Rice was planted at 78 kg/ha with different densities of creeping rivergrass. Creeping rivergrass at stand densities (SD) of 10,000 to 70,000 stolon segments/ha produced 5.4 to 6 stolons per introduced segment; however, 130,000 through 520,000 SD produced 1.4 to 2.1 stolons per segment. Stolon production was 60,000 plants/ha and increased to 760,000 stolons/ha at planting densities of 10,000 to 520,000/ha, respectively. The 260,000 and 520,000 SD produced similar stolon lengths of 217 and 318 km/ha; however, stolon length was less at lower SD. Total node production was 290,000 nodes per ha with an average of 29 nodes per segment in the 10,000 SD and 5.4 to 9.8 nodes per segment with 70,000 or greater SD. Total biomass increased as SD increased. Creeping rivergrass shoot emergence from soil was 31, 63, 44, and 25% for segments planted at 0, 1.3, 2.5, and 5 cm deep, respectively. In a greenhouse study, glyphosate at 1,260 g ai/ha controlled creeping rivergrass 91% and biomass production was 19% of the nontreated creeping rivergrass. Bispyribac, cyhalofop, fenoxaprop/s, fenoxaprop/s plus fenoxaprop, glufosinate, imazethapyr, penoxsulam, propanil, and quinclorac were less effective than glyphosate.

Nomenclature: Bispyribac, clomazone, cyhalofop, fenoxaprop, glufosinate, glyphosate, imazethapyr, penoxsulam, propanil, quinclorac, barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, creeping rivergrass, Echinochloa polystachya (Kunth) A.S. Hitchc., rice, Oryza sativa L

Aquatic plants provide many benefits to the environment, but must be managed when growth reaches nuisance levels or when invasive plant species are released. Management tactics include biological, chemical, cultural, mechanical, and physical tools. Each specific management technique has advantages and disadvantages. In addition, the implementation of these techniques can become complicated because of the multiple users, managers, and stakeholders that may be present on large bodies of water. As an example, hydrilla is the most economically damaging aquatic weed in the United States. It reproduces through fragmentation, turions, and occasionally seed and can colonize a wide variety of aquatic environments. The most common management tactics for hydrilla include biological, chemical, and mechanical tools. Triploid grass carp have been the primary biological control agent, whereas fluridone has been the only systemic herbicide used. Because of heavy utilization of fluridone, biotypes have developed resistance to this herbicide in Florida. Although several acetolactate synthase-inhibiting herbicides are in development, herbicides with additional modes of action are needed for resistance management. Other aquatic plant management needs include additional control tactics for algae and additional extension resources for public education.

Nomenclature: Fluridone, hydrilla, Hydrilla verticillata (L.f.) Royle, triploid grass carp, Ctenopharyngodon idella Val

Field studies were conducted in 2005 and 2006 to determine the most effective chemical options within three individual herbicide-based burndown programs, glyphosate, paraquat and glufosinate, for controlling glyphosate-resistant horseweed in Mississippi. Burndown treatments were applied April 5, 2005 and March 15, 2006 to horseweed plants 15 to 30 cm in height. Glyphosate at 0.86 kg ae/ha alone provided 60 to 65% horseweed control 4 wk after treatment (WAT). Control 4 WAT ranged from 73 to 74% when the glyphosate rate was increased to 1.25 kg/ha. Glyphosate at 0.86 kg/ha applied in combination with 2,4-D at 0.84 kg ae/ha or dicamba at 0.28 ae/ha maximized control of horseweed (≥ 90%) 4 WAT and soybean yield. Horseweed control 4 WAT with paraquat alone at 0.84 kg ai/ha ranged from 55 to 63% and control did not improve by increasing the rate to 0.98 kg/ha. Addition of 2,4-D or dicamba to paraquat maximized horseweed control both years (78 to 89%), whereas soybean yield was maximized with addition of dicamba or metribuzin at 0.42 kg ai/ha. Glufosinate applied alone at 0.47 kg ai/ha resulted in at least 88% control of horseweed and maximized soybean yield. Results indicate that effective management of glyphosate-resistant horseweed can be obtained in glyphosate-resistant soybean in glyphosate-, paraquat-, and glufosinate-based preplant weed control programs.

Nomenclature: Carfentrazone, chlorimuron, 2,4-D, dicamba, flumioxazin, glufosinate, glyphosate, linuron, metribuzin, oxyfluorfen, paraquat, thifensulfuron, tribenuron, horseweed, Conyza canadensis (L.) Cronq. ERICA, soybean, Glycine max. (L.) Merr. DK 4763RR, AG 4801RR

Glyphosate-resistant alfalfa offers new weed control options for alfalfa establishment. Field studies were conducted in 2004 and 2005 to determine the effect of establishment method and weed control method on forage production and alfalfa stand establishment. Seeding methods included clear seeding and companion seeding with oats. Herbicide treatments included glyphosate, imazamox, imazamox clethodim, and no herbicide. Temporary stunting from the glyphosate treatments was observed (< 7%); however, injury did not reduce forage yield or stand density in 2004. No glyphosate injury was observed in 2005. Weed control with glyphosate was more consistent than with imazamox or imazamox clethodim. In 2004, total seasonal forage yield, which consisted of alfalfa, weeds, and oats (in some treatments), was the highest where no herbicide was applied in the oat companion crop and was reduced where herbicides were applied in both establishment systems. In 2005, seeding method or weed control method did not affect total seasonal forage production. Alfalfa established with the clear-seeded method and treated with glyphosate yielded the highest alfalfa dry matter in both years. Imazamox injury reduced first-harvest alfalfa yield in the clear-seeded system in both years. When no herbicide was applied, alfalfa yield was higher in the clear-seeded system. The oat companion crop suppressed alfalfa yield significantly in both years. Alfalfa established with an oat companion crop had a lower weed biomass than the clear-seeded system where no herbicide was applied in both years.

Nomenclature: Clethodim, glyphosate, imazamox, alfalfa, Medicago sativa L., oat, Avena sativa L. ‘Ida’

Alfalfa–orchardgrass hay is popular in the Western United States because of an expanding horse-hay market. However, weed control in mixed alfalfa–orchardgrass stands is problematic, as herbicides must be safe for both species. Most growers rely solely on the competitiveness of the crop for weed control, which is often insufficient, especially in older stands. Field experiments were established in northern California to determine the efficacy and crop safety of several herbicides for winter annual weed control in established alfalfa–orchardgrass. Metribuzin at 560 or 840 g/ha and hexazinone at 420 g/ha applied in late fall provided at least 95% control of shepherd's purse and at least 80% control of downy brome without crop injury. Imazethapyr at 70 g/ha applied shortly after crop green-up provided more than 85% control of emerged mustards without crop injury. Paraquat at 560 g/ha applied shortly after crop green-up gave 50 to 82% weed control and caused significant injury to orchardgrass, which was still noticeable at first cutting.

Nomenclature: Hexazinone, imazethapyr, metribuzin, paraquat, downy brome, Bromus tectorum L., shepherd's purse Capsella bursa-pastoris L,, alfalfa, Medicago sativa L., orchardgrass, Dactylis glomerata L

Field experiments were conducted at Warooka and Rudall on the Yorke and Eyre Peninsula of South Australia during 2004 and 2005 to investigate the effectiveness of metribuzin for the selective control of rigid brome in no-till sown barley. Metribuzin (135 to 203 g ai/ha) incorporated by sowing (IBS) was more effective in controlling rigid brome (> 67%) than the same herbicide dose applied POST. Although IBS metribuzin at the highest rate (270 g/ha) provided effective weed control (82 to 90%), it was more phytotoxic to barley, reducing crop density by 23% relative to the nontreated control at Rudall. Soil at Rudall had low clay and organic matter content. In contrast, tank mixtures of metribuzin (203 g/ha) with pendimethalin, applied IBS, provided reliable rigid brome control (89 to 93%) and resulted in little crop damage (< 5%). Over the site-by-year combinations studied, all herbicide-treated barley at Warooka and Rudall yielded 6 to 50% more grain than the nontreated crop. Although metribuzin provides growers with an opportunity to selectively control rigid brome in no-till barley, high rates (≥ 203 g/ha) of this herbicide on sandy textured soils can result in significant crop damage.

Nomenclature: Metribuzin, rigid brome, Bromus rigidus Roth BRORI, barley, Hordeum vulgare L

Selected fatty acids, such as pelargonic acid and caprylic acid, are effective nonselective herbicides for a wide spectrum of annual weed species. Greenhouse and field studies evaluated the potential of certain food-grade organic acids to enhance herbicide activity of pelargonic acid-based formulations. The addition of diammonium succinate and succinic acid improved the efficacy of a pelargonic acid formulation from 117 to 200% in the greenhouse. l-Lactic acid and glycolic acid enhanced the efficacy of pelargonic acid formulations on velvetleaf and common lambsquarters in the greenhouse by 126 to 168% and in the field by 117 to 138%. Thus, combinations of fatty and organic acids with selected emulsifiers can be highly effective as safe, nonselective herbicides.

Nomenclature: Caprylic acid, pelargonic acid, common lambsquarters, Chenopodium album L., CHEAL, velvetleaf, Abutilon theophrasti Medic. ABUTH

Field experiments were conducted in Missouri in 2004 through 2006 to compare the efficacy of fall and spring herbicide treatments for control of winter and summer annual weeds in no-tillage corn. Applications in the fall and 45 d before planting (45 PP) of 2,4-D and simazine; rimsulfuron, thifensulfuron, and 2,4-D; or glyphosate and 2,4-D controlled at least 90% of all winter annual weeds through 1 wk after corn planting (WAP), with a few exceptions. Applications made 30 d before planting (30 PP) of 2,4-D and glyphosate or rimsulfuron, thifensulfuron, and 2,4-D provided greater than 90% control of most winter annual weeds 1 WAP. Winter annual weed control was reduced with herbicide treatments applied 7 d before planting (7 PP), compared with earlier application timings. Summer annual weed control 5 WAP increased as the time between application and planting decreased. Fall applications resulted in greater weed biomass 5 WAP, compared with spring applications.

Nomenclature: 2,4-D, glyphosate, rimsulfuron, simazine, thifensulfuron, corn, Zea mays L. ‘Pioneer 34B23’

Populations of plumeless thistle and musk thistle were mowed at various growth stages at two separate sites in Maryland during a 6-yr period to elucidate relationships among seed rain, soil seed banks, and population recruitment. The majority of seeds (96%) in the soil profile were distributed within 7.6 cm of the surface at both sites. Mowing plumeless thistle when most of the flower heads were at the full bud or postbloom stage did not reduce seed bank or plant densities, unlike mowing at full bloom, which significantly and quickly reduced both. Musk thistle responded differently, with plant density declining only with the postbloom mowing treatment, which occurred after the parent plant had dispersed seeds and died. Seed bank densities were unchanged by this treatment. This indicates that other factors may limit the recruitment and maintenance of musk thistle, such as allelochemical production by parents and interspecific plant competition. Density of musk thistle declined over an 11-yr period at one monitoring site, whereas plumeless thistle remained unchanged. The disproportionate seed-destroying activities of the weed biological control agent Rhinocyllus conicus on musk thistle may explain this difference.

Nomenclature: musk thistle, Carduus nutans Wienm. CRUNU, plumeless thistle, Carduus acanthoides L. CARAC

A field experiment was conducted in Okinawa, Japan from 2005 to 2007 to evaluate the effect of purple nutsedge and other weeds on turmeric growth and yield and determine the effective weed-control period to minimize crop interference. Treatments consisted of all weeds removed at 70, 115, and 160 d sequentially after planting (DAP), all weeds except purple nutsedge removed at these three dates, plus weedy and weed-free controls. Purple nutsedge density increased until 115 DAP when grown alone with turmeric and thereafter decreased markedly, whereas it increased only until 70 DAP when grown with other weeds. Weed reinfestation in turmeric that was sequentially weeded was high until 115 DAP, but thereafter was negligible. In the weedy control, the weed infestation was severe until 160 DAP. Plant height and leaf and tiller number per plant of turmeric increased rapidly from 70 to 160 DAP. Season-long weed infestation significantly reduced shoot biomass and rhizome yield of turmeric, but both were similarly high among treatments of weed-free turmeric, all weed removal, and removal of all weeds except purple nutsedge. Purple nutsedge (> 3,000 plants/m²) did not significantly reduce turmeric yield, whereas the combined weed species reduced yield by greater than 40%. Thus, crop interference by purple nutsedge was not high, and other weeds could be removed during 70 to 160 DAP for reduced labor requirements and higher yield of turmeric.

Nomenclature: Purple nutsedge, Cyperus rotundus L. CYPRO, turmeric, Curcuma longa L

Field studies were conducted near Lewiston–Woodville and Rocky Mount, NC to evaluate the effects of mixed weed species on peanut yield. A combination of broadleaf and grass weeds were allowed to interfere with peanut for various intervals to determine both the critical timing of weed removal and the critical weed-free period. These periods were then combined to determine the critical period of weed control in peanut. The effects of various weedy intervals on peanut yield were also investigated. The predicted critical period of weed control, in the presence of a mixed population of weeds, was found to be from 3 to 8 wk after planting (WAP). Peanut yield decreased as weed interference intervals increased, demonstrating the need for weed control throughout much of the growing season in the presence of mixed weed populations.

Nomenclature: Peanut, Arachis hypogaea L

Studies were conducted to evaluate the effects of grass and broadleaf weeds on peanut growth and peanut yield. In separate studies, grass or broadleaf weeds were allowed to compete with peanut for various intervals to determine both the critical timing of weed removal and the critical weed-free period. Hand-weeding and selective herbicides were used at appropriate times to remove and terminate weed growth. These periods were then used to determine the critical period of weed control. The effects of various weedy intervals on peanut yield were also investigated. The critical period of grass weed control was found to be from 4.3 to 9 wk after planting (WAP), whereas the critical period of broadleaf weed control was from 2.6 to 8 WAP. Peanut yields decreased as weed interference intervals for both grass and broadleaf weeds increased, demonstrating the need for control of both grass and broadleaf weeds throughout much of the growing season.

Nomenclature: Peanut, Arachis hypogaea L

Field studies were conducted in 2002 and 2003 to determine the effects of herbicides applied below suggested use rates on weed management, yield, and estimated net return of peanut in both narrow and wide row-spacing regimes. In the single row-spacing regime study, diclosulam at 6 g/ha (1/4×) (1/4 labeled use rate) plus flumioxazin at 26 g/ha (1/4×) applied PRE followed by (fb) imazapic POST at 17, (1/4×), 35, (1/2×), or 70, (1×) g/ha was the lowest herbicide input that provided at least 80% control of sicklepod, yellow nutsedge, Florida beggarweed, and hairy indigo at 21 d after treatment (DAT). By 42 DAT, weed control was ≥ 80%, similar to herbicide treatments applied at labeled rates. In the twin row-spacing regime study at Jay, FL, and Citra, FL, in 2003, yellow nutsedge control was lowest (83 to 85%) from diclosulam applied at 1/4× in combination with flumioxazin at 1/4× PRE and flumioxazin at 1/4× or 52 g/ha (1/2×) PRE alone. All other herbicide treatments provided > 90% control. Diclosulam at 13 g/ha (1/2×) fb imazapic at 1/2× and flumioxazin at 1/4× fb imazapic at 1/2× was the lowest rate combination that provided > 80% control of sicklepod. Florida beggarweed control was > 90% with all rate combinations except diclosulam PRE alone, diclosulam at 1/4× PRE fb imazapic at 1/4× POST, and imazapic at 1/4× alone POST. Net return in the single-row spacing regime was highest for flumioxazin at 105 g/ha (1×) PRE alone, diclosulam at 1/4× applied with flumioxazin at 1/4× PRE alone or fb imazapic at 1× ($1,114, $1,094, and $990/ha, respectively). The twin row-spacing regime net return was highest with diclosulam PRE alone at 1/4, 1/2, or 26 g/ha (1×) ($2,063, $1,846, $1,734/ha, respectively). Diclosulam applied with flumioxazin at 1/2× fb imazapic at 1/2× was the lowest herbicide tank-mix input providing high net return at $1,162/ha.

Nomenclature: Diclosulam, flumioxazin, imazapic, Florida beggarweed, Desmodium tortuosum (Sw.) DC., hairy indigo, Indigofera hirsuta Harvey, sicklepod, Senna obtusifolia (L.) H.S. Irwin & Barneby, yellow nutsedge, Cyperus esculentus L., peanut, Arachis hypogaea L. ‘C-99R’

Field trials were conducted in 2005 and 2006 to evaluate application of glyphosate alone or plus the plant growth regulator mepiquat chloride with 20 different insecticides to second-generation glyphosate-resistant cotton at the pinhead square or first bloom growth stages. At 7 DAT, averaged across cotton growth stages and herbicide treatments, combination with insecticides profenofos and methomyl resulted in 5 and 9% plant injury, respectively, and were the only insecticide combinations that resulted in injury greater than glyphosate or glyphosate plus mepiquat chloride applied alone. By 14 DAT, cotton injury was less than 2% for all treatments. Averaged across cotton growth stages and insecticides, addition of mepiquat chloride to glyphosate resulted in a 4 and 6 cm height reduction at 7 and 28 DAT, respectively. Seed cotton yield and percent first harvest were similar for all treatments, indicating that cotton injury and height reductions observed after application did not result in yield reductions or maturity delays. Glyphosate combined with insecticides and mepiquat chloride, in accordance with herbicide labeling for second-generation glyphosate-resistant cotton, offers producers the ability to integrate pest and crop management strategies and reduce application costs with minimal effect on the crop.

Nomenclature: Acephate, acetamiprid, bifenthrin, cyfluthrin, cypermethrin, dicrotophos, dimethoate, emamectin benzoate, gamma-cyhalothrin, glyphosate, imidacloprid, indoxacarb, lambda-cyhalothrin, mepiquat chloride, methomyl, novaluron, oxamyl, profenofos, spinosad, thiamethoxam, thiodicarb, zeta-cypermethrin, cotton, Gossypium hirsutum L

Managing weeds in watermelon is challenging because of the limited availability of herbicides approved for use in this crop. Field experiments on efficacy and crop tolerance were conducted to determine the potential for halosulfuron use in watermelon in Georgia and North Carolina. Halosulfuron was applied PRE, early POST (EPOST; one-leaf watermelon), and late POST (LPOST; watermelon with 30-cm runners) at 26, 39, and 52 g ai/ha. Under weed-free conditions, PRE treatments did not injure watermelon. EPOST and LPOST treatments caused 45 and 34% injury 2 wk after treatment, respectively, averaged over halosulfuron rate. EPOST treatments reduced watermelon fruit number and total weight by 15 and 22%, respectively, and LPOST treatments reduced total fruit weight 12%. Halosulfuron PRE at 39 or 52 g/ha provided 94% or greater control of carpetweed, Palmer amaranth, and smooth pigweed. EPOST treatments controlled 84 and 88% of yellow nutsedge and smooth pigweed, respectively, but LPOST treatments controlled less than 83% of all weed species. Sequential applications of halosulfuron at 26 g/ha PRE and 26 g/ha LPOST controlled 89 to 99% of carpetweed, coffee senna, Palmer amaranth, smooth pigweed, and yellow nutsedge. Our data suggest growers can effectively use halosulfuron PRE in seeded watermelon. However, POST applications should be made only after watermelon has 30-cm runners and as a salvage spot treatment where previous weed control strategies have failed to provide adequate control.

Nomenclature: Halosulfuron, carpetweed, Mollugo verticillata L. MOLVE, coffee senna, Cassia occidentalis (L.) Link CASOC, Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA, smooth pigweed, Amaranthus hybridus L. AMACH, yellow nutsedge, Cyperus esculentus L. CYPES, watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai ‘Legacy’, ‘Sangria’, ‘Stargazer’

Thirty-one Ohio vineyards were surveyed in 2004 to document weeds that persisted following weed control practices. Weeds were identified and density was determined during visits to each vineyard. Herbicide-use history, grape varieties, and grape age were recorded during interviews with the growers. Data were analyzed by SAS 9.1 with the use of the generalized linear model (GLM), and means were compared according to Student–Newman–Keuls (SNK) at the 0.05 level. Crabgrass, dandelion, pigweed, foxtail, fall panicum, clover, chickweed, common ragweed, smartweed, and oxalis were the most prevalent 10 weeds in Ohio vineyards based on relative abundance values. The frequency and density of crabgrass, dandelion, fall panicum, oxalis, and common purslane were significantly higher in vineyards in which glyphosate was the only herbicide used than in vineyards where other herbicides were applied. The number of species and density were higher in vinifera vineyards that had been hilled for winter protection than in vineyards that had not been hilled.

Nomenclature: Glyphosate, chickweed, Stellaria media (L.) Vill. or Cerastium fontanum ssp. vulgare (Hartman) Greuter & Burdet, clover, Trifolium repens L. or Trifolium pratense L., common purslane (Portulaca oleracea), common ragweed, Ambrosia artemisiifolia L., crabgrass, Digitaria sanguinalis (L.) Scop., dandelion, Taraxacum officinale G.H. Weber ex Wiggers, fall panicum, Panicum dichotomiflorum Michx., foxtail, Setaria faberi Herrm. or Setaria pumila (Poir.) Roemer & J.A. Schultes or Setaria viridis (L.) Beauv., oxalis, Oxalis corniculata L., pigweed, Amaranthus hybridus L. or Amaranthus retroflexus L., smartweed, Polygonum pensylvanicum L., vinifera grape, Vitis vinifera L

Field studies were conducted during the 2000 and 2001 growing seasons to evaluate imazapic plus 2,4-D for weed control and bermudagrass tolerance. Imazapic at 140 g ai/ha plus 2,4-D at 280 g ai/ha or greater controlled dallisgrass at least 82% and provided at least 90% control of field sandbur, johnsongrass, and field mint. A mixed stand of Texas panicum and large crabgrass was controlled less than 75% and bahiagrass less than 25% with all rates of imazapic plus 2,4-D. Coastal bermudagrass injury was greater than 24% at three of four locations and Tifton 85 injury was greater than 50% at 3 wk after treatment with rates of imazapic plus 2,4-D as low as 70 plus 140 g/ha. Coastal bermudagrass yield was reduced at the first cutting with imazapic plus 2,4-D at 140 plus 210 g/ha and 240 plus 420 g/ha. Imazapic plus 2,4-D at 200 plus 350 g/ha reduced Tifton 85 forage production at the first two cuttings.

Nomenclature: Imazapic, 2,4-D, dallisgrass, Paspalum dilatatum Poir. PASDI, field mint, Perilla frutescens (L.) Britt. PRJFR, field sandbur, Cenchrus incertus M. A. Curtis CCHIN, johnsongrass, Sorghum halepense (L.) Pers. SORHA, Texas panicum, Panicum texanum Buckl. PANTE, large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, bahiagrass, Paspalum notatum Fluegge PASNO, bermudagrass, Cynodon dactylon (L.) Pers. CYNDA, ‘Coastal’, ‘Tifton 85’

Influence of aqueous leaf extracts, leaf residue, and leached-leaf residue of houndstongue, a noxious rangeland weed, on seedling emergence of forage grasses was studied. Ultraviolet-B (UV-B) effects during houndstongue growth on subsequent germination and growth-inhibitory activity of leaf extracts were investigated. Addition of glasshouse-grown houndstongue leaf extract to mineral soil decreased emergence of crested wheatgrass by 13% and prairie junegrass by 20% at 14 d after sowing. Idaho fescue emergence was unaffected. Incorporation of houndstongue leaf- and leached-leaf residue into soil (0.4 g residue : 20 g soil) delayed emergence of forage grasses. At 14 d after sowing, houndstongue leaf residue spread on the soil surface (0.2 g residue : 20 g soil) tended to inhibit seedling emergence more than leaf residues incorporated into soil. In separate experiments, houndstongue plants were grown at 0, 4, 7, and 11 kJ/m²/d biologically effective UV-B radiation for 6 wk, and leaf extracts (0.5, 1, 2, and 4% wt/v) were prepared. Exposure of houndstongue to increasing UV-B dose during plant growth generally increased the inhibitory activity of their leaf extract on prairie junegrass germination. Crested wheatgrass and Idaho fescue seedlings incubated in extracts of houndstongue leaves exposed to UV-B, compared with leaves grown in a UV-B–free environment, had decreased root lengths. Leaf extracts of plants exposed to elevated UV-B levels had higher absorbance at 300 nm, indicating greater concentration of UV-B–absorbing compounds. This study suggests houndstongue leaf extracts and residues inhibit seed germination and seedling emergence and that UV-B may enhance their allelopathic influence on some forage grasses. Field studies are needed to confirm the allelopathic influence of houndstongue under rangeland conditions.

Nomenclature: Houndstongue, Cynoglossum officinale L. CYWOF, crested wheatgrass, Agropyron cristatum (L.) Gaertn., alternate binomial, Elymus wawawaiensis J. Carlson & Barkworth var. Secar, Idaho fescue, Festuca idahoensis Elmer var. Joseph, prairie junegrass, Koeleria macrantha (Ledeb.) J.A. Schultes

Failure of glyphosate to control Palmer amaranth was first reported in Arkansas in Mississippi County in June, 2005. The objectives of this research were to (a) confirm glyphosate-resistant Palmer amaranth in Arkansas, and (b) determine the effectiveness of 15 postemergence- (POST) applied herbicides comprising eight modes of action in controlling the glyphosate-resistant biotype compared to glyphosate-susceptible accessions. The LD₅₀ values were similar among three susceptible Palmer amaranth accessions, ranging from 24.4 to 35.5 g ae/ha glyphosate. The resistant biotype had an LD₅₀ of 2,820 g/ha glyphosate, which was 79- to 115-fold greater than that of the susceptible biotypes and 3.4 times a normal glyphosate-use rate of 840 g/ha. The glyphosate-resistant biotype was effectively controlled with most of the evaluated herbicides, but the use of acetolactate synthase-inhibiting herbicides such as pyrithiobac, trifloxysulfuron, and imazethapyr is not a viable option for control of this Palmer amaranth population.

Nomenclature: Glyphosate, Amaranthus palmeri S. Wats. AMAPA

Studies were conducted in 2003 and 2004 over seven environments evaluating rice root growth inhibition (RGI) and foliar injury from penoxsulam at 30 and 60 g ai/ha and bispyribac-sodium at 30 g ai/ha applied to four- to five-leaf rice at three flood timings, 1, 7, and 14 d after herbicide treatment (DAT), for five rice cultivars, ‘Bengal’, ‘Cypress’, ‘Wells’, ‘Cocodrie’, and ‘XP712’. Flooding at 1 and 7 DAT resulted in greater RGI compared with flood at 14 DAT when evaluated 1 wk after flood (WAF). By 2 WAF, RGI was greater with flooding at 1 DAT compared with flooding at 7 DAT for cultivars Bengal, Cypress, and Wells. Analyzing flood timing 1 DAT, bispyribac-sodium reduced root growth of Bengal and Cypress compared with penoxsulam at 30 g/ha at 1 week after treatment (WAT). At 2 WAT, RGI for Cocodrie was higher following penoxsulam at 60 g/ha when compared with bispyribac-sodium. By 3 WAT, RGI was higher following penoxsulam at 60 g/ha when compared with penoxsulam at 30 g/ha for Cocodrie and greater than bispyribac-sodium and penoxsulam at 30 g/ha for Cypress. Foliar injury following penoxsulam at both rates was less than injury following bispyribac-sodium for all cultivars except XP712 at 1 WAT. XP712 resulted in < 5% RGI and < 6% foliar injury at each evaluation. Rice grain yield was not affected by herbicide treatment for any cultivar compared with the standard treatment of propanil plus quinclorac.

Nomenclature: Bispyribac-sodium, penoxsulam, propanil, quinclorac, rice, Oryza sativa L. ‘Bengal’, ‘Cocodrie’, ‘Cypress’, ‘Wells’, ‘XP712’

Many agricultural producers apply glyphosate to glyphosate-resistant crops to control weeds, including Palmer amaranth. Populations of this weed in Tennessee not completely controlled by glyphosate were examined. Field and greenhouse research confirmed that two separate populations had reduced biomass sensitivity (1.5× to 5.0×) to glyphosate compared to susceptible populations, although the level of resistance was higher based on plant mortality response (about 10×). Shikimate accumulated in both resistant and susceptible plants, indicating that 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) was inhibited in both biotypes. These results suggest that an altered target site is not responsible for glyphosate resistance in these Palmer amaranth biotypes.

Nomenclature: Glyphosate, Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA

The majority of dry pea (pea) cultivars in current production have semileafless architecture. Although these cultivars tend to yield well and resist lodging, they may not be the best cultivars in terms of competition with weeds. Experiments were conducted at Lacombe and Lethbridge, Alberta, Canada, from 2003 to 2005 to compare semileafless and leafy pea cultivars under different seeding and herbicide regimes. During the study, in terms of weed emergence and biomass, oat (seeded) was usually more dominant than broadleaf weeds. Higher-disturbance sweep seeding led to slightly greater oat populations than lower disturbance seeding with knives. Leafy pea had lower yield potential in less weedy conditions than the semileafless pea, but the former were less susceptible to yield reduction as weed competition increased. Leafy pea often led to lower weed biomass and dockage than the semileafless pea. However, because semileafless pea yield at least as well as leafy pea in all of the environments encountered in this study, integrated weed management principles are currently best served by growing semileafless pea. Breeding to improve leafy cultivar yield potential may lead to greater opportunities for integrated weed management and herbicide input reductions in the future.

Nomenclature: Imazamox, imazethapyr, dry pea, Pisum sativum L., oat, Avena sativa L

A study was conducted to test the effect of water clarity, as related to water seeding system, on herbicide efficacy in water-seeded imidazolinone-resistant rice production. Red rice control was 88 to 89% when 140 g/ha imazethapyr was applied in a single application immediately prior to permanent flood in the clear-water seeding system. All herbicide applications in either clear- and muddy-water systems controlled red rice 90 to 95%. The benefits of reducing soil erosion and surface water contamination from muddy-water discharge at seedling establishment can be obtained in a clear-water system without experiencing a decrease in weed control or rice yield.

Nomenclature: Imazethapyr, red rice, Oryza punctata Kotchy ex. Steud., rice, Oryza sativa L

Yellow nutsedge can readily puncture the plastic mulch used in plasticulture tomato production, compromising the benefits of the mulch and hastening its deterioration. Our objective was to identify a PRE-applied (i.e., under the plastic) treatment to minimize yellow nutsedge puncturing. In a greenhouse study a series of halosulfuron rates were PRE-applied to soil planted with yellow nutsedge tubers. These rates were also applied to established plants but with selective spray contact. Nonlinear regression revealed that the concentration of halosulfuron required to reduce dry weights by 90% (GR₉₀) for PRE-applied halosulfuron was 11.6 g/ha. The GR₉₀ for POST-applied halosulfuron was 17.1, 28.1, and 11.6 g/ha for foliar-only, soil-only and foliar plus soil spray contact, respectively. Thus halosulfuron was more effective as a POST-applied, foliar-contacting treatment. However, soil activity was deemed likely sufficient to suppress plastic puncturing. In a noncrop field study, suppression of puncturing was influenced (P < 0.05) by the rate of both PRE-applied halosulfuron and S-metolachlor. A field study with tomato was conducted to evaluate six selective treatments using plastic mulch, PRE-applied S-metolachlor, and the combination of PRE or PRE/POST-split applications of halosulfuron. Plastic alone increased tomato yield threefold compared with bare ground. The addition of various herbicide programs neither increased nor reduced yield compared with plastic alone. Selected herbicide treatments did reduce mulch puncturing but not to the extent or duration that would allow sequential crops to receive the full benefit of nonpunctured plastic.

Nomenclature: Halosulfuron, S-metolachlor, yellow nutsedge, Cyperus esculentus L. CYPES, tomato, Lycopersicon esculentum Mill. ‘Florida 91’

Seeds from five suspected acetyl-CoA carboxylase (ACCase) inhibitor–resistant wild oat biotypes (R1 to R5) were collected in wheat and lentil fields in the Pacific Northwest. Based on whole plant dose–response experiments, the five resistant biotypes were 2 to 24 times more resistant to the aryloxyphenoxypropionate (APP) herbicides (fenoxaprop, diclofop, and quizalofop) compared with the susceptible biotype. However, none of the resistant biotypes were resistant to the cyclohexanedione (CHD) herbicides, sethoxydim and clethodim. R2 was the only biotype resistant to tralkoxydim and pinoxaden, a phenylpyrazolin herbicide and an ACCase inhibitor. The R2 biotype was 35 and 16 times more resistant to tralkoxydim and pinoxaden, respectively, when compared with the susceptible biotype. The levels of resistance and cross-resistance patterns varied among biotypes indicating either more than one mechanism of resistance or different resistance mutations in these wild oat biotypes. The CHD herbicides, sethoxydim and clethodim, could be used to control these resistant biotypes. Except for the R2 biotype, pinoxaden could be used to control the resistant wild oat biotypes. The resistance patterns of these wild oat biotypes are an indication of the difficulty in predicting cross-resistance among the ACCase inhibitor herbicides.

Nomenclature: Clethodim, diclofop, fenoxaprop, pinoxaden, quizalofop, sethoxydim, tralkoxydim, wild oat, Avena fatua L. AVEFA, lentil, Lens culinaris Medik, wheat, Triticum aestivum L

The submersed macrophyte, sago pondweed, frequently grows to nuisance levels in water conveyance systems throughout the western United States and can cause problems in lakes, reservoirs, and other water bodies. The liquid dipotassium and dimethylalkylamine salt formulations of endothall were evaluated for controlling sago pondweed using short exposure times (3 to 24 h) under controlled environmental conditions (14 : 10 h light : dark; 21.5 C). Endothall treatments ranged from 1 to 10 mg ai/L (dipotassium salt) and 0.5 to 5 mg ae/L (dimethylalkylamine salt). Sixteen concentration and exposure time (CET) combinations were evaluated in each study. At 4 wk after treatment, all CET combinations significantly reduced shoot biomass (43 to 99%) of sago pondweed compared with the untreated reference. Reduction in shoot biomass was greater in plants that received higher herbicide doses and longer exposure times. In addition, more than half of the endothall CET combinations controlled sago pondweed by at least 90%, with some providing > 98% control. At the endothall CETs evaluated, regrowth of sago pondweed could occur after 4 wk, and some level of retreatment might be required to maintain plant control throughout the growing season. Results indicate that endothall shows promise as an alternative vegetation management tool in flowing-water environments.

Nomenclature: Endothall, sago pondweed, Stuckenia pectinata (L.) Boerner PTMPE

Field and greenhouse experiments were conducted in 2005 and 2006 in Guam to evaluate the effects of glyphosate on field dodder control and to describe glyphosate dose–response curves on selected ornamental plants grown with and without dodder infestation. Visual quality of dodder-free plants decreased with increasing dose of glyphosate. The most sensitive species was king's mantle, whereas the most tolerant was hibiscus. The values for the effective dose for a 10% reduction in visual quality (ED₁₀) of glyphosate were 800, 280, 1,250, 370, 590, 830, 660, and 170 g ai/ha for dodder-free croton, allamanda, hibiscus, paper gardenia, ixora, duranta, schefflera, and king's mantle, respectively. However, dodder-infested plants were less tolerant to glyphosate because of the confounded stress from both the parasite and herbicide. Field dodder parasitizing ornamental plants could be adequately controlled on all ornamental species at a dose of about 140 g/ha of glyphosate.

Nomenclature: Glyphosate, N-(phosphonomethyl)glycine, field dodder, Cuscuta campestris Y. CVCCA, duranta, Duranta L. spp., garden croton, Codiaeum variegatum (L.) Blume, hibiscus, Hibiscus L. spp., ixora, Ixora L. spp., king's mantle, Thunbergia erecta (Benth.) T. Anders., miniature schefflera, Schefflera arboricola (Hayata) Merr., paper gardenia, Tabernaemontana divaricata (L.) R. Br. ex Roemer & J.A. Schultes, purple allamanda, Allamanda blanchetii A. DC

Russian thistle is a severe problem in fields after crop harvest in the Pacific Northwest (PNW) and is controlled either by tillage or broadcast applications of various herbicides. A study was conducted in Washington in 2000 and 2001 at four sites to compare the efficacy of two herbicide treatments applied with a light-activated, sensor-controlled (LASC) sprayer and a conventional broadcast sprayer for postharvest Russian thistle control. Additionally, simple economic comparisons, excluding fixed costs, were made among herbicide treatments and application methods. Both herbicide applicators controlled Russian thistle similarly within each herbicide treatment. Weed control was unacceptable (≤ 75%) when glyphosate plus 2,4-D was applied with either applicator. In contrast, Russian thistle control was > 90% with paraquat plus diuron regardless of applicator. The overall reduction in chemical use was 42% with the LASC compared with the broadcast applicator when averaged over the four sites. Herbicide and surfactant cost savings, using 2007 prices for the LASC compared with the broadcast applicator, ranged from $6.68/ha to $18.21/ha with the paraquat plus diuron treatment and averaged $13.27/ha less for the four sites. The use of the LASC for postharvest Russian thistle control can reduce growers' input costs, increase growers' profits, and improve environmental quality by reducing the amount and area of a restricted-use chemical.

Nomenclature: Glyphosate, 2,4-D, paraquat, diuron, Russian thistle, Salsola tragus L

Field studies were conducted in five states at six locations from 2002 through 2003 to evaluate weed control and cotton response to early POST (EPOST), POST/POST-directed spray (PDS), and late POST-directed (LAYBY) systems using glyphosate-trimethylsulfonium salt (TM), s-metolachlor, trifloxysulfuron, prometryn, and MSMA. Early POST applications were made from mid May through mid June; POST/PDS applications were made from early June through mid July; and LAYBY applications were made from early July through mid August. Early season cotton injury and discoloration was minimal (< 1%) with all treatments; mid- and late-season injury was minimal (< 2%) except for trifloxysulfuron POST (11 and 9%, respectively). Annual grasses evaluated included barnyardgrass, broadleaf signalgrass, goosegrass, and large crabgrass. Broadleaf weeds evaluated included entireleaf morningglory, pitted morningglory, sicklepod, and smooth pigweed. For the EPOST, POST/PDS, and LAYBY applications, weeds were at cotyledon to 10 leaf, 1 to 25 leaf, and 2 to 25 leaf stage, respectively. Annual broadleaf and grass control was increased with the addition of s-metolachlor to glyphosate-TM EPOST systems (85 to 98% control) compared with glyphosate-TM EPOST alone (65 to 91% control), except for sicklepod control where equivalent control was observed. Annual grass control was greater with glyphosate-TM plus trifloxysulfuron PDS than with trifloxysulfuron POST or PDS, or trifloxysulfuron plus MSMA PDS (90 to 94% vs. 75 to 83% control). With few exceptions, broadleaf weed control was equivalent for trifloxysulfuron applied POST alone or PDS alone or in combination with glyphosate-TM PDS or MSMA PDS herbicide treatments (81 to 99% control). The addition of a LAYBY herbicide treatment increased broadleaf weed control by 11 to 36 percentage points compared with systems without a LAYBY. Cotton lint yield increased 420 kg/ha with the addition of s-metolachlor to glyphosate-TM EPOST treatments compared with systems without s-metolachlor EPOST. Cotton lint yield was increased 330 to 910 kg/ha with the addition of a POST herbicide treatment compared with systems without a POST/PDS treatment. The addition of a LAYBY herbicide treatment increased cotton lint yield by 440 kg/ha compared with systems without a LAYBY.

Nomenclature: Glyphosate-TM, MSMA, prometryn, s-metolachlor, trifloxysulfuron, barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash. BRAPP, entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray. IPOHG, goosegrass, Eleusine indica (L.) Gaertn. ELEIN, arge crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, pitted morningglory, Ipomoea lacunosa L. IPOLA, sicklepod, Cassia obtusifolia L. CASOB, smooth pigweed, Amaranthus hybridus L. AMACH, cotton, Gossypium hirsutum L. ‘DP 458 RR/BG’, ‘DP 555 RR/BG’, ‘FM 989 RR/BG’, ‘PM 2344 RR/BG’, ‘ST 4793 RR’

Development of conservation tillage practices for dry bean has lagged behind that of many other crops. A field study was conducted to determine the effects of various crop residues and herbicide treatments on weed management and dry bean yield within a zero-tillage system. Main plot treatments included wheat stubble, canola stubble, fall-seeded winter rye, fall-seeded spring rye, and a no-cover control. Subplot treatments included various preplant and POST herbicides. Wheat stubble, canola stubble, and winter rye residue provided sufficient ground cover to prevent soil erosion, and they effectively reduced weed density compared with the no-cover control in all years. Fall-seeded spring rye provided only partial soil-erosion protection and reduced weed density in only 1 of 3 yr. Dry bean emergence was 3 to 5 d slower in the crop residue treatments compared with the no-cover control, but crop density was not adversely affected. However, winter rye residue delayed dry bean maturity by 2 to 6 d. Fall-applied granular ethalfluralin followed by POST bentazon/imazethapyr or imazamox provided the most effective weed control. A sole POST imazamox application also provided good weed control when weed densities were reduced by winter rye residue or wheat stubble. Overall, results indicate that with suitable herbicide programs, similar yields were attained when dry bean was seeded directly into crop stubble or cover crop residues compared with the no-cover control. Information gained in this study will be used to encourage greater farmer adoption of conservation tillage practices for dry bean production on the Canadian prairies.

Nomenclature: Bentazon, ethalfluralin, imazamox, imazethapyr, canola, Brassica napus L., dry bean, Phaseolus vulgaris L., rye, Secale cereale L., wheat, Triticum aestivum L

Producers are interested in tactics for managing crop residues when growing corn after spring wheat. We compared five systems of managing spring wheat residues: conventional tillage, no-till, strip-till, cover crop (hairy vetch) with no-till, and cover crop with strip-till following spring wheat. Conventional tillage consisted of chisel plowing and disking, whereas strip-till consisted of tilling a 15-cm band centered on corn rows, which were spaced 76 cm apart. Plots were split into weed-free and weed-infested subplots. Grain yield in weed-free conditions did not differ among treatments. However, weed-free yield was nearly 40% greater than weed-infested corn in conventional tillage. In contrast, weeds reduced yield only 15% with strip-till. Weed density and biomass was twofold greater with conventional tillage compared with the no-till and strip-till treatments. Weed seedlings also emerged earlier with conventional tillage. Increased weed tolerance with strip-till may be related to fertilizer placement. Corn growth and tolerance to weeds in no-till systems may be improved if a starter fertilizer is placed in the seed furrow.

Nomenclature: Corn, Zea mays L., hairy vetch, Vicia villosa Roth, spring wheat, Triticum aestivum L

Competitive crops or cultivars can be an important component of integrated weed management systems. A study was conducted from 2003 to 2006 at four sites across semiarid prairie ecoregions in western Canada to investigate the weed-suppression ability of canola and mustard cultivars. Four open-pollinated canola cultivars, four hybrid canola cultivars, two canola-quality mustard cultivars, two oriental mustard cultivars, and two yellow mustard cultivars were grown in competition with indigenous weed communities. Yellow mustard was best able to suppress weed growth, followed in decreasing order of weed competitiveness by oriental mustard and hybrid canola, open-pollinated canola, and canola-quality mustard. Competitive response of cultivars, assessed by weed biomass suppression, was negatively correlated with time to crop emergence and positively correlated with early-season crop biomass accumulation (prior to bolting) and plant height.

Nomenclature: Canola, Brassica napus L., oriental mustard or canola-quality mustard, Brassica juncea L. Czern. & Coss., yellow mustard, Sinapis alba L

Field trials were conducted over two spring seasons (2005 and 2006) to investigate the interference between American black nightshade and watermelon in polyethylene-mulched and nonmulched (bare ground) trials. Competition studies were performed with watermelon at 1 plant/m in-row and American black nightshade grown at 0, 2, 4, 6, and 8 plants/m² in-row. Watermelon yield reductions started to plateau at only 2 American black nightshade plants/m². Yield reduction was 80, 89, 96, and 98% and 54, 67, 81, and 85% at 2, 4, 6, and 8 American black nightshade plants/m² in mulched watermelon production in 2005 and 2006, respectively. When watermelon was grown on bare ground, yield reduction was 100% at 2 American black nightshade plants/m² in 2005 and 68, 81, 89, and 93% at 2, 4, 6, and 8 American black nightshade plants/m² in 2006, respectively. Watermelon fruit numbers were reduced due to American black nightshade interference, but no significant differences in individual fruit weight were observed.

Nomenclature: American black nightshade, Solanum americanum Mill., SOLAM, watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai. cv. ‘Mardi Gras’

An experiment was conducted to determine the population dynamics of barnyardgrass under a range of weed management treatments in glyphosate-resistant (GR) cotton in Australia. These treatments consisted of glyphosate herbicide only (Glyphosate only), glyphosate herbicide plus a combination of conventional or integrated weed management practices (Glyphosate IWM), glyphosate herbicide plus a reduced residual herbicide program (Glyphosate Res.), glyphosate herbicide plus a grass herbicide (Glyphosate Grass), and a combination of conventional weed management practices (IWM only). The experiment investigated the effects of weed management on the weed seed bank, weed emergence patterns, and weed populations. After three years, all treatments resulted in commercially acceptable control of barnyardgrass. However, treatments containing soil-applied residual herbicides proved more effective over the period of the experiment. Seed bank reductions were in the order of 100-fold over the period of the experiment for treatments that received residual herbicides compared to 10- to 20-fold reductions for treatments that did not. The experiment highlighted the importance of early-season weed control, as well as the importance of an integrated approach to weed management with residual herbicides to control later-emerging weeds in GR cotton.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, cotton, Gossypium hirsutum L

Four field trials were conducted over a 2-yr period at Exeter (2005, 2006), Harrow (2006) and Ridgetown (2006), Ontario to evaluate the tolerance of pinto and small red Mexican (SRM) bean to the POST application of bentazon, imazethapyr, or their combination. Bentazon applied once or twice (to simulate a spray overlap in the field) at 840 g ai/ha and imazethapyr applied at 37.5 g/ha caused minimal injury (6% or less) in pinto and SRM bean and had no adverse effect on plant height, shoot dry weight, seed moisture content, and yield. Imazethapyr applied twice at 37.5 and all single and repeat applications containing 75 or 150 g/ha caused 15 to 44% injury to dry bean. These injuries were persistent and reduced plant height by as much as 21% and shoot dry weight by as much as 34%, but caused no adverse effect on maturity and yield, except for imazethapyr applied twice at 150 g/ha, which delayed maturity and reduced yield 16%. The addition of bentazon to imazethapyr applied as a tankmix reduced injury by as much as 23%. Imazethapyr at 37.5 or 75 g/ha combined with bentazon at 840 g/ha applied once or twice caused 3 to 23% injury but had no adverse effect on plant height, shoot dry weight, maturity, or yield. Two applications of imazethapyr at 150 g/ha plus bentazon at 840 g/ha reduced plant height 16% and shoot dry weight 28%.

Nomenclature: Bentazon, imazethapyr, pinto bean, small red Mexican bean, Phaseolus vulgaris L

Certified Crop Advisors of Arkansas and members of the Arkansas Crop Consultants Association were surveyed in fall 2006 through direct mail to assess the current situation of the red rice problem and early impact of imidazolinone-resistant (IMR) rice technology on red rice infestation. The information generated represented 40% (226,800 ha) of rice production areas in Arkansas. Barnyardgrass and red rice were the most problematic weeds, with 62% of fields infested with red rice. The estimated economic loss due to red rice averaged $274/ha. Red rice infestation was prevented mostly by crop rotation (96%) and use of certified seed (86%). Of the red rice–infested fields, 38% had light infestation and 26% had severe red rice problems before adopting IMR rice. Thirty-seven percent of infested fields had been planted with IMR rice once and 43% at least twice. Approximately 85% of the consultants reported > 90% red rice control when using IMR rice. The majority (92%) of IMR rice growers rotate to other crops, mostly soybean. Unsuitable field condition was the main reason for growing only rice. After 3 seasons, the consultants perceived that red rice infestation level declined by 77% on average. The herbicide-resistance gene had escaped to red rice in some fields, and 90% of growers are exerting effort to mitigate outcrossing.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, red rice, Oryza sativa L. ORYSA, rice, Oryza sativa L, soybean, Glycine max (L.) Merr