Watermelon growers rotate crops to prevent problems, but weed populations in new fields may hold unexpected control challenges. Having effective POST herbicides would provide growers an opportunity to respond to emerging weeds on an as-needed basis. To address this need, field studies were conducted over 4 yr in Oklahoma to determine efficacy and crop response of POST halosulfuron applications to direct-seeded watermelon that received PRE application of ethalfluralin at 840 g/ha. At 5 wk after crop emergence (WAE) halosulfuron was applied at 18, 27, 36, and 54 g/ha. The 27 g/ha rate was also applied at 1, 2, 3 and 7 WAE. Halosulfuron applications made 5 WAE did not provide acceptable (> 80%) control of pigweeds and cutleaf groundcherry regardless of rate. Applications made 1 WAE provided significantly better control of pigweeds and cutleaf groundcherry than did later applications. Halosulfuron treatments of 36 and 54 g/ha made 5 WAE and of 27 g/ha made 1, 2 and 3 WAE did not result in significant yield increases compared with the hand-weeded check. These studies show that POST halosulfuron application may be a useful treatment for direct-seeded watermelon. This option would enable more judicious use of herbicides and possible reduction in production costs.

Nomenclature: Halosulfuron; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; tumble pigweed, Amaranthus albus L. AMAAL; cutleaf groundcherry, Physalis angulata L. PHYAN; eclipta, Eclipta prostrata L. ECLAL; watermelon, Citrullus lanatus (Thunb.) Matsumura & Nakai var. lanatus ‘Jubilee’, ‘XIT 101’.

The objective of this research was to determine the potential use of commercially available multispectral images to detect weeds at low densities during the critical period of weed control. Common lambsquarters seedlings were transplanted into plots of glyphosate-resistant corn at 0, 1, 2, and 4 plants/m² at two sites, Agronomy Center for Research and Extension (ACRE) and Meig's Horticultural Research Farm at the Throckmorton–Purdue Agricultural Center (TPAC), in Indiana. Aerial multispectral images (12 to 16 cm pixel resolution) were taken 18 and 32 days after planting (DAP) at ACRE and 19 and 32 DAP at TPAC. Corn and common lambsquarters could not be reliably detected and differentiated at either site when weeds were 9 cm or less in height. However, economic threshold densities (2 and 4 plants/m²) of common lambsquarters could be distinguished from weed-free plots at TPAC when weeds were 17 cm in height. At this height, common lambsquarters plants were beyond the optimal height for glyphosate application, but could still be readily controlled with higher rates. Results from this study indicate that commercially available multispectral aerial imagery at current spatial resolutions does not provide consistently reliable data for detection of early season weeds in glyphosate-resistant corn cropping systems. Additional refinement in sensor spatial and spectral resolution is necessary to increase our ability to successfully detect early season weed infestations.

Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. CHEAL; corn, Zea mays L.

Chemical options for weed control in commercial cowpea production are limited. Repeated long-term use of the acetolactate synthase (ALS) inhibitor, imazethapyr, has resulted in selection for ALS-resistant populations of Palmer amaranth. Experiments were conducted at Bixby, OK, and Kibler, AR, from 2001 to 2003 to evaluate the tolerance of cowpea cultivars and advanced breeding lines to fomesafen, a potential alternative for controlling ALS-resistant Palmer amaranth and other problematic broadleaf weeds. Eight commercial cultivars and 42 advanced breeding lines were entered in the preliminary screening, using 0.84 kg/ha fomesafen. Six breeding lines were selected for the first replicated trial and three (00-582, 00-584, and 00-609) were advanced to across-location experiments. Fomesafen doses of 0, 0.17, 0.34, and 0.67 kg/ha were tested across locations. ‘Early Scarlet’ was used as commercial standard. The advanced lines had equal or higher yield potential (1,182 to 1,936 kg/ha) than Early Scarlet (1,108 kg/ha) across locations. Of the cultivars tested, line 00-609 was the best yielder, whereas 00-584 had the highest tolerance to fomesafen. At the commercial fomesafen rate of 0.34 kg/ha, 00-584 had higher yield (974 and 1,735 kg/ha, respectively, at Bixby, OK, and Kibler, AR) than the nontreated, weed-free, Early Scarlet. Thus, fomesafen can be used on the tolerant line, 00-584, without reducing yield potential relative to Early Scarlet.

Nomenclature: Fomesafen; imazethapyr; Palmer amaranth; Amaranthus palmeri S. Watts. AMAPA; cowpea; Vigna unguiculata L. Walp.

Diclosulam is registered for residual and postemergence control of several broadleaf weeds and suppression of annual sedges in peanut in the southeastern United States. Many producers apply herbicides and other pesticides simultaneously to increase the spectrum of pest control or to increase efficiency of operations. However, compatibility of coapplication of pesticides is a concern. Field trials were conducted to evaluate the compatibility of diclosulam with other herbicides and fungicides. Horseweed control by diclosulam in combination with glyphosate, sulfosate, or paraquat was compared to combinations of these herbicides with flumioxazin, tribenuron plus thifensulfuron, or 2,4-D. All treatments that contained diclosulam controlled horseweed at least 86%. Broadleaf signalgrass control by clethodim and sethoxydim was not affected by diclosulam; however, large crabgrass control was reduced when graminicides were coapplied with diclosulam. Common ragweed control was reduced when diclosulam was applied with chlorothalonil and pyraclostrobin but not by azoxystrobin or tebuconazole.

Nomenclature: Bentazon; clethodim; diclosulam; flumioxazin; glyphosate; paraquat; sethoxydim; sulfosate; thifensulfuron; tribenuron; broadleaf signalgrass, Bracharia platyphylla (Nash) R. D. Webster BRAPP; common ragweed, Ambrosia artemisiifolia L. AMBEL; horseweed, Conyza canadensis (L.) Cronq. ERICA; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; peanut, Arachis hypogaea L.

Preemergence herbicides are commonly applied to nursery containers for control of annual weeds in the production of ornamental plants. Pine bark is a popular container growing medium because it is inexpensive, drains well, is easy to transport, and supports acceptable nursery crop growth. However, little is understood about leaching of herbicides through pine bark. The downward movement of these herbicides through container media may inhibit root growth in sensitive nursery crops and also reduce herbicidal efficacy. Four experiments were conducted at two different irrigation volumes to evaluate depth of pendimethalin movement in packed columns of pine bark and field soil. After 17.5 cm of water was applied over 7 d, pendimethalin moved downward into the 6 to 9-cm depth in 100% pine bark, whereas no movement was detected below the 0 to 3-cm depth in a Tetotum loam soil, as determined by a large crabgrass bioassay. Doubling the irrigation volume to 35 cm of water applied over 14 d did not significantly increase pendimethalin movement in pine bark or field soil. However, it did decrease pendimethalin persistence in the top 0 to 3-cm depth in pine bark. The pine bark had a higher cation exchange capacity than did the field soil. However, the physical characteristics of pine bark, a large volume of void space and low bulk density, resulted in higher hydraulic conductivity rates than in field soil. These factors may be the principal reasons that pendimethalin leached to a greater extent through pine bark than the field soil.

Nomenclature: Pendimethalin; large crabgrass, Digitaria sanguinalis (L.) Scop.

A study was conducted in 2004 and 2005 to evaluate the benefit of applying fluometuron PRE versus glyphosate-only POST programs in second-generation GR cotton (Roundup Ready Flex®). Fluometuron was either included or excluded with POST application timings of glyphosate at the following cotton growth stages: (1) 3 leaf (lf) followed by (fb) 7 lf fb 14 lf (over the top) OT (2) 3 fb 7 lf OT (3) 7 lf OT fb 14 lf postemergence directed (PD), and (4) 7 fb 14 lf OT. Control of goosegrass, Palmer amaranth, pitted morningglory, sicklepod, and smellmelon was increased 2 to 8 percentage points with the addition of fluometuron PRE. The inclusion of fluometuron PRE did not improve control of barnyardgrass, browntop millet, hemp sesbania, johnsongrass, or redroot pigweed and control ranged from 81% to 84%, 69% to 75%, 94% to 94%, 87% to 89%, and 92% to 93%, respectively. By 56 d after the last POST application, control of johnsongrass, Palmer amaranth, pitted morningglory, and smellmelon was at least 83%, 93%, 92%, and 86%, respectively, with only slight differences noted among POST glyphosate programs. Control of barnyardgrass, browntop millet, and redroot pigweed was 68%, 47%, 86%, respectively, with the POST glyphosate program of 3 fb 7 lf OT, which was significantly less than all other glyphosate POST programs. Cotton yield increased 32% and 36% with the addition of fluometuron PRE to glyphosate POST programs consisting of 7 lf OT fb 14 lf PD and 7 lf fb 14 lf OT, respectively. Cotton yield for other glyphosate POST programs including an earlier 3 lf application was not improved when fluometuron was applied PRE. Without inclusion of fluometuron PRE, yield was maximized with the glyphosate POST program that included three applications of glyphosate (2,510 kg/ha). Overall, this research emphasizes the fact that weed control is important in the early season as well as in the late season in second-generation GR cotton.

Nomenclature: Fluometuron; glyphosate; barnyardgrass; Echinochloa crus-galli (L.) Beauv. ECHCG; browntop millet, Urochloa ramosa (L.) Nguyen PANRA; goosegrass, Eleusine indica (L.) Gaertn. ELEIN; hemp sesbania, Sesbania herbacea (P. Mill.) McVaugh SEBEX; johnsongrass, Sorghum halepense (L.) Pers. SORHA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; redroot pigweed, Amaranthus retroflexus L. AMARE; sicklepod, Senna obtusifolia (L.) Irwin and Barneby CASOB; smellmelon, Cucumis melo L. CUMMD; cotton, Gossypium hirsutum L.

Preplant applications of two 2,4-D formulations and dicamba were evaluated for injury to no-till soybean. Herbicides applied 28 or 21 d before planting (DBP) at 0.56 kg ae/ha for the 2,4-D formulations and 0.28 kg ae/ha for dicamba did not injure soybean. At 14 DBP soybean injury was lower (< 6%) with applications of 2,4-D than with dicamba (13% to 17%). Injury increased when herbicides were applied at 7 DBP with soybean injury from both 2,4-D (< 11%) and dicamba (< 38%). When the herbicides were applied at planting soybean injury was < 18% with the 2,4-D formulations and < 73% with dicamba. Soybean yields were unaffected by the injury from herbicides applied 21, 14, and 7 DBP. However, soybean yield was decreased to 870 kg/ha in 2005 when dicamba was applied at planting compared to the nontreated check (1,950 kg/ha)

Nomenclature: 2,4-D; dicamba–diglycolamine salt; soybean, Glycine max L.

Isoxaflutole and mesotrione have been used to control creeping bentgrass in cool season turf, these experiments evaluate these two products for selective nimblewill control. Three experiments were conducted in Virginia and Tennessee to evaluate selective control options for nimblewill in cool-season turfgrass. Single applications of isoxaflutole control nimblewill more effectively than single applications of mesotrione. Nimblewill control 8 wk after initial treatment (WAIT) increased as mesotrione rates increased from 28 to 280 g ai/ha, and isoxaflutole rates increased from 28 to 168 g/ha. Isoxaflutole at 84 and 168 g/ha were the only single application treatments that controlled nimblewill greater than 80% 8 WAIT. However, sequential applications of isoxaflutole and mesotrione at 28 g/ha, 10 d apart controlled nimblewill 94 and 80%, respectively 8 WAIT. Triclopyr and fenoxaprop-p did not effectively control nimblewill and caused unacceptable turfgrass injury. Long-term control was not evaluated in these studies. However, it was concluded that isoxaflutole and mesotrione at appropriate rates and applied in sequence selectively control nimblewill without harming desirable turf.

Nomenclature: Isoxaflutole; mesotrione; nimblewill, Muhlenbergia schreberi J. F. Gmel. MUHSC.

Canada thistle is a serious weed of many crop, rangeland, pasture, and natural areas throughout North America. Aminopyralid is a new pyridine carboxylic acid herbicide that has activity on Canada thistle at lower use rates than current standard treatments. The objectives of this study were to compare aminopyralid efficacy, rates, and application timing with several commercial standards for Canada thistle control. Studies were conducted across the Great Plains at ten locations, which encompassed a wide range of environments. Aminopyralid provided Canada thistle control comparable to picloram, picloram 2,4-D amine, and clopyralid and better control than clopyralid 2,4-D amine, dicamba, dicamba 2,4-D amine and dicamba diflufenzopyr. Canada thistle control was similar when aminopyralid was applied between 0.08 and 0.11 kg ai/ha and application timing (spring bolting vs. fall rosette/regrowth) did not strongly influence control 1 yr after treatment (YAT). Aminopyralid provided effective Canada thistle control at lower use rates than current commercial standards and might be useful in areas where herbicides such as picloram and clopyralid are not recommended for use.

Nomenclature: Aminopyralid; clopyralid; dicamba; diflufenzopyr; picloram; 2,4-D amine; Canada thistle, Cirsium arvense L. Scop. CIRAR.

Grass weeds are a major problem in winter wheat fields in the Pacific Northwest (PNW). Control of these weeds is now enhanced with the use of imazamox resistant winter wheat cultivars, which have been rapidly adopted by wheat growers. However, the effect of spray rate and timing on crop injury and agronomic traits of wheat cultivars with different genetic backgrounds has not been adequately evaluated. Thus, experiments were conducted near Moscow and Genesee, ID in the 2003–2004 and 2004–2005 growing seasons to evaluate the effect of imazamox on four resistant cultivars and seven resistant breeding lines. Wheat plants were treated at the 3- to 5-leaf stage and the 3- to 7-tiller stage with 45 and 90 g ai/ha of imazamox. Visible crop injury was evaluated from 14 to 35 d after treatment (DAT). Heading date, plant height, grain yield and test weight, and end-use grain quality also were measured. The cultivar by treatment interaction was significant at 21 DAT, caused by a differential response of wheat lines to imazamox treatment. This interaction also was significant for plant height and grain yield. Although cultivars and breeding lines responded differently to imazamox treatment, two lines consistently showed the least levels (3 to 8%) of crop injury, with no reductions in plant height or grain yield following imazamox application. Orthogonal contrasts of visible crop injury at 21 DAT showed that the 2× imazamox rate caused more crop injury (12%) than the 1× rate (7%). The 2× rate of imazamox reduced plant height 1%, grain yield 8%, test weight 1%, and percent flour yield 1%. All other traits were not affected by application of imazamox. Application timing only minimally affected crop injury, and had no effect on agronomic or end-use quality traits.

Nomenclature: Imazamox; wheat, Triticum aestivum L. ‘FS4’; ‘Brundage’; ‘Brundage 96’; ‘Lambert’; ‘87-52814A’.

A field trial was conducted for 6 yr (1998 through 2003) at Scottsbluff, NE, to measure weed shifts following multiple applications of two rates of glyphosate or alternating glyphosate with nonglyphosate treatments in continuous corn or in a crop rotation of corn, sugarbeet, and spring wheat with all three crops resistant to glyphosate. After 6 yr, plant densities of common lambsquarters, redroot pigweed, hairy nightshade, and common purslane increased in the crop-rotation treatment compared with continuous corn. There were four weed control subplot treatments consisting of two in-crop applications of glyphosate at 0.4 or 0.8 kg ae/ha each spring, alternating two applications of glyphosate at 0.8 kg/ha one year with a nonglyphosate treatment the next year, or a nonglyphosate treatment each year. The composition of the weed population averaged across all four treatments shifted from kochia and wild proso millet to predominately common lambsquarters. After 3 yr of using glyphosate at 0.4 kg/ha twice each year, common lambsquarters density increased compared with that in the 0.8 kg/ha rate of glyphosate or alternating glyphosate treatments. By the sixth year, the density of common lambsquarters in the glyphosate at 0.4 kg/ha treatment had increased to the extent that corn grain yield was reduced 43% compared with corn grain yield in the 0.8 kg/ha glyphosate treatment. Using glyphosate at either rate for 6 yr decreased the densities of kochia, wild proso millet, and longspine sandbur, did not alter densities of redroot pigweed and green foxtail, and increased the density of hairy nightshade. In the low-rate treatment of glyphosate, the number of common lambsquarters seeds in the seed bank were 134 seeds/kg soil in 1998, declined to 15 seeds/kg by 2002, but began to increase in 2003 as the densities of plants not controlled by glyphosate increased.

Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. CHEAL; common purslane, Portulaca oleracea L. POROL; green foxtail, Setaria viridis (L.) P. Beauv. SETVI; hairy nightshade, Solanum physalifolium Rusby SOLSA; kochia, Kochia scoparia (L.) Schrad. KCHSC; longspine sandbur, Cenchrus longispinus (Hack.) Fern. CCHPA; redroot pigweed, Amaranthus retroflexus L. AMARE; wild proso millet, Panicum miliaceum L. PANMI; corn, Zea mays L; spring wheat, Triticum aestivum L; sugarbeet, Beta vulgaris L.

This study documents the physiology and genetics of evolved atrazine resistance in a wild radish population from Western Australia. Plant response to atrazine treatment confirmed a high level of resistance in population WARR5. At 0.25 kg atrazine/ha, all plants from a susceptible population were killed, whereas resistant WARR5 was unaffected at the highest dose tested (4 kg atrazine/ha). Leaf photosynthesis in susceptible plants was inhibited after 1 kg atrazine/ha treatment, whereas leaf photosynthesis in WARR5 plants was unaffected. Furthermore, atrazine resistance was maternally inherited. Sequencing of a psbA gene fragment in resistant WARR5 and susceptible plants revealed a single point mutation resulting in a coding change from Ser₂₆₄ to Gly of the D1 protein in resistant plants. We are confident that this mutation is the basis of resistance to the photosystem II inhibitors in this wild radish population.

Nomenclature: Atrazine; metribuzin; wild radish, Raphanus raphanistrum L. RAPRA.

Field experiments were conducted in Alabama during 1999 and 2000 to test the hypothesis that any glyphosate-induced yield suppression in glyphosate-resistant cotton would be less with irrigation than without irrigation. Yield compensation was monitored by observing alterations in plant growth and fruiting patterns. Glyphosate treatments included a nontreated control, 1.12 kg ai/ha applied POST at the 4-leaf stage, 1.12 kg/ha applied DIR at the prebloom stage, and 1.12 kg/ha applied POST at 4-leaf and postemergence directed (DIR) at the prebloom cotton stages. The second variable, irrigation treatment, was established by irrigating plots individually with overhead sprinklers or maintaining them under dryland, nonirrigated conditions. Cotton yield and all measured parameters including lint quality were positively affected by irrigation. Irrigation increased yield 52% compared to nonirrigated cotton. Yield and fiber quality effects were independent of glyphosate treatments. Neither yield nor any of the measured variables that reflected whole plant response were influenced by glyphosate treatment or by a glyphosate by irrigation interaction.

Nomenclature: Glyphosate; cotton, Gossypium hirsutum L; ‘Delta and Pine Land 458 BGRR’.

Field observations of morningglory (Ipomoea spp.) showed that many plants grew out from places of comparable competitive advantage (alleys in field experiments with little or no vegetation) into neighboring plants or structures that provided climbing support. Of 223 native morningglory plants growing in rows and row middles in a 121-m² area within established corn research plots that contained no other weeds, 68% of the mature plants climbed up corn. More significant, of the 152 climbing morningglory plants, 96% grew toward and climbed the row in its closest proximity instead of growing across the row middle. Greenhouse and field experiments were initiated to determine whether morningglory grew preferentially toward certain colored structures or corn plants. Greenhouse-grown ivyleaf morningglory displayed varying frequency in locating and climbing toward black (17%), blue (58%), red (58%), white (67%), green (75%), and yellow (75%) stakes or corn (92%). Pots containing black stakes had the fewest climbing morningglory plants. In the field study, fewer ivyleaf morningglories climbed black structures compared with white- or green-colored structures or corn. The morningglory initial planting distance from colored structures or corn was also significant in the percentage of ivyleaf morningglories that exhibited climbing growth and in its final weight; morningglories that successfully located and climbed structures or corn weighed more and produced more seed than morningglories that remained on the ground. Ivyleaf morningglory appears to respond to spatial distribution of surrounding objects and possibly uses reflectance to preferentially project its stems toward a likely prospective structure for climbing.

Nomenclature: Ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; corn, Zea mays L.

An experiment was conducted at two locations in 2003 and 2004 to determine the timing and rate of thifensulfuron that is safe to use on sweetpotato. Thifensulfuron was applied 1, 2, and 4 wk after transplanting (WAP) in 2003 and 4, 6, and 8 WAP in 2004. Within each timing, thifensulfuron treatments were 1.1, 2.1, 3.2, 4.3, and 8.5 g ai/ha plus a weed-free control. The 1 and 2 WAP timings of thifensulfuron reduced the yield of number 1 roots greater than 25%. The 4, 6, and 8 WAP timings had less than 15% reduction in yield, with the 6 WAP timing reducing number 1 roots and total yield 10% or less. When 4.3 g/ha of thifensulfuron was applied 4 WAP, total yield was reduced 13%. The 6 and 8 WAP timings had little yield reduction, with no rate response observed. Application of 4.3 g/ha of thifensulfuron at 6 WAP would allow for control of problematic weed species while limiting potential yield loss. Yield loss from a 4 WAP application of thifensulfuron may in fact be a delay in crop maturity that could be recovered if the sweetpotato harvest was delayed to allow for the optimal amount of number 1 grade roots to be produced.

Nomenclature: Thifensulfuron; sweetpotato, Ipomoea batatas (L.) Lam.

Early succession plant communities consisting of a diverse mixture of grasses, forbs, and scattered shrubs are required by a variety of wildlife species. Early seral stages follow some form of disturbance but can become dominated by shrubs and trees rather quickly, especially in areas with abundant rainfall and relatively long growing seasons, such as the southeastern United States. In the absence of natural disturbance regimes, the quality and maintenance of these plant communities for wildlife is largely dependent upon management. Prescribed fire, disking, herbicide applications, and mowing are practices commonly used to maintain early succession plant communities for various wildlife species throughout this region. Prescribed fire consumes vegetative debris, provides open structure at ground level, and facilitates travel and foraging for wildlife throughout the field. Burning during the dormant season may promote cool-season grasses if they are present in the field. Burning in late March or early April generally promotes warm-season grasses and forbs. Late growing-season fire (September) will reduce woody encroachment and may encourage additional forb cover. Disking promotes vegetation decomposition, provides open structure at ground level, and generally promotes annual plant species. Disking in the fall and winter stimulates more forb growth than disking in the spring, which will stimulate undesirable nonnative warm-season grasses if present in the seedbank. Selective herbicides can influence plant composition and can be used to encourage grasses where forbs dominate, to promote forbs where grasses dominate, and to reduce woody cover. Mowing during midsummer encourages additional grasses in fields dominated by forbs but is not recommended for field maintenance because mowing produces thatch, which limits the ability of several wildlife species to travel and forage through the field, suppresses the seedbank, and destroys nests and young wildlife. Several practices can be used in combination to meet specific objectives. Succession should be set back every 2 to 4 yr, depending on plant response and focal wildlife species. It is important to intersperse disturbance in space and time, so that a variety of cover types are always available, even to those animals with small home ranges.

The affect of mesosulfuron and tribenuron applied POST to oat and rye was determined at three locations in Georgia during 2004 and 2005. Five herbicide treatments were applied to oat and rye in Feekes scale (FS) 1.2 or 2 developmental stage. Herbicide treatments consisted of tribenuron at 13 or 26 g ai/ha, tribenuron at 13 g/ha plus MCPA at 561 g ai/ha, MCPA at 561 g/ha, and mesosulfuron at 15 g ai/ha. Tribenuron, MCPA, and tribenuron plus MCPA injured both crops less than 4% and did not affect grain yield. Mesosulfuron applied to rye in FS 1.2 injured the crop 36% at 2 wk after treatment (WAT), 12% at 5 WAT, and 0% at harvest. Mesosulfuron applied at FS 2 injured rye less than 9%. Mesosulfuron did not influence rye-grain yield with either application timing. Mesosulfuron injured oat 65 to 86% at 5 WAT and reduced yield at least 70% regardless of application timing.

Nomenclature: MCPA; mesosulfuron-methyl; tribenuron-methyl; oat, Avena sativa L. ‘Horizon 32’; rye, Secale cereale L. ‘Wrens 96’.

The competitiveness of three phenotypically different sugarcane cultivars with bermudagrass was determined in field trials. In trial one, bermudagrass biomass was 22% less in CP 70-321 than in HoCP 85-845 in the plant-cane crop, but biomass was 130 to 170% greater in CP 70-321 than in the other two cultivars during the second-ratoon crop. CP 70-321 emerges quickly following planting, which might have reduced bermudagrass growth in the plant-cane crop, but the lower stalk population of CP 70-321 might have promoted bermudagrass survival and growth during the second-ratoon crop. In trial two, there were no differences in bermudagrass biomass when comparing its establishment in the different cultivars. Sugarcane, averaged across cultivar, produced fewer stalks and was shorter when competing with bermudagrass. In the plant-cane crop, stalk populations were reduced 13 to 23%. In the first-ratoon crop, stalk population was reduced 8 to 15%. In the second-ratoon crop, stalk population was reduced 8 to 10%. Bermudagrass interference reduced sugar yields by 8 to 32% in the plant-cane crop, with reductions of no more than 9% in the first- and second-ratoon crops. The greater yield loss in the plant-cane crop in the first production year shows the importance of controlling bermudagrass in the summer fallow period prior to planting and during establishment of the plant-cane crop.

Nomenclature: Bermudagrass, Cynodon dactylon L. Pers. CYNDA; sugarcane, Saccharum interspecific hybrids ‘CP 70-321’, ‘LCP 85-384’, ‘HoCP 85-845’.

Greenhouse studies were conducted in 2003 at the Stine–Haskell Research Center to determine whether herbicide inhibitors of six specific sites in the carotenoid biosynthesis pathway would elicit synergistic responses when applied postemergence (POST) in combination with the photosystem II (PSII) inhibitor atrazine. Based on data analysis with the Isobole method, synergistic responses were observed on red morningglory, common cocklebur, and giant foxtail when atrazine was applied in mixtures with the deoxy-D-xylulose-5-phosphate reductoisomerase (DOXP reductoisomerase) inhibitor fosmidomycin, the p-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor mesotrione, and the DuPont proprietary zeta-carotene desaturase (ZDS) inhibitor DFPC. Clomazone (its metabolite ketoclomazone is the actual enzyme inhibitor), an inhibitor of 1-deoxy-D-xylulose-5-phosphate synthatase (DOXP synthase), provided synergistic responses on red morningglory, but antagonistic responses on both common cocklebur and giant foxtail when applied in mixtures with atrazine. Combinations of the lycopene cyclase (LC) inhibitor, CPTA, with atrazine produced synergistic responses on both common cocklebur and giant foxtail but were antagonistic on red morningglory. Norflurazon, a phytoene desaturase (PDS) inhibitor, applied in mixtures with atrazine provided synergistic responses on red morningglory, antagonistic responses on giant foxtail, and independent responses on common cocklebur. Because carotenoids have been determined to play a key role in quenching singlet oxygen species in the chloroplast and also assist in the maintenance of the D1 protein in PSII, this might help explain the synergistic responses with atrazine observed in our studies.

Nomenclature: Atrazine; clomazone; CPTA [2-(4-chloro-phenylsulfanyl)-ethyl]-diethylamine; DFPC N-[5-[(dimethylamino)carbonyl]-2-fluorophenyl]-3-(1,1-dimethylethyl)-1-ethyl-1H-pyrazole-5-carboxamide; fosmidomycin [3-(formyl-hydroxy-amino)-propyl]-phosphonic acid; mesotrione; norflurazon; common cocklebur, Xanthium strumarium L. XANST; giant foxtail, Setaria faberi Herm. SETFA; red morningglory, Ipomoea coccinea L. IPOCC.

Five experiments were conducted during 2001 and 2002 in North Carolina to evaluate peanut injury and pod yield when glyphosate was applied to 10 to 15 cm diameter peanut plants at rates ranging from 9 to 1,120 g ai/ha. Shikimic acid accumulation was determined in three of the five experiments. Visual foliar injury (necrosis and chlorosis) was noted 7 d after treatment (DAT) when glyphosate was applied at 18 g/ha or higher. Glyphosate at 280 g/ha or higher significantly injured the peanut plant and reduced pod yield. Shikimic acid accumulation was negatively correlated with visual injury and pod yield. The presence of shikimic acid can be detected using a leaf tissue assay, which is an effective diagnostic tool for determining exposure of peanut to glyphosate 7 DAT.

Nomenclature: Glyphosate; peanut, Arachis hypogaea L. ARHHY.

A study was conducted in 2005 and 2006 to evaluate the response of 10 rice cultivars to penoxsulam applied at 70 g ai/ha to two- to three-leaf rice. A related study was conducted in 2004 and 2005 to compare the rice response to applications of penoxsulam at 35 and 70 g/ha and bispyribac-sodium at 28 g ai/ha. In the first study, all 10 rice cultivars exhibited tolerance to penoxsulam as evidenced by plant height, number of days to 50% heading, and rice grain yield. In the second study, applications of both rates of penoxsulam and bispyribac-sodium reduced mass of rice roots 65 to 71% 2 wk after treatment compared with a nontreated control. However, rice grain yield was higher following application of penoxsulam at 70 g/ha compared with yield of the nontreated control or yield following penoxsulam at 35 g/ha and bispyribac-sodium. Rice recovered from injury observed following herbicide application with no negative impact on grain yield. Results indicate that, even though rice root injury can be severe following application, penoxsulam is safe for application to rice cultivars currently grown in the southern U.S. Rice Belt.

Nomenclature: Penoxsulam; bispyribac-sodium; rice, Oryza sativa L.

Field experiments were conducted in 1999, 2000, and 2001 to investigate PRE and POST applications of halosulfuron-methyl in combination with clomazone plus ethalfluralin for control of several broadleaf weeds in cucumber and pumpkin. Halosulfuron was applied PRE or POST to cucumber and pumpkin at 9, 18, and 27 g ai/ha in combination with a PRE application of clomazone at 175 g ai/ha plus ethalfluralin at 630 g ai/ha. Halosulfuron applied POST at 27 g/ha in combination with clomazone plus ethalfluralin controlled weed species greater than 62%. Smooth pigweed control by addition of halosulfuron at 27 g/ha PRE or POST was greater than 88%, and common ragweed control was greater than 78% PRE and 88% POST, but control of ivyleaf morningglory and tall morningglory was 43 to 67% PRE and 62 to 76% POST. Cucumber injury with addition of halosulfuron did not exceed 13% PRE or POST, but pumpkin was injured as much as 43% with addition of halosulfuron PRE and 27% by POST applications. In a separate study without clomazone plus ethalfluralin PRE, smooth pigweed up to 13 cm tall was controlled 83% by halosulfuron at 27 g/ha in 2000, but rapidly growing smooth pigweed 15 to 40 cm tall was controlled only 58% in 2001. Cucumber and pumpkin yields were not affected by halosulfuron rate but were higher than yields produced by cucumber and pumpkin treated with only the mixture of clomazone plus ethalfluralin. In these studies, cucumber and pumpkin were tolerant to halosulfuron at 9 to 27 g/ha PRE or POST, making this herbicide acceptable for use in combination with clomazone and ethalfluralin for controlling several common weed species.

Nomenclature: Clomazone; ethalfluralin; halosulfuron; common ragweed, Ambrosia artemisiifolia (L.); ivyleaf morningglory, Ipomoea hederacea (L.) Jacq; smooth pigweed, Amaranthus hybridus L; tall morningglory, Ipomoea purpurea (L.) Roth; cucumber, Cucumis sativus (L.) ‘Dasher II’; pumpkin, Cucurbita maxima (Duch.) ‘Appalachian’.

Six weed control programs with and without irrigation were investigated in a newly established pecan orchard. Irrigation increased crown diameter growth in only one of seven growing seasons but increased nut yield an average of 35% in the first two bearing years. Weed control program significantly influenced crown diameter beginning in the fourth growing season and continued through season six while also impacting final crown diameter. The use of postemergence (POST) herbicides increased crown diameter a minimum 4 mm vs. preemergence (PRE) herbicides. Mowing neither increased nor decreased crown diameter when used with herbicides; however, when used solely, crown diameter was 29% less. Highest growth rates were obtained with a combination PRE plus POST weed management system. Nut yields were closely linked to growth data. No differences in nut yield were observed between PRE- or POST-herbicide programs alone or in combination with mowing. Mowing alone decreased nut yield 57% vs. herbicide-based approaches. A combination PRE- plus POST-weed control program increased yield 38% vs. all other treatments.

Nomenclature: Pecan, Carya illinoinensis (Wang.) K. Koch var. ‘Desirable’.

Cogongrass and guineagrass are serious perennial weeds in small-scale farms in lowland subhumid zones of West Africa. Field studies were conducted in 2002 and 2003 at two sites in Ibadan, Nigeria [Ijaye and the International Institute of Tropical Agriculture (IITA)], to evaluate the effect of rimsulfuron on weed communities dominated by cogongrass and guineagrass in corn. At both sites, treatments were rimsulfuron dosages of 0 (nontreated control), 10, 20, 30, 40, 50, 60, 70, and 80 g ai/ha. Rimsulfuron did not cause any visible phytotoxicity on the corn at any dosage at either site. There was a rapid increase in weed control as the dosage of rimsulfuron increased from 0 to 20 g/ha. Weed control was not improved at rates higher than 20 g/ha. Rimsulfuron was very effective against sedges, Ipomoea involucrata, Bengal dayflower, gulf leafflower, old-world diamond-flower, and wild jute providing more than 80% control at dosages between 10 and 20 g/ha at Ijaye. Rimsulfuron was less effective for cogongrass, with a maximum of only 38% control observed. At IITA, the herbicide was very effective against guineagrass, Bengal dayflower, nodeweed, coat buttons, redfruit passionflower, and waterleaf; all of which were controlled more than 70% with any rate of rimsulfuron. Regression analysis showed that the dosage of rimsulfuron required to reduce shoot dry biomass by 70% was 5 g/ha for guineagrass and 35 g/ha for cogongrass at 3 wk after treatment (WAT). At crop maturity, the dosage of rimsulfuron required to reduce shoot dry biomass by 70% was 43 g/ha for guineagrass and 200 g/ha for cogongrass. The dry biomass of cogongrass and guineagrass was higher at crop harvest than at 2 WAT regardless of herbicide dosage. Corn grain yield was 1.8 times higher at IITA than at Ijaye. At both sites, corn grain yield increased with increased herbicide dosage. Maximum corn grain yields were obtained at a rimsulfuron dosage of 20 g/ha.

Nomenclature: Rimsulfuron; coat buttons, Tridax procumbens L. TRQPR; cogongrass, Imperata cylindrica (L.) Beauv. IMPCY; old-world diamond-flower, Oldenlandia corymbosa L. OLDCO; guineagrass, Panicum maximum Jacq. PANMA; gulf leafflower, Phyllanthus amarus Schum. & Thonn. PYLAM; nodeweed, Synedrella nodiflora (L.) Gaertn SYDNO; redfruit passionflower, Passiflora foetida L. PAQFO; sedges, Cyperus, Mariscus, and Kyllinga spp; Bengal dayflower, Commelina benghalensis L. COMBE; waterleaf, Talinum triangulare (Jacq.) Willd TALTR; wild jute, Corchorus tridens L. CRGTR; corn, Zea mays L. ‘TZL Comp 4W’.

Field and greenhouse experiments were conducted during 2005 and 2006 at Stoneville, MS, to determine control of ragweed parthenium with several preemergence (PRE) and postemergence (POST) herbicides registered for use in corn, cotton, peanut, rice, and soybean. Norflurazon, pendimethalin, clomazone, diuron, fluometuron, pyrithiobac, dimethenamid, flumetsulam, imazaquin, s-metolachlor, metribuzin, chlorimuron, atrazine, simazine, flumioxazin, and quinclorac were applied PRE. Ragweed parthenium control was highest with norflurazon (100%) and clomazone (100%) followed by fluometuron (96%), metribuzin (90%), diuron (87%), flumioxazin (84%), chlorimuron (77%), and quinclorac (67%) at 6 wk after treatment (WAT) under greenhouse conditions. Control of ragweed parthenium was less than 58% with all other herbicides. Ragweed parthenium appears to be highly sensitive to pigment and photosynthetic inhibitors compared to herbicides with other modes of action. Glyphosate, glufosinate, paraquat, bentazon, acifluorfen, chlorimuron, halosulfuron, MSMA, bromoxynil, atrazine, 2,4-D, flumioxazin, trifloxysulfuron, and clomazone were applied POST to field-grown rosette and bolted plants. Glyphosate, glufosinate, chlorimuron, and trifloxysulfuron applied at rosette stage provided greater than 93% control of ragweed parthenium at 3 WAT. Halosulfuron, MSMA, bromoxynil, 2,4-D, and flumioxazin controlled 58 to 90% rosette ragweed parthenium at 3 WAT. Ragweed parthenium control with all other POST herbicides was less than 38%. At bolted stage, glyphosate, glufosinate, and trifloxysulfuron controlled 86 to 95% ragweed parthenium and control was 61 to 70% with chlorimuron, halosulfuron, and 2,4-D 3 WAT. Overall, efficacy of POST herbicides was better on rosette plants than on bolted plants. Amino acid synthesis and glutamine synthase inhibitors were more active than herbicides with other modes of action. These results indicate that norflurazon, clomazone, fluometuron, flumioxazin, halosulfuron, chlorimuron, and trifloxysulfuron could provide effective control of ragweed parthenium.

Nomenclature: Acifluorfen; atrazine; bentazon; bromoxynil; chlorimuron; clomazone; 2,4-D; dimethenamid; diuron; flumetsulam; flumioxazin; fluometuron; glufosinate; glyphosate; halosulfuron; imazaquin; s-metolachlor; metribuzin; MSMA; paraquat; quinclorac; simazine; trifloxysulfuron; ragweed parthenium, Parthenium hysterophorus L. PTNHY; corn, Zea mays L; cotton, Gossypium hirsutum L; peanut, Arachis hypogaea L; rice, Oryza sativa L; soybean, Glycine max (L.) Merr.

Field experiments were conducted at Manhattan and Hesston, KS, in 2004, and at Manhattan, KS, in 2005, to evaluate cotton response to seven hormonal-type herbicides. Herbicides 2,4-D amine, 2,4-D ester, clopyralid, picloram, fluroxypyr, triclopyr, and dicamba were each applied at 0, 1/100, 1/200, 1/300, and 1/400 of the herbicide use rates on cotton in the six- to eight-leaf stage. Herbicide use rates were 210 and 280 g ae/ha for fluroxypyr and clopyralid and 561 g ae/ha, for 2,4-D amine, 2,4-D ester, dicamba, picloram, and triclopyr. At 14 d after treatment (DAT), all herbicides caused leaf cupping and epinasty, except triclopyr and clopyralid, which caused severe bleaching and chlorosis. The order of visual injury ratings was 2,4-D ester > 2,4-D amine > picloram > dicamba > fluroxypyr > triclopyr > clopyralid. By 56 DAT, slight injury symptoms were observed on plants treated with all herbicides, except all rates of 2,4-D, from which symptoms were severe. All rates of 2,4-D and the highest rate of picloram caused more than 60% flower abortion. Ranking of fiber yield reduction after herbicide treatment was 2,4-D ester > 2,4-D amine > picloram > fluroxypyr > dicamba > clopyralid > triclopyr. This research demonstrated that cotton is extremely susceptible to simulated drift rates of 2,4-D and picloram, whereas clopyralid and triclopyr caused early injury, with minimal effect on cotton yield.

Nomenclature: Tribufos; S,S,S-tributyl phosphorotrithioate; cotton, Gossypium hirsutum L. ‘PM 2145 RR’.

Studies were conducted in 2003 and 2004 to determine the effect of application timing and halosulfuron rate on sweetpotato yield and quality. Halosulfuron was applied 1, 2, and 4 wks after transplanting (WAP) sweetpotato in 2003, and 2, 3, and 4 WAP in 2004. Treatments within each timing included halosulfuron at 13, 26, 39, 52, and 65 g ai/ha plus a weed-free control. Combined over year, site, cultivar and rate, halosulfuron applied at 1, 2, 3, and 4 WAP stunted sweetpotato 32, 15, 11, and 14%, respectively, rated 2 wks after treatment. The stunting observed with the 1 and 2 WAP timings caused a 17 and 10% reduction in yield of No. 1 roots, respectively, compared with the weed-free control. The 3 and 4 WAP timings of halosulfuron did not reduce yield of No. 1 roots. Total yield was reduced approximately 11% at the 1, 2, and 3 WAP application timings. Halosulfuron at 4 WAP did not reduce total yield. Combined over year, site, and cultivar, halosulfuron applied at 39 g/ha did not reduce the weight of No. 1 roots or total crop yield and thus could be an effective POST option for weed control in sweetpotato.

Nomenclature: Halosulfuron; sweetpotato, Ipomoea batatas (L.) Lam.

Field studies were conducted 2004 and 2005 to evaluate weed control following POST applications of glyphosate in combination with either S-metolachlor (premix formulation), pyrithiobac, or trifloxysulfuron in conjunction with glyphosate in second-generation glyphosate-resistant cotton (Roundup Ready Flex). These herbicides were applied in combination with glyphosate in a two-application program at the 2-leaf (LF) (followed by glyphosate alone at the 10-LF growth stage), 6-LF (following glyphosate alone at the 2-LF growth stage), or 10-LF (following glyphosate alone at the 2-LF growth stage) cotton growth stages. No differences in weed control between residual herbicide were observed for goosegrass, hemp sesbania, Johnsongrass, Palmer amaranth, redroot pigweed, sicklepod, or smellmelon. Optimum control of barnyardgrass and browntop millet was achieved with glyphosate plus S-metolachlor. No differences were observed among application timings for control of goosegrass, hemp sesbania, Johnsongrass, pitted morningglory, and smellmelon. Control of barnyardgrass, browntop millet, Palmer amaranth, redroot pigweed, and sicklepod was optimized with residual herbicide application at the 2- or 10-LF timing. No yield differences were observed between residual herbicides, and seed cotton yield averaged 2,800 kg/ha. Yield was maximized when residual herbicide was applied at the 2- or 10-LF growth stage (2,960 to 2,730 kg/ha). Analysis based on numerical yield at particular residual-herbicide application timings and calculated yield for each timing based on the percentage of a standard three-application glyphosate program indicated the most consistent residual-herbicide timing for optimizing yield in a reduced-input Roundup Ready Flex weed-control program occurred at the two-leaf growth stage. All reduced-input programs, however, resulted in cotton yield of at least 93% of that obtained with the standard program.

Nomenclature: Glyphosate; pyrithiobac; S-metolachlor; trifloxysulfuron; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; browntop millet, Urochloa ramosa (L.) Nguyen PANRA; goosegrass, Eleusine indica (L.) Gaertn ELEIN; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill SEBEX; Johnsongrass, Sorghum halepense (L.) Pers. SORHA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; redroot pigweed, Amaranthus retroflexus L. AMARE; sicklepod, Senna obtusifolia (L.) H.S. Irwin & Barneby CASOB; smellmellon, Cucumis melo L. CUMMD; cotton, Gossypium hirsutum L.

Field studies were established at two Missouri locations in 2004 and 2005 to evaluate the effects of fall and early spring herbicide applications on soil temperature, soil moisture content, and insect injury in no-till corn production systems. Both experiments received applications of simazine plus 2,4-D, rimsulfuron plus thifensulfuron plus 2,4-D, and glyphosate plus 2,4-D in the fall, 45 d prior to planting (45 d EPP), 30 d prior to planting (30 d EPP), and 7 d prior to planting (7 d EPP). During a period from April 1 to April 14, simazine plus 2,4-D applied 45 d EPP resulted in higher soil temperatures at a 5-cm depth compared to the untreated control. However, there were few differences in soil temperature present from April 15 to May 1. Soil moisture readings taken during this same time period correlated with soil temperature readings. Measurements of soil moisture taken at 1 and 3 wk after planting (WAP) revealed significantly lower soil moisture readings in the untreated compared to herbicide treated plots. This lower soil moisture content allowed untreated plots to warm up more rapidly and thereby eliminated any negative impacts that dense stands of winter annual weeds may have had on soil temperature. Evaluations of corn flea beetle and lepidopteron injury taken at the V2, V4, and V6 corn leaf stages revealed significant differences in injury as a result of these treatments. When dense stands of winter and summer annual weeds were left uncontrolled, corn flea beetle injury was significantly lower than in plots treated with a herbicide. However, when a post herbicide application was made to remove all weed species prior to the V6 sampling date, differences in corn flea beetle injury between the untreated and herbicide treated plots were eliminated. Additionally, removal of all weed species led to higher lepidopteron injury in the untreated.

Nomenclature: Glyphosate; rimsulfuron; simazine; thifensulfuron; 2,4-D; corn, Zea mays L. ‘Pioneer 34B23’, corn flea beetle, Chaetocnema pulicaria Melsheimer.

Glyphosate at simulated drift rates representing 12.5, 6.3, and 1.6% of the usage rate of 1,120 g ai/ha (140, 70, and 18 g/ha, respectively) was applied to wheat at first node, boot stage, or at early flowering. At 14 d after treatment (DAT) wheat injury, expressed as bleaching of leaf foliage and growth inhibition, was 40 to 55% for 70 g/ha applied at first node and for 140 g/ha applied at all growth stages. Wheat height 28 DAT was reduced 47% with glyphosate applied at 140 g/ha at first node and was reduced around 26% for 70 g/ha applied at first node and 140 g/ha applied at boot stage. Wheat height was not reduced with glyphosate at 18 g/ha applied at first node or boot stage and with all rates applied at early flowering. Wheat yield was reduced 72% when glyphosate was applied at 140 g/ha at first node, 45% when applied at boot stage, and 54% when applied at early flowering. For 70 g/ha, wheat yield was reduced 25 to 30% for the three application timings. Wheat yield was not reduced for 18 g/ha glyphosate. In another study, six wheat varieties responded the same to glyphosate applied at 140 and 70 g/ha. Wheat height 28 DAT was reduced an average of 34% for 140 g/ha glyphosate and 17% for 70 g/ha applied at first node, but height was not reduced when applied at early flowering. Yield was reduced an average of 58 and 43% for 140 and 70 g/ha applied at first node and 38 and 19% for 140 and 70 g/ha applied at early flowering. In both studies yield reductions in most cases were reflected in reduced spike density, spikelet number per spike, and seed weight.

Nomenclature: Glyphosate; wheat, Triticum aestivum L. ‘Coker 9663’, ‘Mason’, ‘LA 422’, ‘AGS 2000’, ‘Pioneer/26R61’, and ‘USG 3209’.

Field experiments were conducted at two locations in 2003 and 2004 to determine dark tobacco tolerance and weed control from postemergence over-the-top (POT) and postemergence-directed (PD) applications of trifloxysulfuron and halosulfuron. Trifloxysulfuron was applied at 3.6 or 5.3 g ai/ha and halosulfuron was applied at 36 or 53 g ai/ha. Trifloxysulfuron POT injured ‘Narrowleaf Madole’ dark tobacco 16 to 33% and halosulfuron POT caused 32 to 33% injury at 1 wk after treatment (WAT). Tobacco plant height at 1 WAT with POT applications was also reduced by up to 31% at one of two locations. Tobacco injury from POT applications had dissipated to 6 to 12% by 4 WAT. Despite extensive early-season injury, most POT herbicide applications did not significantly reduce tobacco yield, mean grade index, and gross revenue compared to tobacco that only received pretransplant applications of sulfentrazone plus clomazone. Dark tobacco was much more tolerant to PD applications of either herbicide, with no more than 4% injury observed at 1 WAT. Neither herbicide controlled horsenettle more than 57% at either application rate or method. Although trifloxysulfuron and halosulfuron could contribute to tobacco weed control programs by providing postemergence control of several common weed species, PD applications would be the only acceptable method of application due to excessive injury observed from POT applications of these herbicides.

Nomenclature: Clomazone; halosulfuron; sulfentrazone; trifloxysulfuron; horsenettle, Solanum carolinense L. SOLCA; dark tobacco, Nicotiana tabacum L. ‘Narrowleaf Madole’.

In 2004 and 2005, field research was conducted in Idaho to compare tank mixtures of flumioxazin at the 53 g ai/ha potato use rate with comparable tank mixtures of rimsulfuron at 26 g ai/ha for broad-spectrum weed control. Flumioxazin in two-way tank mixtures with metribuzin, EPTC, pendimethalin, S-metolachlor, or ethalfluralin provided greater than 90% hairy nightshade control, which was comparable with control by similar rimsulfuron two-way tank mixtures. Flumioxazin plus metribuzin or rimsulfuron were the only two-way mixtures with flumioxazin consistently providing 90% or greater redroot pigweed, common lambsquarters, and green foxtail control. Control of these weeds by any of the rimsulfuron two-way mixtures was almost always greater than 90%. Three-way tank mixtures containing flumioxazin or rimsulfuron controlled hairy nightshade, redroot pigweed, and common lambsquarters similarly, and control ranged from 89 to 100%. When metribuzin was not included with flumioxazin in three-way mixtures, control was 80 to 97% and not always comparable with the 89 to 100% control by similar rimsulfuron mixtures. Green foxtail control by flumioxazin or rimsulfuron three-way mixtures usually was similar and greater than 90%.

Nomenclature: Flumioxazin; rimsulfuron; common lambsquarters, Chenopodium album L. CHEAL; green foxtail, Setaria viridis L. SETVI; hairy nightshade, Solanum sarrachoides Sendter SOLSA; redroot pigweed, Amaranthus retroflexus L. AMARE; potato, Solanum tuberosum L. ‘Russet Burbank’.

Annual grasses constitute a major weed problem in winter annual crops in Northern Europe and especially in cropping systems where ploughing is omitted. At the optimum growth stage for control with POST herbicides, grasses have a predominantly vertical leaf orientation. This represents a very difficult spray target using the standard technique where nozzles are mounted more or less vertically downward. In this study, efficacy of the foliar-acting herbicide, haloxyfop, on perennial ryegrass at the two- to three-leaf stage was investigated in field experiments using some alternative configurations of nozzle mounting on the sprayer. Angling the spray either forward or backward relative to the direction of travel increased herbicide efficacy using standard commercially available flat-fan and pre-orifice nozzles. Efficacy increased generally with increasing angling relative to vertically downward and the forward-angled spray improved efficacy most. The largest improvement in efficacy was obtained using a 60° forward-angled spray in combination with a reduced boom height. Using this configuration, herbicide dose could be reduced by approximately 30% without loss of efficacy in comparison with the standard vertical mounting of nozzles. There was no advantage of using combinations of forward- and backward-angled nozzles.

Nomenclature: Haloxyfop; perennial ryegrass, Lolium perenne L. LOLPE.

Much research has evaluated herbicide safety on established bermudagrass turf, but information is lacking on seedling response to herbicides. Three field experiments were conducted in Blacksburg, VA, to assess turfgrass and smooth crabgrass response to selected sulfonylurea herbicides during seedling bermudagrass establishment. Herbicides injured bermudagrass 9 wk after treatment in the following order from most to least injurious: flazasulfuron  =  trifloxysulfuron > rimsulfuron > metsulfuron  =  sulfosulfuron > foramsulfuron. Herbicides applied 3 wk after seeding (WAS) were generally more injurious than when applied 1 WAS. Flazasulfuron and trifloxysulfuron-sodium controlled smooth crabgrass greater than 90% at 6 WAS, and metsulfuron and rimsulfuron suppressed smooth crabgrass 76 and 84%, respectively. Foramsulfuron, metsulfuron, and sulfosulfuron appear safe to apply 1 and 3 WAS, causing very little chlorosis and no reduction in turf cover. Rimsulfuron is injurious when applied at those timings; however, long-term cover is not reduced. Flazasulfuron and trifloxysulfuron-sodium are not safe to use 1 and 3 WAS unless weed pressure is extreme, and a delay in bermudagrass cover is acceptable.

Nomenclature: Flazasulfuron; foramsulfuron; metsulfuron; rimsulfuron; sulfosulfuron; trifloxysulfuron-sodium; smooth crabgrass, Digitaria ischaemum (Schreb.) Schreb ex Muhl. DIGIS; bermudagrass, Cynodon dactylon (L.) Pers. ‘Riviera’.

A 3-yr field experiment was initiated in 2001 to evaluate weed suppression and sweetpotato productivity in three organic sweetpotato production systems. Organic systems were (1) compost and no cover crop with tillage (Org-NC), (2) compost and a cover crop mixture of hairy vetch and rye incorporated before transplanting (Org-CI), and (3) compost and the same cover crop mixture with reduced tillage (Org-RT). A conventional system with tillage and chemical controls (Conv) was included for comparison. Suppression of monocot and dicot weed density and biomass was similar between Org-NC and Org-CI each year, and were frequently similar to Conv. Org-RT was as effective as Org-NC in controlling dicot weed density and biomass each year, but did not suppress monocot weeds. At sweetpotato harvest, an increase in cover crop surface residue biomass in Org-RT was associated with a decrease in cumulative total weed density (R² = 0.43, P = 0.0001); however, the amount of that residue was insufficient to suppress late-emerging monocot weeds. Total sweetpotato yield in Org-RT was at least 45% lower than other systems in 2002 and was most likely due to an increase in monocot weed density and biomass concurrent with a decrease in sweetpotato vine biomass. Total sweetpotato yield was similar among all systems in 2001 and 2004; the exception was lowest yields obtained in the Org-RT system in 2002. Organically managed sweetpotato with or without an incorporated cover crop produced sweetpotato yields equal to conventionally managed systems despite difficulties controlling weeds that emerged later in the season.

Nomenclature: EPTC; napropamide; hairy vetch, Vicia villosa Roth; rye, Secale cereale L. ‘Wrens Abruzzi’; sweetpotato, Ipomoea batatas (L.) Lam. ‘Beauregard’.

The effect of N levels, weed control treatments, and their interaction on maize yield and weed growth in sandy soils is not completely understood. Therefore, field experiments were conducted during 2005 and 2006 to determine if management can improve maize competitiveness with weeds, and thus achieve the yield potential of maize in sandy soils. The experiment included three N levels (300, 338, and 375 kg/ha) and five weed control treatments, e.g., hand hoeing twice, hand hoeing three times, fluroxypr hoeing once, hoeing once bispyribac-Na, and a nonweeded check. N rates affected dry weight of weeds growing with maize except with large crabgrass. Biomass of common purslane, considered a nitrophilous species, was increased by all N levels. Weeds were controlled by all treatments compared with the nontreated check; however, herbicide treatments were not superior to hand-hoeing treatments. Using more N favored growth and yield of maize more than weeds. Adding N fertilizer also improved most yield parameters. Highest grain yield of maize resulted at 375 kg/ha N. All weed control treatments improved grain yield two- to threefold compared with the nonweeded check. The interaction between N rates and weed control treatments had significant effects on dry biomass of common purslane and barnyardgrass, as well as grain index and biological yield parameters of maize. Grain yields were improved with fluroxypyr applied 2 wk after sowing (WAS) maize followed by one hand hoeing 6 WAS or hoeing at 3 WAS followed by bispyribac-Na applied 6 WAS. However, highest yields were obtained by hoeing early during the growing season.

Nomenclature: Maize, Zea mays L; fluroxypyr; bispyribac-Na; common purslane, Portulaca oleracea L; barnyardgrass, Echinochloa crus-galli (L.) Beauv; large crabgrass, Digitaria sanguinalis (L.) Scop.

Field trials were conducted in East Lansing, MI in 2004 and 2005 and in St. Charles, MI in 2004, 2005, and 2006 to compare weed control and sugarbeet tolerance from microrate herbicide treatments that included s-metolachlor and dimethenamid-P. Treatments included the base microrate treatment alone and with full- and split-application rates of s-metolachlor at 1.4 kg/ha or dimethenamid-P at 0.84 kg/ha at the various microrate application timings. All treatments injured sugarbeet. In 2004 and 2006, full rates of both s-metolachlor and dimethenamid-P applied PRE or in the first microrate application injured sugarbeet more than the base microrate treatment. When s-metolachlor or dimethenamid-P were split-applied between PRE and the third microrate application or between the first and the third microrate applications, injury was still greater than from the base microrate treatment. Furthermore, applying dimethenamid-P at one-fourth the full rate in all four microrate applications injured sugarbeet more than the base microrate treatment. A full rate of s-metolachlor or dimethenamid-P applied in either the third or fourth microrate applications or splitting the applications between the second and fourth microrate treatments did not increase sugarbeet injury compared with the base microrate treatment. Control of common lambsquarters and giant foxtail from all treatments containing s-metolachlor or dimethenamid-P, regardless of the time of application, was greater than from the base microrate treatment at all locations. Pigweed spp. control was 94% or greater from all treatments. In 2004, late-season control of giant foxtail was greater from all treatments that included s-metolachlor or dimethenamid-P compared with the base microrate treatment. In 2005, the only treatments that did not improve late-season giant foxtail control compared with the base microrate treatment were the treatments that included a full rate of s-metolachlor or dimethenamid-P applied in the fourth microrate application. Even though some herbicide treatments that included s-metolachlor or dimethenamid-P injured sugarbeet more than the base microrate treatment, recoverable sucrose per hectare was similar among treatments.

Nomenclature: Dimethenamid-P; s-metolachlor; common lambsquarters, Chenopodium album L. CHEAL; pigweed species, Amaranthus retroflexus L. and Amaranthus powellii S. Wats. AMASS; giant foxtail, Setaria faberi Herrm. SETFA; sugarbeet, Beta vulgaris L.

A survey of seven production fields in Indiana, Illinois, and Ohio was conducted to assess henbit and purple deadnettle growth and soybean cyst nematode (SCN) development and reproduction on these weeds. Autumn and spring growth of purple deadnettle and henbit was influenced by location within each state. In general, winter annual weeds were larger in size and reached maturity earlier in the spring at the southern sample sites than those in the north. All growth stages of SCN were found to be associated with henbit and purple deadnettle at both autumn and spring sample timings. SCN juveniles were generally found infecting roots at highest abundance in the spring. SCN cyst and egg production also were widespread and occurred to a much higher degree during the autumn than the spring developmental period. The results of this survey indicate that management tactics designed to minimize the potential for SCN reproduction on winter annual weeds would probably be most effective if conducted in the autumn, when the majority of SCN reproduction occurred. However, spring populations of winter annual weeds that harbor SCN juveniles might facilitate additional SCN reproduction and population increase if the weeds are not controlled in a timely manner prior to planting.

Nomenclature: Henbit, Lamium amplexicaule L. LAMAM; purple deadnettle, Lamium purpureum L. LAMPU; soybean, Glycine max (L.) Merr; soybean cyst nematode, Heterodera glycines Ichinohe.

Medusahead is an introduced, winter-annual grass covering millions of hectares of the semiarid West. It forms exclusive stands and has a dense thatch cover that resists the establishment of desirable species. Prescribed fire can remove medusahead litter and improve plant establishment. Medusahead control is fundamental to establishing desirable species that will, in turn, resist further invasion. Imazapic is an effective herbicide for control of medusahead, but more information is needed on its effects on desirable species. Our objectives were to test how imazapic application rate and timing affected medusahead, seeded desirable species, and other nontarget vegetation on burned and unburned rangeland in southeast Oregon. We burned existing medusahead infestations at two different sites in June 2003. Following the burn, imazapic was applied at rates of 0, 35, 70, 105, 140, 175, and 210 g ai/ha between July and October of 2003 in a randomized strip-plot design. In November 2003, monocultures of seven desirable species were drill-seeded across the imazapic treated areas. Data on cover and density of medusahead and seeded species were collected in 2004 and 2005. Cover data of nontarget species were collected in the summer of 2005. Medusahead cover was highest in control plots and lowest in plots that received the highest herbicide application rates. Medusahead cover was lower in burned plots. The effect of imazapic on nontarget vegetation was less clear. Seeded species established in the study plots, but their response to herbicide rate showed few consistent patterns; some of the seeded species showed little response to herbicide, whereas others appeared to establish best at different herbicide rates, depending on site and whether the plots were burned or unburned. Site and burn treatment also affected how imazapic rate or application month influenced cover of perennial or annual grasses or forbs.

Nomenclature: Imazapic; medusahead, Taeniatherum caput-medusae (L.) Nevski ELYCM.

Field studies were conducted in 2005 at five locations throughout Illinois to determine the effect of maturity date and canopy width characteristics of selected glyphosate-resistant soybean cultivars on competitive ability against weeds. Natural weed populations at all sites were allowed to compete with the soybean cultivars until the V1, V3, V5, or V7 growth stage and then removed with an application of glyphosate. Light-interception readings, weed control ratings, and soybean yield were all measured to compare cultivars. Cultivars of later maturities tended to withstand early season weed competition better and attained higher yields when weeds were removed at later timings than those of earlier maturity. Although canopy width differed moderately among cultivars in some cases, canopy width had no effect on the ability of soybeans to compete with weeds. Thus, choosing soybean cultivars of later maturity might provide more flexibility in weed management and might reduce losses due to weeds, but that benefit needs to be balanced with yield potential.

Nomenclature: Glyphosate; metolachlor; metribuzin; soybean, Glycine max (L.) Merr.

Field studies were conducted from 2003 through 2006 to evaluate bundleflower tolerance to several postemergence (POST) herbicides commonly used in pastures. All herbicides except imazapic, metsulfuron, and 2,4-DB injured bundleflower at least 88% when rated 4 wk after treatment (WAT). When rated 8 WAT, metsulfuron, picloram, and picloram plus 2,4-D injured bundleflower greater than 90%. Imazapic stunted bundleflower (10 to 35% injury) throughout the growing season. When rated 52 WAT, dicamba plus 2,4-D, picloram alone, and picloram plus 2,4-D injured bundleflower at least 97% in one of two years. Emergence of bundleflower with picloram-containing treatments ranged from 16 to 67% of the nontreated control, whereas emergence after dicamba-containing treatments ranged from 67 to 97%.

Nomenclature: Dicamba; glyphosate; imazapic; metsulfuron; picloram; 2,4-D; bundleflower, Desmanthus bicornutus S. Watson ‘BeeTAM-06’, ‘BeeTAM-08’, ‘BeeTAM-37’, ‘BeeTAM-57’.

The annual Southern Weed Contest has been a valuable asset for training graduate students in the applied aspects of weed science since its inception in 1980. Recently, participation in the contest has declined, which spurred the need to assess the contest's utility. Past participants in the contest from 1980 through 2004 were surveyed (1) to determine their perception of the importance, impact, and need for a weed contest activity in the southern region; and (2) to determine whether participation in the contest is contingent upon availability of study material resources and level of emphasis placed on the contest at each university. A total of 88 of 134 electronic surveys was returned, with at least 1 survey from each of the 14 universities in the southern region. Most participants (93%) expressed having had a pleasurable experience in the contest. Fifty-five percent of the respondents indicated that the contest either “increased” or “may have increased” their employment opportunities. Ninety-two percent of the respondents indicated that they had access to “excellent” or “adequate” resources to prepare for the contest. Ninety-eight percent of the respondents felt that the contest is still needed. Faculty involvement in student preparation was closely linked to team performance in the contest. There were numerous ideas put forth to increase participation along with ways to make the contest more interesting and relevant with the changing times. With less than 25% of the graduate students in the southern region competing in the contest for the last 3 years, there is obviously a disconnect between the apparent benefits of participation and the number of students taking advantage of it. However, participation alone without preparation does little to instill within students the confidence and knowledge necessary to make the contest an enjoyable experience. Ultimately, the future of the Southern Weed Contest rests on weed science faculty involvement from each university in the southern region and on recruitment of graduate students.

Voucher specimens and herbarium collections provide the foundation for many aspects of research in the plant sciences. Available for study and verification by contemporary and future workers, voucher specimens promote reproducibility in scientific method because permanent records document identification, distribution, and interspecific and intraspecific variation of species. The utility and importance of voucher specimens and herbarium collections in supporting research in weed science are discussed, and the collection, preparation, documentation, storage, and shipment of voucher specimens are detailed.

Autoradiography is a radioisotope-based technique that allows absorbed and translocated herbicide to be visualized. Autoradiographs are traditionally produced with X-ray film and exposure times of several weeks. Phosphorescence imaging (PI) was investigated as an alternative autoradiography procedure. Smallflower morningglory plants were root-exposed to a series of ¹⁴C-atrazine concentrations, producing a series of increasing foliar radioactivity concentrations (i.e., dosage) that ranged from marginal to excessive with respect to autoradiography. Autoradiographs were subsequently produced from these ¹⁴C-atrazine-dosed plants using both the X-ray film and the PI technique. Autoradiographs from both techniques were of excellent quality and nearly identical when the dosage was ∼20 to 70 Bq/mg. However, PI produces an acceptable image in dosages either above or below this optimum range. A 1-d exposure time was sufficient with PI, and longer exposure times were not detrimental to image quality. In contrast, a 3-wk exposure time was required with X-ray film. Autoradiographs of selected herbicides are presented to further demonstrate the utility of PI.

Nomenclature: Atrazine; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb IAQTA.