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.

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.

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.

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.

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.

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.

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)

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.