R. Gordon Harvey

Effect of postemergence glyphosate application timing on weed control and grain yield in glyphosate-resistant corn: Results of a 2-yr multistate study

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. Nomenclature: Glyphosate; Amaranthus spp. #3 AMASS; Ipomoea spp. # IPOSS; corn, Zea mays L. ‘Roundup Ready®’ # SETFA. Additional index words: Herbicide-resistant crops, weed interference. Abbreviation: POST, postemergence.

Glyphosate with and without residual herbicides in no-till glyphosate-resistant soybean (Glycine max).

Abstract: Field experiments were conducted in 1996 and 1997 near Arlington, WI, to compare the efficacy of glyphosate applied below registered rates in sequential and tank-mix combinations with residual herbicides to no-till, narrow-row, glyphosate-resistant soybean. In the sequential combinations of preplant (PP) residual herbicides and postemergence (POST) glyphosate study, glyphosate followed one of eight burndown treatments. Clomazone applied PP controlled 86% of common lambsquarters in 1996 when followed by 420 g ae/ha glyphosate early POST (EPOST). All other herbicide treatments controlled 94% or greater regardless of weed species, PP treatment, glyphosate timing, or glyphosate rate. The greatest soybean yields occurred in EPOST glyphosate applications in 1996 and late POST (LPOST) glyphosate applications in 1997. The only time PP residual herbicides were beneficial was prior to the LPOST glyphosate application in 1996. In the tank-mix POST combinations of glyphosate and residual herbicides study, glyphosate was applied alone or in combination with four residual herbicides. Soybean injury did not exceed 5% except in the glyphosate and imazethapyr combination in 1997. Control of common lambsquarters, velvetleaf, and giant foxtail was 90% or greater when averaged across all residual combinations and glyphosate timings and rates. Imazethapyr alone controlled velvetleaf 99% and giant foxtail 92% in 1997. When glyphosate was applied alone, soybean yields were similar at all glyphosate rates and application timings, except the 630 g/ha glyphosate LPOST resulted in a lower yield than 420 g/ha glyphosate LPOST. Only one residual herbicide, SAN 582, combined with glyphosate produced yields equivalent to the highest yielding treatments when averaged over both glyphosate rates and timings. Cloransulam added to 420 g/ha glyphosate EPOST and chlorimuron plus thifensulfuron and imazethapyr added to 420 g/ha glyphosate LPOST resulted in lower soybean yields compared to the same rate of glyphosate applied alone at the respective timings. Thus, no herbicide combination preformed better than glyphosate applied in a timely manner alone. However, in situations where early-season weed competition is severe and a timely glyphosate application is not possible, a PP residual herbicide may be beneficial. Nomenclature: Chlorimuron; clomazone; cloransulam; glyphosate; imazethapyr; pendimethalin; SAN 582 (proposed name dimethenamid), 2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)-acetamide; thifensulfuron; common lambsquarters, Chenopodium album L. #3 CHEAL; giant foxtail, Setaria faberi Herrm. # SETFA; velvetleaf, Abutilon theophrasti Medicus # ABUTH; soybean, Glycine max (L.) Merr. Additional index words: Combinations, sequential, tank-mixed. Abbreviations: EPOST, early postemergence; 7DPP, 7 d prior to planting; DAP, days after planting; fb, followed by; LPOST, late postemergence; POST, postemergence; PP, preplant.

Effect of Nicosulfuron Timing on Wild-Proso Millet (Panicum miliaceum) Control in Sweet Corn (Zea mays)1

Abstract: The effect of nicosulfuron application timing on wild-proso millet (Panicum miliaceum) control and sweet corn (Zea mays) yield was evaluated in the field during 1991, 1992, and 1993. Sweet corn yields were equal to hand weeded controls when nicosulfuron was applied to wild-proso millet shorter than 9 cm, but the best (> 95%) wild-proso millet control occurred when nicosulfuron was applied to wild-proso millet plants between 11 and 19 cm tall. However, nicosulfuron controlled wild-proso millet 90 to 95%, 13 wk after planting, when nicosulfuron was applied to plants 8 to 10 cm tall. Nicosulfuron applications made to wild-proso millet plants less than 8 cm were made early in the season and failed to control subsequent wild-proso millet flushes. Additionally, nicosulfuron failed to control completely wild-proso millet plants larger than 20 cm. Consequently, nicosulfuron applied to wild-proso millet plants shorter than 8 cm or taller than 20 cm resulted in a rapid decline in wild-proso millet control 13 wk after planting. Nicosulfuron applied following 6.7 kg ai/ha EPTC plus 2.2 kg ai/ha cyanazine PPI in 1991, could be applied to wild-proso millet 25 cm tall without subsequent losses in wild-proso millet control or sweet corn yield. Wild-proso millet control was 93% and sweet corn yields were equal to hand-weeded controls when nicosulfuron was applied to wild-proso millet 4 cm tall and followed by one cultivation 14 d after application. Nomenclature: Cyanazine, 2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile; EPTC, S-ethyl dipropyl carbamothioate; nicosulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide; wild-proso millet, Panicum miliaceum L. #3 PANMI; sweet corn, Zea mays L. Additional index words: Cultivation, PANMI, yield loss. Abbreviations: DAA, days after application; OEM, oil emulsifier concentrate; PDIR, directed postemergence; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; UAN, urea ammonium nitrate; WAP, weeks after planting.

Common lambsquarters (Chenopodium album) interference with corn across the northcentral United States

Abstract Variation in crop–weed interference relationships has been shown for a number of crop–weed mixtures and may have an important influence on weed management decision-making. Field experiments were conducted at seven locations over 2 yr to evaluate variation in common lambsquarters interference in field corn and whether a single set of model parameters could be used to estimate corn grain yield loss throughout the northcentral United States. Two coefficients (I and A) of a rectangular hyperbola were estimated for each data set using nonlinear regression analysis. The I coefficient represents corn yield loss as weed density approaches zero, and A represents maximum percent yield loss. Estimates of both coefficients varied between years at Wisconsin, and I varied between years at Michigan. When locations with similar sample variances were combined, estimates of both I and A varied. Common lambsquarters interference caused the greatest corn yield reduction in Michigan (100%) and had the least effect in Minnesota, Nebraska, and Indiana (0% yield loss). Variation in I and A parameters resulted in variation in estimates of a single-year economic threshold (0.32 to 4.17 plants m−1 of row). Results of this study fail to support the use of a common yield loss–weed density function for all locations. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; corn, Zea mays L. ‘DK404SR’, ‘DK493SR’, ‘DK592SR’, ‘Asgrow RX602SR’.

Yellow Nutsedge (Cyperus esculentus) and Annual Weed Control in Glyphosate-Resistant Field Corn (Zea mays)'

Field experiments evaluated halosulfuron and glyphosate for yellow nutsedge control in glyphosate-resistant field corn in 1997 and 1998. Treatments included single and sequential glyphosate applications with or without halosulfuron. Single glyphosate applications provided less than 75% yellow nutsedge control. Sequential applications with at least 1.68 kg ae/ha of glyphosate provided 85% or greater yellow nutsedge control 82 or 115 d after treatment (DAT). Halosulfuron was required to consistently obtain 80% or greater yellow nutsedge control. Nearly all treatments resulted in 90% or greater velvetleaf control 82 or 115 DAT. At the same rating times, giant foxtail control was 95% or greater for sequential glyphosate treatments and treatments containing acetochlor. Corn treated with sequential glyphosate applications containing at least 1.26 kg/ha of glyphosate or containing halosulfuron resulted in greater corn yields than with single glyphosate applications. Halosulfuron was required for consistent yellow nutsedge control, but halosulfuron did not control grasses. Nomenclature: Acetochlor; glyphosate; halosulfuron; giant foxtail, Setaria faberi Herrm. #3 SETFA; velvetleaf, Abutilon theophrasti Medicus # ABUTH; yellow nutsedge, Cyperus esculentus L. # CYPES; corn, Zea mays L. ‘MON-802 RR’, ‘Dekalb DK493RR’. Additional index word: Amaranthus retroflexus. Abbreviations: AMS, ammonium sulfate; DAT, days after treatment; gly-R, glyphosate resistant; LPST, late postemergence; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Assessment of Weed Control Strategies for Corn in the North-Central United States

Field experiments were conducted across the north-central United States to determine the benefits of various weed control strategies in corn. Weed control, corn yield, and economic return increased when a preemergence (PRE) broad-spectrum herbicide was followed by (fb) postemergence (POST) herbicides. Weed control decisions based on field scouting after a PRE broad-spectrum herbicide application increased weed control and economic return. Application of a PRE grass herbicide fb a POST herbicide based on field scouting resulted in less control of velvetleaf and morningglory species, corn yield, and economic return compared with a PRE broad-spectrum herbicide application fb scouting. Cultivation after a PRE broad-spectrum herbicide application increased weed control and corn yield compared with the herbicide applied alone, but economic return was not increased. An early-postemergence herbicide application fb cultivation resulted in the highest level of broadleaf weed control, the highest corn yield, and the greatest economic return compared with all other strategies. Weed control based on scouting proved to be useful in reducing the effect of weed escapes on corn yield and increased economic return compared with PRE herbicide application alone. However, economic return was not greater than the PRE fb planned POST or total POST strategies. Nomenclature: Morningglory species, Ipomoea spp.; velvetleaf, Abutilon theophrasti L. Medicus #3 ABUTH; corn, Zea mays L. Additional index words: Abutilon theophrasti, ABUTH, CHEAL, Chenopodium album, cultivation, economic analysis, field scouting, Ipomoea spp., IPOSS, Setaria spp., SETSS, weed control systems. Abbreviations: EPOST, early postemergence; fb, followed by; POST, postemergence; PRE, preemergence.

Influence of simulated seed rain on the seed bank of wild-proso millet

Abstract A field experiment was conducted between 1988 and 1993 to determine the number of wild-proso millet seed that could be returned to the soil without increasing future soil seed bank populations. The first seed bank (1988) was 15,300 seed m−2 and ranged from 14,000 to 21,000 seed m−2, which represented a high seed population for the area. Seed rain treatments of 0, 3, 6, 12, 24, and 48% of the 1988 soil seed bank were returned each fall. By 1993, more than 90% of the original millet seed bank had been depleted for all treatments. It was estimated that 77% of the seed rain and 68% of the spring seed bank were lost each year. As a result, wild-proso millet must produce approximately three times the seed in the soil to maintain a constant seed bank population. Nomenclature: Wild-proso millet, Panicum miliaceum L. PANMI; corn, Zea mays L.; soybean, Glycine max (L) Merr.

Fate and persistence of woolly cupgrass (Eriochloa villosa) seed banks

Abstract Field experiments were conducted to quantify cumulative and annual rates of woolly cupgrass seedling emergence and seed mortality and to characterize woolly cupgrass seedling emergence patterns. Woolly cupgrass seed bank decline was rapid, declining by an average of 73, 96, and 99.5% after 1, 2, and 3 yr, respectively. Woolly cupgrass seed mortality accounted for a much greater portion of seed loss from the seed bank (80%) than germination and emergence (19.5%) during the 3-yr period. Annual rates of emergence ranged from 3 to 17% of the fall seed bank and were similar between seed banks established in different years when compared within the same year. Annual rates of mortality ranged from 50 to 92% and varied between seed banks established in different years when compared within the same year; older seed banks had higher rates of mortality than younger seed banks. For first-year seed banks, 97 to 99% of the total season emergence occurred within the first 3 wk of emergence. However, for second- and third-year seed banks, a greater percentage of the total season emergence occurred later in the season compared with emergence that occurred during the first year. The data suggest that in addition to various environmental and seed-source factors, seed bank age may also play a role in seed mortality rate and seedling emergence pattern. Nomenclature: Woolly cupgrass, Eriochloa villosa (Thunb.) Kunth ERBVI.

Woolly Cupgrass (Eriochloa villosa) Management in Corn (Zea mays) by Sequential Herbicide Applications and Cultivation1

Abstract: Field experiments were conducted in southern Wisconsin from 1996 to 1998 to evaluate the effects of acetochlor applied preemergence (PRE) followed by nicosulfuron or sethoxydim applied postemergence (POST) and of cultivation on woolly cupgrass control, corn grain yield, and woolly cupgrass seed production. Sethoxydim treatments provided greater woolly cupgrass control than nicosulfuron treatments in 1997 and similar control to nicosulfuron treatments in 1996 and 1998. However, neither herbicide killed all emerged woolly cupgrass plants, regardless of herbicide rate or POST application timing. Late postemergence treatments provided greater season-long control than early postemergence treatments in 1996 and 1998, but there was no difference in control between timings in 1997. Acetochlor applied PRE at 1,800 g ai/ha (1×) followed by nicosulfuron (35 g ai/ha) or sethoxydim (213 g ai/ha) at the registered rate (1×) or at one half of the registered rate (0.5×) consistently provided sufficient woolly cupgrass control to maximize corn yield, regardless of cultivation or POST herbicide application timing. Acetochlor PRE treatments, cultivated and noncultivated, followed by sethoxydim POST and cultivated acetochlor PRE treatments followed by nicosulfuron POST treatments provided sufficient control in each year to limit woolly cupgrass seed production to a level that decreased the predicted future seedbank density, regardless of herbicide rate or POST herbicide application timing. However, noncultivated acetochlor treatments followed by nicosulfuron applied at 1× followed by 0.5× or at 0.5× followed by 0.5× did not consistently reduce seed production to a level that decreased the predicted future seedbank density. These results suggest that the rate of sethoxydim can be reduced to 0.5× if a full rate of acetochlor is applied PRE with little effect on corn yield or woolly cupgrass seedbank density. However, reducing the rate of nicosulfuron to 0.5× following an application of acetochlor at the full rate or reducing both the acetochlor and nicosulfuron or sethoxydim rate to 0.5× is recommended only if a cultivation is planned. Nomenclature: Acetochlor; nicosulfuron; sethoxydim; woolly cupgrass, Eriochloa villosa (Thunb.) Kunth #3 ERBVI; corn, Zea mays L. ‘DeKalb SR404’, ‘DeKalb DK493SR’. Additional index words: Acetochlor, herbicide rate, herbicide application timing, nicosulfuron, sethoxydim, sethoxydim-resistant corn, woolly cupgrass seed production. Abbreviations: COC, crop oil concentrate; DAT, days after treatment; EPOST, early postemergence; LPOST, late postemergence; OM, organic matter; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate.

Interactions among weed, insect, and common rust treatments in sweet corn

Abstract Treatment interactions affecting endemic populations of annual grass and broadleaf weeds, corn rootworm larvae (CRW), corn earworm (CEW), European corn borer (ECB), and common rust in sweet corn were investigated in three field studies near Arlington, WI, in 1996 and 1997. In all environments, weed biomass was affected only by the weed control treatments with cultivation resulting in the highest weed biomass. Corn root damage was affected only by the CRW insecticide treatments in the early- and late-planted environments in 1997 (E97 and L97). Both weed control and ear insect (CEW and ECB) control treatments affected corn ear damage by CEW and ECB. In E97 and L97, more insect ear damage occurred in plots with 1× herbicide treatments than in cultivation treatments. In L97, the ear insect treatment decreased ear damage 55% compared to untreated plots. The interaction between ear insect and weed control treatments affected the number of CEW found per 10 ears in L97. The interaction between hybrid rust and weed control treatments influenced common rust severity in all environments. A hybrid rust by CRW by ear insect treatment interaction also affected common rust severity in E97 and L97. ‘Jubilee’ hybrid (rust-susceptible) corn treated with both insecticides had greater common rust severity than nontreated Jubilee corn. Sweet corn yield was affected most by weed control in all environments, with the lowest yields occurring in cultivated plots. Sweet corn yield did not differ between the 1× and ⅓× herbicide treatments in all environments. The interaction among hybrid rust by CRW by ear insect treatments also affected yield in E97 and L97. An important component of this interaction was the CRW treatment, as sweet corn yield was higher in treated than nontreated plots. The interactions in this study indicate that the best chances for developing comprehensive thresholds for sweet corn pests in the Midwest are for CEW, ECB, and common rust. Nomenclature: Cyanazine; metolachlor; permethrin, (3-phenoxyphenyl) methyl ( ± ) - cis, trans -3- ( 2, 2-dichloroethenyl ) -2, 2-dimethylcyclopropane-carboxylate; tefluthrin, (2,3,5,6-tetrafluoro-4-methylphenyl)methyl-(1α,3α)-(Z-(±)-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate; common rust, Puccinia sorghi Schw.; corn earworm, Helicoverpa zea Boddie; corn rootworm, Diabrotica spp.; European corn borer, Ostrinia nubilalis Hubner; sweet corn, Zea mays L. ‘Heritage’, ‘Jubilee’.