Field studies were conducted in 1999, 2000, and 2001 to evaluate weed control and cotton response from PRE herbicides followed by (fb) trifloxysulfuron POST. In the first study, trifloxysulfuron at 3.8, 7.5, or 15 g ai/ha was applied POST with or without pendimethalin at 690 g ai/ha applied PRE in a factorial treatment arrangement. Visible crop injury occurred after all trifloxysulfuron applications, but injury was not affected by application of pendimethalin PRE. Cotton injury was 19 to 22% 7 d after POST treatment (DAT) from trifloxysulfuron at 3.8 to 15 g/ha but was 5 to 12% 28 DAT. Trifloxysulfuron controlled smooth pigweed, common ragweed, and common cocklebur, but spurred anoda, large crabgrass, goosegrass, and stinkgrass were not controlled by trifloxysulfuron. Morningglory species (tall morningglory, ivyleaf morningglory, and pitted morningglory) control with trifloxysulfuron at 7.5 and 15 g/ha was at least 79%, whereas velvetleaf was controlled 66% over all years. In a second study, clomazone, pendimethalin, pendimethalin plus fluometuron, pyrithiobac, or flumioxazin were applied PRE fb 7.5 g/ha trifloxysulfuron POST. Cotton injury from PRE herbicides fb trifloxysulfuron was 13 to 39% 7 DAT. Spurred anoda control exceeded 54% only with treatments that included flumioxazin or pyrithiobac PRE. Common lambsquarters, common cocklebur, and morningglory species were controlled at least 75% with all treatments that included trifloxysulfuron POST, whereas pendimethalin and clomazone usually controlled annual grasses. In both studies, the application of pendimethalin PRE controlled annual grass species and improved control of smooth pigweed and common lambsquarters over that controlled by trifloxysulfuron POST without a PRE herbicide.

Nomenclature:Clomazone, flumioxazin, fluometuron, pendimethalin, pyrithiobac, trifloxysulfuron, common cocklebur, Xanthium strumarium L. XANST, common lambsquarters, Chenopodium album L. CHEAL, common ragweed, Ambrosia artemisiifolia L AMBEL, goosegrass, Eleusine indica (L.) Gaertn. ELEIN, ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE, large crabgrass Digitaria sanguinalis (L.) Scop DIGSA, pitted morningglory, Ipomoea lacunosa L. IPOLA, smooth pigweed, Amaranthus hybridus L. AMACH, spurred anoda, Anoda cristata (L.) Schlecht. ANVCR, stinkgrass, Eragrostis megastachya (Koel.) Link, tall morningglory, Ipomoea purpurea (L.) Roth IPOPU, velvetleaf, Abutilon theophrasti Medicus ABUTH, cotton, Gossypium hirsutum L. ‘SG 125’

Variability in glyphosate efficacy has been observed following late day field applications, but the influence of this “time-of-day effect” on weed control and soybean yield is unknown. Additionally, the basis for differences in weed control due to application time of day has not been fully elucidated. In field trials, broadleaf weed biomass was ≥5-fold greater when glyphosate was applied at 6:00 a.m. compared to 6:00 p.m. in three of four site–years. No consistent time-of-day effect was observed on treated grass weeds. Soybean yield was unaffected by treatments, and was similar to the weed-free control. In a greenhouse study, both barnyardgrass and velvetleaf biomass were as much as 25 to 80% greater when glyphosate was applied at 8:00 p.m. vs. 2:00 p.m. Examination of individual components of the time-of-day effect for velvetleaf indicated that leaf angle and time of application accounted for 82 and 18%, respectively, of the biomass change. This research suggests that diurnal changes in leaf movement of velvetleaf account for much of the time-of-day effect, with the remainder likely due to an unknown physiological component.

Nomenclature: Glyphosate, barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, velvetleaf, Abutilon theophrasti Medicus ABUTH, soybean, Glycine max (L.) Merr., ‘Asgrow 3601 RR*STS’ or ‘Asgrow 3701 RR’

Common dandelion has developed into a troublesome agronomic weed for no-tillage corn producers. A postemergence herbicide application is often required to reduce common dandelion competition. Field experiments were conducted in 2002 and 2003 to evaluate 22 postemergence herbicide treatments for efficacy on established populations of common dandelion in no-tillage corn. All herbicides were applied to five- to six-collar corn at registered rates with typical adjuvants. At 28 d after treatment (DAT) the most effective treatments included glufosinate and mesotrione providing at least 76% control of common dandelion. All other herbicide treatments provided less than 40% common dandelion control 28 DAT. Common dandelion control was evaluated 56 DAT when regrowth of treated plants was observed for some herbicide treatments. AT 56 DAT, dicamba diflufenzopyr was the most effective treatment, providing 83% control of common dandelion. In 2002, all herbicide treatments, with the exception of flumiclorac, resulted in corn yields greater than the nontreated.

Nomenclature: Dicamba, diflufenzopyr, flumiclorac, glufosinate, mesotrione, common dandelion, Taraxacum officinale Weber TAROF, corn, Zea mays L

Common dandelion has developed into a troublesome agronomic weed for no-tillage corn and soybean producers in Michigan and throughout the north central region of the United States. Field experiments were conducted on established populations of common dandelion in 2001 to 2002 and 2002 to 2003 to evaluate the effect of preplant and sequential herbicide applications on established populations of common dandelion. Preplant treatments of glyphosate or 2,4-D ester were applied early fall, late fall, early spring, and late spring. For both glyphosate and 2,4-D ester, the fall applications were more effective than the spring applications. Glyphosate at 840 g ae/ha was more effective than 2,4-D ester at 1,120 g ae/ha at each application timing. A single application of glyphosate or 2,4-D ester applied either in the fall or spring did not provide season-long control of common dandelion. Sequential treatments of glyphosate following preplant applications of either glyphosate or 2,4-D ester provided season-long control of common dandelion.

Nomenclature: Glyphosate, 2,4-D ester, common dandelion, Taraxacum officinale Weber TAROF, glyphosate-resistant soybean, Glycine max (L.) Merr

A high proportion of viable pollen grains must germinate to study the physiology of pollen growth to reduce the confounding effects of environmental influences on pollen germination. The objectives of this study were to evaluate the nuclear state and develop a suitable medium and culture method for in vitro germination of johnsongrass pollen. Johnsongrass pollen was trinucleate, and in vitro tests for pollen viability using Alexander's stain and a fluorochromatic reaction method (FCR) indicated johnsongrass pollen was viable (92.6 to 98.4%). A factorial treatment arrangement of four concentrations of sucrose, two concentrations of boric acid, and two concentrations of calcium nitrate were used to determine the optimum pollen-germination medium composition in suspension culture, agar culture, and cellophane membrane culture. Germination was highest in a suspension culture with a medium containing 0.3 M sucrose, 2.4 mM boric acid, and 3 mM calcium nitrate. Pollen germination using this medium was 78.9% when anthers were harvested just before anthesis.

Nomenclature: Johnsongrass, Sorghum halepense (L.) Pers. SORHA

Field trials were conducted in the spring of 2004 and the spring and summer of 2005 to evaluate cantaloupe tolerance to rimsulfuron and halosulfuron applied to cantaloupe at the two-leaf stage, five- to six-leaf stage, plants having 30- to 40-cm vines, and plants having up to 5-cm-diam melons. Additionally, control of eight weed species was evaluated in these trials in 2005. Cantaloupe plant injury from rimsulfuron differed among application timings and trials, but applications were generally more injurious when applied at the two early crop stages. Halosulfuron was less injurious to cantaloupe, but 31 and 14% injury occurred following the two-leaf and five- to six-leaf applications, respectively, in the second trial in 2005. In the first trial of 2005, number of marketable melons the first week of harvest was lower for all halosulfuron applications compared with the nontreated control (30 to 37% reduction). In the second trial of 2005, total number of marketable melons was comparable to the nontreated control for each of the halosulfuron treatments, except the five- to six-leaf and up to 5-cm-diam melon applications. Injury estimates were poor indicators of occurrence or absence of delays in crop earliness or number of marketable melons. Rimsulfuron was generally effective (≥ 80% control) in controlling seedling Texas panicum, large crabgrass, tall morningglory, pitted morningglory, and Palmer amaranth, but was ineffective against yellow and purple nutsedge and goosegrass. Halosulfuron was effective in controlling yellow and purple nutsedge, but was ineffective against Texas panicum, large crabgrass, goosegrass, pitted morningglory, tall morningglory, and Palmer amaranth.

Nomenclature: Halosulfuron, rimsulfuron, goosegrass, Eleusine indica (L.) Gaertn. ELEIN, large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA, pitted morningglory, Ipomoea lacunosa L. IPOLA, purple nutsedge, Cyperus rotundus L. CYPRO, tall morningglory, Ipomoea purpurea (L.) Roth PHBPU, Texas panicum, Panicum texanum Buckl. PANTE, yellow nutsedge, Cyperus esculentus L. # CYPES, cantaloupe, Cucumis melo L. Reticulatus group ‘Athena’

Field studies were conducted in 1999, 2000, and 2001 to evaluate cotton response to trifloxysulfuron applied postemergence over the top (POT) or postemergence-directed (PDIR) at various growth stages. Treatments included trifloxysulfuron at 3.8 or 7.5 g ai/ha plus nonionic surfactant (NIS) applied POT to one-, three-, and five-leaf cotton or applied PDIR to 30- and 45-cm tall cotton. Crop injury 7 d after treatment (DAT) varied by year and ranged from 17 to 50%, 19 to 46%, and 5 to 23% with trifloxysulfuron applied POT to one-, three-, and five-leaf cotton, respectively. Injury 21 DAT averaged 22, 16, and 6% with one-, three-, and five-leaf applications respectively. Trifloxysulfuron applied PDIR injured cotton 2 to 9% 7 DAT and 0 to 12% 21 DAT. At 30 DAT, cotton height was reduced with one-leaf trifloxysulfuron application, whereas differences were not present across other treatments. Heights at 90 days after planting (DAP) did not differ between treatments. Neither trifloxysulfuron rate or application timing negatively affected cotton yield or fiber quality.

Nomenclature: Trifloxysulfuron, cotton, Gossypium hirsutum L

To date, there have been no reports of Dalmatian toadflax serving as a host for cucumber mosaic virus (CMV). Infestations of Dalmatian toadflax may serve as a reservoir of CMV, thereby facilitating aphid transmission of CMV to both agricultural crops and native plants. The goal of this study was to determine whether Dalmatian toadflax is a host for CMV. Dalmatian toadflax seedlings were randomly assigned to two treatments (18 replicates/treatment): no inoculation (control) and inoculation with CMV (Fast New York strain). The Dalmatian toadflax seedlings were inoculated by standard mechanical methods and tested for the presence of CMV using enzyme-linked immunosorbent assay (ELISA). Ten of the 18 CMV-inoculated toadflax plants tested positive for the virus; 6 of the 18 displayed systemic mosaic chlorosis and leaf curling. All control plants tested negative. Transmission electron microscopy obtained from CMV-positive plants confirmed the presence of CMV based on physical properties. To verify CMV infestation, tobacco plants were assigned to the following treatments (six replicates/treatment): no inoculation (control), CMV-negative (control) inoculation, and a CMV-positive inoculation. Plants were inoculated by standard methods. Five of the 6 tobacco plants treated with the CMV-positive inoculum tested positive for CMV using ELISA. All control plants tested negative for the virus.

Nomenclature: Dalmatian toadflax, Linaria dalmatica (L.) Mill. LINDA, tobacco, Nicotiana tabacum L, cucumber mosaic virus

Studies were conducted to evaluate weed management systems in nontransgenic, bromoxynil-resistant, and glyphosate-resistant cotton in strip- and conventional-tillage environments. Tillage did not affect weed control, cotton lint yields, or net returns. Early season stunting in strip-tillage cotton was 5% or less, regardless of herbicide system or cultivar and was transient. Excellent (> 90%) control of common lambsquarters, common ragweed, and Ipomoea species, including entireleaf, ivyleaf, pitted and tall morningglories, jimsonweed, prickly sida, and velvetleaf, was achieved with systems containing bromoxynil, glyphosate, and pyrithiobac early postemergence (EPOST). Glyphosate systems provided better and more consistent control of fall panicum and large crabgrass than bromoxynil and pyrithiobac systems. Bromoxynil and pyrithiobac EPOST did not control sicklepod unless applied in mixture with MSMA and followed by (fb) a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA. Palmer amaranth was controlled (> 90%) with all glyphosate and pyrithiobac systems and with the bromoxynil system that included a broadcast soil-applied herbicide treatment. Bromoxynil systems without a broadcast soil-applied herbicide treatment controlled Palmer amaranth 87% or less. Herbicide systems that included glyphosate EPOST controlled sicklepod with or without a soil-applied herbicide treatment. The highest yielding cotton included all the glyphosate systems and bromoxynil systems that contained a soil-applied herbicide treatment. Nontransgenic systems that included a soil-applied herbicide treatment yielded less than a system with soil-applied treatment plus glyphosate EPOST. Net returns from glyphosate systems were generally higher than net returns from bromoxynil or pyrithiobac systems.

Nomenclature: Bromoxynil, fluometuron, glyphosate, MSMA, pendimethalin, prometryn, pyrithiobac, common lambsquarters, Chenopodium album L. CHEAL, common ragweed, Ambrosia artemisiifolia L. AMBEL, entireleaf morningglory, Ipomoea hederacea (L.) var. integriuscula Gray IPOHG, fall panicum, Panicum dichotomiflorum (L.) Michx. PANDI, ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE, jimsonweed, Datura stramonium L. DATST, large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA, pitted morningglory, Ipomoea lacunosa L. IPOLA, prickly sida, Sida spinosa L. SIDSP, sicklepod, Senna obtusifolia (L.) Irwin and Barnaby CASOB, tall morningglory, Ipomoea purpurea L. PHBPU, velvetleaf, Abutilon theophrasti Medik. ABUTH, cotton, G. hirsutum L. ‘Paymaster 1220RR’, ‘Stoneville BXN 47’, and ‘Stoneville 474’

Experiments were conducted at Minlaton on the Yorke Peninsula of South Australia in 2004 and 2005 to study the effect of four different seeding systems and dinitroaniline herbicides on the seedling emergence and growth of rigid ryegrass in wheat. The seeding systems were low soil-disturbance discs (DayBreak and K-Hart) and high soil-disturbance tines (narrow point and Ribbon seeder); and the herbicides were oryzalin, pendimethalin, and trifluralin at rate of 0.72 kg ai/ha. The total seedling emergence of rigid ryegrass was higher in nontreated plots planted with the tines compared with the discs. In general, oryzalin was the least-effective herbicide in controlling emergence of rigid ryegrass. All herbicides were more effective in reducing the number of plants, spikes, dry matter, and seed production of rigid ryegrass in combination with tines than with discs. However, in the absence of herbicides, plant and spike numbers, plant dry weight, and seed production of rigid ryegrass were significantly lower where discs were used to sow, rather than tines. In the absence of herbicide, rigid ryegrass was less competitive with wheat under the disc-sown systems. The response of grain yield to herbicides was greater under the tine-sown systems than the disc-sown systems.

Nomenclature: Oryzalin, pendimethalin, trifluralin, rigid ryegrass, Lolium rigidum Gaud. LOLRI, wheat, Triticum aestivum L. ‘Krichauff’

Field studies were conducted near Oxnard, CA, to assess propagule survivability of two annual and two perennial weed species in 7.6 m³ static piles of fresh or aged yard waste mulch over a 56 d period. Mulch temperatures > 60 C generated at depths > 30 cm in fresh mulch caused all weed propagule mortality, whereas sublethal temperatures at shallower depths in fresh, and at all depths in aged piles allowed propagule survival. A controlled environment laboratory experiment suggested ≥ 1 d exposure provides 100% mortality of seed of little mallow at 72 C, California burclover seed (without burs) at 85 C, rhizomes of bermudagrass at 69 C, and nutlets of yellow nutsedge at 70 C. These studies indicate that reinfested, aged mulch does not produce sufficient heat to destroy weed propagules and, therefore, may become a weed-carrying substrate. Fresh mulch should be mixed to expose surviving weed propagules at shallow depths to lethal temperatures found at 30 cm or deeper in fresh mulch piles.

Nomenclature: Bermudagrass, Cynodon dactylon (L.) Pers. CYNDA, California burclover, Medicago polymorpha L. MEDPO, little mallow, Malva parviflora L. MALPA, yellow nutsedge, Cyperus esculentus L. CYPES

Invasive annual grasses, such as medusahead, can reduce forage production capacity and interfere with revegetation projects in California rangelands. Because of the taxonomic similarity to other more desirable grasses, achieving selective control of invasive annual grasses can be difficult. In selectivity trials conducted in Yolo and Siskiyou counties, CA, the herbicide imazapic gave control of many nonnative annual grasses yet provided some level of selectivity to specific perennial grasses used in revegetation projects throughout the western United States. The selectivity difference between newly seeded perennial and annual grasses was greater with PRE applications than with POST treatments. Both perennial and annual grasses within the tribe Hordeae were more tolerant to imazapic than other grass species. In addition, field experiments were conducted at three sites in northern California (Yuba, Yolo, and Lassen counties) and one in southern Oregon (Lake County) to test the response of imazapic to varying management conditions. Imazapic was applied PRE in fall (and also spring in Lake County) at rates from 35 to 210 g/ha on undisturbed rangeland, in comparison with rangeland cleared of standing plant material and thatch by either tillage, mowing and raking, or burning. Imazapic generally showed enhanced weed control when applied following disturbance. Rates as low as 70 g/ha, if combined with thatch removal, provided significant suppression of medusahead. In addition, disturbance alone generally reduced medusahead cover in the following year. Although imazapic showed potential for control of medusahead and other annual grasses, its selectivity window was relatively narrow.

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

Producers in the Great Plains are exploring alternative crop rotations with the goal of reducing the use of fallow. In 1990, a study was established with no-till practices to compare eight rotations comprising various combinations of winter wheat (W), spring wheat (SW), corn (C), chickpea (CP), dry pea (Pea), soybean (SB), or fallow (F). After 12 yr, we characterized weed communities by recording seedling emergence in each rotation. Downy brome, cheat, redroot pigweed, and green foxtail were the most common weeds observed. Weed community density was highest for W–CP, being 13-fold greater than with Pea–W–C–SB. Downy brome and cheat were rarely observed in rotations where winter wheat was grown only once every 3 or 4 yr; in contrast, density of the brome species was 75-fold greater in W–CP. Warm-season weeds were also affected by rotation design; density of redroot pigweed and green foxtail was sixfold greater in W–C–CP compared with Pea–W–C–SB or W–F. One rotation design that was especially favorable for low weed density was arranging crops in a cycle of four, with two cool-season crops followed by two warm-season crops.

Nomenclature: Cheat, Bromus secalinus L. BROSE, downy brome, Bromus tectorum L. BROTE, green foxtail, Setaria viridis L. SETVI, redroot pigweed, Amaranthus retroflexus L. AMARE, chickpea, Cicer arietinum L, corn, Zea mays L, dry peas, Pisum sativum L, soybean, Glycine max Merrill, wheat, Triticum aestivum L

Bamboos are grass species that can escape cultivation and invade lawns, landscapes, and other areas. Limited information is available on ways to control invasive bamboo species. Greenhouse and field studies were initiated to determine the level of bamboo control provided by a single application of selected PRE and POST herbicides. Bamboo species included in the study were golden bamboo in greenhouse experiments and red-margined bamboo in field experiments. In greenhouse trials, MSMA, quinclorac, dithiopyr, clethodim, fenoxaprop, and sethoxydim did not control either species. Glyphosate, glufosinate, and fluazifop significantly reduced bamboo-shoot fresh weight, although regrowth occurred after a single application. In field trials, bamboo control with dichlobenil in the 2002 and 2004 experiments was less than 23%. For the study initiated in 2002, glyphosate and imazapyr provided 76% and 98% bamboo control, respectively, at 58 wk after treatment (WAT). By 161 WAT (approximately 3 yr after treatment), bamboo-control ratings were 40% with glyphosate and 85% with imazapyr. For the study initiated in 2004, at 61 WAT, glyphosate and imazapyr provided 46 and 88% control of bamboo, respectively.

Nomenclature: Clethodim, dichlobenil, dithiopyr, fluazifop, glyphosate, imazapyr, MSMA, quinclorac, sethoxydim, golden bamboo, Phyllostachys aurea Carr. ex A. & C. Rivière, red-margined bamboo, Phyllostachys rubromarginata McClure

Proso and foxtail millets are regionally important dryland crops for the semiarid portions of the Central Great Plains. However, few herbicides are registered for use in either crop. The efficacy of carfentrazone was studied in proso millet from 2003 through 2005 at the University of Nebraska High Plains Agricultural Laboratory located near Sidney, NE, and in foxtail millet in 2004 and 2005 at the University of Wyoming Sustainable Agriculture Research and Extension Center near Lingle, WY. Carfentrazone was applied POST at 9.0, 13.5, and 18.0 g ai/ha with combinations of 2,4-D amine, prosulfuron, and dicamba. Although leaves of treated plants exhibited localized necrosis, leaves emerging after treatment were healthy. Grain and forage yields were not affected by the application of carfentrazone. Dicamba and 2,4-D amine provided visual control of 30% or less for buffalobur. Adding carfentrazone to one or both of these herbicides improved buffalobur control to 85% or greater. Carfentrazone applied at 18.0 g/ha improved Russian thistle, kochia, and volunteer sunflower control in 2003, when plants were drought-stressed, but did not help with these and other weeds during wetter years. Carfentrazone provides proso millet producers with a way to selectively control buffalobur, a noxious weed in several western states. In foxtail millet, carfentrazone provides POST broadleaf weed control with little risk for serious crop injury. Crop injury has been a concern with 2,4-D, which is currently the only other herbicide registered for use in foxtail millet.

Nomenclature: Carfentrazone, 2,4-D, dicamba, prosulfuron, buffalobur, Solanum rostratum Dun. SOLCU, kochia, Kochia scoparia (L.) Schrad. KCHSC, Russian thistle, Salsola iberica Sennen & Pau SASKR, foxtail millet, Setaria italica (L.) P. Beauv, proso millet, Panicum miliaceum L, sunflower, Helianthus annuus L

On-farm trials were conducted in 16 North Carolina peanut fields to obtain estimates of scouting times and quality of herbicide recommendations for different weed scouting methods. The fields were monitored for weed species and population density using four scouting methods: windshield (estimate made from the edge of the field), whole-field (estimate based on walk through the field), range (weed densities rated on 1–5 scale at six locations in the field), and counts (weeds estimated by counting at six locations in the field). The herbicide application decision support system (HADSS) was used to determine theoretical net return over herbicide investment and yield loss ($ and %) for each treatment in each field. Three scouts estimated average weed population densities using each scouting method. These values were entered into HADSS to obtain treatment recommendations. Independently collected count data from all three scouts were combined to determine the optimal treatment in each field and the relative ranking of each available treatment. When using the whole-field method, scouts observed a greater number of weed species than when using the other methods. The windshield, whole-field, and range scouting methods tended to overestimate density slightly at low densities and underestimate density substantially at high densities, compared to the count method. The windshield method required the least amount of time to complete (6 min per field), but also resulted in the greatest average loss. Even for this method, recommendations had theoretical net returns within 10% of the return for the optimal treatment 80% of the time. The count method appears to have less economic risk than the windshield, whole-field, and range scouting methods.

Nomenclature: Peanut, Arachis hypogaea L

Greenhouse experiments were conducted to determine the effect of glyphosate on efficacy of bentazon for glyphosate-resistant (GR) canola control and of quizalofop for GR corn control. Control also was evaluated for glyphosate plus bentazon on wild buckwheat and wheat and glyphosate plus quizalofop on velvetleaf. Glyphosate plus bentazon synergistically controlled GR canola and wild buckwheat but were antagonistic for wheat control. Glyphosate plus quizalofop were additive for control of GR corn and velvetleaf. Inert ingredients in glyphosate formulations, i.e., cationic surfactant, NH₄, or K, contributed to glyphosate synergism of bentazon, but the major contribution came from glyphosate itself. Efficacy of glyphosate plus bentazon on GR canola was enhanced by ammonium nitrate (AMN), ammonium sulfate (AMS), nonionic surfactant (NIS), or silicone surfactant (SiS) but was slightly decreased by methylated seed oil (MSO) or petroleum oil concentrate. AMN, AMS, NIS, and SiS partially overcame the antagonism of bentazon to glyphosate for wheat control. NIS enhanced phytotoxicity of glyphosate plus quizalofop to GR corn and velvetleaf, but the enhancement was less than by SiS or MSO to GR corn and SiS or AMS to velvetleaf.

Nomenclature: Bentazon, glyphosate, quizalofop, velvetleaf, Abutilon theophrasti (L.) Medic. ABUTH, wild buckwheat, Polygonum convolvulus L. POLCO, canola, Brassica napus L, corn, Zea mays L, wheat, Triticum aestivum L

An experiment was conducted at one location in 1999 and two locations in 2000 to determine the critical weed-free period for peach in North Carolina. The cultivars for the three locations were ‘Contender’, ‘Norman’, and ‘Summerprince’. Weed-free intervals of 0, 3, 6, 9, 12, and 15 wk after peach tree bloom were established. Paraquat at 1.1 kg ai/ha plus nonionic surfactant at 0.25% v/v was applied every 10 d, after treatments were initiated at peach bloom, to maintain weed-free plots. Large crabgrass, hairy vetch, and smooth crabgrass were the primary weeds in Contender. Horseweed, smooth crabgrass, and large crabgrass were the primary weeds in Norman. Bermudagrass, smooth pigweed, and common lambsquarters were the primary weeds in Summerprince. No differences in trunk cross-sectional area were observed between the weed-free periods. Maintaining the orchard floor weed-free for 12 wk after peach tree bloom resulted in the greatest fruit size (individual fruit weight and diameter), total yield, and fruit number.

Nomenclature:Paraquat, bermudagrass, Cynodon dactylon (L.) Pers. CYNDA, common lambsquarters, Chenopodium album L. CHEAL, hairy vetch, Vicia villosa Roth. VICVI, horseweed, Conyza canadensis (L.) Cronq. ERICA, large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, smooth crabgrass, Digitaria ischaemum (Schreb.) Muhl. DIGIS, smooth pigweed, Amaranthus hybridus L. AMACH, peach, Prunus persica (L.) Batsch., ‘Contender’, ‘Norman’, and ‘Summerprince’

The objectives of this study were to evaluate the leaching of isoxaflutole and the safeners R-29148 and furilazole to test the hypothesis that safeners and isoxaflutole were moving at different rates through the soil profile. The isoxaflutole movement down soil columns was measured by evaluating the visible injury on crop and weed bioassay species seeded into columns split longitudinally. The movement of the safeners was measured by evaluating the isoxaflutole injury to the crop assay species compared to the injury observed without a safener present. The results indicated that a heavy rainfall event could move isoxaflutole through the soil profile in a pulse pattern. If the herbicide pulse moved into the rooting zone of corn, injury resulted. The herbicide safeners leached more slowly than isoxaflutole. For the safeners to be effective, their movement needed to be similar to that of isoxaflutole. Applying a polymeric carrier with the WDG formulation of isoxaflutole reduced leaching compared to two commercial isoxaflutole formulations.

Nomenclature: Furilazole,isoxaflutole, R-29148, 3-(dichloroacetyl)-2,2,5-trimethyl-1,3-oxazolidine, corn (Zea mays L.)

The response of new, high-yielding rice cultivars to varying barnyardgrass control levels and rice plant densities is not well understood. Studies were conducted in 2002 through 2004 at the Rice Research and Extension Center near Stuttgart, AR, to evaluate three new rice cultivars at plant densities ranging from 79 to 392 plants/m² grown in competition with barnyardgrass. Representatives from each of the three classes of long-grain rice produced in the United States were selected. ‘Wells’ represented conventional, long-grain rice, ‘CL161’ represented semidwarf, imidazolinone-tolerant, long-grain rice, and ‘XL8’ represented hybrid, long-grain rice. Rice density and barnyardgrass control affected rice total aboveground biomass production, panicle weight, and harvest index. As rice density decreased or barnyardgrass control increased, total aboveground biomass production and harvest index increased. Rice density had no effect on panicle density or yield. Panicle density increased 14 panicles/m² for every 10% increase in barnyardgrass control. Cultivar yields were affected similarly by barnyardgrass control, and increased 750 kg/ha for each 10% increase in barnyardgrass control. XL8 and Wells produced the highest average yields, with CL161 producing the lowest over the three-year experiment. XL8 yield components fluctuated more than CL161 or Wells over the range of rice densities and barnyardgrass control levels, indicating that XL8 is highly sensitive to intra- and interspecific competition at high plant populations.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, rice, Oryza sativa L. ‘CL161’, ‘Wells’, ‘XL8’

Field experiments were conducted in 2004 and 2005 to determine the tolerance of direct-seeded green onion to selected herbicides applied before or after green onion emergence. Preemergence herbicides included S-metolachlor, pendimethalin, dimethenamid, quinclorac, pronamide, ethofumesate, and DCPA, a registered standard. Herbicide applied to two- to three-leaf green onion included glyphosate, trifloxysulfuron, flumioxazin, phenmedipham, ethalfluralin, pendimethalin, S-metolachlor, and oxyfluorfen. Plots were cultivated and hand weeded to minimize negative effects of weed interference on the crop. All herbicides applied at seeding, excluding DCPA, caused excessive injury (>25%) to green onion in at least 1 of 2 years. Oxyfluorfen, ethalfluralin, or S-metolachlor applied after crop emergence caused less than 10% injury in both years to green onion. Green onion yields following treatment with oxyfluorfen, ethalfluralin, or S-metolachlor were equivalent to the nontreated control. All other herbicides applied after crop emergence resulted in height, density, or yield reductions relative to a nontreated control in at least 1 of 2 years.

Nomenclature: DCPA, dimethenamid, ethalfluralin, ethofumesate, flumioxazin, glyphosate, oxyfluorfen, pendimethalin, phenmedipham, pronamide, quinclorac, S-metolachlor, trifloxysulfuron, green onion, Allium cepa L. ‘White Spear 85’

Reducing seeding rates in 19- or 76-cm row soybean below the optimum rate may reduce soybean competitiveness with weeds, and indirectly increase production costs to the grower. Field studies in 2001 and 2002 evaluated the effect of soybean seeding rate and row spacing on the emergence, growth, and competitiveness of eastern black nightshade (EBN) in soybean. EBN emergence ceased within 45 d after planting (DAP), and was similar across soybean seeding rates and row spacing. EBN control by glyphosate was not affected by soybean population or row spacing. Soybean planted in 19-cm rows was more competitive with EBN, regardless of seeding rate. Increasing the soybean seeding rate in 76-cm rows from 185,000 seeds/ha to 432,000 seeds/ha reduced EBN dry weight threefold at East Lansing and nearly twofold at Clarksville in 2002. There was no increase in EBN density or dry weight in 19-cm row soybean planted at 308,000 seeds/ha compared with 556,000 seeds/ha, whereas a seeding rate of 432,000 seeds/ha in 76-cm row soybean did not suppress EBN dry weight or increase soybean yield in the presence of EBN compared with a seeding rate of 308,000 seeds/ha.

Nomenclature: Glyphosate, glyphosate-resistant soybean, Glycine max (L.) Merr, eastern black nightshade, Solanum ptycanthum Dun. SOLPT

Producers in the semiarid Great Plains are exploring alternative crop rotations, with the goal of replacing winter wheat–fallow. In 1993, a study was established to compare performance of eight rotations comprised of various combinations with winter wheat (W), spring wheat (SW), dry pea (Pea), safflower (Saf), corn (C), sunflower (Sun), proso millet (M), or fallow (F). After 8 years, we characterized weed communities by recording seedling emergence in each rotation. Seventeen species were observed, with downy brome, kochia, horseweed, and stinkgrass comprising 87% of the community. Rotations with the least number of weed seedlings were W–F and SW–W–C–Sun; in comparison, weed density was six-fold higher in W–M. Density of downy brome and kochia was highest in W–M compared with other rotations, whereas stinkgrass and green foxtail were prominent in proso millet of the W–M and W–C–M rotations. Horseweed established readily in safflower and dry pea. In the semiarid Great Plains, designing rotations in a cycle of four that includes cool- and warm-season crops can be a key component of integrated weed management.

Nomenclature: Downy brome, Bromus tectorum L. BROTE, green foxtail, Setaria viridis L. SETVI, horseweed, Conyza canadensis (L.) Cronq., ERICA, kochia, Kochia scoparia (L.) Schrad. KCHSC, stinkgrass, Eragrostis cilinensis (All.) E. Mosher ERACN, corn, Zea mays L, dry pea, Pisum sativum L, proso millet, Panicum miliaceum L, safflower, Carthamus tinctorius L, sunflower, Helianthus annuus L, wheat, Triticum aestivum L

Volunteer potato is highly competitive with onion and few control tactics are effective for removing this weed from an onion crop. Both volunteer potato density and duration of interference reduce onion yield, but the interaction of these factors is unknown. Field trials were conducted in 2003 in Idaho, Oregon, and Washington to determine the influence of volunteer potato density on the critical time of weed removal (CTWR) in onion. Yield losses of 2.5, 5.0, and 10% were estimated to occur at 534, 654, and 830 growing degree days (GDD) after onion emergence, respectively, with a volunteer potato density of 0.5 plants/m². At 2.0 volunteer potato plants/m², yield losses of 2.5, 5.0, and 10% were estimated to occur at 388, 481, and 598 GDD after onion emergence, respectively. Volunteer potato at 2.0 plants/m² had to be removed at least one onion leaf stage sooner, compared to a weed density of 0.5 plants/m², to avoid yield loss. Yield loss due to volunteer potato density or duration of interference was greatest among jumbo, colossal, and supercolossal market grades (P ≤ 0.1). Lowering potato tuber density in crops preceding onion will extend the critical time for weed removal and reduce the risk of crop loss.

Nomenclature: Volunteer potato, Solanum tuberosum L. ‘Russet Burbank’ and ‘Ranger Russet’, Onion, Allium cepa L. ‘Pinnacle’ and ‘Vaquero’

Cogongrass, a rhizomatous perennial, is among the world's most troublesome weeds. Research was conducted at the Southern Weed Science Research Unit, Stoneville, MS, to determine cogongrass rhizome mortality with increasing temperature and duration of exposure to heat and to determine if 2,3,5 triphenyl tetrazolium chloride (TTC) could be used to evaluate cogongrass rhizome mortality following heat treatment. Cogongrass rhizome mortality was 100% at 65, 79, 93, 107, 121, 149, 177, and 187 C at time periods greater than or equal to 25, 5, 2.5, 2.5, 2.5, 2, 2 and 1 min, respectively. The duration of heat required for cogongrass mortality decreases as temperature increased. The standard greenhouse bioassay was more effective than tetrazolium chloride in predicting viability of cogongrass rhizomes following heat treatments.

Nomenclature: Cogongrass, Imperata cylindrica (L.) Beauv. IMPCY

Improved cultivars of zoysiagrass established by seed are now available, but little is known about the safety of herbicides on zoysiagrass seedlings. Our objective was to determine the turf safety of various herbicides when applied from emergence to 4 wk after emergence (WAE) of ‘Zenith’ zoysiagrass. Oxadiazon (3.4 kg ai/ha), MSMA (2.3 kg ai/ha), and pronamide (1.1 kg ai/ha) did not reduce coverage 7 WAE when applied at emergence or later and caused only temporary discoloration of seedlings. Foramsulfuron (0.03 kg ai/ha) injured seedling zoysiagrass both years of testing and reduced cover in the final year. Fluazifop (0.07 kg ai/ha) caused significant injury in all 3 yr of the study and reduced coverage in the final year. Fenoxaprop (0.14 kg ai/ha) caused visible injury and reduction in zoysiagrass coverage in all 3 yr of the study. Our studies indicate pronamide, MSMA, or oxadiazon are the safest herbicides to use over Zenith zoysiagrass seedlings, and selection among these three depends on the primary weed species present.

Nomenclature: Fenoxaprop, fluazifop-P, foramsulfuron, MSMA, oxadiazon, pronamide, zoysiagrass, Zoysia japonica Steud. ‘Zenith’ ZOYJA

An experiment was conducted at three sites in central Oklahoma to compare the efficacy of Italian ryegrass management options in no-till (NT) and conventional tillage (CT) winter wheat. The Italian ryegrass management options included selected herbicide treatments, wheat-for-hay, and a rotation consisting of double-crop soybean seeded immediately after wheat harvest, followed by early season soybean, and then by wheat. In continuous wheat, before application of glyphosate or tillage, Italian ryegrass plant densities in mid-September were 12,300 to 15,000 plants/m² in NT plots vs. 0 to 500 plants/m² in CT plots. When applied POST, diclofop controlled more Italian ryegrass than tralkoxydim or sulfosulfuron. In continuous wheat, yields were greater in CT plots than in NT plots at two of three sites. None of the Italian ryegrass management options consistently reduced Italian ryegrass density in the following wheat crop. Of the Italian ryegrass control strategies applied to continuous wheat, three herbicide treatments in NT at Chickasha and all treatments in NT at Perry reduced Italian ryegrass density in the following wheat crop. Italian ryegrass plant density in November and spike density were highly related to wheat yield at two and three sites, respectively. No management options were more profitable than rotation to soybean.

Nomenclature: Diclofop, sulfosulfuron, tralkoxydim, Italian ryegrass, Lolium multiflorum Lam. LOLMU, soybean, Glycine max L, winter wheat, Triticum aestivum L

Field and greenhouse studies were conducted to investigate the compatibility of MSMA in a tank mixture with glyphosate or glufosinate for broadleaf and grass weed control. Glyphosate, glufosinate, and MSMA were evaluated at 0.5×, 1×, and 2× rates, with 1× rates of 0.84 kg ae/ha, 0.5 kg ai/ha, and 2.2 kg ai/ha, respectively. Glyphosate and glufosinate provided similar levels of control for most weed species and were often more efficacious than MSMA alone. Glyphosate controlled Palmer amaranth better than glufosinate. Glufosinate controlled hemp sesbania, pitted morningglory, and ivyleaf morningglory better than glyphosate at one location. Weed control was not improved with the addition of MSMA to glyphosate or glufosinate when compared with either herbicide alone. MSMA antagonized glyphosate efficacy on barnyardgrass, browntop millet, hemp sesbania, Palmer amaranth, and redroot pigweed. MSMA antagonized glufosinate efficacy on browntop millet, hemp sesbania, ivyleaf morningglory, johnsongrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, and velvetleaf. Antagonism of glyphosate or glufosinate by MSMA was often overcome by applying the 2× rate of either herbicide alone. MSMA is not a compatible tank-mixture partner with glyphosate or glufosinate for weed control in cotton.

Nomenclature: Glyphosate, glufosinate, MSMA, common barnyardgrass, Echinochloa crus-galli (L.) P. Beauv. ECHCG, browntop millet, Brachiaria ramosa (L.) Stapf PANRA, hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill SEBEX, ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE, johnsongrass, Sorghum halepense (L.) Pers. SORHA, palmer amaranth, Amaranthus palmeri S. Wats. AMAPA, pitted morningglory, Ipomoea lacunosa L. IPOLA, prickly sida, Sida spinosa L. SIDSP, redroot pigweed, Amaranthus retroflexus L. AMARE, velvetleaf, Abutilon theophrasti Medik. ABUTH, cotton, Gossypium hirsutum L

Studies were conducted in growth chambers to characterize absorption and translocation of ¹⁴C-glyphosate applied alone or in mixture with MSMA in browntop millet and Palmer amaranth. MSMA antagonized activity of glyphosate in both weed species. Absorption of ¹⁴C-glyphosate in Palmer amaranth was rapid and increased with time from 11.1% at 0.5 h after treatment to 68.1% at 168 HAT. Absorption of ¹⁴C-glyphosate in browntop millet ranged from 1.6% at 0.5 HAT to 39.1% at 168 HAT. MSMA in mixture with glyphosate did not affect the absorption of glyphosate. In browntop millet, only 2.8% of the applied radioactivity translocated out of the treated leaf to the rest of the plant when glyphosate was applied in mixture with MSMA compared to 10.8% when glyphosate was applied alone at 72 HAT. Similarly, in Palmer amaranth, 3.2% of the applied radioactivity had translocated out of the treated leaf when glyphosate was applied in mixture with MSMA compared to 10.6% when glyphosate was applied alone. Reduced translocation appears to be the cause of the previously observed antagonism of glyphosate by MSMA.

Nomenclature: Glyphosate, MSMA, browntop millet, Brachiaria ramosa (L.) Stapf PANRA, Palmer amaranth, Amaranthus palmerii S. Wats. AMAPA

Laboratory and field studies were conducted to determine the effect of the drift control adjuvants HM 2005B and HM 9752 on the droplet spectra and efficacy of spray mixtures of a potassium salt formulation of glyphosate. Droplet spectra were examined using a laser spray droplet analyzer. The addition of each adjuvant decreased the percentage of the spray volume in small diam spray droplets (<141 μm) and either had no effect or increased glyphosate efficacy. These adjuvants could prove useful for providing management in potential drift situations.

Nomenclature: Glyphosate

Sulfometuron was applied at 0.1, 0.15, and 0.2 kg ai/ha over the top of oak seedlings. Three separate field studies were completed. In 1997, 0.1 and 0.2 kg ai/ha was applied PRE over six oak species. In 1998 and 1999, 0.1 and 0.15 kg ai/ha were applied PRE and 0.1 kg ai/ha was applied POST over two species of oaks. Results demonstrate that first-year survival of oak seedlings is greater in areas which receive competition control. Survival was 21 to 44% greater in treated areas as compared to nontreated areas. Observations indicate that survival differences are increased in droughty years. Competition control appears essential to obtaining desirable levels of survival when oak seedlings are planted in areas with established herbaceous competition.

Nomenclature: Sulfometuron, oak, Quercus spp

Field studies were conducted in Fayetteville, AR, to determine the response of 38 pitted morningglory accessions to fomesafen, chlorimuron, and glyphosate when applied postemergence over-the-top (POT) at 9 g ai/ha, 420 g ai/ha, and 840 g ae/ha, respectively, to four-leaf, 15-cm-tall pitted morningglory. Visual control following chlorimuron application ranged from 82 to 95% 3 wk after treatment (WAT). Visual control of accessions with fomesafen ranged 34 to 84% 3 WAT. Variability in visual control following fomesafen application was documented among accessions collected from similar geographic locations in west-central and southwest Arkansas, central and southeast Louisiana, and west-central Mississippi. Glyphosate controlled pitted morningglory accessions 81 to 89% 3 WAT. Data indicate that weed management programs should be field specific where fomesafen use is intended.

Nomenclature: Chlorimuron, fomesafen, glyphosate, pitted morningglory, Ipomoea lacunosa L. IPOLA

Field research was conducted in 2002 and 2003 to determine the effect of twin- and single-row spacing and POST glyphosate application timing on light interception, weed control, and grain yield of glyphosate-resistant corn and soybean. Row spacing did not affect light interception measured 10 to 11 wk after planting. Corn grain yield in 2002 was 1.0 Mg/ha higher in single rows compared with twin rows when averaged over glyphosate timing, but was unaffected by row spacing in 2003. Soybean grain yield was similar in 19- and 38-cm single rows, and single-row grain yield was 0.2 to 0.4 Mg/ha higher than the twin-row spacing. Corn grain yields were similar to the weed-free control when glyphosate was applied to weeds 10 to 15 cm tall in 2002 and 10 cm tall in 2003. Soybean yield was maximized by application of glyphosate to weeds 15 to 30 cm tall in 2002 and 60 cm tall in 2003.

Nomenclature: glyphosate, corn, Zea mays L. ‘Wilcross 3149’, soybean, Glycine max (L.) Merr. ‘Asgrow 3701’

Four field studies were conducted in 2004 to evaluate corn tolerance, weed control, grain yield, and net returns in glufosinate-resistant (GUR), glyphosate-resistant (GYR), imidazolinone-tolerant (IT), and nontransgenic (NT) corn with various herbicide systems. No significant differences between hybrid systems were observed for weed control. Limited corn injury (< 5%) was observed for all herbicide treatments. A single early POST (EPOST) system without S-metolachlor and sequential POST over the top (POT) herbicide systems, averaged over corn hybrids and PRE and late POST-directed (LAYBY) herbicide options, provide 93 and 99% control of goosegrass, respectively, and at least 83 and 97% control of Texas panicum, respectively. A single EPOST system without S-metolachlor, averaged over corn hybrids and LAYBY treatment options, provided at least 88% control of large crabgrass. When averaged over corn hybrid and PRE herbicide options, a sequential POT herbicide system alone provided at least 98, 99, 98, and 100 control of large crabgrass, morningglory species, Palmer amaranth, and common lambsquarters, respectively. The addition of ametryn at LAYBY to a single EPOST system without S-metolachlor was beneficial for improving control of morningglory species, common lambsquarters, and Palmer amaranth, depending on location. However, the observed increases (7 percentage points or less) are likely of limited biological significance. Grain yield was variable between hybrids and locations because of environmental differences. Consequently, net returns for each hybrid system within a location were also variable. Any POT system with or without ametryn at LAYBY, averaged over corn hybrid and PRE herbicide options, provided at least 101, 97, 92, and 92% yield protection at Clayton, Kinston, Lewiston, and Rocky Mount, NC, respectively. Net returns were maximized with treatments that provided excellent weed control with minimal inputs.

Nomenclature: Glufosinate, glyphosate, common lambsquarters, Chenopodium album L. CHEAL, goosegrass, Eleusine indica (L.) Gaertn. ELEIN, large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, Palmer amaranth, Amaranthus palmeri S.Wats. AMAPA, Texas panicum Buckl. PANTE, corn, Zea mays L

Clomazone is an effective herbicide widely used for PRE grass control in rice. However, use of clomazone on sandy textured soils of the western Texas rice belt can cause serious rice injury. Two field experiments at three locations were conducted in 2002 and 2003 to determine the optimum rate range that maximizes barnyardgrass and broadleaf signalgrass control and minimizes rice injury across a wide variety of soil textures and planting dates. At Beaumont (silty clay loam), Eagle Lake (fine sandy loam), and Ganado (fine sandy loam), TX, PRE application of 0.34 kg ai/ha clomazone applied to rice planted in March, April, or May optimized barnyardgrass and broadleaf signalgrass control and rice yield while minimizing rice injury. Data suggest that, although injury might occur, clomazone is safe to use in rice on sandy textured soils.

Nomenclature: Clomazone, barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, broadleaf signalgrass, Brachiaria platyphylla BRAPP, rice, Oryza sativa L

The manufacturer's recommended rate for fomesafen in snap beans, dry beans, and soybeans may cause carryover injury in sweet corn. A field experiment, a survey, and multiple greenhouse experiments were conducted to (1) estimate the fomesafen residue concentrations in the soil that might result from use of lower than registered rates, (2) estimate fomesafen residue concentrations in growers' fields and evaluate grower practices for their effects on carryover potential, and (3) investigate the effects of soil type and sweet corn variety on the potential for fomesafen to cause injury to sweet corn. Results of the dissipation study predicted average soil concentrations to be approximately 0.019 mg fomesafen/kg soil at the start of the sweet corn planting season. Half-life values ranged between 28 and 66 d, with an average of 50 d. Residues in grower fields were slightly less than those found in the dissipation study. Injury from fomesafen varied significantly by sweet corn variety and by soil type. Sweet corn grown in soils with high organic matter and low pH were most susceptible to injury from fomesafen. At high rates of fomesafen (0.12 mg/kg), reductions in dry weight of sweet corn varieties ranged from 5 to 60%. At rates of fomesafen slightly higher than those detected in field soils at the time of sweet corn planting (0.03 mg/kg), dry weight either increased slightly (variety trial) or decreased by 6 to 12% (soil-effect trial) depending on soil type. The risk of sweet corn yield losses because of fomesafen carryover appear relatively low. Growers can reduce the risk of carryover injury by planting tolerant varieties in fields where fomesafen was applied the preceding year.

Nomenclature: Fomesafen, bean, Phaseolus vulgaris L, soybean, Glycine max (L.) Merr, sweet corn, Zea mays L

A field study was conducted at Vezaiciai branch of the Lithuanian Institute of Agriculture from 1998 to 2000 to determine weed emergence dynamics in potato and to estimate the effect of different intervals of weed crop competition on potato tuber yield. Treatments varying in intervals of weed-free conditions and competition were laid out in a randomized complete block design with six replications. The greatest emergence of annual broadleaf weeds (62 to 86% of the season total) in the crop was observed in the period from potato planting until flowering. Emergence of winter annuals such as field violet and scentless mayweed was greatest in the period from the 20-cm potato plant height until harvesting. Competition was most detrimental to potato tuber yield in the periods from planting until flowering, from planting until 25 d after flowering, or for the entire growing season. Potato tuber yield decreased by 8.1, 8.4, and 6.4%, respectively, during these competition intervals compared to the weed-free treatment. The results indicated that the critical weed-free period, when weed competition was detrimental to yield, started from planting until 25 d after flowering if regular interrow cultivation was applied.

Nomenclature: Field violet, Viola arvensis Mur VIOAR, scentless mayweed, Tripleurospermum perforatum (Merat) M.Lainz MATIN, Potato, Solanum tuberosum L. ‘Mirta’

The ability to accurately estimate herbicide efficacy is critical for any decision-support system used in weed management. Recent efforts by weed scientists in the North Central United States to adopt WeedSOFT across a broad region have resulted in a number of regional research projects designed to assess and improve the predictive capability of WeedSOFT. Field studies were conducted from 2000 to 2002 in Nebraska, Missouri, and Illinois to evaluate herbicide-efficacy predictions made by WeedSOFT in two corn-row spacings. Following crop and weed emergence, input variables, such as weed densities and heights, were entered into WeedSOFT to generate a list of treatments ranked by predicted crop yields. The five treatments evaluated included those predicting highest crop-yield potential (recommended control treatment 1), a 10% yield reduction, a 20% yield reduction, a 10% yield reduction plus cultivation, and cultivation alone. These treatments were applied to corn grown in 38- and 76-cm rows. Generally, treatments applied in 38-cm rows had more accurate herbicide-efficacy predictions compared with 76-cm rows. WeedSOFT provided better control predictions for broadleaf than grass species. WeedSOFT provided excellent herbicide-efficacy predictions for the highest crop-yield potential, which indicates a good potential for practical use of this software for herbicide recommendations.

Nomenclature: Pennsylvania smartweed, Polygonum pensylvanicum L. POLPY, Corn, Zea mays L

The efficacy of metolachlor on rigid ryegrass was determined under a no-till seeding system in an experiment conducted in 2004 and 2005 in South Australia. Metolachlor at a rate of 0.48 and 0.96 kg ai/ha was applied at 40 or 46 d (very early preplant, VEPP) and 20 or 23 d before crop sowing (early preplant, EPP), and at sowing (preplant, PP) in 2004 and 2005; the herbicide was incorporated by sowing. The control of rigid ryegrass was greater than 80% when metolachlor was applied PP; however, that application resulted in phytotoxic effects on emergence and yield of wheat; metolachlor was more phytotoxic when applied at 0.96 kg/ha than at 0.48 kg/ha. Metolachlor applied EPP provided 71 to 83% rigid ryegrass control, whereas VEPP application provided only 33 to 49% control. Reduction in wheat grain yield was not observed at these application times. This study indicates that metolachlor at 0.48 kg/ha could be safely applied around 20 d before crop sowing to selectively control rigid ryegrass in wheat.

Nomenclature: Metolachlor, rigid ryegrass, Lolium rigidum Gaud. LOLRI, wheat, Triticum aestivum L. ‘Krichauff’

Three field trials were conducted over a 2-yr period (2004 and 2005) at Exeter and Ridgetown, Ontario to evaluate the tolerance of eight market classes of dry beans to KIH-485 applied PRE at 210 and 420 g ai/ha. KIH-485 PRE caused as much as 67% visual injury in small-seeded and 44% visual injury in large-seeded dry beans. KIH-485 applied PRE at 420 g/ha reduced plant height up to 47% at Ridgetown and 8% at Exeter in 2004, and reduced height of brown and white bean by 15 and 19%, respectively, but had no effect on the height of the other beans in 2005. Shoot dry weight was not affected at Exeter in 2004 but was reduced by 46% at Ridgetown in 2004 and 14% at Exeter in 2005. In 2004, seed moisture content increased by 5, 6, and 12% in black, otebo, and pinto beans, respectively. Seed yield was reduced up to 27% at Ridgetown and 11% at Exeter in 2004 but was not affected at Exeter in 2005. On the basis of this research, KIH-485 PRE causes unacceptable injury in some dry bean market classes.

Nomenclature: KIH-485, dry bean, Phaseolus vulgaris L. black ‘AC Harblack’, brown ‘Berna’, cranberry ‘Hooter’, kidney ‘Montcalm’, otebo ‘Hime’, pinto ‘GTS 900’, white ‘OAC Thunder’, yellow eye ‘GTS 1701’

Dry peas (pea) usually require early and effective weed management for optimum yields. However, it is not always possible to control all weeds with a single herbicide application. In experiments at Lacombe and Lethbridge, Alberta, Canada, we determined the relative importance of controlling redstem filaree or wild oat, or both species. Bentazon, sethoxydim, or a imazethapyr/imazamox mixture was applied to control redstem filaree, wild oat, or both weeds, respectively. None of the herbicides caused visually detectable crop injury. Time of weed removal effects on pea yield were inconsistent. In addition, applying half or full herbicide rates did not usually influence weed biomass, pea yield, or pea seed weight. Averaged across all variables except herbicide, pea yield losses due to competition from redstem filaree, wild oat, or both species averaged 31, 47, or 53%, respectively. When redstem filaree and wild oat were controlled with imazethapyr/imazamox, pea yields were the same as weed-free check plots in three of four location-years (89% of weed-free yields for all four location-years). Optimal pea yields in weed communities with redstem filaree and wild oat as dominant species were more dependent upon selecting an herbicide that controlled both species than a specific time of weed removal or herbicide rate.

Nomenclature: bentazon, imazamox, imazethapyr, sethoxydim, redstem filaree, Erodium cicutarium (L.) L'Her. Ex Ait, wild oat, Avena fatua L, dry pea, Pisum sativum L

Control of common lambsquarters with glyphosate in Michigan soybean fields has been inconsistent. Stem-boring insects and evidence of insect tunneling were found inside the stems of common lambsquarters plants not controlled with glyphosate. In 2004 and 2005, field surveys and studies were conducted to identify and evaluate the prevalence of stem-boring insects in common lambsquarters in Michigan and Indiana soybean fields to determine whether tunneling by insects occurred before or following POST glyphosate applications and to evaluate the effect of glyphosate rate, application timing, and insect tunneling on the control of common lambsquarters with glyphosate. Two insect species, the beet petiole borer (Cosmobaris americana) from the Curculionidae family and an unidentified leafminer fly larvae from the Agromyzidae family were found inside common lambsquarters stems. Leafminer larvae were present in Michigan soybean fields in mid- to late-June, when most POST glyphosate applications are made in Michigan and Indiana; however, beet petiole borer larvae were not found in common lambsquarters stems until mid-July and would only be present in common lambsquarters plants if glyphosate applications occurred at that time. Results from three field experiments in East Lansing, MI, demonstrated the variability in common lambsquarters control. Control ranged from 79 to 98%, 75 to 99%, and 49 to 97% from glyphosate applied at 0.84 kg ae/ha to 10-, 25-, and 46-cm common lambsquarters, respectively. In general, applying glyphosate to common lambsquarters plants 10 cm or less, or increasing the glyphosate rate beyond 0.84 kg ae/ha, improved common lambsquarters control. Insect tunneling by leafminer and beet petiole borer larvae did not contribute to reduced common lambsquarters control with glyphosate applied to 10- and 25-cm common lambsquarters.

Nomenclature: Glyphosate potassium salt, common lambsquarters, Chenopodium album (L.) CHEAL, soybean, Glycine max (L.) Merr. ‘AG 2701’, Coleoptera: Curculionidae, beet petiole borer, Cosmobaris americana (Casey), Diptera: Agromyzidae, unidentified leafminer fly

Base temperature (T_b) for leaf appearance and the thermal time interval between appearance of successive leaves (phyllochron) were determined for six common weed species from a series of growth chamber experiments. Mean leaf appearance T_b values for giant ragweed, velvetleaf, redroot pigweed, large crabgrass, woolly cupgrass, and wild-proso millet were 1.3, 8.0, 8.5, 4.5, 2.2, and 5.1 C, respectively, and mean phyllochron values were 37.2, 34.4, 17.3, 42.2, 65.2, and 34.2 growing degree-days per leaf, respectively. Phyllochron values increased slightly with mean temperature for each weed species. To our knowledge, these are the first reported leaf appearance T_b and phyllochron values for giant ragweed, woolly cupgrass, and wild-proso millet. The results confirm leaf appearance T_b and phyllochron values reported previously for velvetleaf and redroot pigweed. However, large crabgrass leaf appearance T_b and phyllochron values in our study varied somewhat from those reported previously. The results provide information needed for parameterization of plant growth models that predict leaf development based on thermal time.

Nomenclature: Giant ragweed, Ambrosia trifida L. AMBTR, large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, redroot pigweed, Amaranthus retroflexus L. AMARE, velvetleaf, Abutilon theophrasti Medicus ABUTH, wild-proso millet, Panicum milliaceum L. PANMI, woolly cupgrass, Eriochloa villosa (Thunb.) Kunth ERBVI

Considerable discussion has occurred among the weed science community regarding the potential benefits and limitations of integrated approaches to crop and pest management. This discussion also needs to occur in our weed science classrooms, where students from a wide range of academic disciplines are trained in the fundamentals of weed ecology and management. Although the inherent complexity of integrated crop and pest management can make this adaptation to our weed science courses challenging, the use of experiential learning techniques provides an effective means to promote understanding and retention of these concepts. This paper outlines several classroom activities based on the experiential learning approaches that have been implemented by the authors. The activities focus on (1) weed identification and natural history, (2) weed population processes, and (3) integrated management systems. For each activity, we offer our rationale for the exercise, an example of its implementation in the classroom setting, potential pitfalls, and student feedback regarding their perceptions of the activity's educational value. With this paper, we hope to provide examples that may be useful to other weed science educators wishing to incorporate more experiential learning activities into their courses and to initiate a dialogue between educators that can help our community improve and enliven weed science education.

Eradication is often stated as an essential element of weed management. Assessing the costs and benefits of eradication programs is often difficult because doing so requires speculation about the impacts and spread of weeds if eradication measures were not undertaken. The objective of this article is to describe and assess the Montana Dyer's Woad Cooperative Project, a program aimed at eradicating dyer's woad from Montana. The Project comprises four key components: early detection, treatment technologies, repeated site visits with monitoring, and education. To evaluate the success of the Montana Dyer's Woad Cooperative Project, we used monitoring data to observe the change in the number of counties where dyer's woad is present, plotted the trend in population size over time, and evaluated change in infestation size. We also predicted population spread based on the 1999 population size and demographic characteristics of dyer's woad. Dyer's woad has been eradicated from 9 of 13 infested counties in Montana, and infestation sizes have decreased in the remaining infested counties. In some counties, a containment effort was needed in conjunction with repeated inventories and treatment applications to prevent spread while depleting the seedbank to the point where eradication is possible. If not for the Project, our analysis suggests that some dyer's woad populations might consist of millions of plants, potentially covering 39,021 ha in Montana and costing $1.9 million/yr to manage. In comparison, the Project has reduced the total area infested in Montana to 2.6 ha and cost the state only $142,000 for the past 7 yr of management. In Montana, dyer's woad eradication from individual counties has been successful because of persistence and ongoing cooperative efforts.

Nomenclature: Dyer's woad, Isatis tinctoria L. ISATI

In November 2004, a 29-question survey was mailed to Delaware soybean growers to determine grower perceptions of glyphosate-resistant (GR) horseweed and if glyphosate applications, GR soybean usage, and management practices had been altered in lieu of the presence of resistance. A total of 213 valid responses were received. Ninety-eight percent of respondents reported planting GR soybean at some point in the last 5 yr, with 90% reporting having planted GR soybean 3 or more years. The presence of GR horseweed on-farm was reported by 38% of the respondents and 95% of those growers with GR horseweed on-farm reported implementing one or more changes in GR soybean management. The most frequent change (66% of growers) due to resistant horseweed was the application of another herbicide with a different mode of action before planting. Forty-eight percent of growers with resistance on-farm reported a $5 to $17/ha increase to manage for GR horseweed, with 28% reporting a greater than $17/ha increase. Regardless of experience with GR horseweed, approximately 80% responded that it was worthwhile to incur additional costs now to preserve glyphosate for future use. Soybean grower reliance on glyphosate has not decreased in light of GR horseweed in Delaware. Misconceptions of timing for the selection of GR horseweed biotypes and the future availability of new herbicides with different modes of action exist within the farming community.

Nomenclature: Glyphosate, horseweed, Conyza canadensis (L.) Cronq. ERICA, soybean, Glycine max (L.) Merr

Jointed goatgrass is a prominent weed infesting winter wheat in the western United States. Individual control tactics often are ineffective and inconsistent, but management systems comprised of several tactics designed to disrupt population dynamics of jointed goatgrass can reduce infestation levels in winter wheat. Tactics are planned to favor decline of seedbank density, reduce seedling emergence in winter wheat, and minimize seed production of plants established in winter wheat. We describe a visual guide that will help producers plan management systems for jointed goatgrass with a diversity of cultural tactics. The guide organizes cultural tactics by decision times of producers during the winter wheat production cycle. Scientists are effectively managing jointed goatgrass in a diversity of production systems by integrating cultural tactics across decision times.

Nomenclature: Jointed goatgrass, Aegilops cylindrica Host. AEGCY, winter wheat, Triticum aestivum L