Abstract: Excessive persistence of imazethapyr has been responsible for injury to corn grown after soybean. Factors implicated in corn injury reported from certain parts of the main corn-producing region in South Africa were: leaching of herbicide to deep soil layers during the season of application, followed in the next season by capillary movement to the root zone of corn, and increased bioactivity of herbicide residues following liming of fields. Bioassays were employed to determine to what extent imazethapyr leached in a soil that typically contains less than 10% total clay and 0.1% organic C in the 0- to 300-mm zone and to assess the role of pH and liming in the bioactivity of the herbicide. Undisturbed soil columns were collected in polyvinyl chloride pipe for the leaching experiment. In the greenhouse, the equivalent of 40 g ai/ha imazethapyr was applied on the column surface, followed by leaching with simulated rain of 25 or 50 mm. Leaf area measurements of the test species rapeseed showed that the herbicide was readily leached to at least 30 cm at both water regimes and that it subsequently moved upward in the soil, with evaporation as the driving force. In the other bioassay, the soil was ameliorated with different amounts of Ca(OH)₂ or CaCO₃ to adjust pH levels to between 5.7 and 7.1 These soil samples were each treated with imazethapyr at rates equivalent to 1.8, 3.75, 7.5, 15, and 30 g ai/ha. The growth response of the test species indicated that where Ca(OH)₂ was applied, the bioactivity of imazethapyr in most instances was significantly greater than where CaCO₃ was used. At all the imazethapyr rates, the activity of the herbicide increased significantly with an increase in pH from 5.6 to 6.5 where Ca(OH)₂ was used, but with CaCO₃, activity was significant only at 15 and 30 g ai/ha. Changes in imazethapyr adsorption and in the organic matter in the soil were not monitored, but it is suggested that the increase in herbicide activity caused by Ca(OH)₂ may be due to the degradation of organic matter in the soil or to desorption of the herbicide, which would render the herbicide more available for uptake. These effects, if they do occur, are likely to be of significance for herbicide adsorption only in soil with very low organic matter content. Results indicate that imazethapyr could leach easily in coarse-textured soils low in clay and organic matter content and that the type of lime used on those soils may influence the bioactivity of the herbicide.

Nomenclature: Atrazine; imazamethabenz; imazaquin; imazethapyr; corn, Zea mays L.; rapeseed, Brassica rapa L. ‘Salusia’; soybean, Glycine max (L.) Merr.

Additional index words: Adsorption, bioactivity, herbicide mobility, soil pH.

Abbreviations: FC, field capacity; OM, organic matter; PVC, polyvinyl chloride.

Abstract: Common windgrass is an increasing winter wheat weed problem in Michigan. Postplant incorporated trifluralin, applied at 0.56 kg/ha, reduced common windgrass density by 85% in small plot research and by 70% or greater in production scale sites. In 1994–1995, incorporation implements had no effect on initial wheat density. However in a spring 1995 evaluation, significant wheat injury and stand reduction occurred in response to trifluralin incorporation. Incorporation implement effects on wheat injury were in the order: flex-tine harrow > spike tooth drag > rotary hoe. When trifluralin was shallowly incorporated over wheat planted at least 5 cm deep, no significant wheat injury was observed at any site. Injury from postplant incorporated trifluralin was related to shallow planting depth.

Nomenclature: Trifluralin; common windgrass, Apera spica-venti L. #³ APESV; wheat, Triticum aestivum L.

Abstract: Field studies were conducted near Archer, FL, and Vienna, GA, in 1995 and 1996 to investigate pyridate and SAN 582 for weed management in peanut. At Archer, pyridate plus 2,4-DB applied 3 wk after emergence resulted in 75, 72, 59, and 85% early-season control of yellow nutsedge, Florida beggarweed, hairy indigo, and sicklepod, respectively. In Vienna, pyridate plus 2,4-DB resulted in 87 and 55% early-season control of yellow nutsedge and Florida beggarweed, respectively. At both Archer and Vienna, SAN 582 applied preplant incorporated prior to pyridate postemergence (POST) increased control of yellow nutsedge, Florida beggarweed, and hairy indigo; however, peanut yield was not improved. In greenhouse studies, pyridate plus 2,4-DB controlled prickly sida, common cocklebur, and ivyleaf morningglory. Reduced weed control was observed in greenhouse studies when SAN 582 was added to the pyridate plus 2,4-DB POST tank mix.

Nomenclature: Pyridate; SAN 582 (proposed common name dimethenamid), 2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-yl)-acetamide; 2,4-DB; common cocklebur, Xanthium strumarium L. #³ XANST; Florida beggarweed, Desmodium tortuosum (Sw.) DC. # DEDTO; hairy indigo, Indigofera hirsuta Harvey # INDHI; ivyleaf morningglory, Ipomoea hederaceae (L.) Jacq. # IPOHE; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin et Barneby # CASOB; yellow nutsedge, Cyperus esculentus L. # CYPES; peanut, Arachis hypogaea L. ‘GK-7’, ‘Marc III’, ‘Sunoleic 95R’, ‘Sunrunner’.

Additional index words: Application timing.

Abbreviations: NIS, nonionic surfactant; PPI, preplant incorporated; PRE, preemergence; POST, postemergence; WAE, weeks after emergence; WAT, weeks after treatment.

Abstract: Two field experiments were conducted in Oklahoma to determine whether changing wheat row spacing, seeding rate, and cultivar would reduce interference from rye. Wheat row spacing did not affect rye seed production. Averaged over row spacing, increasing wheat seeding rate from 67 to 134 kg/ha reduced rye seed production 21 and 25% in two experiments. At one site, grain yield of rye-infested wheat was increased 27 and 23% by doubling wheat seeding rate in 10- and 20-cm rows. Doubling the seeding rate of rye-infested wheat in 30-cm rows did not increase wheat yield. At a second site when data were pooled over row spacings, increasing the wheat seeding rate from 67 to 101 kg/ha increased yield of rye-infested wheat 21%, but yield was still 36% less than for rye-free wheat. In two additional experiments, rye seeds in harvested wheat were reduced 36% by increasing the wheat seeding rate from 60 to 162 kg/ha, whereas yield of rye-infested wheat was increased 82%. Nine cultivars were compared for competitive ability against rye in four experiments. Of 32 possible cultivar location situations, the rye-induced yield loss of ‘Jagger’ wheat was less than 16 other cultivar location situations, whereas the yield loss of ‘Triumph 64’ wheat was less than 10 other cultivar location situations. Mature wheat height, wheat yield, and wheat maturity classification were each negatively correlated to rye yield in infested wheat at two of four sites. Wheat plant density, head density, sunlight interception, and fall cover capability classification were each negatively correlated to rye yield at one of four sites.

Nomenclature: Rye, Secale cereale L.; wheat, Triticum aestivum L. ‘2163’, ‘2180’, ‘Agseco 7853’, ‘Jagger’, ‘Karl 92’, ‘Longhorn’, ‘TAM 107’, ‘TAM 202’, ‘Triumph 64’.

Additional index words: Winter wheat, competitive ability.

Abbreviations: PAR, photosynthetically active radiation.

Abstract: Field experiments conducted in Texas at six locations from 1996 to 1998 evaluated peanut tolerance to imazapic applied postemergence. Imazapic at 71 g ai/ha was applied weekly from ground cracking to 56 d after ground cracking (DAGC). Visible injury 70 DAGC ranged from 0 to 40%. No reduction in canopy height, canopy width, yield, or grade was observed at harvest following any imazapic treatment.

Nomenclature: Imazapic; peanut, Arachis hypogaea L., ‘AT 120’, ‘GK 7’, ‘NC 7’, ‘Tamspan 90’.

Additional index words: Herbicide injury, ground cracking, groundnut, herbicide timings, peanut injury, postemergence, yield.

Abbreviations: DAGC, days after ground cracking; DAP, days after planting; POST, postemergence; PPI, preplant incorporated.

Abstract: Field experiments were conducted from 1997 to 1999 at Ejea and at Valdegon (Spain) to study weed control and tolerance of direct-seeded pepper ‘Agridulce SIA’ to clomazone alone or with linuron, napropamide, or pendimethalin. The main weeds at Ejea were redroot pigweed, Diplotaxis erucoides, common purslane, and ivyleaf speedwell, while at Valdegon they were Solanum physalifolium and common purslane. Pepper was tolerant to clomazone applied at 0.18 kg ai/ha, but weed control was less than 77%. Increasing the rate of clomazone to 0.36 kg/ha controlled weeds at least 85% and did not injure pepper. Clomazone at 0.54 and 0.72 kg/ha injured pepper 6 wk after planting (WAP), but plants recovered and the dry weight and yield of paprika were not affected. Napropamide at 2.03 kg ai/ha applied with clomazone improved the control of D. erucoides. Addition of pendimethalin at 0.17 to 0.25 kg ai/ha to clomazone did not improve weed control and increased pepper injury 6 WAP in 1 of 2 yr, but yield was not affected. Linuron at rates ranging from 0.08 to 0.13 kg ai/ha used in combination with clomazone provided complete weed control but injured pepper the most (34 to 88%) and reduced pepper stand by 50% in 1 yr.

Nomenclature: Clomazone; linuron; napropamide; pendimethalin; common purslane, Portulaca oleracea L. #³ POROL; Diplotaxis erucoides (L.) DC.; ivyleaf speedwell, Veronica hederifolia L. # VERHE; redroot pigweed, Amaranthus retroflexus L. # AMARE; Solanum physalifolium Rusby; paprika pepper, Capsicum annuum L., ‘Agridulce SIA’.

Additional index words: Weed control, Convolvulus arvensis, CONAR.

Abbreviations: PRE, preemergence; WAP, weeks after planting.

Abstract: The efficacy of preemergence (PRE) applications of ethalfluralin or pendimethalin incorporated with irrigation was compared with mechanical preplant incorporated (PPI) applications at equivalent rates in peanut. PRE applications of herbicides followed by irrigation were as effective as PPI applications in controlling Texas panicum, southern crabgrass, and crowfootgrass. Split PPI/PRE applications of ethalfluralin were more effective than PPI applications in controlling Texas panicum in 2 of 3 yr. Sequential postemergence applications of clethodim or sethoxydim increased the control of Texas panicum when ethalfluralin or pendimethalin controlled Texas panicum less than 82%. No differences in peanut yield were observed between PPI or PRE applications of either ethalfluralin or pendimethalin.

Nomenclature: Clethodim; ethalfluralin; pendimethalin; sethoxydim; crowfootgrass, Dactyloctenium aegyptium (L.) Willd. #³ DTTAE; southern crabgrass, Digitaria ciliaris (Retz.) Koel. # DIGSP; Texas panicum, Panicum texanum Buckl. # PANTE; peanut, Arachis hypogaea L. ‘Georgia Green’.

Additional index words: Irrigation.

Abbreviations: fb, followed by; PPI, preplant incorporated; PRE, preemergence; POST, postemergence.

Abstract: MON 37500 was registered in 1999 for weed control in wheat and has the potential to injure following crops. Therefore, growth chamber experiments were conducted to determine the effect of soil properties on the phytotoxicity of MON 37500 residues, the relative tolerance of several potential rotational crops, and the joint effect of MON 37500 residues plus other herbicide residues on a susceptible crop. In 13 Alberta soils, the concentrations of MON 37500 and triasulfuron that reduced canola and barley dry matter by 50% (GR₅₀) were correlated with soil organic matter (OM) and pH. The relationship that best described the effect of soil organic matter on GR₅₀ for each herbicide–crop combination was GR₅₀ = a b(OM)². There was no significant improvement in r² when pH and clay content were included in the equation. For soils with 2 and 10% OM content, predicted GR₅₀ values for canola in MON 37500–treated soil are 2 and 26 ηg/g soil, respectively. Little injury to following canola is predicted in soils with OM contents > 4.5%. At similar concentrations, following crops such as canola, flax, lentil, and oriental mustard are predicted to be injured less by MON 37500 than by triasulfuron. The effect of combined residues of MON 37500 with triasulfuron, imazethapyr, or metsulfuron should be additive.

Nomenclature: Imazethapyr; metsulfuron; MON 37500, 1-(4,6-dimethoxypyrimidin-2-yl)-3-(2-ethanesulfonylimidazo[1,2-a]pyridine-3yl)sulfonylurea; triasulfuron; barley, Hordeum vulgare L.; canola, Brassica napus L.; flax, Linum usitatissimum L.; lentil, Lens culinaris Medic; oriental mustard, Brassica juncea L.; wheat, Triticum aestivum L.

Additional index words: Crop rotation, herbicide residue, pH, soil organic matter.

Abbreviations: GR₅₀, growth measurement corresponding to 50% of the untreated; OM, soil organic matter.

Abstract: MKH 6562 is a new acetolactate synthase inhibitor herbicide that would provide an alternative to control wild oat. Three experiments were conducted at Scott, SK, Canada, from 1996 to 1999 to evaluate MKH 6562 rates (20 and 30 g ai/ha), carrier volumes (30, 50, and 100 L/ha), time of applications (two- to three-leaf and three- to four-leaf stages of wild oat), and broadleaf weed herbicide tank mixtures. Reduced wild oat control (lower visual rating of percent control and higher fresh weight) often occurred when MKH 6562 was applied at a rate of 20 vs. 30 g/ha, with carrier volumes of 30 vs. 50 and 100 L/ha, and at the three- to four-leaf vs. two- to three-leaf stages of wild oat. Wild oat control generally was lower for MKH 6562 tank mixed with dicamba mecoprop MCPA 1:1:4.4 and bromoxynil MCPA 1:1 compared with MKH 6562 applied alone or tank mixed with other broadleaf herbicides. MKH 6562 tank mixed with MCPA, and to a lesser extent 2,4-D, resulted in decreased wild oat control when applied at the three- to four-leaf stage of wild oat, but not at the two- to three-leaf stage. Wheat grain yield usually was not affected by MKH 6562 rate and carrier volume. Yield was 7% lower when MKH 6562 was tank mixed with dicamba mecoprop MCPA or fluroxypyr 2,4-D and was 8% lower when MKH 6562 was applied in a mixture with 2,4-D formulations or bromoxynil MCPA at the three- to four-leaf stage compared with the two- to three-leaf stage. Similar yields were achieved when MKH 6562 was applied alone at both leaf stages of wild oat. Wild oat control and wheat yield with MKH 6562 were as good as or better than with ICIA 0604 and imazamethabenz and were as good as or poorer than with CGA 184927. MKH 6562 provides adequate control of wild oat in wheat when applied early with the recommended carrier volume. Satisfactory control may be achieved with reduced rates if wild oat infestations are light.

Nomenclature: CGA 184927 (proposed common name, clodinafop-propargyl), 2-propynyl-(R)-2-[4-(5-chloro-3-fluoro-2-pyridyloxy)-phenoxy]-propionate; MKH 6562 (proposed common name, flucarbazone-sodium), 4,5-dihydro-3-methoxy-4-methyl-5-oxo-N-[[2-(trifluoromethoxy)phenyl]sulfonyl]-1H-1,2,4-triazole-1-carboxamide; clodinafop-propargyl, (R)-2-[4-[(5-chloro-3-fluoro-2-pyridinyl)oxy]phenoxy] propanoic acid 5-chloro-8-quinolinoxyacetic acid-1-methylester; ICIA 0604 (proposed common name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)-2-cyclohexen-1-one; wheat, Triticum aestivum L. ‘CDC Makwa’; wild oat, Avena fatua L. #³ AVEFA.

Additional index words: Acetolactate synthase inhibitor, rate, carrier volume, timing of application, tank mixing.

Abstract: Glyphosate effectively controls most weeds in glyphosate-resistant soybean. However, it is sometimes only marginally effective on Ipomoea spp. A field experiment was conducted at five locations in North Carolina to determine the effects of mixing 2,4-DB with glyphosate on Ipomoea spp. control and on soybean injury and yield. The isopropylamine salt of glyphosate at 560, 840, and 1,120 g ai/ha controlled mixtures of tall morningglory, entireleaf morningglory, and red morningglory at least 96% at two locations. Mixing the dimethylamine salt of 2,4-DB at 35 g ae/ha with glyphosate did not increase control but reduced soybean yield 6%. At two other locations, 2,4-DB increased control of tall morningglory and a mixture of entireleaf morningglory and ivyleaf morningglory 13 to 22% when mixed with glyphosate at 560 g/ha, but not when mixed with glyphosate at 840 or 1,120 g/ha. Soybean yield was reduced 31% at one location and was unaffected at the other. At the fifth location, 2,4-DB increased control of tall morningglory 25, 11, and 7% when mixed with glyphosate at 560, 840, and 1,120 g/ha, respectively. Soybean yield was increased 15%. In separate field experiments, glyphosate at 560, 840, and 1,120 g/ha controlled large crabgrass at least 99%. Mixing 2,4-DB at 35 g/ha with glyphosate did not affect control. In the greenhouse, mixing 2,4-DB at 35, 70, 140, or 280 g/ha with glyphosate at 70 to 560 g/ha did not affect large crabgrass control by glyphosate.

Nomenclature: Glyphosate; 2,4-DB; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray #³ IPOHG; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; red morningglory, Ipomoea coccinea L. # IPOCC; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; soybean, Glycine max (L.) Merr. ‘Hartz 5566 RR’.

Additional index words: Herbicide combinations, herbicide interactions, herbicide-resistant crops.

Abbreviations: WAT, weeks after treatment.

Abstract: Field experiments were carried out during 1997 and 1998 in northern Greece to investigate the effects of tank mixing rimsulfuron and primisulfuron with atrazine or dicamba against johnsongrass in corn. Sequential applications, where the johnsongrass herbicides were applied 5 d after the broadleaf herbicides, were also evaluated. Rimsulfuron applied alone at 10 g ai/ha gave very good control (91%) of johnsongrass, which was significantly higher than that provided by 30 g ai/ha of primisulfuron (43%). Rimsulfuron applied in tank mixture with atrazine (1.0 kg ai/ha) or dicamba (0.28 kg ai/ha) gave 12 and 17% lower johnsongrass control, respectively, than of rimsulfuron applied alone, whereas the corresponding reduction for primisulfuron was 18 and 43%. Efficacy of rimsulfuron applied 5 d after the application of atrazine or dicamba was similar to that applied alone; however, this was not the case for primisulfuron, where reduced antagonism was observed compared to that produced by its tank mixture treatments. Again, primisulfuron was affected more by dicamba than by atrazine. Corn yield with rimsulfuron and primisulfuron applied alone was more than double that of the untreated control and similar to that of the weed-free control. Also, rimsulfuron applied with atrazine or dicamba (in tank mixture or sequentially) produced similar corn yield to that applied alone. However, primisulfuron applied in tank mixture or sequentially with dicamba gave 22 and 14% lower yield, respectively, than when applied alone, and slightly lower when applied with atrazine.

Nomenclature: Atrazine, dicamba, primisulfuron, rimsulfuron, johnsongrass, Sorghum halepense (L.) Pers. #³ SORHA; corn, Zea mays L. ‘Pioneer Costanza’.

Additional index words: Sequential applications, tank mixtures.

Abbreviations: DAT, days after treatment.

Abstract: Of 78 biotypes of wild radish (Raphanus raphanistrum) collected from Western Australia (WA), 42% were resistant and 14% intermediate to acetolactate synthase (ALS)-inhibiting herbicides. Based on the LD₅₀ and GR₅₀ ratios, the resistant biotype K96071 was 81-fold more resistant to chlorsulfuron and 114- to 116-fold more resistant to metosulam than the susceptible biotype K96041. More resistant biotypes were found in northern zones than in southern zones of WA. Resistant biotypes evolved after five applications of chlorsulfuron in a predominantly cereal–lupin rotation. Where resistant biotypes were found, ALS-inhibiting herbicides were not rotated with herbicides with different modes of action as frequently as in fields with susceptible biotypes. Cross-resistance to chlorsulfuron and metosulam was found in the resistant biotypes even though only 15% of the 78 biotypes were exposed to two applications of metosulam over a 10-yr period. All 78 biotypes were effectively controlled by simazine and 2,4-D amine.

Nomenclature: Chlorsulfuron; metosulam; simazine; 2,4-D; wild radish, Raphanus raphanistrum L. #³ RAPRA.

Additional index words: Weed survey, cross-resistance, crop rotations, herbicide rotations.

Abbreviations: ALS, acetolactate synthase; GR₅₀, rate of herbicide required to inhibit growth by 50%; I, intermediate; R, resistant; S, susceptible; SU, sulfonylurea; WAP, weeks after planting.

Abstract: Field studies were conducted to compare venturi-type nozzles to a fan nozzle with respect to the efficacy of postemergence herbicides applied to common cocklebur and broadleaf signalgrass. Spray solutions of glufosinate, glyphosate, and paraquat were applied through all combinations of three nozzles and two application volumes. Venturi nozzles were a Delavan Raindrop Ultra (RU) and a Spraying Systems AI Teejet (AI). A Spraying Systems XR Teejet (XR) fan nozzle was included as a standard. Previous work indicated droplet size spectra differed among these nozzles. There was a difference in common cocklebur control among nozzles (AI = XR > RU), although control was at least 90% for all nozzles. Herbicide choice had a greater effect on broadleaf signalgrass control than nozzle type. Broadleaf signalgrass control differed among herbicides (glufosinate = paraquat > glyphosate) and among nozzles (AI = XR > RU). Herbicide performance varied between nozzles (AI > RU), but the AI nozzle was as effective as the XR fan nozzle.

Nomenclature: Glufosinate; glyphosate; paraquat; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #³ BRAPP; common cocklebur, Xanthium strumarium (L.) # XANST.

Additional index words: Drift.

Abbreviations: AI, Spraying Systems AI Teejet; RU, Delavan Raindrop Ultra; VMD, volume median diameter; WAT, weeks after treatment; XR, Spraying Systems XR Teejet.

Abstract: Field experiments were conducted on a silty clay loam in Corvallis, OR during the summers of 1995 and 1996 to study the effects of soil solarization, spring-planted green manure crops, fumigation with metham, and combinations of these treatments on annual bluegrass seed survival. Annual bluegrass seeds were incorporated into the soil as a bioassay species and soil samples extracted to a depth of 15 cm to determine effects on seed survival. Soil solarization was applied over a 53- or 59-d period using a 0.6-mil clear polyethylene film. Soil samples were collected from four depths after the solarization period in both solarized and nonsolarized plots and surviving seeds germinated in a greenhouse. Maximum soil temperatures recorded at 5-, 10-, and 20-cm depths were 52, 47, and 33 C in solarized soil, respectively. Solarization reduced annual bluegrass seed survival from 89 to 100% in the upper 5 cm of soil, but did not reduce survival below 5 cm. Solarization may have enhanced seed survival below 5 cm. Cover crops of barley, rapeseed, and sudangrass generally increased survival of annual bluegrass seeds buried 2.5 to 15 cm deep in the soil. Green manure cover crops plus solarization did not improve the efficacy of solarization alone and in some cases diminished the effectiveness of solarization. Solarization significantly improved the efficacy of one-quarter rates of metham (230 L/ha) in the top 5 cm of soil, reducing overall annual bluegrass seed survival in the soil by 40% compared with metham alone (230 L/ha) but only 30% compared with solarization alone. The conventional rate of metham (930 L/ha) was the most effective and consistent treatment across all depths.

Nomenclature:Metham, methyldithiocarbamic acid; annual bluegrass, Poa annua L. #³ POANN; spring barley, Hordeum vulgare L. Micah; rapeseed, Brassica napus Dwarf Essex; sudangrass, Sorghum vulgare Trudan 8.

Additional index word: Green manures.

Abbreviations: PE, polyethylene; PNW, Pacific Northwest.

Abstract: Field studies were conducted from 1996 to 1998 at Queenstown, MD to evaluate weed management programs utilizing single and multiple applications of glufosinate, with and without preemergence (PRE) and postemergence herbicides in both glufosinate-resistant (GR) corn and soybean. No herbicide treatment resulted in corn or soybean injury greater than 10% at 7 d after treatment (DAT). No injury was visible at 14 DAT for both GR corn and soybean. In corn, all treatments provided 72% or greater giant foxtail control 14 wk after planting (WAP). With soybean, in 1996 and 1998, few differences in giant foxtail control were observed, with all treatments providing at least 93% giant foxtail control 12 WAP. For common lambsquarters control in GR corn, there were no differences in control among treatments for 1996 and 1997. Over 80% common lambsquarters control was observed both years with all treatments 14 WAP. Glufosinate atrazine at 0.4 kg/ha 1.7 kg ai/ha, respectively, provided 100% season-long common lambsquarters control all three years of the study. For GR soybean, few differences in common lambsquarters control existed between treatments for all three years. Most treatments provided 72% or greater common lambsquarters control 12 WAP. Few differences in grain yield between herbicide treatments were observed for either GR corn or soybean. These studies illustrated that glufosinate, whether applied alone, sequentially, in tank-mixes, or as an overlay to a PRE program in GR corn and soybean is a viable herbicide program for the control of giant foxtail and common lambsquarters.

Nomenclature: Atrazine, glufosinate, common lambsquarters, Chenopodium album L. #³ CHEAL; giant foxtail, Setaria faberi Herrm. # SETFA; corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Additional index words: BAR gene, PAT gene, postemergence herbicides, transgenic herbicide-resistant crops.

Abbreviations: BAR, bialaphos resistance gene; DAT, days after treatment; EPOST, early postemergence; fb, followed by; GR, glufosinate resistant; LPOST, late postemergence; MPOST, mid postemergence; PAT, phosphinothricin acetyl transferase; POST, postemergence; PRE, preemergence; WAP, weeks after planting.

Abstract: Flumioxazin and sulfentrazone were compared for phytotoxicity on 15 soybean varieties in a greenhouse study and four varieties in the field. In the greenhouse, injury from sulfentrazone was greater overall than with flumioxazin, 10% compared with 1%, respectively, when averaged across varieties at the labeled rates. The varieties P9552, P91B01, P9362, and P9305 were more sensitive to sulfentrazone than the 11 other varieties on the basis of visible injury and plant height reductions. Sulfentrazone at 224 g ai/ha (1× rate) reduced plant height 23 to 53% and caused 18 to 38% visible injury on the four sensitive varieties. Visible injury symptoms consisted of stunting, crinkling of leaves, and chlorotic spots. Varieties P9305, P9306, P9352, and P9362 were compared in a field study with flumioxazin at 105, 210, and 420 g ai/ha or sulfentrazone at 224, 448, and 896 g ai/ha, corresponding to 1, 2, and 4× labeled rates. An untreated control of each variety was included for comparison. Contrary to the results of the greenhouse studies, injury from flumioxazin was similar to that from sulfentrazone in the field experiments. In 1998, emergence counts were reduced 19 to 52% with flumioxazin and 27 to 73% with sulfentrazone at the 1× rate. Visible injury and stand count reductions resulting from both herbicides were also apparent in that year. Emergence count reductions, stand count reductions, and visible injury resulting from the herbicides were less severe in 1999. At the 1× rate of each herbicide, yields were not affect in either year, except P9305 treated with sulfentrazone in 1999. At the 4× rate, P9305 was most sensitive to sulfentrazone, as indicated by a 53 and 23% reduction yield in 1998 and 1999, respectively. Avoidance of sensitive varieties will reduce the potential for injury and yield reduction with sulfentrazone, and maybe flumioxazin.

Nomenclature: Flumioxazin, 2-[7-fluoro-3,4-dihydro-3-oxo-4-(2-propynl)-2H-1,4 benzoxazin-6-yl[-4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-dione; sulfentrazone, N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]phenyl] methanesulfonamide; soybean, Glycine max (L.).

Additional index words: Protoporphyrinogen oxidase inhibitors, differential herbicide tolerance.

Abbreviations: DAE, days after emergence; DAP, days after planting; DAT, days after treatment; PPO, protoporphyrinogen oxidase; PRE, preemergence.

Abstract: A study was established to evaluate weed control and crop response of imidazolinone-tolerant (IMI-tolerant) rice in water-seeded culture with imazethapyr at 70, 105, and 140 g ai/ha at four different soil application timings with or without 70 g/ha imazethapyr postemergence (POST). Application timings included preplant incorporated (PPI), surface application prior to seeding (SURFACE), following seeding (SEED), and at pegging (PEG). The PEG treatments were applied when green leaf tissue had emerged from the seed and the root had begun to extend downward into the soil. Response of barnyardgrass, red rice, and rice injury was not affected by the addition of an imazethapyr POST application. Barnyardgrass control was above 90% at 28 d after treatment (DAT) for both years. At 42 DAT, barnyardgrass control decreased to 88% in 1998, compared with 94% control in 1999. Averaged over years, Indian jointvetch control ranged from 44 to 74% at 28 DAT and 41 to 71% at 42 DAT. Indian jointvetch control was inconsistent and lacked uniformity over all factors. Rice injury increased as application timing was delayed from PPI to PEG in 1998 at both rating dates. In 1999, injury was not observed with imazethapyr at 28 DAT, and 1% injury was observed at 42 DAT with all imazethapyr application timings.

Nomenclature: Imazethapyr; Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; Indian jointvetch, Aeschynomene indica L. # AESIN; rice Oryza sativa L, ‘93 AS-3510’.

Additional index words: ALS, acetolactate synthase, Clearfield rice, soil-applied herbicide.

Abbreviations: ALS, acetolactate synthase (E.C. 4.1.3.18); DAT, d after POST treatment; IMI-tolerant, imidazolinone-tolerant; PEG, pegging; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; SEED, following seeding; SURFACE, surface application prior to seeding.

Abstract: S-metolachlor was compared with metolachlor at four field locations in Texas during the 1996 and 1997 growing seasons in terms of yellow nutsedge control, peanut injury, and peanut yield. S-metolachlor caused peanut injury comparable to metolachlor when either herbicide was applied preplant incorporated or preemergence. Yellow nutsedge control was similar and peanut yields were comparable with the two herbicides. At one location where yellow nutsedge failed to develop, the untreated check produced one of the highest yields.

Nomenclature: Metolachlor; S-metolachlor; yellow nutsedge, Cyperus esculentus L. #³ CYPES; peanut, Arachis hypogaea L. ‘Florunner’, ‘AT-120’, ‘GK-7’.

Additional index words: Groundnut, herbicide efficacy, peanut stunting.

Abbreviations: POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Abstract: Field experiments were conducted over 3 yr at three locations in Illinois to evaluate the efficacy of glyphosate in glyphosate-resistant soybean planted in rows spaced 19, 38, and 76 cm. Minimal soybean injury (less than 10%) was observed from any glyphosate treatment. Glyphosate treatments controlled 82 to 99% of giant foxtail. Common waterhemp control was increased as soybean row spacing was decreased. Applying sequential glyphosate applications or increasing the glyphosate rate from 420 g ae/ha to 840 g/ha frequently increased common waterhemp control in 76-cm rows. Velvetleaf control with glyphosate was variable, ranging from 48 to 99%. Decreasing soybean row spacing, utilizing sequential glyphosate applications, or increasing the glyphosate rate improved velvetleaf control in at least four of eight site-years. Glyphosate treatments generally resulted in weed control and soybean yield equal to or greater than the standard herbicide treatments. However, glyphosate treatments yielded less than the hand-weeded control in four of eight site-years, suggesting that weed control from glyphosate treatments was sometimes inadequate.

Nomenclature: Glyphosate; common waterhemp, Amaranthus rudis Sauer #³ AMATA; giant foxtail, Setaria faberi Herrm. # SETFA; velvetleaf, Abutilon theophrasti Medik. # ABUTH; soybean, Glycine max (L.) Merr.

Additional index words: Herbicide-resistant crops.

Abbreviations: EPOST, early postemergence; LPOST, late postemergence; MPOST, mid-postemergence; NIS, nonionic surfactant; UAN, 28% urea ammonium nitrate; WAT, weeks after treatment.

Abstract: Field experiments were conducted near DeKalb and Urbana, IL, and Columbia, MO, in 1997 and 1998 to evaluate weed management systems in glyphosate- and glufosinate-resistant soybean planted in 18-cm rows. Overall weed control was improved to a greater extent when the rate of glufosinate was increased from 300 to 400 g ai/ha than when the rate of glyphosate increased from 630 to 840 g ae/ha. Sequential applications of glufosinate improved control over single applications, whereas sequential treatments of glyphosate generally provided no advantages over single applications. When averaged across all weed species in these trials, the systems that provided 95% or higher average control were sequential applications of glufosinate, sequential applications of glyphosate, and clomazone followed by (fb) glyphosate. Single applications of glufosinate provided somewhat variable control of giant foxtail, common lambsquarters, ragweed, and common cocklebur similar to that observed with pendimethalin fb imazethapyr. The addition of fomesafen to glufosinate did not improve control of any of the weeds in this study with the exception of velvetleaf at DeKalb. The addition of clomazone to glufosinate treatments resulted in slightly better giant foxtail and velvetleaf control. Single applications of glyphosate provided somewhat variable control of giant ragweed at DeKalb in 1997 and ivyleaf morningglory and common cocklebur control at Columbia. The addition of fomesafen to glyphosate provided an increase in ivyleaf morningglory and common cocklebur control at Columbia but did not improve control of any other species. The addition of clomazone to glyphosate-based programs resulted in slightly higher velvetleaf, common cocklebur, and ivyleaf morningglory control. In the glyphosate-based herbicide programs there were no substantial differences in relative yield, with all programs protecting over 95% of soybean yield. Glufosinate-based programs were effective in protecting 85 to 92% of soybean yield.

Nomenclature: Clomazone; fomesafen; glyphosate; glufosinate; imazethapyr; pendimethalin; common cocklebur, Xanthium strumarium L. #³ XANST; common lambsquarters, Chenopodium album L. # CHEAL; giant foxtail; Setaria faberi Herrm. # SETFA; giant ragweed, Ambrosia trifida L. # AMBTR; ivyleaf morningglory, Ipomoea hederacea L. Jacq. # IPOHE; velvetleaf, Abutilon theophrasti Medic. # ABUTH; soybean, Glycine max (L.) Merr.

Abbreviations: EPOST, early postemergence; fb, followed by; LPOST, late postemergence, POST, postemergence; PRE, preemergence; UAN, 28% urea ammonium nitrate.

Abstract: Dissipation of imidazolinone herbicides imazaquin and imazethapyr under no-till field conditions was not affected by straw mulch level (1,300, 3,600, or 5,900 kg/ha) in either of 2 yr of field data. Half-lives averaged 7 d for imazaquin and 8 d for imazethapyr. Chlorimuron half-lives averaged 5 d. Imazaquin and imazethapyr residues did not injure corn (Zea mays) the growing season following application. Injury from chlorimuron to corn planted the next year was greatest where applications were made to the highest straw level, reducing corn yield 6%. In laboratory experiments, uniformly cut wheat (Triticum aestivum) straw placed over sand intercepted all three herbicides equally. Herbicide interception was 16, 43, 69, and 89% for straw levels of 840, 1,680, 3,360, and 6,720 kg/ha, respectively. In the laboratory, simulated rainfall removed more imazaquin and imazethapyr from straw than chlorimuron, and approximately 10% of the applied imazaquin or imazethapyr and 20% of the applied chlorimuron remained on the straw after application of 1.0 cm of water. Imazaquin and imazethapyr dissipated 59 and 20%, respectively, during a 7-d incubation period in the greenhouse. Imazaquin dissipation was equal between sand and straw, whereas imazethapyr dissipation was primarily from sand. Chlorimuron did not dissipate from either straw or sand. This indicated that chlorimuron, a sulfonylurea, was more stable than either imidazolinone under these conditions.

Nomenclature: Chlorimuron; imazaquin; imazethapyr; wheat, Triticum aestivum L. ‘Caldwell’; corn, Zea mays L. ‘Pioneer 3369A’, ‘Pioneer 3320’.

Additional index words: Degradation, imidazolinone, persistence, photodegradation, photolysis, rotational crop, sulfonylurea.

Abbreviations: DAT, days after treatment; HPLC, high-performance liquid chromatography; WAP, weeks after planting.

Abstract: Field studies were conducted in 1996 and 1997 to evaluate response of eight peanut cultivars to flumioxazin applied preemergence (PRE) at 71 g ai/ha. Peanut cultivars evaluated include ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’, ‘NC 9’, and the experimental breeding line ‘N9001OE’. Visible injury 3 wk after planting in 1996 was 3% or less regardless of cultivar. In 1997, all cultivars were injured 15 to 28% with flumioxazin PRE, except VC 1, which was injured 45%. No visible injury was observed at 5 and 9 wk after planting. Flumioxazin did not influence the incidence of early leaf spot, late leaf spot, southern stem rot, cylindrocladium black rot, or tomato spotted wilt virus. Flumioxazin did not affect percentage of extra-large kernels, sound mature kernels, other kernels, and total yield.

Nomenclature: Flumioxazin; peanut, Arachis hypogaea L., ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’, ‘NC 9’, ‘N9001OE’.

Additional index words: Disease interaction, Cylindrocladium crotalariae (Loos) Bell and Sobers, Cercospora arachidicola Hori, Cercosporidium personatum (Berk. and Curt.), Sclerotium rolfsii Sacc., grade parameters, extra-large kernels, sound mature kernels, sound splits, total kernels, other kernels, fancy pods.

Abbreviations: CBR, cylindrocladium black rot; DAP, days after planting; ELK, extra-large kernels; PPI, preplant incorporated; PRE, preemergence; SMK, sound mature kernels; SS, sound splits; TMSK, total sound mature kernels; TSWV, tomato spotted wilt virus; WAP, weeks after planting.

Abstract: Research was conducted in 1997 and 1998 to evaluate narrow row spacing and glufosinate in glufosinate-resistant corn. Glufosinate-resistant corn was planted in 51- and 102-cm row spacings at the same plant populations. Herbicide treatments included glufosinate alone and in different herbicide combinations. Atrazine plus glufosinate enhanced Palmer amaranth control compared to glufosinate alone. Control of johnsongrass, ivyleaf morningglory, entireleaf morningglory, Texas panicum, smellmellon, browntop panicum, and toothed spurge with glufosinate was greater than 82%. Common sunflower control with glufosinate was greater than 95%. Atrazine followed by glufosinate applications provided at least 94% control of all species and was the most consistent herbicide system used. Row spacing had little effect on weed control. Crop injury to glufosinate-resistant corn was minimal with glufosinate and atrazine plus glufosinate combinations.

Nomenclature: Atrazine; glufosinate; browntop panicum Panicum fasciculatum Sw. #³ PANFA; entireleaf morningglory Ipomoea hederacea var. intergriuscula Gray # IPOHG; ivyleaf morningglory Ipomoea hederacea (L.) Jacq. # IPOHE; johnsongrass Sorghum halepense (L.) Pers. # SORHA; Palmer amaranth Amaranthus palmeri S.Wats. # AMAPA; smellmellon Cucumis melo L. var. dudaim Naud. # CUMMD; common sunflower Heliathus annuus L. # HELAN; Texas panicum Panicum texanum Buckl. # PANTE; toothed spurge Euphorbia dentata Michx. # EPHDE; corn (Zea mays L.).

Additional index words: Narrow-row corn, transgenic corn, atrazine, pendimethalin, primisulfuron, CGA 152005 (proposed name, prosulfuron).

Abbreviations: DAT, days after POST treatment; fb, followed by; LPOST, late postemergence; POST, postemergence; PRE, preemergence.

Abstract: Field trials evaluated weed control in corn and soybean with CGA-248757 and flumiclorac. CGA-248757 and flumiclorac were applied to 5-, 45-, and 60-cm-tall velvetleaf. Visual control ratings 7 d after treatment (DAT) indicated the greatest control of velvetleaf in corn with CGA-248757 applied to velvetleaf when 5 or 45 cm tall, whereas the greatest control with flumiclorac occurred when applied to 5-cm-tall velvetleaf. However, ratings 21 DAT to 60-cm-tall velvetleaf indicated velvetleaf control with both herbicides was greatest when applied to plants 45 or 60 cm tall. CGA-248757 or flumiclorac applied postemergence (POST) following metolachlor or metolachlor plus atrazine preemergence (PRE) improved velvetleaf control compared with metolachlor plus atrazine alone. Similarly, tank mixtures of CGA-248757 or flumiclorac with 2,4-D following metolachlor PRE provided greater velvetleaf control compared with metolachlor PRE followed by 2,4-D POST. Velvetleaf control in corn was greater when CGA-248757 or flumiclorac were tank mixed with nicosulfuron plus atrazine or nicosulfuron plus dicamba. In soybean, metolachlor plus metribuzin plus clomazone PRE, metolachlor PRE followed by flumiclorac POST, and metolachlor plus metribuzin PRE followed by CGA-248757 or flumiclorac POST provided greater than 85% control of giant foxtail, common lambsquarters, redroot pigweed, and velvetleaf 56 d after POST treatments (DAPO) in 1997. Additionally, glyphosate applied late postemergence (LPOST) and tank mixtures of glyphosate with CGA-248757 or flumiclorac LPOST provided greater than 90% control of these same weed species in 1997. However, only metolachlor plus metribuzin PRE followed by CGA-248757 or flumiclorac POST and imazethapyr plus CGA-248757 or flumiclorac POST provided greater than 80% giant foxtail, common lambsquarters, redroot pigweed, and velvetleaf control 56 DAPO in 1998.

Nomenclature: Atrazine; 2,4-D; CGA-248757 (proposed common name, fluthiacet), methyl[[2-chloro-4-fluoro-5-[(tetrahydro-3-oxo-1H,3H-[1,3,4]thiadiazolo[3,4-a]pyridazin-1-ylidene)amino]phenyl]thio]acetate; clomazone; dicamba; flumiclorac; glyphosate; imazethapyr; metolachlor; metribuzin; nicosulfuron; common lambsquarters, Chenopodium album L. #³ CHEAL; corn, Zea mays L. # ZEAMA; giant foxtail, Setaria faberi Herrm. # SETFA; redroot pigweed, Amaranthus retroflexus L. # AMARE; soybean, Glycine max (L.) Merr. # GLYMA; velvetleaf, Abutilon theophrasti Medik. # ABUTH.

Additional index words: Antagonism, herbicide interaction, Protox, bromoxynil, clethodim, oxasulfuron, quizalofop, sethoxydim, ABUTH, AMARE, CHEAL, DIGSA, GLYMA, SETFA, XANST, ZEAMA.

Abbreviations: COC, crop oil concentrate; DAP, days after planting; DAPO, days after postemergence treatment; DAT, days after treatment; LPOST, late postemergence; NIS, nonionic surfactant; POST, postemergence; Protox, protoporphyrinogen oxidase; PRE, preemergence; UAN, 28% urea ammonium nitrate.

Abstract: Studies were conducted in 1997 and 1998 at the Northeast Mississippi Research and Extension Center to investigate the effects of row spacing (76, 38, and 19 cm), soybean population, and three weed management systems on sicklepod growth and seed production. The cultivars ‘Hartz 5088RR’ (glyphosate-tolerant) and ‘Hutcheson’ (a conventional cultivar) were used in two separate studies. The average soybean populations over cultivars and year were 245,000 (low), 481,000 (medium), and 676,000 (high) plants/ha. The three weed management systems were: no (untreated), one, and two herbicide applications. In the glyphosate-tolerant system, one or two postemergence (POST) applications of glyphosate were used, whereas in the conventional system, flumetsulam plus metolachlor preemergence was used alone (single) or followed by chlorimuron POST (sequential). Reducing soybean row spacing from 76 cm, coupled with increased soybean population, reduced sicklepod population up to 80%. Except for Hutcheson in 1998, reducing row spacing and increasing soybean population also reduced sicklepod seed production in both the untreated and the single applications. A single herbicide application reduced sicklepod population up to 68% from untreated plots. However, except for Hartz 5088RR in 1998, the sequential application did not further reduce sicklepod population. In a shading study, partial shading increased sicklepod height but reduced dry weight. However, as shading level increased from 65 to 80 and 95%, height was also reduced.

Nomenclature: Chlorimuron; flumetsulam; glyphosate; metolachlor; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby #³ CASOB; soybean, Glycine max (L.) Merr.

Additional index words: Glyphosate-tolerant soybean, sequential herbicide applications, seed production.

Abbreviations: MG, maturity group; POST, postemergence; PRE, preemergence; WAP, weeks after planting.

Abstract: The adaptation of herbicides to control the encroachment of one warm-season grass into another species is an important management practice. A field study was conducted in Georgia to determine the rates and frequency of herbicide applications needed to suppress three seashore paspalum cultivars and determine what effects these treatments will have on three bermudagrass cultivars. MSMA plus triclopyr plus clopyralid applied at a total of 2.7 kg/ha in each of three applications for a cumulative total of 8.1 kg/ha effectively suppressed (> 70%) ‘Sea Isle 1’ and ‘Sea Isle 2000’ for 13 wk during 1998 and 1999 and ‘K-3’ during 1998. The suppression of K-3 in 1999 was 56%. The suppression was higher in all instances when MSMA was applied with triclopyr plus clopyralid than when it was not included (< 45%). Four-way combinations of MSMA plus 2,4-D plus mecoprop plus dicamba applied at a total of 5.3 kg/ha in each of three applications for a cumulative total of 15.9 kg/ha suppressed K-3 from 37 to 66%, Sea Isle 2000 from 55 to 66%, and Sea Isle 1 from 59 to 65% for 13 wk. The suppression of three paspalum cultivars at 13 wk from tank mixes of MSMA plus 2,4-D plus dicamba applied at a total of 4.5 kg/ha in each of three applications for a total cumulative of 13.5 kgsol:ha was 7 to 12% lower using the four-way combination treatments. Injury to the bermudagrass cultivars from herbicide treatments was not a problem. In some instances, all herbicides caused some degree of bermudagrass injury on selected dates of treatment. Maximum injury from the herbicides ranged from 18 to 40% for ‘common’ bermudagrass, 18 to 39% for ‘Tifway’ and 30% for ‘TifEagle’ bermudagrass. When injury occurred, bermudagrass recovery was within 1- to 2-wk following treatments.

Nomenclature: Clopyralid; 2,4-D; dicamba; mecoprop; MSMA; triclopyr; ‘common’ bermudagrass, Cynodon dactylon (L.) Pers. #³ CYNDA; hybrid bermudagrass Cynodon transvaalensis × C. dactylon ‘Tifway’, ‘TifEagle’; seashore paspalum, Paspalum vaginatum Swarz # PASVA ‘Sea Isle 1’, ‘Sea Isle 2000’, ‘K-3’.

Additional index words: Turfgrass injury, turfgrass tolerance.

Abbreviations: WAT, weeks after treatment.

Abstract: Cultural practices used for crop production influence the composition of the weed seed bank in the soil. This paper reports the results of a 5-yr experiment to characterize the weed seed bank conducted on a farmer-managed field in central Iowa. The number of weed seeds in the soil and their vertical distribution were examined each October. At the initial sampling in October 1994, the field had been in hay production and about 80% of the weed seeds were common waterhemp and foxtail species. The cropping sequence over the next 3 yr was corn/soybean/corn using a ridge tillage system. Over this period, the density of common waterhemp seeds declined each year. The density of foxtail seeds declined by almost 90% during the first year of corn and did not change during the following years of soybean and corn production. Prior to moldboard plowing of the hay sward in 1994, weed seeds were concentrated in the upper 10 cm of soil. Moldboard plowing resulted in a more uniform distribution of the weed seeds over the upper 20 cm of soil, and the distribution across depths remained relatively constant during the 3 yr of corn and soybean production. During the final year of the experiment, the field was rotated to oat and reseeded with hay species. The number of common waterhemp and foxtail seeds in the soil greatly increased following oat/hay production and seeds were concentrated in the upper 10 cm of the soil profile. Results indicated that the processes affecting the weed seed bank in production fields are complex and will vary greatly based on the production practices used and the timing of their application.

Nomenclature: Common waterhemp, Amaranthus rudis Sauer #³ AMATA; corn, Zea mays L.; foxtail species, Setaria spp.; oat, Avena sativa L.; soybean, Glycine max (L.) Merr.

Additional index words: Cropping systems, ridge tillage, seed bank, seed distribution.

Abstract: Field studies were conducted in 1997 and 1999 to determine the effect of a broadcast-seeded glyphosate-tolerant/conventional soybean seed mix on soybean seed yield, gross profit margin from weed management, and early-season weed suppression prior to a single glyphosate application. Tests were established by broadcasting and incorporating 494,000 seeds/ha glyphosate-tolerant soybean in combination with 0 to 1,976,000 seeds/ha conventional soybean. Glyphosate at 1.12 kg ai/ha was applied at the V5 to V6 soybean growth stage to kill all conventional soybean plants and emerged weeds. The broadcast planting technique was effective in establishing a soybean stand on a silt loam but was ineffective on a silty clay soil. Hemp sesbania and pitted morningglory control, resulting from interference with soybean, were correlated with percent soybean groundcover (R² = 0.961 to 0.971) and population (R² = 0.821 to 0.860) at the V5 to V6 soybean growth stage. Although not significant, increased yield and gross profit margin of dryland soybean occurred as the total seeding rate of the seed mix increased from 494,000 to 741,000 seeds/ha. A dryland seeding rate of 741,000 compared to 494,000 seeds/ha resulted in 438 kg/ha and $93.78/ha increase in seed yield and gross profit margin, respectively. Interference between the two soybean cultivars at 1,976,000 seeds/ha reduced yield. Irrigated soybean at 988,000 seeds/ha produced the greatest seed yield and gross profit margin at 2,987 kg/ha and $555.86/ha, respectively. Maximum yields were attributed to early-season weed suppression.

Nomenclature: Glyphosate; hemp sesbania, Sesbania exaltata (Raf.) Rybd. ex A. W. Hill #³ SEBEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; soybean, Glycine max (L.) Merr. ‘Delta King 5961 RR’.

Additional index words: Broadcast-seeded soybean, low-input agriculture, Roundup Ready soybean, safe site, soybean groundcover, Amaranthus hybridus, Amaranthus palmeri, AMACH, AMAPA.

Abbreviations: DAP, days after planting; WAT, weeks after treatment.

Abstract: Research was conducted to determine the effects of tillage on fluometuron and norflurazon loss in runoff when applied preemergence in cotton. Cumulative water loss and norflurazon and fluometuron concentrations in runoff were not affected by tillage systems. In 1992, the no-till system had less sediment loss in runoff than the conventional tillage system. Tillage systems did not affect sediment loss in 1993. The highest amount of total fluometuron loss occurred with the conventional tillage system in 1992, whereas the reduced tillage system had the lowest amount in 1993. There were no differences in cumulative norflurazon loss between tillage systems in 1992, and as with fluometuron loss, norflurazon loss in runoff was less with the reduced tillage system in 1993. This research indicates that, while conservation tillage may reduce sediment loss, it may not necessarily be the best management tool for decreasing the loss of herbicides in runoff.

Nomenclature: Cotton, Gossypium hirsutum L. ‘DES 119’.

Additional index words: Conventional tillage, no-till, rainfall simulation, reduced tillage, stale seedbed, surface runoff.

Abbreviations: CT, conventional tillage; DAT, days after herbicide treatment; GC, gas chromatography; HPLC, high-performance liquid chromatography; K_oc, soil organic carbon sorption coefficient; NT, no-till; RT, reduced tillage.

Abstract: Lentil and pea are two important crops grown in rotation with winter wheat in the Palouse region of Idaho and Washington. Imazethapyr plus pendimethalin often is used to control weeds in lentil and pea, but the effects of these herbicides on these crops and the subsequently planted winter wheat crop are not well known. The component and combined effects of several rates of imazethapyr and pendimethalin on growth and yield of lentil and pea and the subsequently planted winter wheat crop were measured in 1997 and 1998 field experiments. No herbicide treatment reduced lentil or pea biomass or seed yield compared with the untreated control. Wheat biomass was reduced 35 to 51%, and grain yield was reduced 11 to 17% in all plots treated with 2,240 g/ha pendimethalin at the lentil hilltop site. Imazethapyr at 106 g/ha plus 1,120 g/ha pendimethalin also reduced wheat biomass 24% at the lentil hilltop site. Wheat was not injured at other sites or by other treatments at the lentil hilltop site.

Nomenclature: Imazethapyr; pendimethalin; lentil, Lens culinaris L.; pea, Pisum sativum L.; wheat, Triticum aestivum L.

Additional index words: Herbicide persistence, rotational crop safety.

Abbreviations: DAP, days after planting; DAT, days after treatment; PPI, preplant incorporated.