclear because of differences in planting date between the two sites. Foxtail may function as a buffer to reduce rootworm damage to corn and serves as an alternate host that should be considered in the development of resistance management strategies for transgenic corn modified for rootworm resistance.

WeedTurf: a predictive model to aid control of annual summer weeds in turf

Predicting weed emergence is useful for planning weed management programs. Unfortunately, our ability to anticipate initial emergence and subsequent levels of emergence from simple field observations or weather reports is often inadequate to achieve optimal control. Weed emergence models may provide predictive tools that help managers anticipate best management options and times and, thereby, improve weed control. In this study, the germination characteristics of four annual grass weeds (large crabgrass, goosegrass, green foxtail, and yellow foxtail) were investigated under different temperatures and water stresses to calculate base temperatures and base water potentials. These parameters were used to develop a mathematical model describing seedling emergence processes in terms of hydrothermal time. Hydrothermal time describes seed germination in a single equation by considering the interaction of soil water potential and soil temperature. The model, called WeedTurf, predicted emergence with some accuracy, especially for large crabgrass (lowest efficiency index [EF] value 0.95) and green foxtail (lowest EF value 0.91). These results suggest the possibility of developing interactive computer software to determine the critical timing of weed removal and provide improved recommendations for herbicide application timing.

Effect of cover-cropping systems on invertebrate seed predation

Abstract Contrasting cover-cropping systems were compared to determine whether fundamental differences in cover-cropping strategies affect weed seed predators and resulting seed predation. We conducted typical “feeding” trials in which 25 seeds of each of six weed species, including velvetleaf, wild mustard, yellow foxtail, common lambsquarters, redroot pigweed, and hairy galinsoga, were placed in the field. Exclosures showed that the majority of seed predation could be attributed to invertebrates: 43% out of a total of 56% seed predation for 11 d in 2002 and 40% out of a total of 58% seed predation for 4 d in 2003. The predominant invertebrate seed predator across all entry points of four cropping systems was a ground-dwelling carabid beetle, Harpalus rufipes, which was more abundant in vegetated treatments, particularly red clover, compared with treatments recently tilled and planted to a fall cover crop. In the absence of vertebrates, H. rufipes activity–density was positively correlated with mean seed...

Predicting weed emergence for eight annual species in the northeastern United States

A 2-yr experiment assessed the potential for using soil degree days (DD) to predict cumulative weed emergence. Emerged weeds, by species, were monitored every 2 wk in undisturbed plots. Soil DD were calculated at each location using a base temperature of 9 C. Weed emergence was fit with logistic regression for common ragweed, common lambsquarters, velvetleaf, giant foxtail, yellow foxtail, large crabgrass, smooth pigweed, and eastern black nightshade. Coefficients of determination for the logistic models fit to the field data ranged between 0.90 and 0.95 for the eight weed species. Common ragweed and common lambsquarters were among the earliest species to emerge, reaching 10% emergence before 150 DD. Velvetleaf, giant foxtail, and yellow foxtail were next, completing 10% emergence by 180 DD. The last weeds to emerge were large crabgrass, smooth pigweed, and eastern black nightshade, which emerged after 280 DD. The developed models were verified by predicting cumulative weed emergence in adjacent plots. The coefficients of determination for the model verification plots ranged from 0.66 to 0.99 and averaged 0.90 across all eight weed species. These results suggest that soil DD are good predictors for weed emergence. Forecasting weed emergence will help growers make better crop and weed management decisions.

Cadmium Bioaccumulation in Yellow Foxtail (Setaria glauca L. P. Beauv): Impact on Seed Head Morphology

Yellow foxtail (Setaria glauca L. P. Beauv) growing on a cadmium-contaminated site was sampled to determine the extent of cadmium bioaccumulation in aerial tissues and the impact of cadmium on growth and development. Water-extractable Cd concentrations in the soil ranged from 5.0 to 18.0 mg L-1. Aerial tissues contained elevated concentrations of Cd (16-48 μg g-1 DW), with mean concentration ratios of >3.0. Since foxtail frequently colonizes disturbed sites, the bioaccumulation of Cd in aerial tissues of foxtail suggests that wildlife feeding upon this plant species could be exposed to elevated Cd levels. A significant negative correlation (r2=0.98) was observed between water-extractable Cd in the soil and seed head length in foxtail, indicative of an adverse effect of Cd on reproductive development. This correlation further suggests seed head length as a biomarker for soluble Cd in contaminated soils. KEYWORDS: Cadmium, bioaccumulation, biomarker, phytotoxicity

Weed Efficacy Evaluations for Bromoxynil, Glufosinate, Glyphosate, Pyrithiobac, and Sulfosate

Thirteen field trials were conducted in 1999 and 2000 to evaluate postemergence (POST) weed control with single applications of bromoxynil at 420 or 560 g ai/ha, glufosinate at 291 or 409 g ai/ha, glyphosate at 1,120 g ai/ha, pyrithiobac at 36 or 72 g ai/ha, or sulfosate at 1,120 g ai/ha. Additional treatments evaluated included two applications with glufosinate at both rates in all possible combinations, two applications of glyphosate, and two applications of sulfosate. Weeds were 2 to 5 cm or 8 to 10 cm tall for annual grass and broadleaf weeds whereas yellow nutsedge and glyphosate-resistant corn were 8 to 10 cm tall. All herbicide treatments controlled 2- to 5-cm common cocklebur, Florida beggarweed, jimsonweed, ladysthumb smartweed, Pennsylvania smartweed, pitted morningglory, prickly sida, redroot pigweed, smooth pigweed, and velvetleaf at least 90%. All herbicide treatments except pyrithiobac at either rate controlled 2- to 5-cm common lambsquarters, common ragweed, and tall morningglory at least 90%; pyrithiobac at the lower rate was the only treatment that failed to control entireleaf and ivyleaf morningglory at least 90%. Bromoxynil and pyrithiobac at either rate controlled 2- to 5-cm sicklepod 33 to 68% whereas glufosinate, glyphosate, and sulfostate controlled ≥99%. Glyphosate and sulfosate applied once or twice controlled hemp sesbania less than 70% and volunteer peanut less than 80%. Bromoxynil and pyrithiobac were the least effective treatments for control of annual grass species and bromoxynil controlled Palmer amaranth less than 80%. Glufosinate controlled broadleaf signalgrass, fall panicum, giant foxtail, green foxtail, large crabgrass, yellow foxtail, seedling johnsongrass, Texas panicum, and glyphosate-resistant corn at least 90% but controlled goosegrass less than 60%. Glyphosate and sulfosate controlled all grass species except glyphosate-resistant corn at least 90%. In greenhouse research, goosegrass could be controlled with glufosinate POST plus a late POST-directed treatment of prometryn plus monosodium salt of methylarsonic acid.

Effect of Glyphosate Application Timing and Row Spacing on Corn (Zea mays) and Soybean (Glycine max) Yields1

Corn and soybean were planted in narrow and wide row spacings to determine the effect of glyphosate application timing and row spacing on crop yield. Glyphosate was applied when average weed canopy height reached 5, 10, 15, 23, and 30 cm. Weeds present in these studies included velvetleaf, redroot pigweed, common ragweed, common lambsquarters, jimsonweed, barnyardgrass, fall panicum, giant foxtail, yellow foxtail, green foxtail, and eastern black nightshade. Under highly competitive growing conditions (below normal rainfall and high weed density), corn yield was first reduced when weeds reached 10 and 15 cm in height with corn planted in 38- and 76-cm rows, respectively. Under similar conditions, soybean yield was first reduced when weeds reached 15 and 23 cm with soybean planted in 19- and 38-cm rows, respectively. Yield losses occurred only in the untreated control when soybean was planted in 76-cm rows. When growing conditions were less competitive (adequate rainfall and lower weed density), yield loss...

Postdispersal predation of giant ragweed (Ambrosia trifida) seed in no-tillage corn

Giant ragweed seeds have high nutritional value, consisting of 47% crude protein and 38% crude fat, and may be an important food source for rodent and invertebrate populations in agricultural and early successional ecosystems. We investigated temporal patterns of postdispersal giant ragweed seed predation on the soil surface of a no-tillage cornfield as affected by involucre (seed dispersal unit) size and presence or absence of crop residue. Cage exclusion experiments indicated that rodents and invertebrates were the principal predators of giant ragweed seed, and total predation of involucres over a 12-mo period beginning in November was 88%. Rodents were the greatest predators of giant ragweed involucres during fall and winter, and cumulative predation by February 1 in treatments with rodent access ranged from 39 to 43%. In contrast, giant ragweed involucre predation by invertebrates occurred mainly from May 1 to November 1. When rodent access to involucres was prevented, total involucre predation by invertebrates over a 12-mo period ranged from 57 to 78%. Rodents showed an initial preference for large involucres (> 4.8-mm diameter), and invertebrates preferred small involucres (< 4.8-mm diameter). Involucres covered with corn plant residue underwent less predation by rodents from November to February than uncovered involucres, but residue cover had no effect on seed predation by invertebrates. In a laboratory feeding trial, the carabidHarpalus pensylvanicuspreferred seed of smooth pigweed and yellow foxtail to giant ragweed seed, suggesting that giant ragweed seed is an incidental rather than a preferred food source for some carabids. Because giant ragweed exhibits relatively low fecundity and short seed bank persistence, results of this study suggest that postdispersal predation may directly reduce giant ragweed recruitment the next year by reducing new seed bank inputs. However, seed losses from predation alone may be insufficient to maintain giant ragweed populations below economic threshold levels in no-tillage cornfields.