Postemergence herbicides to control grass weeds in grain sorghum are limited. Acetolactate synthase (ALS) –inhibiting herbicides are very effective at controlling many grass species in many crops; unfortunately, use of ALS-inhibiting herbicides is not an option in conventional grain sorghum because of its susceptibility to these herbicides. With the development of ALS-resistant grain sorghum, several POST ALS-inhibiting herbicides can be used to control weeds in grain sorghum. Field experiments were conducted in 2007 and 2008 to evaluate the efficacy of tank mixtures of nicosulfuron rimsulfuron applied alone or in combination with bromoxynil, carfentrazone–ethyl, halosulfuron dicamba, prosulfuron, 2,4-D, or metsulfuron methyl 2,4-D. In addition, these treatments were applied with and without atrazine. Nicosulfuron rimsulfuron controlled barnyardgrass, green foxtail, and giant foxtail 99, 86, and 91% 6 wk after treatment (WAT), respectively. A decrease in annual grass control was observed when nicosulfuron rimsulfuron was tank mixed with some broadleaf herbicides, although the differences were not always significant. In addition, nicosulfuron rimsulfuron controlled velvetleaf and ivyleaf moringglory 64 and 78% 6 WAT, respectively. Control of velvetleaf was improved when nicosulfuron rimsulfuron was tank mixed with all broadleaf herbicides included in this study with the exception of atrazine, bromoxynil, and prosulfuron atrazine. Control of ivyleaf morningglory was improved when nicosulfuron rimsulfuron was tank mixed with all of the herbicides included in this study with the exception of metsulfuron methyl 2,4-D. Weed populations and biomass were lower when nicosulfuron rimsulfuron were applied with various broadleaf herbicides than when it was applied alone. Grain sorghum yield was greater in all herbicide treatments than in the weedy check, with the highest grain yield from nicosulfuron rimsulfuron prosulfuron. This research showed that postemergence application of nicosulfuron rimsulfuron effectively controls grass weeds, including barnyardgrass, green foxtail, and giant foxtail. The research also showed that velvetleaf and ivyleaf morningglory control was more effective when nicosulfuron rimsulfuron were applied with other broadleaf herbicides.

Nomenclature: Atrazine; bromoxynil; carfentrazone–ethyl; dicamba; halosulfuron; mesotrione; metsulfuron methyl; nicosulfuron; rimsulfuron; prosulfuron; S-metolachlor; 2,4-D; barnyardgrass, Echinochloa crus-galli (L.) P. Beauv.; giant foxtail, Setaria faberi Herrm.; grain sorghum, Sorghum bicolor (L.) Moench.; green foxtail, Setaria virdis (L.) Beauv.; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq.; velvetleaf, Abutilon theophrasti Medicus.

Intensive selection pressure from repeated use of propanil and quinclorac led to the evolution of herbicide-resistant barnyardgrass biotypes. Twenty-two composite field samples were tested for level of resistance in 2002 and 2003, and field studies were conducted at the Rice Research and Extension Center, Stuttgart, AR, in 2002 and 2003 to evaluate alternative rice herbicides to control propanil-resistant (PR) and quinclorac-resistant (QR) barnyardgrass. Of the 22 composite samples, four were PR (30 to 40% control); four had a mixed population of PR, QR, and susceptible (S) barnyardgrass; and two had multiple resistance to propanil and quinclorac (P/QR), with control from propanil of 15 to 30% and control from quinclorac of 5 to 10%. ‘Wells’ rice was used where conventional herbicide programs were evaluated, and Clearfield rice ‘CL-161’ (imidazolinone-resistant) was used for herbicide programs involving imazethapyr. All PR and QR barnyardgrass were controlled > 90% by alternative herbicides, including all preemergence (PRE) and delayed preemergence (DPRE) treatments. By 56 d after emergence (DAE), cyhalofop or fenoxaprop applied to two- to three-leaf barnyardgrass (early postemergence [EPOST]), followed by (fb) a preflood application, controlled barnyardgrass > 93%. Pendimethalin controlled PR barnyardgrass 21 DAE, but not all season long. In contrast, imazethapyr in Clearfield rice controlled all grass weeds 100% all season long. Midpostemergence (MPOST) bispyribac application at the four- to five-leaf stage also provided season-long control of all barnyardgrass biotypes (> 88%, 56 DAE). Rice yields ranged from 5,300 to 5,700 kg ha⁻¹ in conventional weed-control treatments and from 2,800 to 5,000 kg ha⁻¹ in imazethapyr-treated plots. Nontreated plots yielded 1,500 kg ha⁻¹.

Nomenclature: Bispyribac; clomazone; cyhalofop; fenoxaprop; imazethapyr; molinate; pendimethalin; propanil; quinclorac; thiobencarb; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; rice, Oryza sativa L. ‘Wells’ and ‘CL-161’.

Deciding on the most efficacious PRE and POST herbicide options and their ideal application timing can be challenging for soybean producers. Climatic events during the 14 d before and after herbicide application can further complicate decisions because of their influence on herbicide effectiveness. Nine field trials were conducted at three locations in southwestern Ontario from 2003 to 2006, to determine the most effective PRE and POST soybean herbicides for control of common lambsquarters, common ragweed, green foxtail, and redroot pigweed. When precipitation was low at least 7 d before and after herbicide application weed control was reduced in treatments that included imazethapyr (PRE or POST) or flumetsulam/S-metolachlor (a premix formulation) (PRE). Cumulative precipitation during the 12 d after PRE application that exceeded the monthly average by at least 60% reduced common lambsquarters control when metribuzin was applied and green foxtail control when imazethapyr was applied. Delaying application of imazethapyr bentazon to a later soybean growth stage decreased control of common lambsquarters and green foxtail; however, environmental conditions appeared to influence these results. Precipitation on the day of application decreased control of common ragweed and redroot pigweed more with quizalofop-p-ethyl thifensulfuron-methyl bentazon compared with imazethapyr bentazon. Soybean yield varied among POST herbicide treatments because of reduced weed control. This research confirms that environmental conditions pre- and postapplication, as well as application timing, influence herbicide efficacy and should be considered by growers when selecting an herbicide program.

Nomenclature: Bentazon; cloransulam-methyl; flumetsulam; glyphosate; imazethapyr; linuron; metribuzin; quizalofop-p-ethyl; S-metolachlor; thifensulfuron-methyl; redroot pigweed, Amaranthus retroflexusL.; common ragweed, Ambrosia artemisiifolia L.; common lambsquarters, Chenopodium album L.; green foxtail, Setaria viridis (L.) Beauv.; soybean, Glycine max L.

Flax is in the process of development as a crop for bio-industrial and nutraceutical products predicated on the use of genetic modification. Before genetically modified (GM) flax is commercially released, effective management practices should be developed to minimize adventitious presence (AP) of GM volunteer flax in subsequent crops. Field research was conducted at four locations during 2007 and 2008 in central Alberta to quantify and mitigate AP of volunteer flax in glufosinate-resistant (GR) and imidazolinone-resistant (IR) canola. A single preplant application of glyphosate at 1,250 g ae ha⁻¹ in GR canola reduced volunteer flax density from 54 to 3 plants m⁻² and seed production from 5,963 to 233 seeds m⁻². Similarly, the recommended rate of POST glufosinate (600 g ai ha⁻¹) alone effectively controlled volunteer flax and reduced flax seed viability to < 8% and AP to 0.2%. A combination of preplant (glyphosate) and POST (glufosinate) at recommended rates reduced volunteer flax seed production, yield, and AP to near zero in GR canola. Glyphosate applied preplant was equally effective in IR canola, reducing volunteer flax density from 56 to 2 plants m⁻², and seed production from 5,571 to 472 seeds m⁻². Imazamox imazethapyr applied POST at all the rates poorly controlled volunteer flax and, even in combination with preplant glyphosate, cannot be recommended for control of flax volunteers in IR canola.

Nomenclature: Glufosinate; glyphosate; imazamox; imazethapyr; Canola, Brassica napus L. ‘Invigor 5030’, ‘45H73-CL’; flax, Linum usitatissimum L. ‘CDC Bethune’.

Cover crop management with a roller/crimper might reduce the need for herbicide. Weed suppression from a rolled cereal rye cover crop was compared to no cover crop with and without postemergence herbicide application in no-till soybean. The experiment was designed as a two-way factorial with rye termination and soybean planting date as the first factor and weed control treatment as the second. Cereal rye was drill-seeded in late September and managed using glyphosate followed by a roller/crimper in the spring. Soybean was no-till seeded after rolling and glyphosate was applied postemergence about 6 wk after planting to half the plots. Rye biomass doubled when delaying rye kill by 10 to 20 d. Weed density and biomass were reduced by the rye cover crop in all site–location combinations except one, but delaying rye kill and soybean planting date only reduced both weed density and biomass at a single location. The cover crop mulch provided weed control similar to the postemergence herbicide in two of four locations. Treatments did not affect soybean grain yield in 2007. In 2008, yield at Landisville with rye alone was equal to those yields receiving the postemergence herbicide, whereas at Rock Springs, it was equivalent or less. The net added cost of a rye cover crop was $123 ha⁻¹ with or $68.50 ha⁻¹ without a postemergence herbicide application. A rolled-rye cover crop sometimes provided acceptable weed control, but weed control alone did not justify the use of the cover crop. The potential for reduced herbicide use and other ecosystem services provided by a cover crop justify further refinement and research in this area.

Nomenclature: Glyphosate; rye, Secale cereale L.; soybean, Glycine max L.

Growth chamber experiments were conducted in the fall of 2006 and spring of 2007 to determine winter wheat, flixweed, and henbit response to POST treatments of saflufenacil at 13, 25, and 50 g ai ha⁻¹ applied alone and in combinations with bentazon at 560 g ai ha⁻¹ or 2,4-D amine at 533 g ae ha⁻¹ and nonionic surfactant (NIS) at 0.25% v/v. Mixtures of saflufenacil and 2,4-D amine were also applied without NIS. Necrosis was observed on wheat leaves within 1 d after treatment (DAT) and peaked at 5 to 7 DAT. Saflufenacil at 13, 25, or 50 g ai ha⁻¹ applied alone or in combination with 533 g ae ha⁻¹ of 2,4-D amine plus NIS caused 19 to 38% (alone) and 24 to 40% (in combination) wheat foliar necrosis, respectively. Foliar necrosis of wheat was 14% or less when saflufenacil, at any rate, was mixed with bentazon or 2,4-D amine without NIS. Combinations of saflufenacil at any of the rates tested plus bentazon and NIS did not reduce wheat dry weight. Saflufenacil plus 2,4-D amine without adjuvant resulted in similar wheat dry weights as 2,4-D amine. Saflufenacil plus 2,4-D amine without NIS provided 99% control of flixweed at 21 DAT, but henbit control ranged from 81 to 88%. In comparison, saflufenacil at 50 g ha⁻¹ mixed with bentazon and NIS controlled flixweed at 92% and henbit at 63% at 21 DAT. This research indicates saflufenacil has potential for POST use in winter wheat to control winter annual broadleaf weeds when tank-mixed with 2,4-D amine without NIS, but additional research is needed to discover ways to improve crop safety without reducing weed control.

Nomenclature: 2,4-D amine; bentazon; saflufenacil; flixweed, Descurainia sophia L. Webb. ex Prantl DESSO; henbit, Lamium amplexicaule L. LAMAM; winter wheat, Triticum aestivum L. ‘KS03HW6-1’.

Research was conducted at Marianna, AR, for 2 yr to determine whether hairy vetch and Austrian winter pea cover crops would aid weed management programs in conservation-tilled, enhanced glyphosate-resistant cotton. Both cover crops were easily established and produced rapid growth in early spring, with biomass production of 435 to 491 g m⁻² by Austrian winter pea and 415 to 438 g m⁻² by hairy vetch. The effect of cover crops on weed control was short-lived in both years, with herbicide programs being the major determinant of weed control and seed-cotton yield. Averaged over cover crops, seed-cotton yields when the initial in-crop glyphosate application was delayed to the four-node cotton stage were up to 710 kg ha⁻¹ less than in a PRE herbicide program. In 1 of 2 yr, seed-cotton yields were greater in PRE-treated plots compared with a program where initial weed management was delayed to the one-leaf stage of cotton. As a result of rapid decay of hairy vetch and Austrian winter pea biomass following cotton planting and the lack of adequate Palmer amaranth, pitted morningglory, and goosegrass control in the absence of herbicides, it appears there may be minimal weed management benefits from the use of hairy vetch and Austrian winter pea in Midsouth cotton production.

Nomenclature: Goosegrass, Eleusine indica (L.) Gaertn. ELEIN; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; Austrian winter pea, Pisum sativum L. ssp. arvense (L.) Poir.; cotton, Gossypium hirsutum L.; hairy vetch, Vicia villosa Roth.

Research was conducted to determine the effect of planting pattern, plant density, and levels of weed management intensity on intercepted photosynthetically active radiation (IPAR), weed control, and cotton lint yield in glyphosate-resistant cotton. Twin-row planting pattern canopy IPAR was 55% 7 wk after emergence (WAE) and 76% 9 WAE compared to 48% for single-row planting pattern 7 WAE and 59% 9 WAE. Regardless of cotton density, row spacing, or weed management intensity, control of browntop millet and Florida beggarweed was at least 88% 18 WAE. Benghal dayflower, sicklepod, and smallflower morningglory control was greater in twin-rows compared to single-rows at a cotton density of 7 plants m⁻². Control of Benghal dayflower and sicklepod increased when cotton density increased at low weed management intensities; however, cotton density had no effect on weed control at higher levels of weed management input. At a cotton plant density of 7 plants m⁻², twin-row cotton yielded 220 kg ha⁻¹ more than the single-row planting pattern. Data indicates twin-row cotton production is feasible and that control of various weeds was better in twin-row than single-row pattern at lower cotton density and weed management intensity.

Nomenclature: Glyphosate; MSMA; prometryn; S-metolachlor; Benghal dayflower, Commelina benghalensis L. COMBE; browntop millet, Urochloa ramosa (L.) Nguyan PANRA; Florida beggarweed, Desmodium tortuosum (Sw.) DC. DEDTO; sicklepod, Senna obtusifolia (L.) Irwin and Barneby CASOB; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb. IAQTA; cotton, Gossypium hirsutum L.

Persistent use of herbicides has resulted in the selection of many herbicide-resistant weeds worldwide. A survey of 75 fields in the Palouse region of the inland Pacific Northwest was conducted to determine the extent of Italian ryegrass resistance to grass herbicides commonly used in winter wheat-cropping systems. Plants grown from collected seed samples were tested for resistance to diclofop, clodinafop, quizalofop, tralkoxydim, sethoxydim, clethodim, pinoxaden, triasulfuron, mesosulfuron, flucarbazone, imazamox, and flufenacet/metribuzin. Averaged across herbicide families within a herbicide group, some level of resistance was exhibited in 73, 31, and 31% of the populations to the aryloxyphenoxypropionates, cyclohexanediones, and phenylpyrazoline herbicides, respectively, and 39, 53, and 55% of the populations to the sulfonylureas, sulfonylaminocarbonyltriazolinone, and imidazolinone herbicides, respectively. Twelve percent of the populations showed some level of resistance to flufenacet/metribuzin. Cross-resistance to all acetyl coenzyme A carboxylase-inhibiting (group 1) herbicides was observed in 12% of the populations, whereas 25% of the populations were cross-resistant to all acetolactate synthase-inhibiting (group 2) herbicides tested. Of all the populations tested, 7% exhibited multiple resistance to at least one herbicide within all three groups tested. Only 5% of populations were completely susceptible to all 12 herbicides tested. These results indicate that herbicide-resistant Italian ryegrass populations are now common across much of the Palouse region in northern Idaho and eastern Washington.

Nomenclature: Clethodim; clodinafop; diclofop; flucarbazone; flufenacet/metribuzin; imazamox; mesosulfuron; pinoxaden; quizalofop; sethoxydim; tralkoxydim; triasulfuron; Italian ryegrass, Lolium multiflorum L. LOLMU; winter wheat, Triticum aestivum L.

Glyphosate applied to glyphosate-resistant (RR) cotton varieties after the four-leaf stage can decrease boll retention resulting in severe yield reductions. Enhanced glyphosate-resistant cotton (RR Flex), released for commercial use in 2006, offers a wider window of glyphosate applications without the risk of yield loss. However, no data exist regarding the effect of glyphosate application, especially late season applications, on fruit partitioning in RR Flex cotton. The objective of this research was to determine the effect of glyphosate rate and application timing on RR Flex cotton yield and fruit partitioning compared with current RR cotton. Studies were conducted during a 3-yr period (2004 to 2006), throughout the cotton growing regions of Mississippi. Roundup Ready (ST 4892 Bollgard/Roundup Ready [BR]) and Roundup Ready Flex (Mon 171 Enhanced Roundup Ready and ST 4554 Bollgard II/Roundup Ready Flex [B2RF]) cotton was planted, and glyphosate was applied at various rates and cotton growth stages. Data were collected using box mapping, a technique designed to depict yield partitioning on a cotton plant. RR Flex cotton yields were unaffected by glyphosate application timing or rate. Yields for ST 4892 BR were affected by application timings after the sixth leaf. ST 4892 BR had increased yield partitioning to position-three bolls and upper nodes with later application timings of glyphosate. Increases in seed cotton partitioned to higher nodes and outer fruiting positions were unable to compensate for fruit shed from innermost, lower fruiting sites. These data indicate that RR Flex cotton has excellent tolerance to late-season glyphosate applications.

Nomenclature: Glyphosate; cotton, Gossypium hirsutum L.

Weeds are the major biotic constraint to rice production. Field observations have suggested that certain fertilizer regimes could enhance infestations of particular weed species emerging with rice. The study objective was to determine the effect of surface-applied calcium phosphate on weed growth in flooded California rice systems. In field and pot studies, triple superphosphate (TSP) applied to the soil surface increased weed emergence. Surface-applied TSP increased the number of sedge and broadleaf weeds, including smallflower umbrella sedge, blue-flowered ducksalad, redstem, ricefield bulrush, waterhyssop, and California arrowhead. A laboratory study measured germination of smallflower umbrella sedge and ricefield bulrush in response to the application of phosphorus (P) and calcium (Ca), which comprise 20 and 15% of TSP, respectively. Calcium stimulated smallflower umbrella sedge germination and had no effect on ricefield bulrush germination. Phosphorus did not stimulate either smallflower umbrella sedge or ricefield bulrush germination. Results indicate that surface applications of calcium phosphate increase the growth of certain weed species and that Ca may stimulate germination of smallflower umbrella sedge. By incorporating preplant applications of calcium phosphate into the soil profile, growers can reduce weed pressure from certain species. Alternatively, surface applications of calcium phosphate may be useful to stimulate weed emergence in stale-seedbed management.

Nomenclature: Blue-flowered ducksalad, Heteranthera rotundifolia (Kunth) Griseb.; California arrowhead, Sagittaria montevidensis Cham. & Schlecht.; redstem, Ammannia coccinea Rottb.; ricefield bulrush, Schoenoplectus mucronatus (L.) Palla; waterhyssop, Bacopa spp. L.; smallflower umbrella sedge, Cyperus difformis L.; rice, Oryza sativa L.

Italian ryegrass resistance to diclofop has been documented in several countries, including the United States. The purpose of this research was to screen selected putative resistant populations of Italian ryegrass for resistance to the acetyl-CoA carboxylase (ACCase)–inhibiting herbicides diclofop and pinoxaden and the acetolactate synthase (ALS)–inhibiting herbicides imazamox, pyroxsulam, and mesosulfuron in the greenhouse and to use field experiments to develop herbicide programs for Italian ryegrass control. Resistance to diclofop was confirmed in eight populations from Tennessee. These eight populations did not show cross-resistance to pinoxaden. One additional population (R1) from Union County, North Carolina, was found to be resistant to both diclofop and pinoxaden. The level of resistance to pinoxaden of the R1 population was 15 times that of the susceptible population. No resistance was confirmed to any of the ALS-inhibiting herbicides examined in this research. Field experiments demonstrated PRE Italian ryegrass control with chlorsulfuron (71 to 94%) and flufenacet metribuzin (84 to 96%). Italian ryegrass control with pendimethalin applied PRE or delayed preemergence (DPRE) was variable (0 to 85%). POST control of Italian ryegrass was acceptable with pinoxaden, mesosulfuron, flufenacet metribuzin, and chlorsulfuron flucarbazone (> 80%). Application timing and herbicide treatment had no effect on wheat yield, except for diclofop and pendimethalin treatments, in which uncontrolled Italian ryegrass reduced wheat yield.

Nomenclature: Chlorsulfuron; diclofop; flucarbazone; flufenacet; imazamox; mesosulfuron; metribuzin; pendimethalin; pinoxaden; pyroxsulam; Italian ryegrass, Lolium perenne L. ssp. multiflorum Lam. Husnot LOLMU; wheat, Triticum aestivum L.

Field studies compared the grain yield of four two-row spring barley cultivars at four sites when sown at two-row spacing in competition with two densities of rigid ryegrass. The sites chosen had low background populations of rigid ryegrass. Although the four cultivars sown differed in their grain yield, row spacing did not influence cultivar performance. Doubling the row spacing decreased barley grain yield at three of the four sites. The impact of row spacing on grain yield was more noticeable when doubled to 48 or 50 cm compared with 36 cm. Rigid ryegrass competition reduced barley grain yield at two of the four sites. At both locations the influence of weed competition on barley grain yield was the same at both narrow and wide row spacing and at one location the impact of weed competition was modified by cultivar. Planting barley in wide rows was found to favor rigid ryegrass production through an increase in both rigid ryegrass biomass production and tiller number. The development of farming systems for barley on the basis of a row spacing greater than 25 cm is likely to be associated with an increase in weed productivity unless good integrated weed management principles are implemented. Modifications to the current system may allow an increase in row spacing without any yield loss or increased weed seed set.

Nomenclature: Rigid ryegrass, Lolium rigidum Gaudin LOLRI ‘Safeguard’; barley, Hordeum vulgare L. ‘Baudin’, ‘Dash’, ‘Gairdner’, and ‘Vlamingh’.

Propane flaming could be an effective alternative tool for weed control in organic cropping systems. However, response of major weeds to broadcast flaming must be determined to optimize its proper use. Therefore, field experiments were conducted at the Haskell Agricultural Laboratory, Concord, NE in 2007 and 2008 using six propane doses and four weed species, including green foxtail, yellow foxtail, redroot pigweed, and common waterhemp. Our objective was to describe dose–response curves for weed control with propane. Propane flaming response was evaluated at three different growth stages for each weed species. The propane doses were 0, 12, 31, 50, 68, and 87 kg ha⁻¹. Flaming treatments were applied utilizing a custom-built flamer mounted on a four-wheeler (all-terrain vehicle) moving at a constant speed of 6.4 km h⁻¹. The response of the weed species to propane flaming was evaluated in terms of visual ratings of weed control and dry matter recorded at 14 d after treatment. Weed species response to propane doses were described by log-logistic models relating propane dose to visual ratings or plant dry matter. Overall, response of the weed species to propane flaming varied among species, growth stages, and propane dose. In general, foxtail species were more tolerant than pigweed species. For example, about 85 and 86 kg ha⁻¹ were the calculated doses needed for 90% dry matter reduction in five-leaf green foxtail and four-leaf yellow foxtail compared with significantly lower doses of 68 and 46 kg ha⁻¹ of propane for five-leaf redroot pigweed and common waterhemp, respectively. About 90% dry matter reduction in pigweed species was achieved with propane dose ranging from 40 to 80 kg ha⁻¹, depending on the growth stage when flaming was conducted. A similar dose of 40 to 60 kg ha⁻¹ provided 80% reduction in dry matter for both foxtail species when flaming was done at their vegetative growth stage. However, none of the doses we tested could provide 90% dry matter reduction in foxtail species at flowering stage. It is important to note that foxtail species started regrowing 2 to 3 wk after flaming. Broadcast flaming has potential for control or suppression of weeds in organic farming.

Nomenclature: Redroot pigweed, Amaranthus retroflexus L.; common waterhemp, Amaranthus rudis Sauer; green foxtail, Setaria viridis (L.) Beauv.; yellow foxtail, Setaria pumila (Poir.) Roemer and J. A. Schultes.

Bispyribac-sodium selectively controls annual bluegrass in cool-season turf but efficacy may be influenced by management practices, such as plant growth regulator use. Experiments were conducted in New Jersey to investigate efficacy and absorption of bispyribac-sodium applied with trinexapac-ethyl for annual bluegrass control and turfgrass tolerance. In laboratory experiments with annual bluegrass, creeping bentgrass, and perennial ryegrass, tank-mixing trinexapac-ethyl with ¹⁴C-bispyribac-sodium increased presumed foliar absorption of ¹⁴C-bispyribac-sodium compared with nontrinexapac-ethyl treated; absorption increased with trinexapac-ethyl rate. Differences in ¹⁴C-bispyribac-sodium absorption were not detected among emulsifiable concentration, microencapsulated concentration, and wettable powder trinexapac-ethyl formulations. In field experiments, sequential bispyribac-sodium applications controlled annual bluegrass 93%, but trinexapac-ethyl did not affect efficacy. Tank-mixing all trinexapac-ethyl formulations with bispyribac-sodium provided similar annual bluegrass control and creeping bentgrass quality compared with bispyribac-sodium alone. Applications of bispyribac-sodium reduced dollar spot cover in both years, whereas trinexapac-ethyl reduced dollar spot cover only in 2005.

Nomenclature: Bispyribac-sodium; annual bluegrass, Poa annua L.; creeping bentgrass, Agrostis stolonifera L., ‘L-93’, ‘G-2; perennial ryegrass, Lolium perenne L., ‘Applaud’.

Bispyribac-sodium effectively controls annual bluegrass in creeping bentgrass fairways but efficacy on putting greens may be affected by management differences and thus, application regimes may need to be modified for effective annual bluegrass control. To test this hypothesis, field experiments investigated various bispyribac-sodium application regimens for annual bluegrass control on creeping bentgrass putting greens. Bispyribac-sodium regimes totaling 148, 222, and 296 g ha⁻¹ controlled annual bluegrass 81, 83, and 91%, respectively, over 2 yr. Pooled over herbicide rates, bispyribac-sodium applied two, three, and six times controlled annual bluegrass 78, 83, and 94%, respectively. The most effective bispyribac-sodium regime was 24.6 g ha⁻¹ applied weekly, which controlled annual bluegrass 90% after 8 wk with acceptable levels of creeping bentgrass discoloration. After 8 wk, all regimes reduced turf quality as a result of voids in turf following annual bluegrass control; regimes with six applications reduced turf quality the most.

Nomenclature: Bispyribac-sodium; annual bluegrass, Poa annua L.; creeping bentgrass, Agrostis stolonifera L. ‘L-93’.

Annual grass weed control and switchgrass cultivar response to PRE-applied pendimethalin and POST-applied mesotrione and quinclorac was evaluated in 2005 and 2006 near Paterson, WA, in both newly seeded and 1-yr-old established switchgrass. Pendimethalin applied to newly planted switchgrass at 1.1 kg ai ha⁻¹ at the one-leaf stage in 2005 or at 0.67 kg ha⁻¹ PRE in 2006 severely injured and greatly reduced switchgrass stands. Mesotrione applied POST at 0.07 kg ai ha⁻¹ injured newly planted switchgrass, reduced switchgrass height for several weeks after treatment, and reduced final switchgrass biomass by 54% both years. ‘Kanlow’ and ‘Cave-in-Rock’ cultivars were injured less by mesotrione than ‘Shawnee’ in 2005, whereas in 2006, Kanlow was injured less than Shawnee and Cave-in-Rock. Quinclorac applied POST at 0.56 kg ai ha⁻¹ injured newly planted switchgrass less than mesotrione and pendimethalin but reduced final switchgrass biomass by 33% both years compared with treatment with atrazine alone. All three herbicide treatments controlled large crabgrass in the year of establishment. Green foxtail counts were reduced 93% or more by pendimethalin and quinclorac compared with nontreated controls, but mesotrione failed to control green foxtail. Pendimethalin applied PRE at 1.1 kg ha⁻¹ did not injure 1-yr-old established switchgrass or reduce switchgrass biomass. Quinclorac applied POST at 0.56 kg ha⁻¹ to established switchgrass reduced switchgrass biomass of the first harvest by 16% in 1 of 2 yr. Mesotrione applied POST at 0.07 kg ha⁻¹ injured established switchgrass and reduced biomass of the first harvest by 33 and 17% in 2005 and 2006, respectively. Kanlow was injured the least by mesotrione in both years. Established switchgrass suppressed late-emerging annual grass weeds sufficiently to avoid the need for a grass-specific herbicide application.

Nomenclature: Mesotrione; pendimethalin; quinclorac; green foxtail, Setaria viridis L. SETVI; large crabgrass, Digitaria sanguinalis L. Scop. DIGSA; switchgrass, Panicum virgatum L. ‘Cave-in-Rock’, ‘Kanlow’, ‘Shawnee’.

Several sulfonylurea herbicides are labeled for use on established bermudagrass or seashore paspalum, but label recommendations for many of these chemicals vary for sprigged turf. The objective of this study was to determine the safety of various sulfonylurea herbicides on newly planted, ‘Tifway’ bermudagrass and ‘Aloha’ seashore paspalum sprigs in Arkansas and Louisiana. Treatments were arranged as a five by two by two factorial with five herbicides (foramsulfuron at 29 and 59 g ai ha⁻¹, halosulfuron at 35 and 70 g ai ha⁻¹, metsulfuron at 21 and 42 g ai ha⁻¹, sulfosulfuron at 66 and 131 g ai ha⁻¹, and trifloxysulfuron at 28 and 56 g ai ha⁻¹), two herbicide rates (low and high), and two application timings at 2 or 4 wk after sprigging (WAS). There was no discernable herbicide injury to, or reduction in, Tifway bermudagrass coverage in Arkansas, regardless of herbicide, application timing, or application rate. Trifloxysulfuron and metsulfuron were more injurious than other herbicides in Louisiana when applied at 2 WAS to Tifway bermudagrass, but injury levels were acceptable (< 15%), and there was no long-term reduction in establishment. Metsulfuron or halosulfuron applied at 2 or 4 WAS and sulfosulfuron applied at 4 WAS allowed > 90% establishment of Aloha seashore paspalum at both locations. Both trifloxysulfuron and foramsulfuron were injurious to seashore paspalum and reduced its establishment. These results suggest that sulfonylurea herbicides can be safely applied shortly after sprigging to Tifway bermudagrass and that metsulfuron, halosulfuron, and sulfosulfuron could be useful herbicides for establishing Aloha seashore paspalum from sprigs.

Nomenclature: Foramsulfuron; halosulfuron; metsulfuron; sulfosulfuron; trifloxysulfuron; hybrid bermudagrass, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy ‘Tifway’ CYNDA; seashore paspalum, Paspalum vaginatum Sw. ‘Aloha’ PASVA.

Proso millet is an important short-season summer cereal in western Nebraska, southeast Wyoming, and eastern Colorado. The objective of this study was to evaluate proso millet tolerance to saflufenacil applied early preplant (EPP) or PRE. Field studies were conducted in Lingle, WY and Sidney, NE in 2008 and 2009. A dose–response study was conducted in the greenhouse at the University of Wyoming in Laramie, WY to determine proso millet cultivar response to saflufenacil applied at six rates from 0 to 400 g ai ha⁻¹. In the field, saflufenacil was applied EPP and PRE at 50 and 100 g ha⁻¹. Proso millet stands were reduced by an average of 33 and 23% by PRE and EPP treatments compared with the nontreated check; however, proso seed yields were not affected by saflufenacil timing or rate. In the greenhouse, ‘Panhandle’ and ‘Dawn’ exhibited less tolerance to saflufenacil than ‘Sunrise’, the cultivar used in the field studies.

Nomenclature: Saflufenacil; 2-chloro-5-[3,6-dihydro-3-methyl-2,6-dioxo-4-(trifluoromethyl)-1(2H)-pyrimidinyl[-4-fluoro-N-[[methyl(1-methylethyl)amino]sulfonyl]benzamide; proso millet, Panicum miliaceum L.

Glyphosate plus flumioxazin tank mixtures have become popular in the nursery production and landscape maintenance industries in the southeastern United States. Research was conducted to compare the efficacy of such a mixture relative to the components applied alone. Glyphosate, flumioxazin, and glyphosate plus flumioxazin (2 ∶ 1, w/w) were applied POST in container trials to four weed species at a series of rates that ranged from no effect to death. Regression analyses revealed that control data from all three treatment series could be described by the four-parameter, log-logistic model. With respect to glyphosate and flumioxazin applied alone, analysis revealed that across all four species, a lower rate of flumioxazin was required for 90% control than of glyphosate. The rate of the mixture required for 90% control was generally intermediate to the components applied alone and ranged from 0.36 kg ha⁻¹ for hairy bittercress to 1.52 kg ha⁻¹ for eclipta. Glyphosate alone was more cost effective than either flumioxazin alone or the mixture for the POST-applied control of all four species. The popularity of the tank mixture might be the result of flumioxazin-based PRE activity that was not measured in this study.

Nomenclature: Flumioxazin; glyphosate; eclipta, Eclipta prostrata L. ECLAL. hairy bittercress, Cardamine hirsuta L. CARHI.

The effect of soil properties and weather on herbicide persistence and injury to following crops were studied at a site near Lethbridge, Alberta, Canada, with undulating topography that included no-tillage and conventional tillage systems on adjacent fields. Soil pH ranged from 5.2 (lower slope no-tillage) to 7.8 (upper slope conventional tillage) and soil organic matter content ranged from 2.3% (upper slope conventional tillage) to 4.4% (lower slope no-tillage). During the years when the experiments were conducted rainfall ranged from < 50% of normal to > 150% of normal. During dry years atrazine and metsulfuron severely injured wheat and lentil crops, seeded 1 yr after herbicide application, on upper slope locations. The most severe injury occurred on the upper slope conventional tillage location. In years with high rainfall, no crop injury occurred 1 yr after atrazine and metsulfuron application on either upper or lower slope locations in both tillage systems. Imazamox plus imazethapyr caused almost 100% injury in the lower slope position in the no-tillage system (pH 5.2) in the driest year. Following-crop injury due to the imidazolinone herbicides decreased with increasing rainfall and increasing soil pH. The most severe injury to following crops seemed to occur when herbicide dissipation was dependent on microbial activity and rainfall was below normal.

Nomenclature: Atrazine; imazamox; imazethapyr; metsulfuron; lentil, Lens culinaris Medic; wheat, Triticum aestivum L.

Three years of field trials have been carried out in Zaragoza, Spain, using different biodegradable mulch materials in processing tomatoes. The aim was to evaluate weed control with several biodegradable mulches as alternatives to black polyethylene (PE) mulch. The treatments were rice straw, barley straw, maize harvest residue, absinth wormwood plants, black biodegradable plastic, brown kraft paper, PE, herbicide, manual weeding, and unweeded control. Assessments focused on weeds and on crop yield. A laboratory study showed that 1 kg/m² of organic mulch was sufficient to cover the soil for rice, barley straw, and maize harvest residue. The most abundant weed species in the field were purple nutsedge, common purslane, common lambsquarters, and large crabgrass and a change in weed composition was observed between treatments and years. Most weed species were controlled by the mulching materials except that purple nutsedge was controlled only by paper mulch. The other species were well controlled by PE and biodegradable plastic and also by some of the organic mulch treatments. Best weed control and lowest weed biomass were achieved by paper followed by PE and biodegradable plastic. The best organic mulch was rice straw and the worst weed control was from absinth wormwood. Tomato yield was highest for PE followed by paper, manual weeding, biodegradable plastic, and rice straw and was clearly related to weed control. Paper, biodegradable plastic, and rice straw are potential substitutes for PE and herbicides.

Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; common purslane, Portulaca oleracea L. POROL; large crabgrass, Digitaria sanguinalis L. Scop. DIGSA; purple nutsedge, Cyperus rotundus L. CYPRO; absinth wormwood, Artemisia absinthium L.; barley, Hordeum vulgare L.; maize, Zea mays L.; rice, Oryza sativa L.; tomato, Lycopersicon esculentum Mill. ‘Perfect Peel’.

Jerusalem artichoke has been reported to colonize several ecological niches and agronomic crops in southern Europe. This plant is also of interest because of its high biomass production and its potential to produce ethanol for biofuel. Allelopathy may be an advantageous trait in Jerusalem artichoke under cultivation, as it potentially reduces weed interference with the crop, theoretically allowing a reduction of mechanical or chemical input required for weed management. However, this trait may also be unfavorable if other crops are cultivated in rotation with Jerusalem artichoke or in areas infested by this species. The aim of this study was to investigate the sensitivity of selected diverse crops (wheat, lettuce, corn, tomato, rice, and zucchini) and weeds (barnyardgrass, black nightshade, common lambsquarters, common purslane, large crabgrass, and pigweed) to the presence of Jerusalem artichoke dried leaf tissues in laboratory experiments performed under controlled conditions. The simulated soil incorporation of different Jerusalem artichoke residues (four cultivars and a weedy population) was carried out in a series of laboratory and greenhouse experiments. Jerusalem artichoke reduced the radicle growth of seedling lettuce (60%), tomato (30%), large crabgrass (70%), and barnyardgrass (30%), whereas total germination of these species was less affected. Sensitivity to Jerusalem artichoke residues was species dependent; germination and initial growth of corn were not affected, whereas winter wheat, lettuce, tomato, rice, and zucchini seedlings were more sensitive to residue presence. Our experiments show that both wild and cultivated decomposing Jerusalem artichoke residues, particularly leaves and stems, possess phytotoxic potential. Additional field experimentation remains to be conducted to determine if allelopathy in the field contributes to its invasibility.

Nomenclature: Jerusalem artichoke, Helianthus tuberosus L.; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; black nightshade, Solanum nigrum L. SOLNI; common lambsquarters, Chenopodium album L. CHEAL; common purslane, Portulaca oleracea POROL; corn, Zea mays L.; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; lettuce, Lactuca sativa L.; pea, Pisum sativum L.; redroot pigweed, Amaranthus retroflexus L. AMARE; rice, Oryza sativa L.; tomato, Lycopersicon esculentum Mill.; wheat, Triticum aestivum L.; zucchini, Cucurbita pepo L.

Information linking seed movement, along with changes in seed viability, is critical for understanding weed seed dynamics. Studies were conducted to examine the use of passive integrated transponder (PIT) tags placed in nylon mesh packets in combination with GPS (Global Positioning System) technology to track weed seed movement after tillage. Cylindrical PIT tags 11.5, 12, 20, and 23 mm long by 2 mm wide were evaluated in water and soil. Detection improved as tag size increased because of greater signal strength. Tags with the main axis oriented vertically were recovered at greater depths than when placed horizontally. Average detection depths for 12-mm PIT tags were 29.5 cm in water, 18.2 cm in sand, 24 cm in artificial soil, and 21.2 cm in sandy loam soil. Tests also showed that PIT tags and nylon mesh packets were resilient to intense tillage with a rototiller. No significant differences in displacement because of tillage were observed between free PIT tags and PIT-tagged packets. PIT tag performance was further tested in a 2-yr field experiment conducted between September 2003 and October 2005 at six sites in Nebraska and Wyoming. Tilled and no-till blocks were established at each site. PIT-tagged packets in the tilled block and untagged packets in the no-till block were used. Sample burial depths were 0, 2.5, 7.5, and 15 cm. Sample recovery rate did not differ between tilled and no-till blocks. Time of recovery was the main factor affecting recovery of packets buried at 0 and 2.5 cm in both blocks. Seed predation by small rodents and movement of samples beyond the area of study by tillage implements were the main sources of packet loss. Nevertheless, 2 yr after initiation of the study, more than 85% of the samples were recovered. Future development of PIT tag technology will lead to an enhanced ability to monitor seed movement.

Kochia control in continuous corn became increasingly difficult in experimental plots where isoxaflutole was used PRE for 8 yr. Studies were conducted to determine if poor kochia control resulted from an escape mechanism based on different germination rates or from a difference in sensitivity to isoxaflutole. Germination at constant temperatures showed that the kochia population in the experimental plot had greater seed dormancy compared with populations growing in adjacent fields. Germination at 25 C for seeds collected from the isoxaflutole-treated area was near 20% after 20 d, whereas germination for the other populations was above 80%. The optimal temperatures to release seed dormancy for seeds from the experimental plot were alternating 35/25 C day/night temperatures. The kochia biotype that predominated where isoxaflutole was applied PRE had elevated levels of seed dormancy and required higher alternating temperatures to release dormancy than untreated control kochia. These characteristics were unique and not found in populations never exposed to isoxaflutole. Chlorophyll content was measured to determine if differences in sensitivity to isoxaflutole existed among biotypes. Absorption at 660 nm by photosynthetic pigments was similar among the biotypes at increasing herbicide rates, indicating no differences in sensitivity to isoxaflutole among populations. Reduced kochia control in the experimental plot was due to delayed seed germination, which allowed isoxaflutole to degrade before seeds germinated. The rapid herbicide dissipation from soil can be attributed in part to coarse soils, soil moisture, and the low isoxaflutole rate.

Nomenclature: Isoxaflutole; kochia, Kochia scoparia (L.) Schrad; corn, Zea mays L.

Field trials were conducted in the spring of 2007 and 2008 to investigate the critical period of interference between American black nightshade and triploid watermelon. To determine the critical period, the maximum period of competition and minimum weed-free period were examined. American black nightshade (2 plants m⁻²) was established into watermelon plots at watermelon transplanting and removed at 0, 1, 2, 3, 4, and 5 wk after transplanting to determine the maximum period of competition. American black nightshade (2 plants m⁻²) was established into watermelon plots at 0, 1, 2, 3, 4, and 5 wk after transplanting and remained until watermelon harvest to determine the minimum weed-free period. To avoid yield loss from exceeding 10% of a crop grown weed-free, the maximum period of competition and minimum weed-free period were found to be 3.9 and 3.6 weeks after transplanting, respectively. Therefore, if American black nightshade is controlled at any time during the critical period of 3.6 to 3.9 wk after transplanting, yield loss should not exceed 10% of a crop grown weed-free.

Nomenclature: American black nightshade, Solanum americanum Mill. SOLAM; watermelon, Citrullus lanatus (Thunb.) Matsumura and Nakai cv. ‘Super Crisp’.