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.

Studies were conducted to compare foliar- and root-based absorption and translocation of SC-0051 in corn and soybean using radio-tracer techniques. Visual injury symptoms expressed in soybean by SC-0051 were bleaching in newly formed (meristematic) tissue followed by necrosis. Corn expressed little to no visual injury. SC-0051 was absorbed more rapidly by foliage of corn and soybean than by their roots. Although soybean absorbed more SC-0051 through roots than did corn, there was no difference between species in foliar absorption of SC-0051. SC-0051 was rapidly translocated throughout corn plants but was concentrated mainly in the meristematic tissue of soybean. Even though there were slight differences in absorption and translocation of SC-0051 in corn and soybean, it is likely that differential metabolism of the herbicide explains selectivity.

Nomenclature: SC-0051 (proposed name sulcotrione), 2-[2-chloro-4-(methylsulfonyl)benzoyl]-1,3-cyclohexanedione; corn, Zea mays L ‘Gutwein 69B’; soybean Glycine max (L.) Merr ‘Essex’.

Additional index words: Bleaching herbicides, radiolabeled herbicides, triketone herbicides.

Abbreviations: HAT, hours after treatment; POST, postemergence; PRE, preemergence.

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

Nomenclature: Hard fescue, Festuca longifolia var. Reliant; perennial ryegrass, Lolium perenne L.; tall fescue, Festuca arundinaceae Schreb. var. Kentucky-31; vole, Microtus sp.; peach, Prunus persica (L.) Batsch var. Candor.

Additional index words: Drive row, orchard floor management, summer annual weeds, tree row.

Abbreviations: OFMA, orchard floor management; PRE, preemergence; PRS, perennial ryegrass sod; SAW, summer annual weed; TCSA, trunk cross-sectional area.

Imazethapyr applied to the soil at 0, 35, 53, 70, 87, 105, and 140 g ai/ha followed by (fb) early-postemergence (EPOST) or late-postemergence (LPOST) applications at 140, 105, 87, 70, 53, 35, and 0 g ai/ha, respectively, was evaluated for weed control, crop tolerance, and grain yield in imidazolinone-tolerant rice. In drill- and water-seeded rice, imazethapyr effectively controlled barnyardgrass 91 to 97% with a soil fb EPOST or LPOST application except when applied at 105 fb 35 g/ha EPOST at 49 d after late-postemergence treatment. Rice yields were 5,920 and 3,920 kg/ ha in the drill-seeded study with a single application of imazethapyr at 140 g/ha EPOST in 2000 and 2001, respectively. These yields were greater than or equal to those from treatments with two imazethapyr applications.

Nomenclature: Imazethapyr; barnyardgrass, Echinochloa crus-galli (L.) Beauv #³ ECHCG; rice, Oryza sativa L. ‘93 AS-3510’, ‘CL 141’.

Additional index words: Acetolactate synthase, ALS, Clearfield rice.

Abbreviations: DAT, days after late-postemergence treatment; EPOST, early postemergence; fb, followed by; IT, imidazolinone tolerant; LPOST, late postemergence; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; SURF, surface.

The earliest possible seeding of wheat crops in the southern Australian dryland cropping zone is prevented by the lack of a weed control practice that adequately controls initial weed seedling emergence at the start of the growing season. The objective of this study was to determine the potential for using residual herbicides applied up to 1 mo before the start of the growing season to control rigid ryegrass seedlings that emerge after the season-opening rains. In a series of glasshouse studies, S-metolachlor and propyzamide were found to effectively persist on the soil surface through prolonged exposure to hot, dry, and intense sunlight conditions, preventing the establishment of rigid ryegrass seedlings. In addition, these herbicides caused little or no effect on subsequently seeded wheat. It also was determined that S-metolachlor had the potential to retain efficacy on rigid ryegrass seedlings after 12 wk of exposure on the soil surface to these conditions. These studies have identified two herbicides with the potential for use at the novel application timing, i.e., before the commencement of the growing season, in Mediterranean climates of southern Australia.

Nomenclature: S-Metolachlor; propyzamide; rigid ryegrass, Lolium rigidum Gaudin #³ LOLRI; wheat, Triticum aestivum cv. Spear.

Additional index words: Preseason treatment application, residual herbicide.

The effects of cogongrass foliage and root residue extracts on germination and radicle and coleoptile growth of barnyardgrass, browntop millet, bermudagrass, hemp sesbania, Italian ryegrass, and prickly sida were investigated in laboratory experiments. Liquid extracts of cogongrass foliage and root residues at concentrations of 0, 0.25, 0.5, 1, 2, 4, and 8% were evaluated on bermudagrass and Italian ryegrass. Effects of 8% foliage or root residue extracts were investigated on hemp sesbania, prickly sida, barnyardgrass, and browntop millet. Cogongrass residue (foliage and root) extracts at concentrations as low as 0.5% inhibited germination and seedling growth of bermudagrass and Italian ryegrass. Germination of bermudagrass and Italian ryegrass was reduced by as much as 62% and radicle and coleoptile growth by as much as 96% at the highest extract concentrations. Foliage and root residue extracts reduced germination of barnyardgrass, browntop millet, and prickly sida 52 to 64% and seedling growth by as much as 96%. Cogongrass extracts had no effect on germination or seedling development of hemp sesbania. Results indicate that extracts of cogongrass may contain allelochemicals that may contribute to its invasiveness and extreme competitiveness.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; bermudagrass, Cynodon dactylon (L.) Pers. # CYNDA; browntop millet, Brachiaria ramosa (L.) Stapf. # PANRA; cogongrass, Imperata cylindrica (L.) Beauv. # IMPCY; hemp sesbania, Sesbania exaltata (Raf.) Rydb. Ex A. W. Hill # SEBEX; Italian ryegrass, Lolium multiflorum Lam. # LOLMU; prickly sida, Sida spinosa L. # SIDSP.

Additional index words: Allelopathy, coleoptile, germination, plant extracts, plant residues, radicle.

Effects of soil pH and cation exchange capacity (CEC) on sunflower tolerance to sulfentrazone were investigated in a greenhouse study. Variables were soil pH (7.0, 7.3, 7.5, and 7.8), soil CEC (8.2, 13.7, 18.4, and 23.3 cmol/kg), and sulfentrazone rate (0, 105, 158, and 184 g ai/ha). Sulfentrazone-induced leaf chlorosis was affected by soil pH at 12 d after planting (DAP), but plants recovered, and earlier differences were not visible 9 d later. At 12 DAP, leaf chlorosis was 3 or 4% more severe in soils with pH 7.3 or higher compared with soils with pH 7.0 when averaged over both sulfentrazone rate and soil CEC. Leaf chlorosis resulting from sulfentrazone rates of 105, 158, and 184 g/ha was 17, 25, and 35% less at 23 cmol/kg than at 8.2 cmol/kg, respectively. Differences in chlorosis among sulfentrazone rates were greatest in soil with low CEC and lessened as soil CEC increased. Plants regained normal color over time, and newly emerging leaves were not affected. However, plant dry weights were reduced when sulfentrazone rate was ≥158 g/ha. Averaged over sulfentrazone rate and soil pH, sunflower dry weights were less when soil CEC was 8.2 compared with a CEC of 13.7 cmol/kg or higher, indicating a greater response at low CEC. Sunflower plant dry matter was not different in sulfentrazone-treated soil with a CEC above 13.7 cmol/kg. At the ranges tested, soil CEC had a considerably greater effect than did pH on sunflower tolerance to sulfentrazone.

Nomenclature: Sulfentrazone; sunflower, Helianthus annuus L. ‘Triumph 562’.

Additional index words: Bioactivity, chlorosis, crop injury, soil factors.

Abbreviations: CEC, cation exchange capacity; DAP, days after planting; OM, organic matter.

A replicated field trial was conducted to determine the effective rates of tebuthiuron for control of individual tall larkspur plants in the mountains near Emery, UT, Cedar City, UT, and Yampa, CO. The size of larkspur plants was measured, and tebuthiuron was applied to the base of each plant at 0.1, 0.21, and 0.5 g product/1,000 cm² of foliar crown cover. Tebuthiuron at 0.21 g/ 1,000 cm² rate controlled 62% of the plants. Tebuthiuron at 0.5 g/1,000 cm controlled 78% of the plants (2.5 g for an average-sized plant of 5,000 cm²). The high clay content of the soils at Emery or high organic matter content of soils at Cedar City or Yampa did not adversely affect efficacy.

Nomenclature: Tebuthiuron; tall larkspur, Delphinium barbeyi Huth #³ DELBA.

Additional index words: Cattle poisoning, poisonous plant.

Tolerance of six soft red winter wheat cultivars to AE F130060 00 plus AE F115008 00 applied at 12.5 plus 2.5 g ai/ha and 25 plus 5 g ai/ha, respectively, at the two- to three-tiller stage was examined under weed-free conditions at four locations over 2 yr. Visible injury averaged 5 and 15% 3 wk after treatment (WAT) in years 1 and 2, respectively. Injury was 2% or less 10 WAT. No differences among cultivars were noted for visible injury, and AE F130060 00 plus AE F115008 00 did not reduce grain yield in year 1. In year 2, averaged over herbicide rates, grain yields of the cultivars ‘Coker 9663’, ‘Pioneer 2580’, ‘Coker 9704’, ‘Pioneer 2684’, ‘FFR 555’, and ‘Jackson’ were reduced 3, 5, 6, 8, 10, and 16%, respectively. The yield reduction for Jackson was different from those for the other cultivars. Yield reduction was attributed to reduced numbers of kernels per spike.

Nomenclature: AEF 115008 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; wheat, Triticum aestivum L. ‘Coker 9663’, ‘Coker 9704’, ‘FFR 555’, ‘Jackson’, ‘Pioneer 2580’, ‘Pioneer 2684’.

Additional index words: Cultivar response, yield components.

Abbreviations: WAT, weeks after treatment.

Studies were conducted to determine whether glufosinate treatments to glufosinate-resistant cotton caused changes in floral morphology, pollen viability, and seed set. Four glufosinate treatments were included: (1) glufosinate applied postemergence over the top (POST) at the four-leaf stage, (2) glufosinate applied POST at the eight-leaf stage, (3) the first two treatments sequentially, and (4) a POST application at the four-leaf stage followed by (fb) a postemergence-directed stem application (PDS) at the eight-leaf stage. Glufosinate was consistently applied at 0.49 kg ai/ha. A nontreated control was included. Glufosinate treatments did not affect stigma height, length of the staminal column, or pollen viability. However, the distance from the top anther to the tip of the stigma was less in plants treated with an eight-leaf POST treatment than in nontreated plants, although this difference is not likely to influence pollen deposition because in both cases anthers reached above the stigma tip. Plants receiving four-leaf POST fb eight-leaf PDS treatment with glufosinate had eight seeds per boll less than nontreated plants; however, the more rigorous four-leaf POST fb eight-leaf POST treatment did not differ from the nontreated in seeds per boll.

Nomenclature: Glufosinate; cotton, Gossypium hirsutum L.

Additional index words: Glyphosate, herbicide-resistant crops, transgenic crops.

Abbreviations: fb, followed by; PDS, postemergence-directed stem application; POST, postemergence over the top.

Germination experiments were conducted in petri dishes to test the effect of vetiver oil and one of its minor components, nootkatone, on six common weed species. Vetiver oil inhibited germination of redroot pigweed, common lambsquarters, giant ragweed, pitted morningglory, and velvetleaf. Nootkatone, at much higher concentrations than it occurs in the oil, exhibited germination inhibition for all weed species except velvetleaf. Redroot pigweed was the most sensitive species with germination inhibition at 0.1 to 1.0 mg/ml of vetiver oil and nootkatone. At 1.0 to 8.0 mg/ml, nootkatone reduced germination of giant ragweed by 24 to 92%, whereas vetiver oil reduced the germination only by 6 to 11%. Vetiver oil and nootkatone also inhibited seedling expansion of redroot pigweed and common lambsquarters. No significant inhibition of germination and seedling expansion was found for sicklepod. These laboratory studies provide preliminary evidence that nootkatone and vetiver oil may have use as herbicides.

Nomenclature: Nootkatone, 5,6 dimethyl-8-isopropenylbicyclo[4.4.0]dec-1-en-3-one; common lambsquarters, Chenopodium album L. #³ CHEAL; giant ragweed, Ambrosia trifida L. # AMBTR; pitted morningglory, Ipomoea lacunosa L. # IPOLA; redroot pigweed, Amaranthus retroflexus L. # AMARE; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby # CASOB; velvetleaf, Abutilon theophrasti Medicus # ABUTH.

Additional index words: Amaranthus retroflexus, Ambrosia trifida, Chenopodium album, essential oil, herbicidal activity, sesquiterpene.

Abbreviations: I₅₀, concentration required to inhibit 50% of seed germination.

An experiment was conducted at five locations in North Carolina during 2000 and 2001 to evaluate weed control, crop injury, and cotton yield. Weed management systems included different combinations of pyrithiobac preemergence (PRE), fluometuron PRE, CGA-362622 postemergence (POST), pyrithiobac POST, and monosodium salt of methylarsonic acid (MSMA) plus prometryn applied late POST-directed (LAYBY). At Goldsboro in 2000, cotton was injured 74 to 78% by CGA-362622 POST when evaluated 4 to 7 d after treatment (DAT). Injury at Clayton, Goldsboro, and Lewiston in 2001 and Rocky Mount in 2000 was less than 16% 4 to 7 DAT with the same treatment and was not apparent by 62 DAT. CGA-362622 controlled common lambsquarters, common ragweed, Palmer amaranth, sicklepod, smooth pigweed, and Ipomoea species including entireleaf, ivyleaf, and pitted morningglory, and the addition of pyrithiobac to the herbicide system, either PRE or POST, increased control of Amaranthus species, jimsonweed, and prickly sida. CGA-362622 did not control jimsonweed or prickly sida. Fluometuron PRE, pyrithiobac PRE, and MSMA plus prometryn LAYBY were beneficial for increasing weed control and cotton lint yields. Prometryn plus MSMA LAYBY increased control of common ragweed, entireleaf morningglory, jimsonweed, pitted morningglory, and smooth pigweed and provided higher cotton yields than similar systems without a LAYBY. The greatest weed control and greatest cotton lint yields required complete weed management systems that included a combination of PRE, POST, and LAYBY treatments.

Nomenclature: CGA-362622, N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; fluometuron; monosodium salt of methylarsonic acid; prometryn; pyrithiobac; common lambsquarters, Chenopodium album L. #³ CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; jimsonweed, Datura stramonium L. # DATST; Palmer amaranth, Amaranthus palmerii L. # AMAPA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; cotton, Gossypium hirsutum L. ‘Paymaster 1218 BG/RR’, ‘Fibermax 989’, ‘Stoneville 474’.

Additional index words: Crop injury, crop yield.

Abbreviations: DAT, days after treatment; EPOST, early postemergence; fb, followed by; LAYBY, late postemergence directed; MSMA, monosodium salt of methylarsonic acid; POST, postemergence; PRE, preemergence.

Knowing when weed species are likely to emerge can aid in developing effective integrated weed management programs. When using nonresidual herbicides such as glyphosate for weed control, treatment timing is critical. This study characterized the emergence patterns of common lambsquarters, common sunflower, common waterhemp, eastern black nightshade, ivyleaf morningglory, shattercane, and woolly cupgrass in soybean, in relation to common glyphosate application timings. Approximately 90% or more of common lambsquarters, common sunflower, and common waterhemp seedlings emerged before the end of May, both in 2000 and 2001. Both ivyleaf morningglory and shattercane emerged from late April to mid-August, allowing these species to avoid glyphosate applications timed to prevent early-season weed competition. Avoidance through periodicity in emergence underscores the importance of integrating multiple tactics to ensure that difficult to manage weeds are not selected for in this management system.

Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L.#³ CHEAL; common sunflower, Helianthus annuus L. # HELAN; common waterhemp, Amaranthus rudis Sauer # AMATA; eastern black nightshade, Solanum ptycanthum Dun. ex DC. # SOLPT; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; shattercane, Sorghum bicolor (L.) Moench # SORVU; woolly cupgrass, Eriochloa villosa (Thunb.) Kunth # ERBVI; soybean, Glycine max (L.) Merr. ‘Asgrow 3003RR’.

Additional index words: Cohorts, germination, growing degree days, heat units, integrated weed management, periodicity.

Abbreviations: DAP, days after planting; IWM, integrated weed management; POST, postemergence.

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

Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L.#³ CHEAL; common sunflower, Helianthus annuus L. # HELAN; common waterhemp, Amaranthus rudis Sauer # AMATA; eastern black nightshade, Solanum ptycanthum Dun. ex DC. # SOLPT; ivyleaf morningglory, Ipomoea hederacea [L.] Jacq. # IPOHE; shattercane, Sorghum bicolor [L.] Moench # SORVU; woolly cupgrass, Eriochloa villosa [Thunb.] Kunth # ERBVI; soybean, Glycine max (L.) Merr. ‘Asgrow 3003RR’.

Additional index words: Differential sensitivity, fecundity, herbicide tolerance, population dynamics, relative abundance.

Abbreviations: DAP, days after planting; POST, postemergence; SB_t, seedbank at time = 0; SB_{t 1}, seedbank at time = 1 yr.

Experiments were conducted from 2000 to 2002 at two locations each year to determine if lactofen and imazethapyr injury to soybean could be detected using digital aerial imagery and ground-based optical remote sensing. Lactofen and imazethapyr were applied at base rates of 105 and 71 g/ha, respectively, and at 0, 2X, and 4X rates. Treated plots were evaluated between 7 and 21 d after treatment for crop injury using a ground-based radiometer and a system using computer analysis of digital aerial imagery. Both the ground-based radiometer and the digital aerial imagery were effective in detecting herbicide injury under most conditions. The digital aerial imagery system was found to be more sensitive in detecting herbicide injury than the ground-based radiometer system. Herbicide or herbicide rate had a significant effect on normalized differential vegetation indices (NDVI) derived from digital aerial imagery in four of four site-years. NDVI values derived from a multispectral ground-based radiometer were significant for herbicide or herbicide rate in four of six site-years. NDVI values from treated plots were subtracted from the NDVI value of the untreated check to generate a ΔNDVI. The resulting ΔNDVI values from the ground-based radiometer system were significant for herbicide or herbicide rate in six of six site-years. Neither optical remote-sensing system was effective at estimating actual application rates of lactofen and imazethapyr across a broad range of field and weather conditions due to temporal and spatial variability in crop response to the herbicides.

Nomenclature: Imazethapyr; lactofen; soybean, Glycine max (L.) Merr. ‘Asgrow 2001’, ‘Becks 243’, ‘Becks 323’, ‘Mycogen 5251’, ‘Pioneer 19B91’, ‘Pioneer 92B38’.

Additional index words: Aerial imagery, light reflectance, vegetation index.

Abbreviations: Fc, fractional cover; LAI, leaf area index; NDVI, normalized differential vegetation index; NIR, near-infrared; SVI, spectral vegetation index.

Field trials were conducted in Virginia to evaluate trumpetcreeper control with glyphosate and conventional herbicide systems in double-crop glyphosate-resistant soybean. When compared with the untreated control, none of the conventional herbicide systems evaluated in these trials provided any reductions in the trumpetcreeper stem density at 1 yr after treatment (YAT). Glyphosate systems generally provided much higher levels of trumpetcreeper stem reduction than conventional herbicide systems. By 1 YAT, densities of trumpetcreeper that received conventional herbicide treatments ranged from 97 to 141% of the initial population, whereas densities of trumpetcreeper that received preemergence (PRE) followed by postemergence (POST) or POST-only applications of the isopropylamine (IPA) or diammonium (DIA) salts of glyphosate ranged from 30 to 66% of the initial population. However, PRE applications of the IPA or DIA salts of glyphosate generally provided lower levels of trumpetcreeper stem reduction than PRE followed by POST or POST-only applications. These results indicate that glyphosate applications made later in the growing season will provide greater trumpetcreeper stem reductions than those made at or close to soybean planting in double-crop soybean production systems. Glyphosate systems did not provide higher soybean yields than the untreated control that contained trumpetcreeper only when densities averaged 6 trumpetcreeper stems/m² in 2000, but 12 of the 16 glyphosate-containing treatments provided higher soybean yields than the untreated control that contained trumpetcreeper only when densities averaged 13 stems/m² in 2001.

Nomenclature: Glyphosate; imazamox; lactofen; paraquat; trumpetcreeper, Campsis radicans (L.) Seem. ex Bureau #³ CMIRA; soybean, Glycine max (L.) Merr. ‘Asgrow 4902 RR’, ‘Asgrow 5401 RR’.

Additional index words: Acifluorfen, cloransulam, fomesafen, formulations, herbicide application timing, no-till, perennial weed control.

Abbreviations: DIA, diammonium; IPA, isopropylamine; POST, postemergence; PRE, preemergence; YAT, years after treatment.

Field studies conducted for two growing seasons evaluated the effect of 2,4-D applied at 1.6 kg ai/ha to ‘LCP 85-384’ sugarcane 7, 5, 3, and 1 wk before planting (WBP). Sugarcane was planted in mid September using both whole stalks and billet (45 cm) stem sections. When 2,4-D was applied 5 wk or closer to planting, sugarcane shoot emergence and population averaged across planting methods and years were reduced up to 28 wk after planting (WAP) relative to the nontreated control. By 52 WAP, sugarcane had compensated and stalk population was equivalent among treatments. Sugarcane height in response to 2,4-D varied between years, and only in 2001 at 52 WAP was a height reduction observed when 2,4-D was applied 1, 3, or 5 WBP. Crop injury in 2001 was further reflected in reduced sugarcane yield (at least 11%) and sugar yield (at least 12%) more than 1 yr after 2,4-D had been applied 5 wk or closer to harvest of sugarcane for seed. Sugarcane and sugar yields were equivalent for the nontreated control and the 7 WBP 2,4-D treatment in 2001, but 2,4-D application in 2002 did not negatively affect yield. Even though sugarcane shoot populations across the growing seasons were consistently higher for the billet planting system, yields averaged across 2,4-D application timings were greater for billets (18%) compared with whole stalks only for the first year. Because 2,4-D can have a residual effect on sugarcane yield more than 1 yr after the initial foliar application, a 7-wk period should be allowed between herbicide application and harvest of LCP 85-384 for billet or whole-stalk planting.

Nomenclature: 2,4-D; sugarcane, Saccharum interspecific hybrids ‘LCP 85-384’.

Additional index words: Crop tolerance.

Abbreviations: WAP, weeks after planting; WBP, weeks before planting.

Three experiments were conducted in Lewiston, NC, from 1999 through 2002 to evaluate the influence of various application timings of flumioxazin preplant (PP) and postemergence-directed spray (PDS) on cotton injury. In experiment 1, flumioxazin was evaluated in a reduced-tillage system at 71, 105, or 140 g ai/ha in mixture with glyphosate, applied at 28, 14, or 7 d before planting (DBP), followed by irrigation at cotton emergence. Flumioxazin applied PP at any rate and irrigated at emergence injured cotton less than 7% at 2 wk after emergence (WAE) and less than 6% 5 WAE. In experiment 2, flumioxazin was evaluated in a conventional-tillage system at 71 or 105 g/ha as a PDS treatment applied to dry soil, wet soil, and dry soil irrigated immediately after application when cotton was 20 to 30 cm height. Cotton treated with flumioxazin PDS at either rate applied to dry soil, wet soil, or dry soil followed immediately by irrigation was not injured. In the third experiment, flumioxazin at 71 g/ha alone or in mixture with glyphosate at 1.12 g/ha was applied at 30, 21, 14, and 0 DBP in a conventional-tillage system. Flumioxazin applied alone or in mixture with glyphosate applied at any time did not injure cotton. In all experiments, cotton lint yields were not influenced by herbicide treatment.

Nomenclature: Flumioxazin; glyphosate; cotton, Gossypium hirsutum L., ‘Deltapine 5415 RRBG’, ‘Paymaster 1218 RRBG’, ‘Suregrow 125’.

Additional index words: Burndown treatment, LAYBY treatment.

Abbreviations: COC, crop oil concentrate; DBP, days before planting; MSMA, monosodium salt of methylarsonic acid; NIS, nonionic surfactant; PDS, postemergence-directed spray; POST, postemergence; PP, preplant; PRE, preemergence; WAE, weeks after emergence.

Field experiments were conducted in 1999 and 2000 to evaluate and adapt the Herbicide Application Decision Support System (HADSS®) program for Texas Southern High Plains cotton production. Weed management systems (in glyphosate-resistant, bromoxynil-resistant, and nontransgenic cotton varieties) included trifluralin preplant incorporated (PPI) followed by (fb) HADSS postemergence-topical (POST) recommendations (PPI fb POST HADSS), HADSS recommendations alone (POST HADSS), and Texas Agricultural Experiment Station (TAES) recommendations for the Texas Southern High Plains. In both years, effective season-long weed control was achieved with all weed management systems in the glyphosate-resistant variety, but only the PPI fb POST HADSS and TAES weed management systems controlled Palmer amaranth and devil's-claw in the bromoxynil-resistant and nontransgenic varieties, compared with POST HADSS alone. No differences in cotton lint yield or net returns over weed control costs were observed with weed management systems across variety in 1999; however, in general, the glyphosate-resistant and nontransgenic varieties produced higher yields and net returns than the bromoxynil-resistant variety. In 2000, plots from the TAES weed management system produced higher lint yields than the plots of PPI fb POST HADSS recommendations in the glyphosate- and bromoxynil-resistant varieties, but plots of all management systems yielded similarly in the nontransgenic variety. In 2000, plots from the TAES system produced the highest net returns in the glyphosate- and bromoxynil-resistant varieties. In the nontransgenic variety, the PPI fb POST HADSS and TAES weed management systems produced higher net returns over weed control costs than the POST HADSS system.

Nomenclature: Bromoxynil; glyphosate; trifluralin; Palmer amaranth, Amaranthus palmeri S. Wats. #³ AMAPA; devil's-claw, Proboscidea louisianica (Mill.) Thellung # PROLO; cotton, Gossypium hirsutum L. ‘Paymaster 2326RR’, ‘Stoneville BXN 47’, ‘Paymaster HS26’.

Additional index words: Computer decision aid, herbicide-tolerant cotton, HERB.

Abbreviations: fb, followed by; HADSS, Herbicide Application Decision Support System; NHA, no herbicide application; PDIR, postemergence directed; POST, postemergence topical; PPI, preplant incorporated; PRE, preemergence; TAES, Texas Agricultural Experiment Station.

An experiment was initiated at two sites in 1998 near Crowder, MS, to evaluate the effect of in-season applications of glyphosate on redvine populations in glyphosate-resistant soybean. In the year of application, most treatments containing multiple in-season applications of glyphosate reduced redvine populations. However, at 16 mo after treatment (October 1999), 0.63 kg ai/ha paraquat preplant followed by sequential postemergence applications of glyphosate at 1.1 and 2.2 kg ai/ ha reduced redvine stems by 45% compared with the untreated check. Redvine control with this treatment also was comparable with 2.2 kg ai/ha dicamba preharvest. The same results were observed at 12 and 14 mo after application with many treatments containing sequential applications of glyphosate, but glyphosate at 1.1 and 2.2 kg ai/ha was the only in-season treatment to maintain redvine suppression during the entire growing season the year after herbicide application. However, a number of treatments delayed redvine reinfestation; thus, soybean yield was improved over the untreated check with all treatments from the previous year containing in-season applications of glyphosate, except for 0.84 kg/ha followed by 0.56 kg/ha. Increasing rates of in-season glyphosate applications to 1.1 followed by 2.2 kg/ha will adequately suppress redvine populations in glyphosate-resistant soybean, controlling annual weeds in the process.

Nomenclature: Redvine, Brunnichia ovata (Walt.) Shinners #³ BRVCI; soybean, Glycine max (L.) Merr. ‘Asgrow 4701’, ‘Delta & Pine Land 5644’.

Additional index words: Perennial weeds, glyphosate.

Abbreviations: POST, postemergence.

Field experiments were conducted in 2001 and 2002 to evaluate the efficacy of herbicides on protoporphyrinogen oxidase (protox, EC 1.3.3.4) inhibitor–resistant common waterhemp in corn and soybean. All corn herbicides tested gave greater than 90% common waterhemp control by 8 wk after postemergence herbicide treatment (WAPT). In soybean, common waterhemp control was less than 40% by 8 WAPT with postemergence protox-inhibiting herbicides lactofen and acifluorfen. However, preemergence protox-inhibiting herbicides sulfentrazone and flumioxazin gave greater than 85% common waterhemp control in both years. The greatest common waterhemp control in soybean was with glyphosate alone, alachlor metribuzin, alachlor followed by (fb) glyphosate, and S-metolachlor metribuzin fb glyphosate.

Nomenclature: Acifluorfen; alachlor; flumioxazin; glyphosate; lactofen; S-metolachlor; metribuzin; sulfentrazone; common waterhemp, Amaranthus rudis Sauer #³ AMATA; corn, Zea mays L. # ZEAMX ‘RRX740RR’; soybean, Glycine max (L.) Merr. ‘Asgrow 3701’.

Additional index words: Acetochlor, ALS-resistance, atrazine, bromoxynil, carfentrazone, clomazone, clopyralid, dicamba, diflufenzopyr, dimethenamid-P, flumetsulam, glufosinate, halosulfuron-methyl, imazamox, imazaquin, imazethapyr, isoxaflutole, mesotrione, pendimethalin, primisulfuron-methyl, prosulfuron, protox-resistance, thifensulfuron-methyl.

Abbreviations: ALS, acetolactate synthase; proto, protoporphyrin IX; protogen, protoporphyrinogen IX; protox, protoporphyrinogen oxidase; WAPT, weeks after postemergence herbicide treatment.

Field trials were conducted to compare the effect of various soil fumigants along with in-bed pebulate and row-middle metribuzin applications on purple nutsedge control and on tomato and bell pepper growth and yield. Treatments consisted of combinations of soil fumigants, pebulate, and metribuzin. Fumigants levels were (1) untreated control, (2) methyl bromide (MBr) chloropicrin (Pic) (67 33%, respectively), (3) Pic, (4) metham, (5) dazomet, and (6) 1,3-dichloropropene (1,3-D) Pic (83 17%, respectively). Pebulate levels were either applied in-bed or not applied. Row middles were either sprayed with metribuzin or untreated. In both crops, purple nutsedge populations were independently influenced by fumigants and pebulate applications, with the highest number of purple nutsedge plants in the untreated control. The addition of pebulate reduced purple nutsedge populations in all treatments. In tomato trials, the yield was affected by fumigants, with the highest losses (53 and 50% reductions in fruit number and weight) observed in the nonfumigated control. In pepper trials, fruit number and weight were individually influenced by fumigants and metribuzin sprayings. Application of metribuzin to row middles increased yields 10% relative to nontreated plots.

Nomenclature: Purple nutsedge, Cyperus rotundus L. #³ CYPRO; pepper, Capsicum annuum L.; tomato, Lycopersicon esculentum Mill.

Additional index words: Chloropicrin, dazomet, 1,3-dichloropropene, interference, metham, metribuzin, pebulate, soil fumigants.

Abbreviations: 1,3-D, 1,3-dichlopropene; MBr, methyl bromide; Pic, chloropicrin; WAT, weeks after transplanting.

Field studies were conducted from 1998 to 2000 in Tennessee, North Carolina, Arkansas, and Oklahoma to determine the effects of sulfentrazone carryover to a cotton rotational crop from sulfentrazone applied the previous year. Sulfentrazone applied the previous year at 400 g/ha caused no yield loss in Tennessee, >30% yield reduction in Oklahoma, and 20% yield loss in Arkansas and North Carolina. In most experiments in this study, visual evaluations of injury closely correlated with final cotton lint yield (r² =0.84).

Nomenclature: Sulfentrazone; cotton, Gossypium hirsutum L.

Additional index words: Bioassay, herbicide carryover, PROTOX inhibitor, rotational crops.

Effects of cogongrass foliage and rhizome plus root residues on germination and shoot and root growth of barnyardgrass, bermudagrass, browntop millet, hemp sesbania, Italian ryegrass, and prickly sida were investigated in greenhouse experiments. Ground residues of dried cogongrass foliage and rhizomes plus roots were mixed separately with sterilized sand to obtain residue concentrations of 0, 0.25, 0.5, 1, 2, 4, and 8%. These residue concentrations were investigated on bermudagrass and Italian ryegrass, and the 8% residue concentrations were also evaluated on hemp sesbania, prickly sida, barnyardgrass, and browntop millet. Foliage and rhizome plus root residues at concentrations as low as 0.25% inhibited seed germination and shoot and root growth of all species except hemp sesbania. Germination of bermudagrass and Italian ryegrass was reduced by as much as 97% and shoot and root growth by as much as 94% at the highest residue concentrations. Rhizome plus root residues reduced germination and shoot and root growth of bermudagrass and Italian ryegrass more than foliage residues. Foliage and rhizome plus root residues reduced germination and shoot and root biomass of prickly sida, barnyardgrass, and browntop millet at similar levels. Results indicate that cogongrass tissue may contain allelochemicals that contribute to its invasiveness and extreme competitiveness.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; bermudagrass, Cynodon dactylon (L.) Pers. # CYNDA; browntop millet, Brachiaria ramosa (L.) Stapf. # PANRA; cogongrass, Imperata cylindrica (L.) Beauv. # IMPCY; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; Italian ryegrass, Lolium multiflorum Lam. # LOLMU; prickly sida, Sida spinosa L. # SIDSP.

Additional index words: Allelochemical, allelopathy, germination, growth inhibition, plant residues, root growth, seedling, shoot growth.

Abbreviations: DAP, days after planting; DDW, double-distilled water.

Glyphosate and paraquat herbicide drift injury to crops may substantially reduce growth or yield. Determining the type and degree of injury is of importance to a producer. This research was conducted to determine whether remote sensing could be used to identify and quantify herbicide injury to crops. Soybean and corn plants were grown in 3.8-L pots to the five- to seven-leaf stage, at which time, applications of nonselective herbicides were made. Visual injury estimates were made, and hyperspectral reflectance data were recorded 1, 4, and 7 d after application (DAA). Several analysis techniques including multiple indices, signature amplitude (SA) with spectral bands as features, and wavelet analysis were used to distinguish between herbicide-treated and nontreated plants. Classification accuracy using SA analysis of paraquat injury on soybean was better than 75% for both 1/2- and 1/8× rates at 1, 4, and 7 DAA. Classification accuracy of paraquat injury on corn was better than 72% for the 1/2× rate at 1, 4, and 7 DAA. These data suggest that hyperspectral reflectance may be used to distinguish between healthy plants and injured plants to which herbicides have been applied; however, the classification accuracies remained at 75% or higher only when the higher rates of herbicide were applied. Applications of a 1/2× rate of glyphosate produced 55 to 81% soybean injury and 20 to 50% corn injury 4 and 7 DAA, respectively. However, using SA analysis, the moderately injured plants were indistinguishable from the uninjured controls, as represented by the low classification accuracies at the 1/8-, 1/32-, and 1/64× rates. The most promising technique for identifying drift injury was wavelet analysis, which successfully distinguished between corn plants treated with either the 1/8- or the 1/2× rates of paraquat compared with the nontreated corn plants better than 92% 1, 4, and 7 DAA. These analysis techniques, once tested and validated on field scale data, may help determine the extent and the degree of herbicide drift for making appropriate and, more importantly, timely management decisions.

Nomenclature: Corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Additional index words: Glyphosate, hyperspectral imagery, indices, paraquat, ROC curve, wavelet analysis.

Abbreviations: DAA, days after application; DINO, differential index of normalized observations; DWT, discrete wavelet transform; EPSP, 5-enolpyruvylshikimate-3-phosphate; LDA, linear discriminant analysis; NDVI, normalized difference vegetation index; NIR, near-infrared; POST, postemergence; ROC, receiver operator characteristics; SA, signature amplitudes.

Split application of herbicides for wild oat control may minimize wild oat competition with wheat while reducing the number of wild oat seeds returned to the soil. Field experiments were conducted in 2000 and 2001 to evaluate the effects of CGA-184927, fenoxaprop-P, flucarbazone, and ICIA 0604 at labeled and reduced rates on wild oat control, wild oat seed rain, and wheat yield. Each herbicide was applied once at 25, 33, and 100% of the labeled rate at the two-leaf stage of wild oat or split applied at 50 and 66% of the full rate as two equal applications. Excellent full-season wild oat control was obtained with CGA-184927, flucarbazone, and ICIA 0604 applied twice at reduced rates. ICIA 0604 or CGA-184927 split applied at 25 and 33% rates (totaled 50 and 66% of the full rate) provided wild oat control equal to one application of labeled rates. Wild oat seed rain was similar among all herbicide treatments, except plots treated with fenoxaprop-P once at 25 and 33% rates where seed rain was higher and equal to 47% of untreated plots. Wheat yields and net returns were highest and similar after treatment with CGA-184927 or ICIA 0604 applied either once at the labeled rate or split applied at 25 or 33% rates.

Nomenclature: Fenoxaprop-P; ICIA 0604 (proposed name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)cyclohex-2-enone; CGA-184927 (proposed name, clodinafop-propargyl), propanoic acid, 2-[4-[(5-chloro-3-fluoro-2-pyridinyl)oxy]phenoxy]-2-propynyl ester; flucarbazone; wild oat, Avena fatua L. #³ AVEFA; hard red spring wheat, Triticum aestivum L.

Additional index words: Hard red spring wheat, reduced herbicide rates.

Abbreviation: DAT, days after treatment.

Field trials were conducted in 2000 and 2001 in New Jersey to evaluate quinclorac and siduron for large crabgrass control in summer-seeded creeping bentgrass (‘L-93’). Bentgrass was surface seeded on June 30 and June 26 in 2000 and 2001, respectively. Treatments consisted of preemergence (PRE) applications of siduron at 3.4, 5.0, and 6.7 kg ai/ha and PRE and postemergence (POST) applications of quinclorac at 0.4, 0.6, 0.8, and 1.7 kg ai/ha. POST applications were timed to a crabgrass growth stage of three leaves to one tiller. All POST quinclorac applications included methylated seed oil at 1% (v/v). Percent crabgrass cover in untreated plots at 30 d after planting (DAP) averaged 10 and 50% in 2000 and 2001, respectively. All PRE treatments, with the exception of quinclorac applied at 0.4 kg/ha in 2001, reduced crabgrass cover by 80% or more at 30 DAP. Crabgrass control decreased in late August when siduron and quinclorac were applied at the lower rates in 2001. PRE quinclorac applications at the rate of 0.6 kg/ha or higher in 2000 or 1.7 kg/ha in 2001 caused significant thinning of the bentgrass stand at 30 DAP. All POST quinclorac treatments provided excellent crabgrass control in 2000, but the 0.8-kg/ha or higher rate was required to reduce crabgrass infestation levels by at least 80% in 2001. All POST quinclorac applications caused significant chlorosis to the creeping bentgrass in both years. However, significant thinning of the bentgrass stand was not evident, with the exception of 1.7 kg/ha, in 2001. These studies suggest that PRE applications of siduron should be used for the highest level of creeping bentgrass safety in summer restoration projects. The use of quinclorac should be limited to POST applications to control escaped crabgrass once the newly emerging creeping bentgrass has become well established.

Nomenclature: Quinclorac; siduron; Creeping bentgrass, Agrostis stolonifera L. #³ AGSST ‘L-93’; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA.

Additional index words: Bentgrass fairway renovation, herbicide response.

Abbreviations: DAE, days after emergence; DAP, days after planting; DAT, days after treatment; POST, postemergence; PRE, preemergence.

Biennial wormwood has become an important weed for soybean producers in the northern Great Plains states of the United States. Research was conducted at Fargo, Leonard, and Wyndmere, ND, in 2000 and 2001 to evaluate postemergence control of biennial wormwood in soybean. Biennial wormwood densities at Fargo, Leonard, and Wyndmere were 290, 290, and 130 plants/m² in 2000 and 22, 670, and 88 plants/m² in 2001, respectively. Across years, biennial wormwood control with postemergence herbicides 4 wk after treatment was 81 to 97% at Fargo, 5 to 89% at Leonard, and 2 to 95% at Wyndmere. Biennial wormwood control was greater at Fargo than at the other locations probably because of smaller seedling size at the time of treatment. Bentazon split applied at the rate of 560 g ai/ha followed by 560 g/ha approximately 12 d after the first treatment generally provided the least amount of injury to soybean, the greatest control of biennial wormwood, and the fewest escaped plants. Lactofen at 220 g ai/ha or split applied at 110 g/ha followed by 110 g/ha approximately 12 d after the first treatment provided 84% or greater biennial wormwood control at Fargo but less than 40% control at Leonard and Wyndmere. The 4.5:1 bentazon plus acifluorfen premix full-rate and split treatments provided slightly better control than the 2:1 bentazon plus acifluorfen premix full-rate and split treatments. High levels of biennial wormwood control can be achieved with a better understanding of seedling emergence patterns and by targeting postemergence herbicide applications to seedlings less than 5 cm tall.

Nomenclature: Acifluorfen; bentazon; lactofen; biennial wormwood, Artemisia biennis Willd. #³ ARTBI; soybean, Glycine max (L.) Merr.

Additional index words: AMARE, ARTBI, postemergence, SOLPT, split treatments, weed control, weed density, XANST.

Abbreviations: DOT, day of treatment; WAT, weeks after treatment.

Field experiments were conducted near Scottsbluff, NE, in 2001 and 2002 to compare economic aspects of glyphosate applied to different glyphosate-resistant sugar beet cultivars with that of conventional herbicide programs applied to near-equivalent, non–glyphosate-resistant conventional cultivars. Glyphosate applied two or three times at 2-wk intervals, beginning when weeds were 10 cm tall, provided excellent weed control, yield, and net economic return regardless of the glyphosate-resistant sugar beet cultivar. All conventional herbicide treatments resulted in similar net economic returns. Although the conventional sugar beet cultivars ‘HM 1640’ and ‘Beta 4546’ responded similarly to herbicide treatments with respect to sucrose content, ‘Beta 4546RR’ produced roots with 1% more sucrose than ‘HM 1640RR’. When averaged over herbicide treatments, a producer planting Beta 4546RR could afford to pay US $185/ha more for glyphosate-resistant technology as could a producer planting HM 1640RR. When averaged over cultivars and herbicide treatments, it is estimated that a producer could afford to pay an additional US $385/ha for glyphosate-resistant technology without decreasing net return.

Nomenclature: Glyphosate; sugar beet, Beta vulgaris (L.) ‘Beta 4546’, ‘Beta 4546RR’, ‘HM 1640’, ‘HM 1640RR’.

Additional index words: Herbicide-tolerant crops, technology fee, weed management, clopyralid, desmedipham, ethofumesate, phenmedipham, triflusulfuron.

Abbreviations: DES, desmedipham; fb, followed by; PHEN, phenmedipham; R_G, gross return; TRIF, triflusulfuron; Y, root yield.

The activity of emulsifiable concentrate (EC) formulation of pendimethalin was studied using a petri dish bioassay based on root response of corn, oat, sorghum, and sugar beet grown in soil. Furthermore, the oat bioassay was used to determine the activity of EC, microencapsulated (ME), and water-dispersible granule (WDG) formulations of pendimethalin. Also, field persistence in soil of these pendimethalin formulations was studied with petri dish and pot bioassays, based on root response of oat and sugar beet. All bioassays indicated that activity of all pendimethalin formulations was increased with increasing herbicide concentration. In silty clay loam soil, oat and sugar beet exhibited the highest sensitivity to EC-pendimethalin concentrations and corn the lowest; sorghum showed intermediate herbicide sensitivity. EC of pendimethalin showed the highest activity on oat and ME pendimethalin the lowest; WDG-pendimethalin showed similar activity to that of ME pendimethalin. Field persistence was significantly increased with increasing rate of application, but it was slightly increased by the ME formulation.

Nomenclature: Pendimethalin; corn, Zea mays L. ‘Pioneer Costanza’; oat, Avena sativa L. ‘Kassandra’; sorghum, Sorghum bicolor L. ‘5515’; sugar beet, Beta vulgaris L. ‘Bianca’.

Additional index words: Microencapsulated formulation, pendimethalin.

Abbreviations: DAT, days after treatment; EC, emulsifiable concentrate; GI₁₀, days after treatment for 10% oat root growth inhibition; GR₅₀, herbicide concentration required to give 50% inhibition of plant indicator root growth; ME, microencapsulated; PRE, preemergence; WDG, water-dispersible granule.

Field studies were conducted to assess two sulfur-containing additives for use with glyphosate applied postemergence to glyphosate-resistant cotton for the control of sicklepod and yellow nutsedge. Neither diammonium sulfate (AMS) nor ammonium thiosulfate (ATS), both applied at 2.24 kg/ha, increased control of either species. Effective control of both species was dependent on glyphosate (isopropylamine salt) rate alone, with optimum control at 1.26 kg ae/ha. Plant-mapping data further indicated that sulfur-containing additives generally had no effect on either cotton fruiting patterns or yield. However, applying glyphosate at any rate did increase seed cotton yield in 2 of 3 yr vs. no glyphosate. In addition, applying glyphosate at any rate resulted in an increase in the number of bolls vs. no glyphosate in the following plant-mapping responses: total number of bolls per plant, number of abcised bolls per plant, bolls at the top five sympodial nodes, and bolls at positions 1 and 2 on the sympodia. Glyphosate absorption and subsequent translocation, as influenced by the addition of the sulfur-containing additives, was evaluated using radiotracer techniques. Glyphosate absorption after 48 h was 86, 63, and 37% of amount applied in cotton, sicklepod, and yellow nutsedge, respectively. Absorption by sicklepod and yellow nutsedge was not affected by the addition of either of the additives. Absorption by cotton was reduced by ATS but was not affected by AMS. In yellow nutsedge and cotton, glyphosate concentration in the treated area and adjacent tissue was not affected by either additive. A greater portion of glyphosate was translocated away from the treated area in sicklepod with glyphosate plus AMS (32%) than with glyphosate plus ATS (21%). AMS and ATS may be used in glyphosate-resistant cotton without the risk of either crop injury or yield reduction. However, their use for increased control of annual weed species, such as sicklepod and yellow nutsedge, may not be warranted.

Nomenclature: Glyphosate; ammonium thiosulfate; diammonium sulfate; sicklepod, Senna obtusifolia (L.) Irwin & Barneby #³ CASOB; yellow nutsedge, Cyperus esculentus L. # CYPES; cotton, Gossypium hirsutum L. ‘Paymaster 1218 BR’.

Additional index words: Ammonium thiosulfate, CASOB, CYPES, diammonium sulfate, glyphosate absorption, glyphosate additives, glyphosate-resistant cotton.

Abbreviations: AMS, diammonium sulfate; ATS, ammonium thiosulfate; DAT, days after treatment.

Seed production from weeds that are missed by herbicide application can affect future weed populations and management decisions. It may be possible to expand the utility of computerized weed management decision aids to include an estimate of weed seed production resulting from selected treatments based on crop yield potential. Field studies were conducted in soybean near Columbia, MO, to determine whether weed control recommendations based on crop yield potential from a computerized weed management decision aid influence weed seed production in two soybean row spacings. At approximately 28 d after planting, weed densities and heights were entered into WeedSOFT® to generate a list of treatments ranked by predicted crop yields. Treatments included: (1) highest predicted crop yield in a glyphosate-resistant system, (2) highest predicted crop yield in a nonglyphosate-resistant system, (3) a 10% yield reduction, (4) a 20% yield reduction, and (5) an untreated control. These treatments were applied to soybean grown in 38- and 76-cm rows. Treatments that provided 90% or higher control of an individual species at 22 d after treatment usually produced less seed than untreated checks. Weed seed production based on early-season herbicide efficacy showed a linear relationship and was relatively predictable (r² ≥ 0.52) for the predominant weed species. For less dominant weed species, weed seed production was not strongly correlated (r² ≤ 0.27) to early-season herbicide efficacy but apparently influenced by control of other weed species. Narrow row spacing reduced giant foxtail biomass both years but did not reduce common ragweed and ivyleaf morningglory biomass. Narrow rows did not decrease giant foxtail, common ragweed, and ivyleaf morningglory seed production.

Nomenclature: Glyphosate; common ragweed, Ambrosia artemisiifolia (L.) #³ AMBEL; giant foxtail, Setaria faberi (L.) Herrm. # SETFA; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; soybean, Glycine max.

Additional index words: Decision support system, herbicide decision aid.

Abbreviations: AP, at planting; DAT, days after treatment; HPMY-G, highest percent maximum yield that used glyphosate-resistant soybean; HPMY-NG, highest percent maximum yield that did not use glyphosate.

Tropical signalgrass is one of the most serious weed problems in the St. Augustinegrass sod production in Florida, and its presence increases production costs and lowers turfgrass quality. The objectives of our research were to: (1) evaluate herbicides preemergence and postemergence for control of tropical signalgrass and (2) compare control of tropical signalgrass and other problem weeds (torpedograss, blanket crabgrass, and India crabgrass) with postemergence herbicides. In preemergence herbicide field trials, only benefin oryzalin, imazapic, imazapic 2,4-D, and oryzalin provided ≥75% tropical signalgrass control 8 wk after application (WAA). By 11 WAA, only benefin oryzalin and imazapic 2,4-D provided ≥75% tropical signalgrass control. In greenhouse experiments, eight herbicide treatments were applied postemergence to tropical signalgrass seedlings at the two-, four-, six-, and eight-leaf stages. Asulam and CGA 362622 provided ≥89% tropical signalgrass control at all application timings. Imazaquin controlled tropical signalgrass ≥98% when applied before the eight-leaf stage. However, in field trials with mature tropical signalgrass (>20 cm stolons), none of the 20 herbicide treatments applied postemergence provided acceptable control.

Nomenclature: Asulam; benefin; CGA 362622, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(2,2,2-trifluoroethoxy)-2-pyridinesulfonamide; 2,4-D; imazapic; imazaquin; oryzalin; blanket crabgrass, Digitaria serotina (Walt.) Michx. #³ DIGSO; India crabgrass, Digitaria longiflora (Retz.) Pers. # DIGLO; St. Augustinegrass, Stenotaphrum secondatum (Walt.) Kuntz; torpedograss, Panicum repens L. # PANRE; tropical signalgrass, Urochloa subquadripara (Trin.) R. D. Webster # BRASU.

Additional index words: BRASU, DIGLO, DIGSO, PANRE.

Abbreviation: WAA, weeks after application.

Uncontrolled kochia plants that regrow after small-grain harvest can produce substantial numbers of seeds. An average of 4,100 seeds per plant were produced between harvest (late July to mid August) and the first killing frost (late September) at three locations in Montana. Field experiments were conducted to determine the optimal timing of postharvest herbicide applications to prevent kochia from producing viable seeds. Herbicide treatments were applied at three timings from late August to mid September. The most effective treatments were glyphosate (631 g/ha) and paraquat (701 g/ha) applied at the second application timing (late August to early September). These treatments reduced kochia seed production by 92% or greater at each site. Kochia regrowth by this time had sufficient leaf area for herbicide absorption, but few viable seed had been produced. Herbicide treatments at the first and third application timings were generally less effective and more variable in reducing kochia seed production. Sulfentrazone (157 g/ha) and 2,4-D (561 g/ha) were not as effective at reducing seed production as other herbicide treatments.

Nomenclature: Glyphosate; paraquat; sulfentrazone; 2,4-D; kochia, Kochia scoparia (L.) Schrad. #³ KCHSC.

Additional index words: Seed production.

Abbreviations: AMS, ammonium sulfate.

Tropical spiderwort has recently become the most troublesome weed in Georgia cotton. Most of Georgia's cotton is glyphosate resistant (GR), and glyphosate is only marginally effective on tropical spiderwort. An experiment was conducted at four locations to determine tropical spiderwort control in GR cotton by 27 herbicide systems. Treatments consisted of three early-postemergence over-the-top (POT) herbicide options and nine late–postemergence-directed (LPD) options arranged factorially. Glyphosate POT controlled tropical spiderwort only 53% 21 d after treatment (DAT). Glyphosate plus pyrithiobac or S-metolachlor controlled tropical spiderwort 60 and 80%, respectively. Pyrithiobac improved control of emerged spiderwort, whereas S-metolachlor provided residual control. Pooled over POT treatments, glyphosate LPD controlled tropical spiderwort 70% 21 DAT. Dimethipin mixed with glyphosate did not improve control. Carfentrazone, diuron, or flumioxazin mixed with glyphosate LPD improved control 9 to 15%. MSMA and MSMA plus flumioxazin were 8 and 19% more effective than glyphosate LPD. At time of cotton harvest, systems without residual herbicides at LPD controlled tropical spiderwort 42 to 45% compared with 64 to 76% with LPD treatments that included diuron or flumioxazin.

Nomenclature: Carfentrazone; dimethipin; diuron; flumioxazin; glyphosate; MSMA; pyrithiobac; S-metolachlor; tropical spiderwort, Commelina benghalensis L.; cotton, Gossypium hirsutum L. ‘DP 458 B/RR’, ‘FM 989 B/RR’, ‘ST 4793 BR’.

Additional index words: Invasive weed, noxious weed, weed shift.

Abbreviations: DAP, days after planting; DAT, days after treatment; GR, glyphosate resistant; LPD, late postemergence directed; POT, postemergence over-the-top.

Brazilian pepper is a small evergreen tree that forms dense colonies. It was introduced for horticultural use in the United States in the early 1800s and was widely distributed in Florida in the late 1920s. Previous remote-sensing projects to detect Brazilian pepper achieved moderate success and warranted additional research using a hyperspectral sensor. Detection with remote sensing is desirable because complete access to ground survey crews is not practical. The western half of the Everglades National Park was imaged at a 5-m spatial resolution with a hyperspectral sensor by Earth Search Sciences Inc. of Kalispell, MT, on December 12, 2000, and January 10, 2001. The sensor has 128 channels and spectral resolution between 450 and 2,500 nm. The purpose of this research was to develop spectral reflectance curves for Brazilian pepper and establish the accuracy of classified images. Classified images showed that a hyperspectral sensor could detect a “pure” Brazilian pepper pixel representing the center of an infestation but not “mixed” Brazilian pepper pixels at the sparsely populated edges. To define the sparse populations, images were classified using a spatial buffer (15- to 100-m radius) based on a low–omissional error image. A 25-m buffer reduced the amount of commissional error for Brazilian pepper in mangrove-dominated forest to 8.2% and buttonwood-dominated forest to 0%. Wider buffers did not significantly improve image accuracy when compared with the 25-m buffer distance. Results indicate that removal crews using hyperspectral images will be able to reliably find the colonies of Brazilian pepper but will not be able to use the images to find isolated scattered trees.

Nomenclature: Brazilian pepper (Schinus terebinthifolius Raddi) #³ SCITE.

Additional index words: Hyperspectral sensor, imaging spectrometer, invasive plant detection, whiskbroom scanner.

Abbreviations: GPS, global positioning system without differential correction; PLOS, posteriori least-squares orthogonal subspace projection; SAM, spectral angle mapper; USGS-BRD/SERP, United States Geological Survey—Biological Resource Division/Southeast Environmental Research Program.

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

Nomenclature: Bromoxynil; glufosinate; glyphosate; monosodium salt of methylarsonic acid; prometryn; pyrithiobac; sulfosate; broadleaf signalgrass, Bracharia platyphylla (Griseb.) Nash #³ BRAPP; common cocklebur, Xanthium strumarium L. # XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; fall panicum, Panicum dichotomiflorum Michx. # PANDI; Florida beggarweed, Desmodium tortuosum (Sw.) DC. # DEDTO; giant foxtail, Setaria faberi Herm. # SETFA; goosegrass, Eleusine indica (L.) Gaertn. # ELIEN; green foxtail, Setaria viridis (L.) Beauv. # SETVI; hemp sesbania, Sesbania exaltata (Raf.) Rybd. ex A. W. Hill # SEBEX; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; jimsonweed, Datura stramonium L. # DATST; seedling johnsongrass, Sorghum halepense (L.) Pers. # SORHA; ladysthumb smartweed, Polygonum persicaria L. # POLPE; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; volunteer peanut, Arachis hypogaea L. # ARAHY; Penns

Tolerance and yield of ‘H8001 RR’ soybean to single and sequential glyphosate applications made during vegetative and reproductive stages were examined in field trials in 2000 and 2001. In addition, germination and seedling characteristics from harvested seed were assessed. Glyphosate-resistant soybean tolerated single and sequential applications of 1.7 kg ae/ha glyphosate with minimal injury (≤5%), except for an R2 application in 2000 that caused 20% injury. All observed injury was transient and did not adversely affect soybean density, height, seed weight, or seed yield. Germination and seedling growth of harvested seed were similar to those of a nontreated control. These results suggest that glyphosate-resistant soybean can withstand sequential applications of glyphosate during vegetative and reproductive stages without prolonged adverse effects.

Nomenclature: Glyphosate; soybean, Glycine max (L.) Merr ‘H8001 RR’.

Additional index words: Injury, transgenic soybean, yield.

Field studies were conducted at the Alabama Agricultural Experiment Station near Shorter, AL, from 1998 to 2000 to evaluate six commercial spray adjuvants and their effects on glyphosate applied to cotton with an air-assisted sprayer. Each adjuvant was evaluated with a conventional sprayer calibrated to deliver 94 L/ha solution and a low-volume, air-assisted sprayer calibrated to deliver 19 L/ha solution. Glyphosate was applied to two-leaf pitted and entireleaf morningglory growing in glyphosate-resistant cotton. Visual control of pitted and entireleaf morningglory was more dependent on the rate of herbicide application than on a particular adjuvant or sprayer, with glyphosate at 0.42 kg ae/ha providing 70% control 21 d after treatment. Pitted and entireleaf morningglory biomass measurements generally reflected visual control data. Ammonium sulfate and formulated glyphosate consistently gave the highest visual control and the greatest biomass reduction. Glyphosate application rate was more important than adjuvant addition or sprayer type, with the higher rates of application providing greater control. No differences in weed control were observed between spray systems; therefore, air-assisted sprayers may be used on a field-scale basis with consistent and adequate results.

Nomenclature: Glyphosate; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray #³ IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; cotton, Gossypium hirsutum L. ‘Paymaster 1220BG/RR’.

Additional index words: Glyphosate-resistant cotton, IPOHE, IPOLA, surfactant.

Abbreviations: AMS, ammonium sulfate; COC, crop oil concentrate; DAT, days after treatment; GLY , formulated glyphosate; NIS-1, nonionic surfactant; NIS-2, nonionic wetter–spreader–penetrant; NIS-3, nonionic surfactant–penetrant–acidifier; POST, postemergence; PPI, preplant incorporated; WCA, water conditioning agent.

When herbicides are applied in mixture, and infestation by weeds is less than expected compared with when herbicides are applied alone, a synergistic effect is said to exist. The inverse response is described as being antagonistic. However, if the expected response is defined as a multiplicative, nonlinear function of the means for the herbicides when applied alone, then standard linear model methodology for tests of hypotheses does not apply directly. Consequently, nonlinear mixed-model methodology was explored using the nonlinear mixed-model procedure (PROC NLMIXED) of SAS System®. Generality of the methodology is illustrated using data from a randomized block design with repeated measures in time. Nonlinear mixed-model estimates and tests of synergistic and antagonistic effects were more sensitive in detecting significance, and PROC NLMIXED was a versatile tool for implementation.

Additional index words: Least significant difference, linear mixed models, repeated measures, tank mixture.

Abbreviations: DAT, days after treatment; GH, glufosinate plus mixture herbicide; GHD, glufosinate plus mixture herbicide by DAT; ML, maximum likelihood; MSE, mean square error; Rep, replication.

The influence of weed seed burial depth on seedling emergence is a common and important topic in undergraduate weed science courses. A laboratory exercise was developed at Iowa State University to actively demonstrate changes in weed seedling emergence with increased seed-burial depth. Twenty-five ivyleaf morningglory and wild mustard seeds were sown in pots in monoculture, and the number of emerging seedlings was counted for 3 wk. The results from two semesters were analyzed to determine whether the experiment was successful in meeting its intended outcomes. Assessment of student perceptions and attitudes indicated that the activity increased students' understanding of weed biology; improved students' critical thinking, reading, and writing skills; and improved students' ability to make scientific observations, interpret graphical information, and analyze and summarize research data.

Nomenclature: Ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. #³ IPOHE; wild mustard, Brassica kaber (D.C.) L.C. Wheeler SINAR.

Additional index words: Brassica kaber, education, IPOHE, Ipomoea hederacea, SINAR, weed biology, weed ecology.