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Greenhouse and field experiments were conducted under weed-free conditions in 2000 and 2001 to investigate the responses of 10 soft red winter wheat cultivars to postemergence applications of the experimental herbicide AE F130060 03 at 15 g ai/ha with the crop safener AE F107892 at 30 g ai/ha. In the greenhouse, AE F130060 03 injured wheat 7 to 12% and reduced height 11 to 14% at 3 wk after treatment (WAT) across all cultivars but did not reduce biomass of any cultivar. In the field, AE F130060 03 injured wheat 11 to 32%, reduced tiller number of all cultivars except ‘Roane’, ‘Coker 9663’, and ‘VA98W-593’, and reduced height of all cultivars except ‘USG 3209’ and VA98W-593 at 3 WAT. By 9 WAT, tiller number and height of treated wheat was similar to that of nontreated wheat. AE F130060 03 did not influence moisture content or kernel weight of any cultivar. However, AE F130060 03 reduced grain yield in ‘FFR 518’, Coker 9663, and VA98W-593 in both years as well as in ‘AgriPro Patton’ in 2001. These yield reductions suggest that further investigation into soft red winter wheat cultivar tolerance to AE F130060 03 is needed.
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; winter wheat, Triticum aestivum L. ‘AgriPro Patton’, ‘AGS 2000’, ‘Coker 9663’, ‘FFR 518’, ‘Pioneer 2643’, ‘Pioneer 26R24’, ‘Roane’, ‘Sisson (VA96W-250)’, ‘USG 3209’, ‘VA98W-593’.
Additional index words: Differential cultivar response.
Abbreviations: POST, postemergence; WAT, week after treatment.
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.
Nomenclature: Chlorimuron; glyphosate; metribuzin; sulfentrazone; 2,4-D ester; annual bluegrass, Poa annua L. #3 POAAN; common chickweed, Stellaria media L. Vill. # STEME; cressleaf groundsel, Senecio glabellus Poir. # SENGL; shepherd's-purse, Capsella bursa-pastoris (L.) Medicus # CAPBP; soybean, Glycine max (L.) Merr.
Additional index words: AMATA, AMBEL, AMBTR, CHEAL, fall applied, LAMAM, LAMPU, no till, residual control, winter annuals.
Weed control in white beans is currently limited by the small number of registered herbicides. The tolerance of two white bean cultivars, ‘AC Compass’ and ‘OAC Thunder’, to various postemergence (POST) herbicides at the maximum use rate and twice the maximum use rate for soybean or corn was evaluated at two Ontario locations in 2001 and 2002. Generally, the two cultivars did not differ in their response to the POST herbicides. POST applications of imazamox plus fomesafen, imazamox plus bentazon, and cloransulam-methyl decreased plant height, shoot dry weight, and yield by as much as 29, 41, and 55%, respectively, and increased seed moisture content up to 3.9%. POST applications of thifensulfuron, chlorimuron, and bromoxynil decreased plant height as much as 57%, shoot dry weight by up to 71%, yield as much as 93% and increased seed moisture content up to 15.5%. Based on these results, AC Compass and OAC Thunder white beans do not possess sufficient tolerance to support the registration of imazamox plus bentazon, imazamox plus fomesafen, cloransulam-methyl, thifensulfuron, chlorimuron, and bromoxynil.
Nomenclature: Bentazon; bromoxynil; chlorimuron; cloransulam-methyl; fomesafen; imazamox; thifensulfuron; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; white bean, Phaseolus vulgaris L. ‘AC Compass’, ‘OAC Thunder’.
Additional index words: Crop tolerance, herbicide injury, postemergence herbicides, seed moisture content, white beans, yield.
Abbreviations: DAP, days after planting; DAT, days after treatment; POST, postemergence.
Field experiments were conducted in 1994 and 1995 under sprinkler irrigation at the University of Wyoming Research and Extension Center at Torrington to evaluate the effects of season-long interference and the effects of duration of interference of several common sunflower and green foxtail densities, alone or in combination, on pinto bean yield. Green foxtail densities did not significantly affect pinto bean yield in 1994 and reduced yield only at the highest density in 1995. In contrast, sunflower densities reduced pinto bean yield, except at the lowest density in 1994. Pinto bean yield was reduced as the combined density of green foxtail and sunflower increased. Compared with yield losses from each weed species alone, yield reductions from mixed species were additive in 1994 and at low weed densities in 1995 and less than additive at higher weed densities in 1995. The minimum number of weeds per m of row that will economically reduce pinto bean yield was estimated to be 1.6 to 2.9 for green foxtail and 0.12 to 0.2 for sunflower. Pinto bean yield reduction increased as the duration of green foxtail and sunflower interference increased, whether grown alone or in combination. The maximum duration that green foxtail, sunflower, and green foxtail plus sunflower can interfere with pinto bean before causing economical losses was estimated to be 4.5, 3.2, and 2.5 wk, respectively.
Nomenclature: Common sunflower, Helianthus annuus L. #3 HELAN; green foxtail, Setaria viridis (L.) Beauv. # SETVI; pinto bean, Phaseolus vulgaris L. ‘Bill Z’.
Additional index words: Competition, time of removal.
Field studies were conducted over 3 yr at two locations to evaluate the effect of glyphosate rate and time of application on common lambsquarters control, density, dry weight, seed production, and the number of seedlings emerging from soil cores taken the year after herbicide application in glyphosate-resistant corn. Glyphosate was applied at 0, 112, 225, 450, 675, or 900 g ai/ha when common lambsquarters were at the two-, four-, or six-leaf stage of growth. Nicosulfuron was applied to all experimental areas to control annual grasses. Visual estimates of percent control increased, whereas density, dry weight, seed production, and seedlings emerging the year after treatment decreased as the rate of glyphosate was increased from 0 to 450 g/ha. Increasing the glyphosate rate above 450 g/ha had little effect on these parameters. Corn yield declined only at glyphosate rates below 450 g/ha. Time of application had no effect on common lambsquarters control and corn yield because little emergence occurred after the first glyphosate application. There was no interaction between glyphosate rate and time of application for any of the parameters evaluated. In these studies, the application of glyphosate at half the manufacturer's registered rate provided control of common lambsquarters equivalent to the full-registered rate with no measured increase in weed seed production and no increase in weed seedlings emerging from soil cores the year after herbicide application. The results suggest that in some cases the use of reduced herbicide rates can provide excellent weed control and maintain crop yields, while reducing the cost of production and the environmental impact of herbicides. The use of extremely low rates (112 or 225 g/ha), however, resulted in reduced corn yields, increased common lambsquarters seed production and seedlings emerging the year after application, and possibly increased weed management costs in subsequent years.
Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. #3 CHEAL; corn, Zea mays L. ‘Pride G4286’, ‘DeKalb 493RR’.
Additional index words: Reduced rates, weed control, weed seed production.
Ground ivy is a stoloniferous, perennial weed that persists in lawn turf. With the widespread use of 2,4-D on turf sites, the development of 2,4-D–tolerant ground ivy is a possibility. Ground ivy populations showed a highly variable response to foliar 2,4-D application. Ground ivy from Nebraska (NE) was tolerant to 2,4-D, whereas Ohio (OH) ground ivy was susceptible. The 2,4-D–susceptible OH population absorbed 37% more foliar-applied 14C–2,4-D than the 2,4-D–tolerant NE population. Although OH and NE populations total translocation of applied 14C was similar and averaged 5%, the OH population translocated 42% more toward the apical meristem of the primary stolon than the NE population, primarily because of the OH population's higher 14C–2,4-D absorption. The variation in response to 2,4-D found between these two populations occurred after exposure of roots to 2,4-D, but the effect was less pronounced. These results suggest that the difference in foliar uptake may partially contribute to differences in response to 2,4-D between these two populations. Likewise, differences in acropetal translocation may contribute to the differential sensitivity of 2,4-D–tolerant and –susceptible ground ivy populations.
Nomenclature: 2,4-D; ground ivy, Glechoma hederacea L. #3 GLEHE.
Field experiments were conducted at five locations in Kansas, Nebraska, and Wyoming to determine the effects of imazamox rate and application timing on winter annual grass control and crop response in imidazolinone-tolerant winter wheat. Imazamox at 35, 44, or 53 g ai/ha applied early-fall postemergence (EFP), late-fall postemergence, early-spring postemergence (ESP), or late-spring postemergence (LSP) controlled jointed goatgrass at least 95% in all experiments. Feral rye control with imazamox was 95 to 99%, regardless of rate or application timing at Hays, KS, in 2001. Feral rye control at Sidney, NE, and Torrington, WY, was highest (78 to 85%) with imazamox at 44 or 53 g/ha. At Sidney and Torrington, feral rye control was greatest when imazamox was applied EFP. Imazamox stunted wheat <10% in two experiments at Torrington, but EFP or LSP herbicide treatments in the Sidney experiment and ESP or LSP treatments in two Hays experiments caused moderate (12 to 34%) wheat injury. Wheat injury increased as imazamox rate increased. Wheat receiving imazamox LSP yielded less grain than wheat treated at other application timings in each Hays experiment and at Sidney in 2001. No yield differences occurred in one Torrington experiment. However, yields generally decreased as imazamox application timing was delayed in the other Torrington experiment. Generally, imazamox applied in the fall provided the greatest weed control, caused the least wheat injury, and maximized wheat yield.
Field and growth chamber experiments determined the efficacy of temporal glyphosate applications on velvetleaf. Glyphosate was applied postemergence to velvetleaf periodically before and during light and after dark. In 1999, glyphosate at 840 g ae/ha applied before sunrise and after midday provided 54 and 100% velvetleaf control, respectively. In 2000, glyphosate at 840 g/ha applied before sunrise, midday, and after sunset provided 69, 100, and 37% velvetleaf control, respectively. In the growth chamber, glyphosate at 840 g/ha applied before or after light reduced velvetleaf biomass 15 to 20% or 32 to 47%, respectively, and reduced velvetleaf height 24% or 45 to 54%, respectively. Velvetleaf control was consistently greater with glyphosate applications during light compared with dark, regardless of constant air temperature and relative humidity (growth chamber), dew absence or presence (field and growth chamber), or leaf blade orientation (growth chamber) with natural light–dark movements or a fixed horizontal position.
Field studies were conducted from 1998 through 2000 to determine the influence of crop rotation and level of herbicide system for johnsongrass, entireleaf morningglory, and smellmelon control in glyphosate-resistant cotton and corn. Three different crop rotation schedules were used including cotton–cotton–cotton, cotton–corn–cotton, and corn–cotton–corn. Herbicide systems involving various degrees of input levels (low, medium, and high) were compared with a conventional standard program. In 1998, weed control ranged from 80 to 95% for all herbicide systems when the rotation was corn–cotton–corn. In 1999 and 2000, the low-input herbicide system controlled entireleaf morningglory 76 to 78% late in the season. Decreased smellmelon control (78%) was also observed with the conventional standard during this same period. In the cotton–corn–cotton rotation, late-season entireleaf morningglory control decreased each year in the low-input system, regardless of crop. In 2000, late-season evaluations indicated lower weed control of all three species with the conventional standard program compared with the other input systems. Yield data from 2000 suggested that corn and seed cotton yields were influenced by crop rotation.
Nomenclature: Glyphosate; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray #3 IPOHE; johnsongrass, Sorghum halepense (L.) Pers., # SORHA; smellmelon, Cucumis melo var. dudaim Naud. # CUMMD; corn, Zea mays L. ‘DK 580RR’; cotton, Gossypium hirsutum L. ‘DPL 5690RR’.
Additional index words: Entireleaf morningglory, johnsongrass, reduced herbicide inputs, smellmelon, weed control systems.
Abbreviations: DAT, days after treatment; EPOST, early postemergence; LAYBY, layby; LPOST, late postemergence; PD, postemergence-directed; POST, postemergence; PRE, preemergence.
Field studies were conducted in 2000, 2001, and 2002 at Urbana, IL, to examine the interference potential of common waterhemp that emerged at soybean growth stages VE, V2-V3, V4-V5, R1-R2, and R3-R4 in 19- and 76-cm row soybean. Soybean row width and common waterhemp emergence timing significantly influenced common waterhemp density, biomass, seed production, mortality, and soybean yield loss. Common waterhemp density declined as emergence timings were at later soybean growth stages. This decline happened at earlier growth stages in narrow-row soybean. Significant reductions in common waterhemp biomass and seed production occurred at the V2-V3 and V4-V5 emergence timings for the narrow- and wide-row soybean, respectively. Common waterhemp seed production was more than 23,000 seeds per plant at the VE emergence timing for both soybean row widths. Survival of common waterhemp that emerged after the V4-V5 soybean growth stage was less than 20% in both row widths. Common waterhemp interference reduced soybean seed yield at the VE, V2-V3, and the V4-V5 emergence timings. Row width affected the magnitude of yield reductions at these interference timings, with reductions being less in narrow-row soybean. This research suggests that control measures need to be implemented to common waterhemp plants that emerge before V4-V5 soybean to protect soybean yield and reduce common waterhemp seed production.
Nomenclature: Common waterhemp, Amaranthus rudis Sauer #3 AMATA; soybean, Glycine max (L.) Merr. ‘Asgrow 3701RR’.
Additional index words: Interference, integrated weed management, late-season competition.
Field experiments were conducted to study the effects of various tillage and mulching practices on fruit maturity and weed suppression in pumpkins. Conventional tillage (CT), disking, no tillage with rye removed (RR), no tillage with standing rye (SR), and strip tillage (ST) were evaluated with and without ethalfluralin plus halosulfuron (1.5 plus 0.036 kg ai/ha, respectively) applied preemergence. In 2001, when heavy rain after herbicide application caused significant crop injury, the herbicides delayed maturity and significantly reduced yields of mature pumpkins within each herbicide treatment, total yields did not differ with tillage. In 2002, weed populations were significantly greater than those in 2001, and in 2002, regardless of herbicides, yields of mature fruit were greater in tillage treatments with higher rye residues (SR, ST). Although weed populations were less in one year than the other, herbicides provided effective control in both seasons, and RR, ST, and SR effectively suppressed weeds compared with CT. Averaged over treatments, greater yield losses were attributable to weed competition (42%) in 2002 than to herbicide injury (32%) in 2001.
Nomenclature: Ethalfluralin; halosulfuron; pumpkin, Cucurbita pepo L. var. ‘Howden’; winter rye, Secale cereale L.
Additional index words: Conservation tillage, cover crop, disk, no till, strip till.
Abbreviations: CT, conventional tillage; D, disking; OM, organic matter; RR, no tillage with rye removed; SR, no tillage with standing rye; ST, strip tillage; WAP, weeks after planting.
Snap bean was evaluated for sensitivity to a number of herbicides in field studies conducted during a 2-yr period in Exeter, ON. Preemergence (PRE) applications of metolachlor (1,600 and 3,200 g ai/ha), imazethapyr (75 and 150 g ai/ha), and clomazone plus metobromuron (840 1,000 g ai/ha and 1,680 2,000 g/ha) were evaluated for visual injury at 7, 14, and 28 d after emergence. Postemergence (POST) applications of imazamox plus fomesafen (25 200 g ai/ha and 50 400 g/ha), quizalofop-P (72 and 144 g ai/ha), and clethodim (90 and 180 g ai/ha) also were evaluated for visual injury 7, 14, and 28 d after treatment. Plant height and crop yield were assessed for all treatments. Visual injury, stunting, and yield loss were not observed in the metolachlor treatments. Imazethapyr (150 g/ha) caused stunting and reduced snap bean yield in both study years. Clomazone plus metobromuron (1,680 2,000 g/ha) injured and stunted snap bean in both years of the study and reduced yield in 2000. Imazamox plus fomesafen (50 400 g/ha) injured snap bean in both years but only reduced yield in 2000. Quizalofop-P injured snap bean but did not reduce plant height or yield. Clethodim did not injure, stunt, or reduce yield of snap bean. Metolachlor (PRE), imazamox plus fomesafen (POST), quizalofop-P (POST), and clethodim (POST) have excellent potential as weed management tools in snap bean in Ontario.
Additional index words: Herbicide injury, sensitivity.
Abbreviations: COC, crop oil concentrate; DAE, days after emergence; DAT, days after treatment; NIS, nonionic surfactant; OM, organic matter; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; UAN, urea ammonium nitrate.
Field studies were conducted to investigate the effects of different rates of herbicides on weed control, agronomic characteristics, and quality of sugar beet at Shiraz, Iran, in 2000 and 2001. Separate and combined applications of herbicides, including 14 combinations and different rates of grass and broadleaf herbicides, at two rates were used. Herbicides reduced weed biomass compared with the weedy check. In both years, maximum reduction in weed biomass was observed with desmedipham plus phenmedipham plus ethofumesate at 0.23 0.23 0.23 kg ai/ha and desmedipham plus phenmedipham plus propaquizafop at 0.46 0.46 0.1 kg ai/ha. Efficacy of grass herbicides was reduced when they were combined with pyrazon. Highest crop injury in both years was observed with desmedipham plus phenmedipham plus ethofumesate at 0.23 0.23 0.23 kg/ ha. Highest and lowest root yields in both years were produced in weed-free and weedy check plots, respectively. All herbicide treatments produced lower sugar beet yields than the hand-weeded check. Of the herbicide treatments evaluated, the highest sugar beet yields were with desmedipham plus phenmedipham plus propaquizafop at 0.46 0.46 0.1 kg/ha in 2001 and with desmedipham plus phenmedipham plus ethofumesate at 0.23 0.23 0.23 kg/ha in 2000. Sucrose content and other sugar beet brei characteristics were not affected by the herbicide treatments.
Field experiments were conducted at Adelphia, NJ, in 2001 and 2002 to evaluate the response of Kentucky bluegrass, perennial ryegrass, tall fescue, and Chewings fine fescue to sulfosulfuron. Single applications of sulfosulfuron at 6 to 67 g ai/ha were applied to mature swards of each species. Visual chlorosis ratings were taken and clippings were collected 4 wk after treatment (WAT), and turf injury was rated 8 WAT. Chlorosis on all species increased with increasing sulfosulfuron rate. In 2001, Kentucky bluegrass, perennial ryegrass, tall fescue, and fine fescue chlorosis reached 33, 43, 65, and 61% at 4 WAT, respectively, whereas in 2002, chlorosis only reached 13, 26, 46, and 26%, respectively. Clipping weights of all species decreased as application rate increased. Reductions in Kentucky bluegrass and perennial ryegrass clipping weights were less severe than those in tall and fine fescue. By 8 WAT, Kentucky bluegrass, perennial ryegrass, and fine fescue had nearly complete recovery from any initial visual injury symptoms. However, tall fescue injury was still evident 8 WAT in both years. Initial injury of Kentucky bluegrass, perennial ryegrass, and Chewings fine fescue was in the form of discoloration and stunting. Significant stand thinning was only evident in the tall fescue studies. These studies suggest that Kentucky bluegrass and perennial ryegrass may be more tolerant than tall fescue to applications of sulfosulfuron and fine fescue is intermediately tolerant to sulfosulfuron.
Five sweet corn cultivars were evaluated for tolerance to bentazon in five field experiments conducted during 2 yr in Ontario. Bentazon was applied postemergence (POST) at 1.08 and 2.16 kg ai/ha, the highest registered rate and twice the highest registered rate, respectively, used in sweet corn in Ontario. When bentazon was applied POST at 1.08 and 2.16 kg/ha to sweet corn cultivar ‘DelMonte 2038’, injury included plant stunting and leaf damage ranging from 6 to 69% and 15 to 90%, respectively. Plant height was reduced to 48 and 100% of the untreated check when treated with bentazon at 1.08 and 2.16 kg/ha, respectively. The visual injury and height reductions were reflected in the marketable yields, which were reduced to 94% when treated with bentazon. Significant reductions in height and marketable yield were not observed in the other four cultivars tested. No correlation was observed between bentazon sensitivity and endosperm genotype. Based on visual injury ratings, sweet corn height, and marketable yield, it was concluded that ‘Calico Belle’, ‘GH 2684’, ‘Reveille’, and ‘Rival’ are tolerant to POST application of bentazon.
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.
Nomenclature: Stinkgrass, Eragrostis cilianensis (All.) E. Mosher #3 ERACN; witchgrass, Panicum capillare L. # PANCA; winter wheat, Triticum aestivum L.; leaf rust, Puccinia recondita f. sp. tritici.
Waterhemp has emerged as one of the most problematic weeds in agronomic crops in the Midwest because of an extended germination period and widespread occurrence of biotypes resistant to atrazine and sulfonylurea herbicides. However, the competitive effects of late-emerging cohorts on corn yield are not known. Field studies were conducted in 2001 and 2002 at Columbia, Novelty, and Albany, MO, to determine the effects of late-emerging waterhemp interference on corn growth, nitrogen (N) accumulation, and yield. Waterhemp emerged approximately 20 d after planting (DAP) and was treated at heights of 8, 15, 23, 31, 38, or 46 cm with directed applications of dicamba diflufenzopyr followed by hand hoeing. Soil water status, corn leaf chlorophyll content, and corn and common waterhemp height were recorded at the time of waterhemp removal. N stress was detected with a chlorophyll meter at four of six removal timings at high waterhemp densities (362 or more plants/m2) but only at one of six removal timings at lower densities (82 or less plants/m2). Water stress was observed at five of the six removal timings at high densities but at none of the removal timings at low densities. High waterhemp densities reduced corn yield when allowed to reach 15 cm before removal, and yields were reduced 36% when not controlled. At low densities, yield losses did not occur unless waterhemp was allowed to remain with corn season long. Our research suggests that waterhemp is less competitive with corn than redroot pigweed, smooth pigweed, and Palmer amaranth. In addition, low densities of late-emerging waterhemp would not warrant removal to protect corn yield.
Additional index words: Chlorophyll content, nitrogen accumulation, soil moisture deficit.
Abbreviations: CEC, cation exchange capacity; DAP, days after planting; K, potassium; N, nitrogen; OM, organic matter; P, phosphorus; SPAD, single photon avalanche diode; TDR, time domain reflectrometry; VWC, volumetric water content.
Herbicide-resistant canola dominates the canola market in Canada. A multiyear field experiment was conducted at three locations to investigate the effect of time of weed removal (two-, four-, or six-leaf canola) and herbicide rate (50 or 100% recommended) in three herbicide-resistant canola systems. Weeds were controlled in glufosinate-resistant canola (GLU) with glufosinate, in glyphosate-resistant canola (GLY) with glyphosate, and in imidazolinone-resistant canola (IMI) with a 50:50 mixture of imazamox and imazethapyr. Canola yields were similar among the three canola cultivar–herbicide systems. Yields were not influenced by 50 vs. 100% herbicide rates. Timing of weed removal had the greatest effect on canola yield, with weed removal at the four-leaf stage giving the highest yields in most cases. Percent dockage was often greater for GLU and IMI than for GLY. In comparison with the other treatments, dockage levels doubled for GLU after application at 50% herbicide rates. The consistency of monocot weed control was usually greater for GLY than for GLU or IMI systems. However, weed biomass data revealed no differences in dicot weed control consistency between IMI and GLY systems. Greater dockage and weed biomass variability after weed removal at the six-leaf stage or after low herbicide rates suggests higher weed seed production, which could constrain the adoption of integrated weed management practices in subsequent years.
Nomenclature: Glufosinate; glyphosate; imazamox; imazethapyr; canola, Brassica napus L.
Additional index words: GMO, herbicide-tolerant canola, integrated weed management, time of weed removal.
Area-of-influence experiments were conducted on high–organic matter soils to assess the effect of common lambsquarters distances from ‘South Bay’ lettuce on yield and quality under two phosphorus (P) regimens. P was applied either banded (125 kg P/ha) or broadcast (250 kg P/ha) before lettuce planting. Lettuce plants were harvested at 0, 25, 50, 75, 100, and 125 cm from each side of the common lambsquarters plant after season-long interference. The regression equations were y = 0.40 0.36/(1 e−0.09(x−52.5)), r2 = 0.92, for banded P; and y = 0.40 0.29/(1 e−0.07(x−69.3)), r2 = 0.94 for broadcast P. Banded P produced 9% more fresh weight per head than the broadcast P treatment under weed-free conditions. Within the broadcast P treatments, common lambsquarters growing at 125 and 100 cm did not affect fresh weight of harvested lettuce. Values for fresh weight per head declined 18, 34, 38, and 38% when lettuce grew at 75, 50, 25, and 0 cm distance from common lambsquarters, respectively. Fresh weight of lettuce in banded P treatments was reduced only at 50, 25, and 0 cm distance from common lambsquarters plants, representing 31, 44, and 44% less than its weed-free control, respectively. Banding P at 50% (125 kg/ha) of the recommended broadcast rate reduced the area of influence of common lambsquarters with lettuce.
Nomenclature: Common lambsquarters, Chenopodium album L. #3 CHEAL; lettuce, Lactuca sativa L.
Additional index words: Competition, integrated weed management, interference, nutrients.
Field studies were conducted in 1992 and 1993 to evaluate imazapic alone and in postemergence (POST) mixtures with atrazine or bentazon for weed control in imidazolinone-resistant corn treated with carbofuran. Nicosulfuron and nicosulfuron plus atrazine also were evaluated. Imazapic at 36 and 72 g ai/ha controlled large crabgrass 85 and 92%, respectively, which was equivalent to control obtained with nicosulfuron plus atrazine. Imazapic at the higher rate controlled large crabgrass better than nicosulfuron alone. Imazapic at 36 and 72 g/ha controlled Texas panicum 88 and 99%, respectively, and at the higher rate control was equivalent to that obtained with nicosulfuron alone or in mixture with atrazine. Imazapic plus bentazon POST controlled Texas panicum less than imazapic at the lower rate applied alone. Redroot pigweed was controlled 100% with all herbicide treatments. Imazapic at either rate alone or in tank mixture with bentazon or atrazine controlled prickly sida >99%, which was superior to control obtained with nicosulfuron or nicosulfuron plus atrazine. Smallflower, entireleaf, ivyleaf, pitted, and tall morningglories were controlled 96% or greater with all herbicide treatments except nicosulfuron alone. Sicklepod control was >88% with all imazapic treatments, whereas control from nicosulfuron alone was 72%. Corn yields were improved by the addition of POST herbicides with no differences among POST herbicide treatments.
The effect of planting system and cover crop residues on weed emergence in irrigated vegetable row crops was studied in field experiments from 1995 through 1997. Vegetable crops were either no-till planted (NTP) through cover crop residues or conventionally planted (CP) into soil with cover crop residues incorporated. NTP reduced emergence of hairy nightshade by 77 to 99% and Powell amaranth emergence by 50 to 87% compared with CP. Cover crop treatments were much less important than planting system in regulating weed emergence. Tillage in the spring did not increase the number of viable seeds near the soil surface. Hairy nightshade emergence ranged from 0.6 to 9.8% of the intact seeds in CP compared with 0 to 0.1% emergence of the seeds in the NTP plots. Powell amaranth emergence ranged from 4.9 to 6.5% of the intact seeds in CP contrasted with only 0.4 to 0.9% emergence of the seeds in NTP plots.
Efficacy of trifloxysulfuron with and without surfactant was evaluated against balsamapple, cat's claw vine, Florida beggarweed, hairy beggarticks, ivyleaf morningglory, johnsongrass, prickly sida, redroot pigweed, sicklepod, strangler vine, tall morningglory, and yellow nutsedge at 21, 42, and 63 g ai/ha applied at the four- or six-leaf stages and compared with glyphosate at 280, 560, and 840 g ae/ha. Delayed application from the four- to six-leaf stage significantly reduced trifloxysulfuron efficacy; reduction was less with glyphosate. Trifloxysulfuron plus 0.25% X-77 was more effective on the four-leaf stage than on the six-leaf stage plants of redroot pigweed, johnsongrass, hairy beggarticks, strangler vine, and prickly sida; effect was similar on yellow nutsedge, sicklepod, Florida beggarweed, balsamapple, ivyleaf morningglory, and tall morningglory. Trifloxysulfuron at 63 g/ha plus surfactant reduced the fresh weight of all test plants more than 80% compared with control, except prickly sida, strangler vine, and cat's claw vine. Glyphosate was less effective than trifloxysulfuron plus surfactant against tall morningglory, sicklepod, ivyleaf morningglory, and yellow nutsedge but was significantly better against balsamapple, prickly sida, and cat's claw vine. None of the herbicides provided satisfactory control of cat's claw vine, strangler vine, and prickly sida.
The efficacy of imazethapyr in drill-seeded imidazolinone-resistant rice was evaluated in Louisiana in 2000 and 2001. Imazethapyr was applied preemergence (PRE), or no PRE, followed by a postemergence (POST) application of imazethapyr alone, or in a mixture with bensulfuron, bentazon plus aciflurofen, carfentrazone, halosulfuron, propanil plus molinate, triclopyr, or V-10029. Imazethapyr applied PRE followed by a POST application of imazethapyr controlled barnyardgrass equivalent to or higher than other treatments evaluated. Red rice control at 35 days after postemergence treatment (DAT) was 66 to 81% with imazethapyr applied PRE followed by any POST application, but a reduction in control was observed with a POST application of imazethapyr. Although alligatorweed control increased with POST applications, these treatments suggested only suppression. Hemp sesbania control never exceeded 10% with imazethapyr-only treatments and at 35 DAT, all POST applications, except bensulfuron, increased control above 84%. Rice yield increased with treatments receiving a PRE application of imazethapyr compared with no imazethapyr applied PRE.
Nomenclature: Acifluorfen; bensulfuron; bentazon; carfentrazone; halosulfuron; imazethapyr; molinate; propanil; V-10029, sodium 2,6-bis[(4,6-dimethoxypyrimidin-2-yl)oxy]benzoate; alligatorweed, Alternanthera philoxeroides (Mart.) Griseb. #3 ALRPH; barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A.W. Hill # SEBEX; red rice, Oryza sativa L. # ORYSA; rice, Oryza sativa L. imidazolinone-resistant ‘93 AS-3510’ and ‘CL 121’.
Additional index words: Acetolactate synthase; Clearfield rice, herbicide mixtures.
Abbreviations: ALS, acetolactate synthase (EC 184.108.40.206); DAT, days after postemergence treatment; IR, imidazolinone-resistant; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.
Field experiments were conducted at Kalispell, MT, and Corvallis, OR, to determine the optimum rate and application timing of imazamox for downy brome control in winter wheat. Crop injury occurred as a reduction in plant height and was minimal at Kalispell, never exceeding 10%. Crop injury at Corvallis was more severe and was dependant on application timing. No injury was observed with spring applications, but fall applications resulted in as much as 33% injury at the highest rate of imazamox. Fall applications generally provided more consistent control of downy brome, as evidenced by the lower dosage required to reduce downy brome dry weight by 50% (lower I50 values). Nonetheless, spring applications generally provided control comparable with that of fall applications when imazamox was applied at the highest rate. The one exception was at Corvallis during 1997 to 1998, where spring applications failed to provide adequate control of downy brome even at the highest rate applied. Although imazamox generally provided excellent control of downy brome, wheat yield response to downy brome interference was negligible, declining by less than 10% in the absence of imazamox. The absence of a yield response to downy brome interference was attributed to the lack of competition for soil moisture from downy brome under the high-rainfall conditions of the experiment.
Nomenclature: Imazamox; downy brome, Bromus tectorum L. #3 BROTE; winter wheat, Triticum aestivum L.
Additional index words: Dose–response, reduced rates.
Three field studies were conducted at Lewiston Woodville, NC, in 2001 and 2002 to evaluate crop tolerance, weed control, grain yield, and net returns in glyphosate-resistant corn with various herbicide systems. Crop injury, weed control, and grain yield were not influenced by glyphosate formulation. Atrazine preemergence (PRE) and atrazine plus metolachlor PRE, averaged over postemergence (POST) systems, controlled Texas panicum at least 80 and 87%, respectively. Sequential glyphosate applications (early postemergence [EPOST] followed by [fb] POST) provided at least 99% control of Texas panicum compared with at least 86 and 88% control with glyphosate EPOST and glyphosate plus halosulfuron EPOST, respectively. Atrazine plus metolachlor PRE fb any glyphosate system controlled large crabgrass and goosegrass 89 to 100% and 94 to 100%, respectively. Sequential glyphosate treatments controlled large crabgrass and goosegrass at least 99 and 95%, respectively. Regardless of PRE system, glyphosate plus halosulfuron EPOST and sequential applications of glyphosate controlled common ragweed and common lambsquarters at least 99%, whereas glyphosate EPOST alone provided at least 88 and 96% control, respectively. Glyphosate plus halosulfuron EPOST and glyphosate sequentially controlled yellow nutsedge similarly and more consistently than glyphosate EPOST. Regardless of PRE treatment, sequential glyphosate applications provided at least 98% control of entireleaf and pitted morningglory, whereas glyphosate EPOST controlled at least 64 and 62%, respectively. Glyphosate EPOST and the sequential glyphosate EPOST fb POST systems yielded similarly at all three locations. Net returns were highest at all three locations with the glyphosate sequential system, with similar net returns obtained with glyphosate EPOST and glyphosate plus halosulfuron EPOST at two and one locations, respectively.
Nomenclature: Atrazine; glyphosate; halosulfuron; metolachlor; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; entireleaf morningglory, Ipomoea hederacea var. integruiscula Gray # IPOHG; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; Texas panicum, Panicum texanum Buckl. # PANTE; yellow nutsedge, Cyperus esculentus L. # CYPES; corn, Zea mays L. # ZEAMX.
Additional index words: Diammonium salt, isopropylamine salt, net returns.
Abbreviations: DAT, days after treatment; EPOST, early postemergence; fb, followed by; POST, postemergence; PRE, preemergence.
Three field studies were conducted during 1998 to 2002 at Stoneville, MS, to examine the efficacy of glufosinate and glyphosate on redvine and trumpetcreeper control in glufosinate- and glyphosate-resistant soybean. Glyphosate at 2.52 kg ae/ha applied approximately 3 wk before planting soybean reduced trumpetcreeper density (45 to 52%) but not redvine compared with no glyphosate in both glufosinate- and glyphosate-resistant soybean. However, glyphosate applied preplant reduced biomass of both species in glufosinate-resistant soybean. Glyphosate early postemergence (EPOST) followed by (fb) late postemergence (LPOST) had no effect on redvine density but reduced trumpetcreeper density (70%) compared with the no-herbicide control. There were no differences in densities and biomass of redvine and trumpetcreeper and soybean yield among isopropylamine, diammonium, and aminomethanamide dihydrogen tetraoxosulfate salts of glyphosate. Overall, trumpetcreeper is more susceptible to glyphosate than redvine. Glufosinate EPOST with or without acifluorfen or glufosinate EPOST fb LPOST had no effect on densities of redvine and trumpetcreeper but reduced biomass 45 to 76% and 35 to 58%, respectively, compared with the nontreated control. These results show that glyphosate preplant and POST in-crop applications can reduce trumpetcreeper density but not redvine, and glufosinate POST applications can suppress growth of both species.
Nomenclature: Acifluorfen; clomazone; glufosinate; glyphosate; lactofen; redvine, Brunnichia ovata (Walt.) Shinners #3 BRVCI; soybean, Glycine max (L.) Merr. ‘DP4690 RR’, ‘DP 5806 RR’, ‘AG 4702 RR’, ‘A 5547 LL’; trumpetcreeper, Campsis radicans (L.) Seem. ex Bureau # CMIRA.
Abbreviations: Adt, aminomethanamide dihydrogen tetraoxosulfate; Dia, diammonium; EPOST, early postemergence; fb, followed by; Ipa, isopropylamine; LPOST, late postemergence; POST, postemergence; PRE, preemergence; WAP, weeks after planting soybean; WAT, weeks after late postemergence.
Herbicides with residual activity more effectively control infestations of yellow starthistle, a facultative winter annual, because seed banks quickly furnish replacement plants after nonresidual herbicide treatments. Picloram has been applied to rosettes in fall or spring, but new infestations of yellow starthistle are often discovered when plants are more noticeable in bud or flower stages. Eradication, containment, and revegetation are facilitated if weed seed rain can be stopped. This study evaluated whether registered rates (0.14, 0.28, and 0.42 kg ae/ha) of picloram, alone and with 2,4-D at 1.12 kg ae/ha, can prevent seed production when applied to yellow starthistle at bud or flower stage. Picloram applied at bud stage curtailed both seed production and germination, reducing seed production by 42 to 86% and viability by 80 to 99%. Neither the picloram rate nor the addition of 2,4-D to the spray solution affected the percentage of nonviable seeds. The addition of 2,4-D further decreased germination of developed seeds only at the lowest picloram rate. At flower stage, picloram and 2,4-D neither killed mature plants nor consistently reduced the quantity and quality (viability) of seeds. Bud stage was the phenological limit for effective reduction of viable seed by picloram, which caused both bud abortion and lower seed germination.
Nomenclature: 2,4-D; picloram; yellow starthistle, Centaurea solstitialis L. #3 CENSO.
Bensulide and dithiopyr may be used in late summer–fall as a preventative treatment to reduce the potential of annual bluegrass encroachment onto newly constructed or renovated creeping bentgrass putting greens. In 1999, no herbicide treatment reduced bentgrass cover or root mass 1 mo after treatment (MAT). In April of 2000, root mass was lower with bensulide applied at 11.2 kg/ha in October and 22.4 kg/ha applied at both timings or by dithiopyr applied at all rates and timings compared with the untreated bentgrass. In April, bentgrass cover was reduced by bensulide applied at 22.4 kg/ha and dithiopyr applied at 0.4 and 0.8 kg/ha at both timings. In contrast to 1999, significant reductions in root mass were observed 1 MAT in 2000 with bensulide applied at 22.4 kg/ ha and all rates of dithiopyr. Reductions in root mass and bentgrass cover continued into April of 2001 with dithiopyr at 0.4 or 0.8 kg/ha applied at either application timing. Bentgrass cover was lower than the untreated with dithiopyr applied at 0.8 kg/ha until August of 2001. These results suggest that bensulide may be used on creeping bentgrass greens in late summer–fall with a greater degree of safety than dithiopyr.
Nomenclature: Bensulide; dithiopyr; annual bluegrass, Poa annua L. #3 POAAN; creeping bentgrass, Agrostis stolonifera L. # AGSST.
Additional index words: Phytotoxicity, turfgrass cover.
Abbreviations: MAT, month after treatment; PRE, preemergence.
Field experiments were conducted from 1999 to 2001 to evaluate preemergence (PRE) activity of cloransulam on broadleaf weed species and to determine the effectiveness of cloransulam as a PRE herbicide in glyphosate-resistant soybean weed management systems. Cloransulam PRE controlled prickly sida, velvetleaf, and morningglory species even at reduced rates (recommended rate 36 g ai/ha) but only suppressed growth of Palmer amaranth, hemp sesbania, and sicklepod. Cloransulam applied PRE provided initial control or suppression of most weeds, but late-season control declined appreciably. Adding metribuzin to cloransulam PRE generally improved control of hemp sesbania, Palmer amaranth, annual grasses, and morningglory species, leading to soybean yield increases. Control of weeds was greater on a silt loam soil compared with a silty clay soil. Delayed herbicide activation by rainfall or irrigation reduced control of hemp sesbania and prickly sida and affected efficacy more than soil texture. Single postemergence (POST) applications of glyphosate or fomesafen plus fluazifop-P provided 90% or less control of most weed species. When glyphosate POST or fomesafen plus fluazifop-P POST followed PRE applications of cloransulam or cloransulam plus metribuzin PRE, control of all weeds was generally greater than 85%. The highest soybean yields were recorded from treatments that contained sequential PRE followed by (fb) POST herbicide applications. Composition of weed flora determined the effect of herbicide program on soybean seed yield. No yield benefit was gained from the sequential program when the dominant species was Palmer amaranth, which was controlled by glyphosate. When hemp sesbania was the dominant species, PRE herbicides fb glyphosate POST increased yield compared with total POST glyphosate.
Nomenclature: Cloransulam; fluazifop-P; fomesafen; glyphosate; metribuzin; hemp sesbania, Sesbania exaltata (Raf) Rydb. ex A. W. Hill #3 SEBEX; morningglory species, Ipomoea spp.; Palmer amaranth, Amaranthus palmeri S. Wats # AMAPA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia L. Irwin and Barnaby # CASOB; velvetleaf, Abutilon theophrasti Medicus # ABUTH; soybean, Glycine max (L.) Merr. GLXMA.
Herbicide treatments (4:1 ratio of 2,4-D amine:picloram) at 0.7 and 1.4 kg ae/ha at early postemergence (10- to 15-cm horsenettle height), midpostemergence (early flower), and late postemergence (fruit initiation) applied both early and late in the growing season provided >80% horsenettle control. Horsenettle density at season's end in all treated plots was less than 0.25 stems/m2, whereas untreated plots contained about 5 stems/m2. Horsenettle control the next spring was between 47 and 66% for all rates and application timings, and horsenettle density in treated plots was less than 3 stems/m2 as opposed to about 6 stems/m2 in the untreated plots. Clover drilled into the treated area the year after herbicide application was injured, indicating clover establishment the season after application of this package mixture would be difficult.
A study was conducted in 2001 and 2002 in Texas to evaluate red rice control and crop response of imidazolinone-tolerant rice with imazethapyr on coarse-textured soils. Because imazethapyr was not registered for use on imidazolinone-tolerant rice on coarse-textured soils in Texas, crop response was evaluated to determine whether imidazolinone-tolerant rice yields would be reduced with sequential applications of imazethapyr on soils having greater than 50% sand content. The treatment factors consisted of preemergence (PRE) applications of imazethapyr at 50, 70, or 87 g ai/ ha followed by (fb) preflood (PREFLD) applications of 35 or 50 g/ha. Imazethapyr at 70 g/ha PRE fb 70 g/ha PREFLD was added as a seventh treatment. PRE applications were activated by rainfall or surface irrigation after application, and PREFLD applications were sprayed 1 to 2 d before application of the permanent flood. In both years, 100% red rice control was achieved with all rate combinations. Early-season visual rice injury ranged from 5 to 21% and did not result in yield losses, indicating that imazethapyr is safe on coarse-textured soils.
Nomenclature: Imazethapyr; red rice, Oryza sativa L. #3 ORYSA; rice, Oryza sativa L. ‘CL121’.
Abbreviations: DAT, days after treatment; fb, followed by; PRE, preemergence; PREFLD, preflood.
Field experiments were conducted on two North Carolina research stations in 1999, 2000, and 2001; on-farm in Lenoir, Wayne, and Wilson counties, NC, in 2002; and on-farm in Port Royal, VA, in 2000, 2001, and 2002 to evaluate possible gains from site-specific herbicide applications at these locations. Fields were scouted for weed populations using custom software on a handheld computer linked to a Global Positioning System. Scouts generated field-specific sampling grids and recorded weed density information for each grid cell. The decision aid HADSS™ (Herbicide Application Decision Support System) was used to estimate expected net return and yield loss remaining after treatment in each sample grid of every field under differing assumptions of weed size and soil moisture conditions, assuming the field was planted with either conventional or glyphosate-resistant (GR) soybean. The optimal whole-field treatment (that treatment with the highest expected net return summed across all grid cells within a field) resulted in average theoretical net returns of $79/ha (U.S. dollars) and $139/ha for conventional and GR soybean, respectively. When the most economical treatment for each grid cell was used in site-specific weed management, theoretical net returns increased by $13/ha (conventional) and $4.50/ha (GR), and expected yield loss after treatment was reduced by 10.5 and 4%, respectively, compared with the whole-field optimal treatment. When the most effective treatment for each grid cell was used in site-specific weed management, theoretical net returns decreased by $18/ha (conventional) and $4/ha (GR), and expected yield loss after treatment was reduced by 27 and 19%, respectively, compared with the whole-field optimal treatment. Site-specific herbicide applications could have reduced the volume of herbicides sprayed by as much as 70% in some situations but increased herbicide amounts in others. On average, the whole-field treatment was optimal in terms of net return for only 35% (conventional) and 57% (GR) of grid cells.
Nomenclature: Glyphosate; soybean, Glycine max L., ‘Natto.’
Additional index words: Computer decision aids, economic threshold, integrated pest management, variable rate herbicide application.
Abbreviations: CEFS, Center for Environmental Farming Systems; GPS, Global Positioning System; GR, glyphosate resistant; HADSS, Herbicide Application Decision Support System; TNR, theoretical net return over herbicide investment; YL, yield loss remaining after treatment.
Field studies were conducted in Arkansas in 1999, 2000, and 2001 to evaluate mesotrione applied preemergence (PRE) and postemergence (POST) for weed control in corn grown in the Mississippi Delta region of the United States. Mesotrione was applied PRE (140, 210, and 280 g/ ha) alone and POST (70, 105, and 140 g/ha), alone or in tank mixtures with atrazine (280 g/ha). Standard treatments for comparison were S-metolachlor/atrazine PRE and S-metolachlor plus atrazine PRE followed by atrazine POST. All PRE treatments controlled velvetleaf, pitted morningglory, entireleaf morningglory, prickly sida, and broadleaf signalgrass 95% 2 wk after emergence (WAE). Mesotrione controlled velvetleaf 89% or more 4 and 6 WAE. Control of morningglory species by mesotrione POST averaged 92% 6 WAE. Prickly sida was controlled at least 90% by all treatments 4 WAE. Mesotrione applied alone PRE and POST controlled broadleaf signalgrass 83 to 91% 4 WAE. All treatments controlled broadleaf signalgrass less than 90% 6 WAE, except treatments that contained S-metolachlor, which gave 94% or greater control. Corn yield ranged from 10.5 to 12.4 Mg/ha and did not differ among treatments. Mesotrione PRE and POST provided excellent control of broadleaf weeds, but S-metolachlor was needed for broadleaf signalgrass control.
Nomenclature: Atrazine; mesotrione; S-metolachlor; broadleaf signalgrass, Brachiaria platyphylla Griseb. Nash #3 BRAPP; entireleaf morningglory, Ipomoea hederacea var. integriuscula L. Jacq. # IPOHG; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; velvetleaf, Abutilon theophrasti Medicus. # ABUTH; corn, Zea mays L. ‘Pioneer YieldGuard 31B13’.
Additional index words: HPPD-inhibiting herbicides, triketone herbicides.
Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence; WAE, weeks after emergence; WAP, weeks after planting; WAT, weeks after treatment.
Field studies were conducted near Knoxville, TN, during late March and early April 2002 and 2003, respectively, for star-of-Bethlehem control in dormant bermudagrass turf that was established over 25 yr ago. Halosulfuron, imazaquin, metsulfuron, 2,4-D plus dicamba plus mecoprop, and triclopyr plus clopyralid controlled star-of-Bethlehem 35% at most 35 d after treatment (DAT). Bromoxynil alone or mixed with halosulfuron, imazaquin, or metsulfuron controlled star-of-Bethlehem at least 80% at 35 DAT. Imazaquin and imazaquin plus bromoxynil injured bermudagrass 51% 35 DAT. This injury was characterized by decreased bermudagrass postdormancy transition and was transient.
Tropical soda apple samples were collected from 31 populations across the southeastern United States and from four populations in a portion of its native range in Brazil. The genetic relationships among these populations were examined by single primer amplification reactions (SPAR) and by sequencing a portion of the chloroplast genome. SPAR revealed no variation among the 132 individuals and only two chloroplast haplotypes were detected in the 50 individuals sequenced. The most common haplotype was present in all samples from the United States and most of the Brazilian samples, whereas the second haplotype was only found in one of the Brazilian populations. Within the limitations of these data, we conclude that Brazil is the best location to seek a potential biological control agent for tropical soda apple, and that, if identified, this agent should prove useful for populations throughout the United States.
Nomenclature: Tropical soda apple, Solanum viarum Dunal.
Crop injury caused by drift of auxin-like herbicides has been a concern since their development. Research was conducted to describe a method of quantifying injury from auxin-like herbicides as a first step in determining crop damage. Reduced rates of 2,4-D, dicamba, and triclopyr were applied to cotton and soybean plants in the three- to six-leaf stage in field and greenhouse studies. Injury to leaves and stems were evaluated separately, and the values were combined so that one injury estimate was obtained for each individual plant rated. Injury symptoms were typical for auxin-type herbicides and ranged from slight bending of stems or petioles and wrinkled leaves to necrosis. Specific descriptions of leaf and stem injury levels were used to describe plant injury consistently. These descriptions were very detailed for the lower injury levels, but the characterizations became more general as the injury increased because of the prominence of factors such as necrosis. The injury evaluation method provided repeatable results for each herbicide and herbicide rate used. This injury evaluation method has many possible uses in auxin-like herbicide research and lays the foundation for forecasting the impact of early-season injury to cotton and soybean yield.
Nomenclature: 2,4-D; dicamba; triclopyr; cotton, Gossypium hirsutum L. ‘Delta Pine 50’ #3 GOSHI; soybean, Glycine max (L.) ‘Delta Pine 415’ Merr. # GLYMA.
Additional index words: Epinasty, method, plant injury, rating scale.
Volatility and drift are problems commonly associated with auxin-like herbicides. Field and greenhouse studies were conducted at Texas A & M University to develop a method of quantifying volatility and subsequent off-target movement of 2,4-D, dicamba, and triclopyr. Rate–response curves were established by applying reduced rates ranging from 4 × 10−1 to 1 × 10−5 times the normal use rates of the herbicides to cotton and soybean and recording injury for 14 d after treatment (DAT) using a rating scale designed to quantify auxin-like herbicide injury. Injury from herbicide volatility was then produced on additional cotton and soybean plants through exposure to vapors of the dimethylamine salt of 2,4-D, diglycolamine salt of dicamba, and butoxyethyl ester of triclopyr using air chambers inside a greenhouse and volatility plots in the field. Injury resulting from this exposure was evaluated for 14 d using the same injury-evaluation scale that was used to produce the rate–response curves. Volatility-injury data were then applied to the rate–response curves so that herbicide rates corresponding with observed injury could be calculated. Using this method, herbicide volatility rates estimated from greenhouse-cotton injury were determined to be 3.0 × 10−3, 1.0 × 10−3, and 4.9 × 10−2 times the use rates of 2,4-D, dicamba, and triclopyr, respectively. Greenhouse-grown soybean developed injury consistent with 1.4 × 10−2, 1.0 × 10−3, and 2.5 × 10−2 times the normal use rate of 2,4-D, dicamba, and triclopyr, respectively. Under field conditions, cotton developed injury symptoms that were consistent with 4.0 × 10−3, 2.0 × 10−3, and 1.25 × 10−1 times the recommended use rates of 2,4-D, dicamba, and triclopyr, respectively. Field soybean displayed injury symptomology concordant with 1.6 × 10−1, 1.0 × 10−2, and 1.1 × 10−1 times the normal use rates of 2,4-D, dicamba, and triclopyr, respectively. This procedure provided herbicide volatility rate estimates that were consistent with rates and injury from the rate–response injury curves. Additional research is needed to ascertain its usefulness in determining long-term effects of drift injury on crop variables such as yield.
Nomenclature: 2,4-D, dicamba, triclopyr, cotton, Gossypium hirsutum L. ‘Delta Pine 50’, #3 GOSHI, soybean, Glycine max (L.) Merr. ‘Delta Pine 415’, # GLYMA.
Additional index words: Injury modeling, plant injury, rate of exposure.
Abbreviations: BEE, butoxyethyl ester; DAT, days after treatment; DGA, diglycolamine; DMA, dimethylamine; WAE, weeks after emergence.
Weed scientists are facing research problems, such as invasive weeds, that may require multidisciplinary approaches to solve. One example is jointed goatgrass, a winter annual grass invading winter wheat fields and not easily managed with conventional control tactics. A national research program was started in 1994 to develop jointed goatgrass management strategies. Involving more than 35 scientists with diverse scientific expertise, this national approach fostered cooperative research projects across 11 states. Research involved entomology, economics, plant breeding, plant physiology, genetics, and weed science, leading to successful management systems for jointed goatgrass. To help other scientists organize regional or national programs, we describe development and performance of the jointed goatgrass program as well as suggest ideas for possible improvement. Pivotal to the success of the program was a Steering Committee, whose role was to establish research priorities and coordinate research across the western United States.
Weed science is an important component of pest management. Weeds cause approximately 12% loss in United States crop production, reduce crop quality, poison livestock, and adversely affect human health, recreation, and transportation. Herbicides comprise approximately 65% of pesticide expenditures, whereas insecticides and fungicides each comprise less than 20%. The total effect of weeds, including crop losses and costs of control, in the United States was estimated in 1994 to be $20 billion annually. A survey was prepared and mailed to weed scientists at universities and experiment stations in the northeastern United States to determine the number of faculty positions and course offerings devoted to weed science. There are approximately five times as many entomologists and more than three times as many plant pathologists as weed scientists at universities in the northeast. There are more than six times as many graduate students currently in entomology and more than four times as many in plant pathology compared with weed science. Few undergraduate courses in weed science are taught, and most universities have no graduate classes in weed science. There are almost seven times as many undergraduate entomology courses and more than twice as many plant pathology courses as weed science classes in this region. There are more than 17 times as many graduate entomology courses and more than 15 times as many plant pathology courses compared with weed science graduate classes. There are no departments devoted solely to weed science in the northeast, whereas entomology and plant pathology departments are both common. Most universities have little to no faculty assigned to aquatic, forestry, noncrop weed control, weed ecology, or laboratory trials, and numbers assigned to agronomic and horticultural crop weed management are limited. Additional university resources are needed if weed science research, teaching, and extension efforts are to meet the priority needs in weed management.
Identification of the appropriate use rate is a critical first step in the herbicide development process because use rates affect product utility, market value, and the various risk assessments within the regulatory review process prior to registration. For a given herbicide to be commercially successful, it must provide consistent and sustained efficacy based on a use rate structure that meets customer requirements over a wide range of conditions. Recently, recommendations have been made that advocate the use of herbicide use rates below those outlined on registered product label text. Such advice tends to be based on field work and predictive models designed to identify specific conditions where reduced herbicide use rates are theoretically optimized as dictated by threshold values with assumed levels of commercially acceptable weed control. Unfortunately, many other studies indicate that the use of reduced herbicide rates is not without variability of herbicide efficacy and economic risk. Consequently, reduced use rate theories and related predictive models are often of limited practical value to growers. Aside from inconsistent performance, weed control strategies based on reduced herbicide use rates are not a solution to prevent or even delay target site resistance. In fact, prolonged use of sublethal use rates may select for metabolic resistance and add future weed management challenges by replenishing the weed seed bank. Much effort in terms of development time and resources are invested before product commercialization to ensure that product labels are easily understood and provide value to growers. In this regard, every effort is made to identify the lowest effective use rate that will consistently control target weeds and lead to economic optimization for both the grower and manufacturer.
Additional index words: Lowest effective use rate.