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Field studies were conducted to evaluate soybean injury and yield reduction from foliar applications of mesotrione. Mesotrione was applied at 1.1, 3.2, 11, 35, and 105 g ai/ha to ‘BT 386C’ soybeans at the V1 stage of growth. All rates of mesotrione resulted in visual injury to soybean at 7 and 14 d after treatment (DAT). Overall soybean injury from mesotrione was greatest at 14 DAT, with 25 to 78% injury observed. By 28 DAT, soybean injury was 31 and 66% from mesotrione at 35 and 105 g/ha, respectively, and less than 10% from mesotrione at 1.1, 3.2, and 11 g/ha. Soybean yield was reduced 11 and 22% by mesotrione at 35 and 105 g/ha, respectively. No reduction in soybean yield was observed from mesotrione at rates up to 11 g/ha. Regression analysis indicated that soybean injury from mesotrione at 28 DAT was the best predictor of yield loss (r2 = 0.77), compared with injury evaluations at 7, 14, and 56 DAT. Greenhouse studies were conducted to determine whether soybean injury from mesotrione was affected by soybean growth stage and variety. Soybean varieties BT 386C, ‘Asgrow 4602RR’, ‘Pioneer 94B01’, and ‘LS 930375’ were more sensitive to mesotrione at the VC growth stage than at the V1 and V2 stages. At the V2 stage, Asgrow 4602RR was three to five times more sensitive to mesotrione than the other three varieties.
Nomenclature: Mesotrione; soybean, Glycine max L. (Merr.) ‘Asgrow 4602RR’, ‘BT 386C’, ‘LS 930375’, ‘Pioneer 94B01’.
Additional index words: Herbicide drift, tank contamination.
Abbreviations: DAT, days after treatment; POST, postemergence.
Field experiments were conducted in 1994 and 1995 at Vegreville, Legal, and Lacombe, AB, to determine the effects of a preharvest application of glyphosate on seedling emergence and growth of field pea. Glyphosate was applied at 0.9 kg ai/ha at each of the three crop development stages, as determined by seed moisture content (SMC), to determinate (‘Ascona’ and ‘Radley’) and indeterminate (‘Miko’ and ‘Trapper’) cultivars. Applying glyphosate when the SMC was less than 30% had little to no effect on seedling emergence but reduced seedling shoot fresh weight in two of six experiments. Applying glyphosate at SMC above 40% reduced seedling emergence and shoot fresh weight in two and three of the six experiments, respectively. Reductions in seedling emergence and shoot fresh weight were greater from seeds collected from the top than from seeds collected from the bottom one-third of sprayed plants. Differences in response between determinate and indeterminate cultivars occurred, but there was no consistent trend. Given the variable maturity in most fields and on individual pea plants, applications of preharvest glyphosate to peas destined for seed production may decrease seed germination and biomass accumulation.
Nomenclature: Glyphosate; field pea, Pisum sativum L. ‘Ascona’, ‘Miko’, ‘Radley’, ‘Trapper’.
Additional index words: Crop desiccation, determinate and indeterminate pea cultivars, harvest aid.
Row spacing affects the time of canopy closure, thus influencing the growth and development of both crop and weeds. Field studies were conducted in 1999, 2000, and 2001 at Mead, NE, and 2000 and 2001 at Concord in eastern Nebraska to determine the effects of three row spacings (19, 38, and 76 cm) on the critical time for weed removal (CTWR) in dryland soybean. A three-parameter logistic equation was fit to data relating relative crop yield to increasing duration of weed presence. In general, earliest CTWR occurred in the 76-cm rows, and coincided with the first trifoliate stage of soybean. Latest CTWR occurred in the 19-cm rows and coincided with the third trifoliate. The CTWR in 38-cm rows occurred at the second trifoliate. Practical implications are that planting soybean in wide rows reduces early-season crop tolerance to weeds requiring earlier weed management programs than in narrower rows.
Nomenclature: Glyphosate-resistant soybean, Glycine max (L.) Merr.
Additional index words: Integrated weed management, row spacing, timing of removal, weed interference.
Abbreviations: CPWC, critical period of weed control; CTWR, critical time for weed removal; DAE, days after emergence; DM, dry matter; GDD, growing degree days; HTCs, herbicide tolerant crops; IWM, integrated weed management; POST, postemergence.
Field studies were conducted in 1999, 2000, and 2001 to evaluate mesotrione at 105 and 210 g ai/ha alone and in mixtures with imazethapyr at 70 g ai/ha and the prepackage mixture of imazethapyr at 47 g/ha plus imazapyr at 16 g ai/ha postemergence. Mixtures of mesotrione with imazethapyr and imazethapyr plus imazapyr controlled common ragweed, common lambsquarters, and morningglory species better than imazethapyr or imazethapyr plus imazapyr alone. Similarly, mixtures of mesotrione with these imidazolinone herbicides improved the control of giant foxtail over that by mesotrione alone. Crop injury did not exceed 11% with all treatments and appeared as transient stunting. Yields of corn treated with mixtures of mesotrione plus imidazolinone herbicides were highest in 2000 and 2001, when rainfall was higher than in 1999.
Nomenclature: Imazapyr; imazethapyr; mesotrione; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; morningglory species, Ipomoea spp. # IPOSS; corn, Zea mays L. ‘Pioneer 3395 IR’, ‘Pioneer 32Z1B IR’.
Field studies were conducted in 1999, 2000, and 2001 to investigate weed control and glyphosate-resistant corn tolerance to postemergence applications of mesotrione at 70, 105, and 140 g ai/ha applied with and without glyphosate at 560 g ai/ha. Mesotrione alone and mixed with glyphosate controlled smooth pigweed greater than 97% and common lambsquarters 93 to 99%. Control of common ragweed and morningglory species was variable. Common ragweed control was generally best when mesotrione was applied at 105 or 140 g/ha, and control increased only in 2000 with the addition of glyphosate. Giant foxtail control was below 25% with all rates of mesotrione, but mixtures of mesotrione plus glyphosate controlled giant foxtail 65 to 75%. Mesotrione injured glyphosate-resistant corn 4 to 24% when averaged over glyphosate rates, and injury was usually increased by higher mesotrione rates, with rainfall after herbicide applications, and in mixtures with glyphosate. Injury was transient and did not reduce corn yields. Mesotrione injury on glyphosate-resistant corn was confirmed in the greenhouse, where all mesotrione treatments reduced glyphosate-resistant corn biomass 9 to 23% compared with the nontreated check.
Nomenclature: Glyphosate; mesotrione; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; morningglory species, Ipomoea spp. # IPOSS; smooth pigweed, Amaranthus hybridus L. # AMACH; corn, Zea mays L. ‘Dekalb 626RR’, ‘Dekalb 5863RR’.
Additional index words: IPOHE, IPOLA, Ipomoea hederacea (L.) Jacq., Ipomoea lacunosa L., Ipomoea purpurea L. Roth, IPOPU, total postemergence, transgenic crops, triketone herbicide.
Abbreviations: DAT, days after treatment; POST, postemergence; WAT, weeks after treatment.
Studies were initiated at two different planting dates and conducted at two different locations in 2001 to determine the critical weed-free period for certain populations of weeds in organically produced ‘Beauregard’ sweetpotato. Naturally occurring weed populations were used, and they included sicklepod, redroot pigweed, and yellow nutsedge. Treatments included allowing weeds to grow for 2, 4, 6, or 8 wk after transplanting (WAT) sweetpotato before weed removal and maintaining the sweetpotato weed-free for 2, 4, 6, or 8 WAT. Weedy and weed-free checks were also included in the study. These treatments were used to determine the length of time weeds can compete with sweetpotato without reducing yield and the length of time sweetpotato must grow before yield is no longer affected by newly emerging weeds. Yield of number one grade sweetpotato roots best fit a quadratic plateau curve for the grow-back treatments and a logistic curve for the removal treatments. Yields in weed-free plots of sweetpotato were higher at the early planting date, whereas yields in plots of weedy sweetpotato were higher at the late planting date. Weed biomass was lower in the grow-back treatments at the late planting date. Data indicate that sweetpotato may gain a competitive advantage over weeds when planted at a later date. At both planting dates, a critical weed-free period of 2 to 6 WAT was observed.
Nomenclature: Redroot pigweed, Amaranthus retroflexus L. #3 AMARE; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; yellow nutsedge, Cyperus esculentus L. # CYPES; sweetpotato, Ipomoea batatas (L.) Lam. ‘Beauregard’.
Field experiments were conducted in 1999 at Stoneville, MS, to determine the potential of multispectral imagery for late-season discrimination of weed-infested and weed-free soybean. Plant canopy composition for soybean and weeds was estimated after soybean or weed canopy closure. Weed canopy estimates ranged from 30 to 36% for all weed-infested soybean plots, and weeds present were browntop millet, barnyardgrass, and large crabgrass. In each experiment, data were collected for the green, red, and near-infrared (NIR) spectrums four times after canopy closure. The red and NIR bands were used to develop a normalized difference vegetation index (NDVI) for each plot, and all spectral bands and NDVI were used as classification features to discriminate between weed-infested and weed-free soybean. Spectral response for all bands and NDVI were often higher in weed-infested soybean than in weed-free soybean. Weed infestations were discriminated from weed-free soybean with at least 90% accuracy. Discriminant analysis models formed from one image were 78 to 90% accurate in discriminating weed infestations for other images obtained from the same and other experiments. Multispectral imagery has the potential for discriminating late-season weed infestations across a range of crop growth stages by using discriminant models developed from other imagery data sets.
Dioscorea oppositifolia (Chinese yam) is an exotic perennial vine invading natural areas in the temperate regions of the eastern United States. Rapid early-season growth of D. oppositifolia is facilitated by an extensive tuber system. Plants can reach heights greater than 370 cm, as the plants climb trees and other vegetation. Shoot length increased 3.6 cm/d from late May to mid-August under field conditions, and primary and secondary tuber length increased 0.28 and 0.2 cm/d, respectively. This indicated rapid vegetative growth and substantial food reserves to form new plants in subsequent years. Dioscorea oppositifolia plants also formed aerial bulbils of 0.8- to 1.2-cm diameter, which are important in dissemination of the species over geographical areas. A field study indicated incomplete control from manual removal, clipping by hand, or glyphosate (2% v/v) application to control D. oppositifolia, although glyphosate was the most effective. Additionally, the use of herbicides was more efficient from a time-utilization perspective than either manual removal or clipping. In a separate study, glyphosate application at flowering was more effective in reducing D. oppositifolia growth the year after application as compared with glyphosate applications soon after emergence. Under greenhouse conditions, however, glyphosate at 0.84 kg ae/ha provided <15% control. The ester formulation of triclopyr at 2.5 kg ai/ha provided >90% D. oppositifolia control. Metsulfuron provided 31% control, and mesotrione provided 36% control and at higher rates may reduce D. oppositifolia growth. Several other herbicides having diverse modes of action provided minimal control of D. oppositifolia.
Site-specific weed management can increase crop production efficiency by minimizing herbicide input costs without compromising crop yields. A reduction in herbicide inputs resulting from site-specific weed management may also decrease the probability level of nonpoint pollution compared with conventional herbicide applications. A 4.5-ha field was selected to compare site-specific and conventional weed management techniques in 1997 and 1998 at Knoxville, TN. Variable rate applications (VRAs) of atrazine preemergence (PRE) followed by dicamba postemergence (POST) were investigated for the reduction of herbicide inputs and their resulting impact on weed control and corn yield. VRAs of atrazine were on the basis of weed density data collected in 1996. VRAs of dicamba were according to common cocklebur density evaluations within the field. Compared with conventional applications, atrazine usage was decreased by 43 and 32% in the site-specific application treatments in 1997 and 1998, respectively. VRAs of dicamba reduced herbicide inputs by greater than 45% for 1997 and 1998. Corn yields were similar for the conventional and site-specific treatments in both years. On the basis of these data, site-specific herbicide applications have the greatest potential and least risk for managing weeds when POST or PRE POST variable rate herbicide applications are used.
Nomenclature: Atrazine; dicamba; common cocklebur, Xanthium strumarium L. #3 XANST; corn, Zea mays L. ‘Dekalb 689’.
Additional index words:Brachiaria platyphylla (Griseb.) Nash, broadleaf signalgrass, geographical information systems, global positioning systems, variable rate application.
Abbreviations: DGPS, differential global positioning system; GIS, geographic information system; OM, organic matter; POST, postemergence; PRE, preemergence; VRA, variable rate application.
Field trials were conducted in Virginia during 2000 and 2001 to evaluate long-term trumpetcreeper control in corn with dicamba, BAS 654 plus dicamba, 2,4-D, CGA 152005 plus primisulfuron, halosulfuron, primisulfuron, and mesotrione. Each of these herbicides was applied alone as a single postemergence (POST) treatment or as a component of a POST herbicide combination. Trumpetcreeper suppression ratings 3 mo after treatment (MAT) revealed a general trend toward higher levels of suppression with combinations of dicamba, BAS 654 plus dicamba, or 2,4-D with any of the sulfonylurea herbicides and lower levels of suppression with applications of any of the sulfonylurea herbicides alone. Combinations of dicamba, BAS 654 plus dicamba, or 2,4-D with mesotrione also provided some of the highest levels of trumpetcreeper suppression 3 MAT in both years. At 1 yr after treatment (YAT), 2,4-D alone, BAS 654 plus dicamba, CGA 152005 plus primisulfuron plus 280 g ai/ha dicamba, primisulfuron plus 280 g/ha dicamba, primisulfuron plus 2,4-D, mesotrione plus BAS 654 plus dicamba, and mesotrione plus 2,4-D reduced trumpetcreeper stem density by at least 52% when compared with that of the nontreated control. These herbicide treatments were the only ones that provided reductions in trumpetcreeper stem density 1 YAT when compared with that of the nontreated control. In 2000 and 2001, there were few differences in corn yield among the treatments evaluated in these trials, and no treatment resulted in corn yields that were lower than the nontreated control. Acceptable trumpetcreeper suppression may be achieved during the season of treatment with any of these herbicide combinations, but only a few treatments will provide long-term trumpetcreeper control.
Nomenclature: BAS 654, 2-(1-[([3, 5-difluorophenylamino]carbonyl)-hydrazono]ethyl)-3-pyridine-carboxylic acid, proposed common name diflufenzopyr; CGA 152005, 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3, 3, 3-trifluoropropyl)-phenylsulfonyl]-urea, proposed common name prosulfuron; dicamba; 2,4-D dimethylamine salt; halosulfuron; mesotrione; primisulfuron; trumpetcreeper, Campsis radicans (L.) Seem. ex Bureau #3 CMIRA; corn, Zea mays L.
The objective of this 2-yr study was to determine the optimal length of time between stale-seedbed preparation and planting that maximized weed control along with growth, development, and yield of cucumbers, compared with conventional seedbeds. Stale-seedbeds were prepared 40, 30, 20, and 10 d before planting (DBP), with an additional treatment of 40-DBP seedbed that received an application of glyphosate at 0.9 kg ae/ha, 20 DBP (40 and 20 DBP). The control (0 DBP) was prepared at planting. Glyphosate plus glufosinate ammonium at 1.26 and 0.042 kg ae/ha were applied after cucumber seeding to kill any emerged weeds. The experiment was a split-plot design in which one half of the main plots were treated with a preemergence application of clomazone at 0.42 kg ai/ha after cucumber seeding. Management of the stale-seedbed influenced the level of weed control and final crop yield. Generally, the 40-DBP seedbed had the highest weed biomass at planting and the lowest at harvest. Cucumber density, leaf number, and vine length were reduced in this treatment, and flowering was delayed because of the high weed biomass present during seedling emergence. All stale-seedbeds, with the exception of the 40-DBP stale-seedbed, had greater yields compared with the control (0 DBP) seedbed. The optimal timing of stale-seedbed preparation was 20 to 30 DBP. Seedbed preparation could be expanded to 40 DBP; however, an application of glyphosate at 20 DBP would be required to optimize yield. The stale-seedbed in combination with herbicides was a superior integrated weed management tool compared with conventional weed management practices.
Five herbicides were tested in green pea, and their residual effects on several rotational crops were investigated in northwestern Washington from 1998 through 2000. In both years, imazamox applied postemergence caused 21 and 28% early-season injury at 0.036 and 0.045 kg/ha, respectively, but only in 1999 did early-season injury result in yield loss compared with nontreated, weedy pea. Trifluralin, clomazone, and sulfentrazone caused 15 to 19% injury to pea in 1998 but not in 1999. Although pea treated with sulfentrazone produced more harvestable pods than nontreated pea (5.0 and 4.1 pods/plant, respectively), pod numbers were similar to peas treated with clomazone, pendimethalin, pendimethalin plus imazamox, or trifluralin. All rotationally grown crops were tolerant to herbicides used in green pea, except for strawberry in 1999, in which leaf area was reduced 23% in plots treated with 0.045 kg/ha imazamox compared with nontreated plots. Intensive tillage combined with favorable soil and climatic conditions in this study indicate that western Washington green pea producers may have greater flexibility in their choice of herbicides and rotational crop alternatives than previously believed.
Field studies were conducted in Arizona and California to evaluate the performance of glyphosate-tolerant lettuce and to determine the critical time of weed removal. Glyphosate was applied as a single or as a sequential application at 840 g ae/ha. Single glyphosate applications were made to lettuce at the two-, four-, six-, and eight-leaf stages. Sequential applications were made to lettuce at the two- or four-leaf stage followed by (fb) a second application 14 d after the first. Weed control efficacy, weeding times, and lettuce yield were all measured. Overall, glyphosate applied postemergence (POST) provided better weed control than the commercial standards bensulide or pronamide applied preemergence. Single glyphosate applications at the four-leaf stage and sequential applications at the two-leaf stage fb a second application 14 d later provided excellent control of most weeds, including redroot pigweed. Estimates of the critical time of weed removal were 26 to 29 d after emergence. Glyphosate treatments caused no adverse effects on lettuce. Lettuce head fresh weights in the glyphosate treatments were equal to or higher than those in bensulide or pronamide treatments. For crops such as lettuce, with few effective herbicides, the development of glyphosate-tolerant lettuce offers the opportunity to develop effective POST weed control programs.
Nomenclature: Bensulide; glyphosate; pronamide; redroot pigweed, Amaranthus retroflexus L. #3 AMARE; lettuce, Lactuca sativa L. ‘RR Raider 323’.
Field studies evaluated the effect of brown patch control on preemergence herbicide efficacy in tall fescue. Pendimethalin (1.7 followed by [fb] 1.7; 3.4 kg ai/ha), prodiamine (0.7 fb 0.6; 1.3 kg ai/ha), and oxadiazon (2.2 fb 2.2; 4.5 kg/ha), applied sequentially and as a single application, were evaluated for smooth crabgrass control with and without the use of azoxystrobin, a fungicide that controls brown patch. Azoxystrobin suppressed brown patch and increased smooth crabgrass control with pendimethalin in both years. This enhanced efficacy with azoxystrobin was attributed to improved tall fescue turf density and thus increased competition between this turf species and smooth crabgrass. Longer soil-residual herbicides such as oxadiazon and prodiamine provided high levels of smooth crabgrass control (often >90%). With the exception of oxadiazon at 4.5 kg ai/ha in 2000, smooth crabgrass control with oxadiazon and prodiamine was unaffected by the use of azoxystrobin.
Field studies were conducted in the spring of 1997 and 1998 to quantify the effect of season-long yellow nutsedge interference on watermelon yield. The competitive ability of watermelon with yellow nutsedge was compared in two establishment methods (watermelon transplanted and direct seeded). Critical yellow nutsedge densities and the biological threshold (BT) were used to characterize the competitive ability of watermelon. The critical density in both direct-seeded and transplanted watermelons was 2 yellow nutsedge plants/m2. The BT of yellow nutsedge in seeded watermelons was 37 yellow nutsedge plants/m2, whereas the BT in transplanted watermelons was 25 plants/m2. Transplanting watermelons did not improve their competitive ability with yellow nutsedge. Percent yield loss was similar for both establishment methods at the respective yellow nutsedge densities. Over 40% yield loss was incurred with 12 yellow nutsedge plants/m2 for both establishment methods. Furthermore, it was concluded that watermelons are poor competitors with yellow nutsedge.
Nomenclature: Yellow nutsedge, Cyperus esculentus L. #3 CYPES; watermelon, Citrullus lanatus L.
Additional index words: Additive design, competition, crop establishment.
The effect of season-long interference by bands of weeds growing only between rows (BR) on field corn yields has not been reported before or compared with weedy and weed-free (i.e., weeded) plots or bands of weeds growing only in row (IR). The null hypothesis of this research was that field corn yields would be ranked as weed-free > BR weedy only > IR weedy only > weedy (IR BR weedy) in response to season-long weed interference by these four treatments. Weeds growing as bands closest to field corn were expected to reduce field corn yields more than those growing as bands further away between field corn rows. Field corn yield response to these four weed interference treatments was studied in Missouri for 4 yr. In late summer, most weed ground cover consisted of giant foxtail, the chief weed present, and common waterhemp, a lesser weed. Observed field corn yields averaged for 4 yr were ranked as weed-free > IR weedy only > BR weedy only > weedy. Field corn yields of the IR weedy only, BR weedy only, and weedy treatments averaged 76, 63, and 41%, respectively, of the weed-free treatment (=7,820 kg/ha). In two of the 4 yr, field corn yield of the IR weedy treatment exceeded that of the BR weedy treatment, whereas these treatments could not be statistically distinguished from one another in the other 2 yr. These research results refute the null hypothesis and demonstrate that it may be more critical to control BR than IR weeds, although controlling both BR and IR weeds maximized field corn yields.
Nomenclature: Common waterhemp, Amaranthus rudus Sauer #3 AMATA; giant foxtail, Setaria faberii Herrm. SETFA; corn, Zea mays L. ‘Pioneer 3379’ and ‘Pioneer 33G28’.
Additional index words: Banding, competition, interference.
Common management alternatives were compared in a factorial arrangement for 2 yr to determine their effects on green foxtail and yellow foxtail seed production in spring wheat in the Northern Great Plains of the United States. Seed production was measured twice, at wheat harvest (in August) and postharvest (after first lethal frost in autumn). Management alternatives were early, middle, and late crop-sowing dates; no-till, chisel, and moldboard plow tillage systems; and broadleaf herbicide only and broadleaf herbicide plus fenoxaprop applications. Fenoxaprop reduced foxtail seed production at wheat harvest but not at postharvest. Early sowing also decreased seed production at wheat harvest but increased postharvest seed production. Tillage system had no consistent effects on foxtail seed production. Postharvest seed production often was greater than or equal to that at wheat harvest regardless of management system. These results indicate that in-crop management alternatives, such as postemergence grass herbicide and early crop sowing, may lower the number of foxtail seeds at harvest substantially, but they must be accompanied by postharvest weed control to reduce overall seed production.
Nomenclature: Fenoxaprop; green foxtail, Setaria viridis (L.) Beauv. #3 SETVI; yellow foxtail, Setaria pumila (Poir.) Roem. & Schult. [=Setaria glauca (L.) Beauv.] # SETLU; spring wheat, Triticum aestivum L. ‘Sharpe’.
Additional index words: Sowing date, tillage regime.
The postemergence herbicide ethofumesate and the plant growth regulator paclobutrazol were evaluated for annual bluegrass control in creeping bentgrass turf managed as golf fairways. Both products were applied under several different timing regimes relative to the time of the year. Paclobutrazol treatments provided significantly greater annual bluegrass control than ethofumesate. There were no differences between rates of paclobutrazol (0.28 and 0.14 kg ai/ha) when applied from spring through summer. Annual bluegrass control after spring and summer applications of paclobutrazol was 85% or more. Clipping weight data indicated that paclobutrazol suppressed growth in annual bluegrass longer than in creeping bentgrass. It was concluded that prolonged suppression of annual bluegrass by paclobutrazol resulted in creeping bentgrass dominance and subsequent annual bluegrass control. Additionally, applications of ethofumesate in autumn–winter, followed by paclobutrazol applied in spring–summer, provided significant control of annual bluegrass in 1 yr of the study.
Nonfungicidal effects of agricultural fungicides on crop plants have been reported previously; however, there are few reports of nontarget effects of fungicides on weedy species. Field research trials in Oregon demonstrated that the growth of several broadleaf weeds was reduced after multiple applications of the fungicide propiconazole. Greenhouse experiments confirmed that preemergence applications of propiconazole reduced the biomass accumulation of several common broadleaf and grass weeds 15 to 63%. Laboratory experiments were performed on redroot pigweed, the most sensitive species, to examine the effects of propiconazole on germination and early seedling growth. Redroot pigweed germination and total seedling length (root plus shoot) were reduced at propiconazole concentrations above 37 and 0.36 mg/L, respectively. Growth-regulating effects of fungicides such as propiconazole on the germination and early growth of weeds may contribute to integrated weed management, especially when adequate moisture ensures the presence of germinating seeds and small seedlings throughout the growing season.
Nomenclature: Propiconazole; redroot pigweed, Amaranthus retroflexus L. #3 AMARE.
Diminishing availability and increasing costs of herbicides cause strawberry growers to seek both chemical and nonchemical alternatives, especially for within-row weed control soon after strawberries are transplanted. Several weed control treatments for strawberry establishment were examined during 2 yr in Minnesota. Treatments included: woolen landscaping fabric centered over the crop row; as above, but 2-ply fabric; spring canola incorporated into soil when 30 cm tall; as above, but canola killed with burndown herbicide and left as mulch; standard herbicide, DCPA; hand weeded; and no weed control. Areas between all strawberry rows were cultivated. Measurements included weed densities and weights, numbers of strawberry daughter plants, and fruit yield 1 yr after transplantation. The best alternative treatment was the 1-ply woolen fabric. It nearly eliminated weeds from rows, promoted daughter plant rooting, and allowed maximum fruit yields, equivalent to those of the DCPA and hand-weeded treatments. Canola mulch controlled weeds inconsistently and achieved only modest to low production of daughter plants and fruit. Weed control and fruit yield with incorporated canola were similar to the weedy check treatment.
Research was designed to reduce herbicide use by replacing POST herbicides with readily available ocean water to control weeds in turfgrasses. Sensitivity to salt stress was evaluated for large crabgrass, goosegrass, mimosa-vine, alyceclover, and yellow nutsedge, as well as the turfgrasses such as seashore paspalum, bermudagrass, St. Augustinegrass, and centipedegrass. Three different salinity levels, (55, 37, and 19 dS/m) and two salt-stress durations (3 and 6 d) were tested. Mimosa-vine was fully controlled at 55 and 37 dS/m. Alyceclover showed maximum injury at 95% when treated at 55 dS/m for 6 d and 90% when treated for 3 d. Large crabgrass was controlled at 55 dS/m. Goosegrass injury was up to 90% at 55 dS/m, but injured plants recovered to 48% at 30 d. Yellow nutsedge showed a maximum of 38% injury but showed 0% injury at 30 d. Among tested turfgrasses, seashore paspalum showed tolerance to pure ocean water at 55 dS/m, with maximum injury at 18%. At the same level of stress, maximum injury for bermudagrass was 30%, for St. Augustinegrass 60%, and for centipedegrass 100%. Lower levels of salt stress resulted in less injury but were still excessive for St. Augustinegrass and centipedegrass. Ocean water was shown to be an effective method to control mimosa-vine, and large crabgrass in seashore paspalum and bermudagrass turfs.
MON 37500 is a sulfonylurea herbicide that selectively controls Bromus spp. in winter wheat. Field studies were conducted near Sidney, NE, and Archer, WY, to determine the sensitivity of corn, foxtail millet, grain sorghum, proso millet, and sunflower to soil residues of MON 37500. MON 37500 was applied to winter wheat at 0, 35, 69, and 139 g/ha in the autumn of 1997. Rotational crops were no-till seeded into the standing residues of the previous year's crop from 1999 through 2001. Grain yields for corn, foxtail millet, and proso millet planted 18 to 20 mo after herbicide application were not affected by soil residues of MON 37500. In contrast, average grain yields of grain sorghum were reduced from 1,760 to 30 kg/ha at Archer and from 4,480 to 390 kg/ha at Sidney as MON 37500 rates increased from 0 to 139 g/ha. Thirty to 32 mo after herbicide application, average grain yields of grain sorghum were reduced from 2,360 to 620 kg/ha at Sidney and average aboveground biomass was reduced from 4,000 to 1,800 kg/ha at Archer as MON 37500 rates increased from 0 to 139 g/ha. Nineteen to 20 mo after herbicide application, average sunflower seed yields were reduced from 1,450 to 20 kg/ha at Archer and from 1,830 to 540 kg/ha at Sidney as MON 37500 rates increased from 0 to 139 g/ha. Visual injury was observed 31 to 32 mo after herbicide application, but drought in 2000 prevented collection of seed yield data. In the High Plains, foxtail millet, proso millet, and corn may be successfully grown 18 to 20 mo after the application of MON 37500 to winter wheat. Successful production of grain sorghum and sunflower may require a minimum recrop interval between treatment and planting of >36 mo.
Calcium ion in the spray water can reduce glyphosate efficacy. Ammonium sulfate (AMS) is commonly added to the spray tank to overcome the reduced efficacy. However, it is sometimes claimed that ethoxylated tallow amine surfactant (EA) is also efficacious, provided that calcium concentration is moderate (= 5 mM, 200 ppm). On response curves of ‘Plaisant’ barley treated with glyphosate, the presence of calcium ion increased the glyphosate dose needed to obtain 50% (ED50) barley growth reduction. The addition of AMS to the spray tank overcame the antagonistic effect of the calcium ion and restored glyphosate efficacy. EA was less effective than AMS at 5 or 10 mM calcium ion concentration as measured by ED50. However, at 90% growth reduction (ED90), EA was more effective than AMS at the 5 mM calcium ion concentration but less effective at the 10 mM concentration. Hence, at a moderate (= 5 mM) calcium concentration, EA would be an effective adjuvant. Calcium ion decreased the foliar uptake of glyphosate but did not affect the rate of uptake. AMS but not EA restored foliar uptake to values observed without calcium ion. EA increased spray retention, and this probably accounted for the increased glyphosate efficacy at low calcium concentration.
Nomenclature: Glyphosate; barley, Hordeum vulgare L.
A 4-yr field study was conducted during 1998 through 2001 at Stoneville, MS, to determine the effects of narrow-row transgenic cotton and soybean rotation on purple nutsedge populations and crop yield. Crop rotations over 4 yr included cotton and soybean sown in the following patterns: CCSS, CSCS, SCSC, SSCC, and continuous cotton (CCCC) and soybean (SSSS), where cotton is denoted as (C) and soybean as (S), all with herbicide programs that were glyphosate based, non–glyphosate based, or no purple-nutsedge control (NPNC). Purple nutsedge populations and shoot dry biomass were reduced in cotton and soybean rotation and continuous soybean by 72 and 92%, respectively, whereas in continuous cotton, purple nutsedge populations increased by 67% and shoot dry biomass was reduced by 32% after 4 yr. Reductions in purple nutsedge populations also occurred in soybean when cotton was rotated with soybean (CSCS and SCSC), compared with continuous cotton. Among herbicide programs, the glyphosate-based program was more effective in reducing purple nutsedge populations, compared with the non–glyphosate-based program. Seed cotton yield was greater with cotton following soybean (SCSC) than with cotton following cotton (CCCC, CCSS) in 1999. However, seed cotton yields were similar regardless of crop rotation systems in 2000 and 2001. Seed cotton yields were equivalent in the glyphosate-based and non–glyphosate-based programs in 1999 and 2001. During 1999 to 2001, seed cotton yields were reduced by 62 to 85% in NPNC compared with yields in glyphosate- and non–glyphosate-based programs. Soybean yields were unaffected by crop rotation systems in all the 4 yr. Among herbicide programs, non–glyphosate-based program in all 4 yr and glyphosate-based program in 1999 and 2000 gave higher soybean yield compared with NPNC. After 4 yr of rotation, purple nutsedge tubers and plant density were highest in continuous cotton and lowest in continuous soybean. Both herbicide programs reduced tubers per core and plant density compared with NPNC, and the glyphosate-based program was more effective than the non–glyphosate-based program. These results show that in cotton production, severe infestations of purple nutsedge can be managed by rotating cotton with soybean or by using glyphosate-based herbicide program in glyphosate-resistant cotton.
Nomenclature: Glyphosate; purple nutsedge, Cyperus rotundus L. #3 CYPRO; cotton, Gossypium hirsutum L. ‘DP 436RR’; soybean, Glycine max (L.) Merr. ‘DP 5806RR’.
Additional index words: Purple nutsedge tuber, transgenic crop.
Abbreviations: fb, followed by; NPNC, herbicide program with no purple-nutsedge control; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.
Mapping weed infestations in an annual crop has implications not only for site-specific herbicide applications but also for planning future management strategies and understanding weed ecology. A controlled laboratory experiment, involving detached leaves, was conducted to investigate the potential to discriminate two crop and five weed species using hyperspectral and multispectral remote sensing. Stepwise discriminant function analyses showed that reflectance in the visible and “red-edge” regions of the spectrum were consistently required for species discrimination. The seven species were correctly identified 90 and 89% of the time using the hyperspectral and multispectral data, respectively, and the classification rules derived from discriminant function analyses. Errant species prediction with the hyperspectral data resulted in a grass being predicted as a grass and a broadleaf as a broadleaf. However, for multispectral data, incorrect classifications were more serious because errant predictions sometimes resulted in a grass being classified as a broadleaf and vice-versa. Further studies using plants at a variety of growth stages, from a variety of environments, and at the canopy level are warranted.
Field studies were conducted at 35 sites throughout the north-central United States in 1998 and 1999 to determine the effect of postemergence glyphosate application timing on weed control and grain yield in glyphosate-resistant corn. Glyphosate was applied at various timings based on the height of the most dominant weed species. Weed control and corn grain yields were considerably more variable when glyphosate was applied only once. The most effective and consistent season-long annual grass and broadleaf weed control occurred when a single glyphosate application was delayed until weeds were 15 cm or taller. Two glyphosate applications provided more consistent weed control when weeds were 10 cm tall or less and higher corn grain yields when weeds were 5 cm tall or less, compared with a single application. Weed control averaged at least 94 and 97% across all sites in 1998 and 1999, respectively, with two glyphosate applications but was occasionally less than 70% because of late emergence of annual grass and Amaranthus spp. or reduced control of Ipomoea spp. With a single application of glyphosate, corn grain yield was most often reduced when the application was delayed until weeds were 23 cm or taller. Averaged across all sites in 1998 and 1999, corn grain yields from a single glyphosate application at the 5-, 10-, 15-, 23-, and 30-cm timings were 93, 94, 93, 91, and 79% of the weed-free control, respectively. There was a significant effect of herbicide treatment on corn grain yield in 23 of the 35 sites when weed reinfestation was prevented with a second glyphosate application. When weed reinfestation was prevented, corn grain yield at the 5-, 10-, and 15-cm application timings was 101, 97, and 93% of the weed-free control, respectively, averaged across all sites. Results of this study suggested that the optimum timing for initial glyphosate application to avoid corn grain yield loss was when weeds were less than 10 cm in height, no more than 23 d after corn planting, and when corn growth was not more advanced than the V4 stage.
Determination of the active growth state of weeds may lead to more reliable predictions of herbicide efficacy. Experiments were conducted at Lacombe and Lethbridge, Alberta, Canada, from 1996 to 1998 to determine if wild oat leaf extension (growth) rate could be used to predict the efficacy of imazamethabenz and ICIA 0604. As expected, wild oat control increased and wild oat biomass decreased with increasing imazamethabenz and ICIA 0604 rates. Mean wild oat growth rates ranged from 6 to 44 mm over a 24-h time interval. Wild oat control at 25% of the recommended doses of ICIA 0604 or imazamethabenz increased as wild oat growth rate increased. However, wild oat growth rate did not influence herbicide efficacy at higher herbicide rates. Regression analysis confirmed that wild oat control at the lowest application rates increased 6 or 14% for every 10 mm of wild oat growth during the 24 h preceding herbicide application of ICIA 0604 or imazamethabenz, respectively. Covariance analysis confirmed the influence of wild oat growth rate on wild oat control by imazamethabenz but not by ICIA 0604. Monocot leaf extension rates may be useful for predicting herbicide efficacy in integrated weed management or decision support systems.
Nomenclature: ICIA 0604, 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)-cyclohex-2-enone (proposed common name: tralkoxydim); imazamethabenz; wild oat, Avena fatua L. #3 AVEFA.
Additional index words: Active growth, integrated weed management, predicting efficacy, reduced rates.
Imazethapyr-based weed control treatments were evaluated in water-seeded imidazolinone-resistant (IR) rice in Louisiana in 2000 and 2001. Treatments included imazethapyr applied to soil before seedling flood (surface [SURF] applied) or no soil application (no SURF), followed by imazethapyr applied postemergence (POST). Averaged over SURF application treatments (SURF, no SURF), all imazethapyr mixtures increased control of barnyardgrass at 14 and 42 d after POST treatment (DAT) compared with imazethapyr alone. Treatments containing imazethapyr-applied SURF followed by POST treatments controlled red rice 90 to 96% at 21 DAT. Alligatorweed and hemp sesbania control increased with POST mixtures compared with imazethapyr-only treatments at 35 DAT. Rice yield increased with imazethapyr applied SURF compared with no SURF application, averaged over POST applications. Other herbicides will be required to control troublesome weeds such as hemp sesbania and alligatorweed in an IR rice production system.
Experiments were conducted in Virginia in 2000 and 2001 to investigate responses of winter wheat and diclofop-sensitive and -resistant Italian ryegrass to the experimental herbicide mixture AE F130060 03 and crop safener AE F107892 applied postemergence. AE F130060 03 at 15 or 18 g ai/ha with or without methylated seed oil controlled both diclofop-sensitive and -resistant Italian ryegrass 82 to 99% and reduced inflorescence emergence 59 to 98%. Although AE F130060 03 controlled existing Italian ryegrass 4 wk after any application, timing of application influenced late-season Italian ryegrass control and inflorescence emergence. Applications to two- to three-leaf Italian ryegrass resulted in greater emergence of Italian ryegrass after application than applications made to two- to three-tiller or four- to five-tiller Italian ryegrass. Wheat injury by AE F130060 03 was greater than injury from diclofop, but wheat appeared to fully recover; and yields from AE F130060 03–treated wheat were similar to yields of diclofop-treated wheat and at least 21% greater than yields from nontreated wheat. In greenhouse experiments, differential growth responses between diclofop-sensitive and -resistant Italian ryegrass occurred after AE F130060 03 application at normal (15 g ai/ha) and below-normal application rates. When rates were increased beyond normal application rates, growth responses were similar between diclofop-sensitive and -resistant Italian ryegrass.
Nomenclature: AE F130060 03 (8.3:1.7 mixture of AE F130060 00, proposed common name mesosulfuron-methyl, 2-[(4,6-dimethoxypyrimidin-2-yl carbamoyl)sulfamoyl]-4-methanesulfonamido-p-toluic acid, plus AE F115008 00, proposed common name iodosulfuron-methyl-sodium, 4-iodo-2-[3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)ureidosulfonyl]benzoic acid); AE F107892, proposed common name mefenpyr-diethyl, 1-(2,4-dichlorophenyl)-4,5-dihydro-5-methyl-1H-pyrazole-3,5-dicarboxylic acid; diclofop; Italian ryegrass, Lolium multiflorum Lam. LOLMU #3; winter wheat, Triticum aestivum. L. ‘Pioneer 2643’, ‘Pioneer 26R24’, ‘Pocohontas’.
Additional index words: Diclofop resistance, resistance management.
Abbreviations: ACCase, acetyl coenzyme A carboxylase; ALS, acetolactate synthase; MSO, methylated seed oil; POST, postemergence.
Field studies were conducted to evaluate weed control, tuber yield, gross return, economic return on investment (EROI), and net return in glyphosate-resistant ‘Ranger Russet’ potato in 2000 and 2001 at the University of Idaho Aberdeen Research and Extension Center near Aberdeen, ID. Three types of weed control programs were evaluated: a total glyphosate program of single or sequential applications (TGLY), tank mixtures of glyphosate and residual herbicides applied early postemergence (GLY RES EPOST), and residual preemergence herbicides followed by (fb) a late postemergence glyphosate application (RES PRE fb LPOST GLY). A standard rimsulfuron metribuzin nonionic surfactant EPOST treatment was included for comparison. The standard EPOST treatment and all glyphosate-containing treatments controlled hairy nightshade 88 to 99%. RES PRE fb LPOST GLY treatments improved hairy nightshade control compared with the RES PRE components applied alone. All herbicide treatments controlled kochia 87 to 99% and green foxtail 87 to 100%. Redroot pigweed and common lambsquarters were controlled ≥85 and ≥89%, respectively, by all herbicide treatments except a single EPOST application of glyphosate at 420 g ae/ha. Depending on the year, sequential applications of glyphosate, GLY RES EPOST, or RES PRE fb GLY LPOST treatments controlled weeds better than single EPOST glyphosate applications. Single LPOST glyphosate applications generally controlled kochia, redroot pigweed, common lambsquarters, and green foxtail better than single EPOST applications. However, single EPOST glyphosate applications controlled hairy nightshade better than a single LPOST application of glyphosate at 420 g/ha. RES PRE fb GLY LPOST treatments improved redroot pigweed, common lambsquarters, and green foxtail control, compared with the RES PRE components applied alone, depending on the RES PRE component and the year. Sequential applications of glyphosate at 840 g ae/ha and the standard nonglyphosate EPOST, GLY RES EPOST, and RES PRE fb GLY LPOST treatments generally provided similar weed control. No crop injury was observed as a result of any herbicide treatment. Sequential applications of glyphosate at 840 g/ha had better tuber yields and economic returns than a single EPOST or LPOST application of glyphosate at 420 g/ha or a single LPOST application of glyphosate at 840 g/ha. A single EPOST application of glyphosate at 420 g/ha had lower tuber yields and economic returns than a single EPOST application of glyphosate at 840 g/ha. The RES PRE alone treatments, except metribuzin pendimethalin, had similar tuber yields, EROI, and net returns as sequential applications of glyphosate at 840 g/ha. Glyphosate rimsulfuron resulted in lower tuber yields than sequential applications of glyphosate at 840 g/ha, whereas EROI and net returns were similar. All other combinations of glyphosate and residual herbicides except glyphosate pendimethalin EPOST, had similar tuber yields, EROI, and net returns as sequential applications of glyphosate at 840 g/ha.
Nomenclature: Glyphosate; metribuzin; pendimethalin; rimsulfuron; common lambsquarters, Chenopodium album L. #3 CHEAL; green foxtail, Setaria viridis (L.) Beauv. # SETVI; hairy nightshade, Solanum sarrachoides L. Sendt. # SOLSA; kochia, Kochia scoparia L. Shrad. # KCHSC; redroot pigweed, Amaranthus retroflexus L. # AMARE; potato, Solanum tuberosum L. ‘Ranger Russet’.
Additional index words: Economic return on investment, gross return, net return, sequential, tuber yield.
Abbreviations: AMS, ammonium sulfate; EPOST, early postemergence; EROI, economic return on
Experiments were conducted in 2000 and 2001 to evaluate efficacy of AE F130060 03 plus AE F107892 applied postemergence for the control of Italian ryegrass in barley. AE F130060 03 plus AE F107892 controlled Italian ryegrass when applied at two application rates and at three timings. Barley successfully recovered from initial injury caused by early-postemergence (EP) and middle-postemergence (MP) application timings. The late-postemergence (LP) timing resulted in lower yield than the EP or MP application timings. AE F130060 03 plus AE F107892 applied EP controlled Italian ryegrass similar to flufenacet plus metribuzin applied delayed preemergence (DPRE) when rainfall was received. Barley yields were also similar. However, with insufficient rainfall, AE F130060 03 plus AE F107892 provided superior Italian ryegrass control. EP treatments of AE F130060 03 plus AE F107892 after a DPRE application of flufenacet plus metribuzin or chlorsulfuron plus metsulfuron completely controlled Italian ryegrass and resulted in excellent yields.
Field studies were conducted in 2001 and 2002 to determine the effect of clethodim, sethoxydim, and halosulfuron on centipedegrass seedhead suppression, seed yield, and seed germination. Clethodim (0.28 kg/ha), sethoxydim (0.31 kg/ha), and halosulfuron (0.06 kg/ha) applications were made at −2, 0, 2, 4, and 6 wk after mowing stopped (WAMS) in each year. Seedhead suppression varied in severity between 2001 and 2002, with increased suppression in 2001. Clethodim reduced seedhead emergence 50 and 33% when applied at 2 and 4 WAMS, respectively, in 2001. Sethoxydim reduced seedhead emergence by 21 and 18% when applied at 2 and 4 WAMS, respectively, in 2001. Halosulfuron had no effect on seedhead emergence in either year and did not reduce seed yield at any application timing. Clethodim reduced seed yield between 22 and 44% at all application timings. The pattern of yield reduction from sethoxydim was similar to that caused by clethodim; however, yield reduction with sethoxydim ranged between 7 and 48% for all application timings. The greatest reduction in seed yield occurred when clethodim and sethoxydim were applied 4 WAMS. Seed germination was not affected by halosulfuron or sethoxydim at any application timing. Clethodim, when applied at 4 and 6 WAMS, decreased seed germination by 17 and 20%, respectively.
Effect of weed interference duration and weed-free period on glufosinate-resistant rice was evaluated in 1998 and 1999. Weed interference for more than 2 wk reduced plant height 12 wk after emergence compared with the season-long weed-free treatment. Grain yield loss of 1,090 to 4,880 kg/ha was observed when weeds were allowed to interfere with rice from 2 wk to season-long. The weed-free period study indicated that early control of weeds could sustain rice growth and yield potential. This research suggests that effective weed control from 1 to 6 wk after rice emergence is important in fields with high weed densities for maximizing yield potential of glufosinate-resistant rice.
Nomenclature: Glufosinate; rice, Oryza sativa L. ‘Bengal’, ‘BNGL HC-11’, ‘BNGL-62’.
Soft red winter wheat tolerance and Italian ryegrass control with AE F130060 00 plus AE F115008 00 at 12.5 plus 2.5 g ai/ha applied alone and mixed with dicamba, 2,4-D, or thifensulfuron plus tribenuron were examined in separate field experiments. AE F130060 00 plus AE F115008 00 applied alone in December injured wheat 12% or less, whereas mixtures with thifensulfuron plus tribenuron injured wheat 15% or less. AE F130060 00 plus AE F115008 00 applied alone in February or mixed with dicamba, 2,4-D, or thifensulfuron plus tribenuron injured wheat 3% or less. No treatment affected yield of weed-free wheat. AE F130060 00 plus AE F115008 00 applied in December controlled Italian ryegrass 86 to 99% in May and increased wheat yield 142 to 254%. At two of four locations, Italian ryegrass control was greater with the December application of AE F130060 00 plus AE F115008 as compared with the February application. Dicamba or 2,4-D mixed with AE F130060 00 plus AE F115008 00 reduced Italian ryegrass control in May approximately 10% in half the trials but did not affect wheat yield compared with AE F130060 00 plus AE F115008 00 applied alone. Thifensulfuron plus tribenuron mixed with AE F130060 00 plus AE F115008 00 did not affect Italian ryegrass control or wheat yield. Under greenhouse conditions, the rate of AE F130060 00 plus AE F115008 00 needed for 80% Italian ryegrass visible control and 80% shoot fresh weight reduction was increased 60 to 68% in mixtures with 2,4-D. Dicamba increased the rate needed for 80% visible control and shoot fresh weight reduction 132 to 139%.
Nomenclature: AE F115008 00 (proposed name iodosulfuron-methyl-sodium), 4-iodo-2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid methyl ester; AE F130060 00 (proposed name mesosulfuron-methyl), methyl 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-4-[[(methylsulfonyl)amino]methyl]benzoate; Italian ryegrass, Lolium multiflorum Lam. #3 LOLMU; wheat, Triticum aestivum L. ‘Coker 9704’.