Increasing Herbicide Rate Research Articles

Discrimination of ACCase-inhibiting herbicides-resistant Digitaria ciliaris populations with three diagnostic bioassays

Background Diagnostic bioassays are used to screen the suspected R population. They are conducted at a single herbicide dose and evaluated at a specific time after treatment that can differentiate resistant from susceptible population. Objective Three different bioassays were evaluated to assess the detection of acetyl CoA carboxylase-inhibiting herbicides resistance in D. ciliaris. Method Increasing herbicide rates were used to evaluate the three bioassays for differentiating R from S populations. Results R1 and R2 differed from S in all [...]

Adjuvants to Improve Phenmedipham + Desmedipham + Ethofumesate Efficacy Against Weeds in Sugar Beet (Beta vulgaris)

ABSTRACT: The efficacy of reduced (411.5 and 617.2 a.i. ha-1) and recommended (823.0 g a.i. ha-1) rates of phenmedipham + desmedipham + ethofumesate on the control of Amaranthus retroflexus, Amaranthus blitoides, Chenopodium album, and Tribulus terrestris in sugar beet field was investigated when they were tank-mixed with and without Adigor (0.5% v/v), Ammonium sulphate (2% v/v), Citogate (0.2% v/v), D-Octil (0.3% v/v), Hydro-Max (0.5% v/v), and Volck (0.5% v/v). When the herbicide was applied alone, there was no significant difference between the rates of 617.2 and 823.0 g a.i. ha-1 for reduction of total weed density and biomass. Significantly, the adjuvants decreased total weed density and biomass. However, there was no significant difference among the performance of adjuvants. The sugar beet root and sucrose yields were increased significantly by increasing herbicide rate as a result of an improvement in weed control. Although herbicide efficacy was influenced in a similar manner by all the adjuvants, the best results were found as follows: root yield was increased up to 9.66% (71.31 Mg ha-1) by applying the recommended rate of phenmedipham + desmedipham + ethofumesate plus Adigor compared to weed-free check (64.68 Mg ha-1) whereas sucrose yield was increased up to 26.48% (13.21 t ha-1) by applying the recommended rate of phenmedipham + desmedipham + ethofumesate plus HydroMax compared to weed-free check (10.45 t ha-1). From an economic and ecological standpoint, these two adjuvants can be suggested to optimize the recommended rate of phenmedipham + desmedipham + ethofumesate in weed management.

INTERAÇÃO ENTRE TAMANHOS DE VASO E DOSES DE GLYPHOSATE NO CONTROLE DE BRAQUIÁRIA

RESUMO Objetivou-se com este trabalho avaliar a interação entre o tamanho do vaso de cultivo e doses de glyphosate no crescimento, na fisiologia e na eficácia de controle de Brachiaria decumbens. A semeadura foi feita em vasos contendo 2, 5, 10 e 20 L de substrato, mantidos em casa de vegetação. Entre os 41 e 63 dias após a emergência (DAE), avaliou-se o crescimento deB. decumbens. Aos 64 DAE, fez-se a aplicação do glyphosate nas doses de 0,0, 0,8, 1,6 e 3,2 kg ha-1 de equivalente ácido. Foram avaliadas as trocas gasosas e a fluorescência da clorofila a, aos dois dias após a aplicação (DAA), bem como a eficácia de controle, aos 7, 14, 21 e 28 DAA, sendo nesta última avaliação determinada ainda a matéria seca da parte aérea. Por fim, aferiu-se ainda a capacidade de rebrota de B. decunbens aos 28 dias após o corte. O crescimento de B. decumbens aumentou linearmente com o aumento do tamanho do vaso. As trocas gasosas e os parâmetros de fluorescência foram afetados pelas doses de glyphosate, mas não pela variação do tamanho do vaso. Não houve interação significativa entre doses e tamanhos de vasos sobre a eficácia de controle, porém essa variável aumentou consideravelmente com o aumento da dose e, discretamente, com o aumento do tamanho de vaso, sobretudo nas avaliações até os 14 DAA. A matéria seca da parte área aos 28 DAA e de rebrota foi dependente da interação entre tamanho do vaso e dose de glyphosate. O tamanho do vaso deve ser escolhido com critério para ensaios de eficácia de controle de B. decumbens com herbicida sistêmico.

Gossypium Lines Resistant to Rotylenchulus reniformis Vary in Sensitivity to the Herbicide Fluometuron

Reniform nematode (Rotylenchulus reniformis) resistance is being transferred to Gossypium hirsutum from its distant relatives. Reports of fluometuron damage to LONREN lines with nematode resistance from G. longicalyx raised concerns about introducing herbicide sensitivity from other nematode resistance sources. The research objective was to evaluate 15 sources of reniform nematode resistance for their reaction to fluometuron three weeks after planting in a replicated greenhouse trial: two G. herbaceum accessions, four G. arboreum accessions, three G. barbadense accessions, three G. hirsutum accessions, and three G. hirsutum lines with resistance introgressed from G. barbadense (FR-05) or G. longicalyx (LONREN-1 and LONREN-2). The control genotype was G. hirsutum cultivar Deltapine 161 B2RF. Across all herbicide rates tested, mean herbicide injury ratings for G. arboreum accessions were greater than the control, whereas G. barbadense GB 713 and TX 110 were less. Regression analysis of herbicide rates indicated that injury increased linearly with increasing herbicide rate for all accessions, although G. arboreum A2-083 had more injury than the control. Regression analysis of herbicide rates indicated that biomass decreased linearly with increasing herbicide rate for all accessions, although G. barbadense GB 713 and Pima PHY 800 exhibited greater biomass reduction than the control. Across all herbicide rates tested, mean electron transport rates of all G. herbaceum and G. arboreum accessions and G. barbadense Pima PHY 800 were lower than the control. The relationship between herbicide rate and electron transport rate was curvilinear, with similar decreases in electron transport rate in response to increasing herbicide concentration for all lines. Increased sensitivity to fluometuron could be introduced into G. hirsutum through crosses with distantly related species, but with the exception of G. arboreum A2-083, the lines did not respond to the herbicide differently from the control.

Combining Cultural Practices with Herbicides Reduces Wild Oat (Avena fatua) Seed in the Soil Seed Bank and Improves Barley Yield

A study was initiated in 2001at four locations in western Canada to investigate an integrated approach to managing wild oat, the region's worst weed. The study examined the effects of combining semidwarf or tall barley cultivars with normal or twice-normal barley seeding rates in either continuous barley or a barley–canola–barley–field pea–barley rotation. Herbicides were applied at 25, 50, and 100% of recommended rates. The first phase of the study was completed in 2005. This paper reports on the second phase, which was continued for four more years at two of the locations, Beaverlodge and Fort Vermilion, AB, Canada. The objective was to determine the long-term impact of the treatments on wild oat seed in the soil seed bank. In 2009 (final year), the diverse rotation combined with the higher barley seeding rate (optimal cultural practice) resulted in higher barley yields and reduced wild oat biomass compared to continuous barley and lower barley seeding rate (suboptimal cultural practice). In contrast to the first phase, barley yield was higher with the semidwarf cultivar, and cultivar had no effect on wild oat management. Wild oat seed in the soil seed bank decreased with increasing herbicide rate, but amounts were often lower with the optimal cultural practice. For example, at the recommended herbicide rate at Beaverlodge, an approximate 40-fold reduction in wild oat seed occurred with the optimal compared to the suboptimal cultural practice. The results indicate that combining optimal cultural practices with herbicides will reduce the amount of wild oat seed in the soil seed bank, and result in higher barley yields. Optimal cultural practices may also compensate for reduced herbicidal effects in terms of reducing wild oat seed accumulation in the soil seed bank and increasing barley yield. The results have implications for mitigating the evolution of herbicide resistance in wild oat.

Tolerance of Tomato to Herbicides Applied through Drip Irrigation

Greenhouse and field studies were conducted to determine tolerance of tomato to halosulfuron, imazosulfuron, and trifloxysulfuron herbicides applied through drip irrigation. In greenhouse studies, PRE- and POST-applied trifloxysulfuron caused greater tomato injury (14 and 54% injury, respectively) than PRE- and POST-applied halosulfuron (5 and 26% injury, respectively) or imazosulfuron (5 and 23% injury, respectively). All herbicide treatments in the greenhouse studies caused greater injury to tomato than the nontreated. Greater tomato injury was observed in the greenhouse from herbicides applied POST than when soil applied. Tomato injury from POST-applied halosulfuron, imazosulfuron, or trifloxysulfuron followed a linear relationship, with tomato injury increasing with increasing herbicide rate. Tomato photosynthetic rate did not differ among the herbicide treatments (32.7 to 55.0 μmol m−2 s−1) and the nontreated (38.0 to 55.0 μmol m−2 s−1). At 5 to 16 days after treatment (DAT), tomato treated with imazosulfuron POST (0.26 to 0.46 cm s−1) or trifloxysulfuron POST (0.27 to 0.51 cm s−1) had lower stomatal conductance compared to the stomatal conductance of the nontreated tomato (0.65 to 0.76 cm s−1). Chlorophyll content did not differ among treatments at 0 to 6 DAT. At 7 to 12 DAT, tomato treated with imazosulfuron POST (34.0 to 40.1 SPAD) and trifloxysulfuron POST (35.0 to 41.6 SPAD) had lower chlorophyll content compared to the nontreated (39.1 to 48.1 SPAD). In 2008 and 2009 field studies, no tomato injury was observed. Herbicide, herbicide application method, and herbicide rate had no effect on tomato height (73 to 77 cm 14 DAT, 79 to 84 cm 21 DAT) and total fruit yield (62,722 to 80,328 kg ha−1).

Influence of nitrogen fertilization and isoxaflutole on the nodulation of chickpea (Cicer arietinum)

The effects of soil nitrate and the herbicide, isoxaflutole, on chickpea nodulation were examined in a glasshouse experiment. The treatments consisted of one isoxaflutole‐tolerant and one isoxaflutole‐sensitive chickpea cultivar, five nitrate concentrations (0, 0.75, 1.5, 3.0, and 6.0 mmol L−1), and three herbicide rates (0, 75 [the recommended rate], and 300 g ha−1). The sensitive cultivar was more susceptible to isoxaflutole damage with an increasing herbicide rate and nitrate concentration, compared with the tolerant cultivar. Isoxaflutole at the recommended rate reduced the nodule dry weight of the sensitive cultivar by 51% and by 33% in the tolerant cultivar. The nodule dry weight of the sensitive cultivar was reduced by 28%, 40%, 64%, and 76% with the addition of the 0.75, 1.5, 3.0, and 6.0 mmol L−1 nitrate concentrations, respectively. In comparison, the nodule dry weight of the tolerant cultivar was reduced by 50% and 79% at the 3.0 and 6.0 mmol L−1 nitrate concentrations, respectively. In addition, the level of damage from increasing rates of isoxaflutole increased with the highest nitrate concentrations of 3.0 and 6.0 mmol L−1, regardless of the cultivar. Isoxaflutole at the recommended application rate had a detrimental effect on the nodulation of both chickpea cultivars, but the isoxaflutole‐tolerant cultivar suffered less injury than the sensitive one in relation to some growth parameters. The damage to chickpea from the recommended rate of isoxaflutole also increased with soils of higher nitrate content.

The impact of herbicide management on long‐term changes in the diversity and species composition of weed populations

GrundyAC,MeadA,BondW,ClarkG &BurstonS (2011). The impact of herbicide management on long‐term changes in the diversity and species composition of weed populations.Weed Research51, 187–200.SummaryField vegetable systems face challenges to maintain sustainable weed management, including a reduction in available herbicides and encouragement towards reduced tillage. In a 9‐year study, six herbicide products were compared, each at three rates, with a single product per plot. These were assessed in a minimal cultivation system designed to exert maximum pressure for change in weed populations, to assess for predictable changes in these populations. Weed density and species number declined with increasing herbicide rate, confirming that some species are able to survive in reduced rates. Pre‐emergence herbicides resulted in a larger number of species, greater species diversity and lower species dominance, compared with post‐emergence products. Species numbers increased over the first 6 years, with emergence periodicity coinciding with springtime soil disturbance. The number of species with ecological functional value increased in response to repeated use of single herbicide products. Observed species shifts illustrated complex responses to the combination of three separate drivers: changes in the dominant periodicity associated with tillage timing; a response to herbicide product and rate related to species susceptibility; and changes in community dynamics caused by variability in weather and the interaction with herbicide efficacy. Improved understanding of the effects on weed communities of the interactions between these drivers and the cropping system is essential in achieving a balance between sustainable weed management and the provision of ecological function.

Isoxaflutole Shifts Kochia (Kochia scoparia) Populations in Continuous Corn

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.

Herbicide Efficacy in Alternative Substrates for Container-grown Nursery Crops

Abstract Three experiments were conducted to evaluate the influence of alternative substrates on herbicide efficacy in container grown nursery crops. In Experiment 1, alternative substrates evaluated were either pine wood chips hammer-milled, to pass between 0.48 cm (0.19 in) screen (PWCH1) or 0.64 cm (0.25 in) screen (PWCH2), whole pine trees chipped or hammer-milled (WTCH), to pass between a 0.48 cm (0.19 in) screen, or the previously mentioned combined with pinebark. A commercial pine bark substrate (PB) with a 6: 1 (by vol) ratio of pine bark to sand was maintained as a control treatment. Rout® at 3 lbs aia (oxyfluorfen + oryzalin at 2.24 + 1.12 kg·ha−1) and Ronstar at 4.0 lb aia (oxadiazon at 4.48 kg·ha−1) were applied at recommended label rates. Herbicides were applied and irrigated, and each container was overseeded with 25 spotted spurge (Euphorbia maculata) seed per container. In general, the greatest spurge numbers occurred in PB substrates. Rout provided superior spurge control compared to Ronstar. In Experiment 2, substrates evaluated were PWCH2, WTCH and PBS with 7.0 kgm−3 (12 lbsyd−3) of Polyon 17-6-12 or with an additional 8 lbs·yd−3 of Polyon 17-6-12, or PWCH2 and WTCH combined with composted poultry litter (CPL). PWCH2 tended to have the fewest spurge numbers throughout the experiment, while WTCH and PBS tended to have similar spurge numbers and spurge fresh weight. Addition of CPL and additional fertilizer tended to increase spurge numbers and spurge fresh weight in all substrates. Rout and Ronstar provided similar spurge control in this study. In Experiment 3, substrates evaluated were PB (100%), WTCH (100%), CCR (100%), and PB: S (6: 1 vol), WTCH: S (6: 1 vol), and CCR: S (6: 1 vol). Rout and Ronstar were each applied at 0.25×, 0.50×, 075×, and 1.0× label rate. There was a significant substrate affect on all dates except 14 DAT. Spurge numbers and spurge fresh weight were greatest in PB or PB: S substrates. Spurge numbers and spurge fresh weight in general decreased with increasing herbicide rates. At 45 DAT and 60 DAT, Rout had superior spurge control compared to Ronstar. With WT and CCR substrates, Rout provided excellent control (less than 1.0 gram fresh weight) at the 0.50× and 1.0× rates. In general, weed control in alternative substrates was superior to that obtained in commercially used pinebark.

Wheat Seeding Rate Influences Herbicide Performance in Wild Oat (Avena fatua L.)

Field experiments were conducted at three locations in Alberta for 3 yr to determine if spring wheat (Triticum aestivum L.) seeding rate (75 and 150 kg ha−1) influenced the effects of recommended and reduced herbicide rates on wild oat (Avena fatua L.) shoot biomass, wild oat seed in the soil seed bank, and wheat yield and net economic return. Wild oat biomass and seed in the soil seed bank decreased nonlinearly at both seeding rates as herbicide rates increased. The herbicides were more effective in reducing wild oat shoot biomass and seed in the soil seed bank when wheat was seeded at the higher rate. The lowest wheat yields and net economic returns occurred when no herbicides were applied and both variables increased nonlinearly with increasing herbicide rate. In most cases, wheat yield and net economic return were greater at the higher seeding rate. On average, wheat yield improved by 19% and net economic return by 16% when wheat was seeded at the higher rate. The results indicate that seeding wheat at relatively high rates can contribute positively to herbicide performance and result in better wild oat management and higher wheat yields and economic returns. In some cases, there was little difference between applying the herbicides at 75 or 100% of the recommended rate but reducing rates below 75% almost always resulted in higher wild oat shoot biomass and seed, and reduced yields and net economic returns, even at the higher wheat seeding rate.

Rapid Assay Evaluation of Plant Response to Protoporphyrinogen Oxidase (Protox)-Inhibiting Herbicides

Protoporphyrinogen oxidase (protox)-inhibiting herbicides damage cell membranes, resulting in electrolyte leakage. A whole-plant dose-response study and a rapid assay that measured electrolyte leakage was used to determine the response of wild mustard, soybean, and protox inhibitor–susceptible and protox inhibitor–resistant common waterhemp to increasing doses of three protox inhibitors: acifluorfen, fomesafen, and sulfentrazone. For the dose-response study, whole plants were treated with the three protox-inhibitor herbicides. Electroconductivity assay 1 consisted of cutting discs from leaf tissue and submerging them in an incubation medium containing concentrations of acifluorfen, fomesafen, or sulfentrazone. In electroconductivity assay 2, the entire leaf was treated with solutions containing acifluorfen, fomesafen, or sulfentrazone. The whole-plant dose-response study showed increasing visible injury with increasing herbicide rates for all species and all herbicides. The order of visible injury was wild mustard > susceptible common waterhemp > resistant common waterhemp > soybean. In assay 1, electrolyte leakage from leaf discs treated with acifluorfen or fomesafen increased with increasing herbicide concentrations, and was similar for all species. In contrast, electrolyte leakage from leaf discs treated with sulfentrazone did not increase with increasing herbicide concentrations for any species. In assay 2, only wild mustard leaf discs increased in electrolyte leakage with increasing herbicide rates of acifluorfen, fomesafen, and sulfentrazone and followed the regression curves established by the whole-plant dose-response study. However, assay 2 was not able to distinguish between susceptible wild mustard and tolerant soybean, or between susceptible and resistant waterhemp.

Repeated Reduced Rates of Broadleaf Herbicides in Combination with Methylated Seed Oil for Postemergence Weed Control in Sugarbeet (Beta vulgaris)1

Field trials were conducted at five sites from 2001 through 2003 to determine the influence on sugarbeet and weeds of repeated broadcast and banded reduced rates of desmedipham plus phenmedipham, triflusulfuron, and clopyralid in combination with either 1.5 or 3% v/v methylated seed oil (MSO). Desmedipham plus phenmedipham, triflusulfuron, and clopyralid were applied POST three times at 5 to 7 d intervals at either 25, 50, 75, or 100% of a 180 plus 180 plus 18 plus 100 g ai/ha dosage (full rate). When averaged over all herbicide rates, crop injury was 6% greater, but common lambsquarters control was 5% higher, and crop yield was 15% greater with broadcast compared with banded herbicide application. In most situations, adding MSO at 3% rather than 1.5% did not improve weed control. Sugarbeet injury was lowest (11%) and the average weed control was 86% when herbicide rates (with 1.5% MSO) were 25% of the full rate (microrate). Applying an herbicide rate (with 1.5% MSO) that was 50% of the full rate (half rate) increased crop injury from 11% with the microrate to 18% with the half rate and elevated average weed control from 86% with the microrate to 92% with the half rate. Common lambsquarters control increased from 81% with the microrate to 89% with the half rate. Sugarbeet root yield was 23 t/ha when no herbicide was used, 48 t/ha with the microrate, and 49 t/ha with the half rate compared with 54 t/ha when the full rate was applied without MSO. Increasing herbicide rates to 75% of the full rate (three-quarter rate) (with 1.5% MSO) increased crop injury to 27% and average weed control to 96%. Applying 1.5% MSO to the full rate increased crop injury to 35% with no improvement in average weed control over that achieved with the full rate without MSO.Nomenclature: Clopyralid; desmedipham; phenmedipham; triflusulfuron; common lambsquarters, Chenopodium album L. #3 CHEAL; sugarbeet, Beta vulgaris L. ‘Beta 1775’, ‘Beta 4546’, ‘HM1639RZ’.Additional index words: Adjuvants, crop tolerance, crop yield.Abbreviations: DAT, days after treatment; full rate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 180 plus 180 plus 18 plus 100 g/ha; half rate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 90 plus 90 plus 9 plus 50 g/ha; microrate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 45 plus 45 plus 4.5 plus 25 g/ha; MSO, methylated seed oil; three-quarters rate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 135 plus 135 plus 13.5 plus 75 g/ha.

Fertilizer Placement and Herbicide Rate Affect Weed Control and Crop Growth in Containers

Abstract Three experiments were conducted in Oregon and Mississippi to evaluate the effect of fertilizer placement and rate of herbicide application on weed control and crop growth. In Expt. 1, Osmocote 18N–2.6P–10.0K (18–6–12) controlled release fertilizer (CRF) was applied at 12 g (0.4 oz) per container (#1) either topdressed, incorporated, or dibbled (placed under the liner prior to potting); and OH2 (pendimethalin + oxyfluorfen) was applied at 0, 28, 56, or 112 kg/ha (0, 25, 50, or 100 lbs/A). Containers were overseeded with common groundsel (Senecio vulgaris). In Expt. 2, Osmocote 17N–3.0P–10.1K (17–7–12) CRF was applied at 18 g (0.6 oz) per container using the same placement methods as Expt. 1; and Rout (oryzalin + oxyfluorfen) was applied at 0, 28, 56, or 112 kg/ha (0, 25, 50, or 100 lbs/A). A hand-weeded check was also included, and containers were overseeded with prostrate spurge (Chamaesyce prostrata). In Expt. 3, containers were fertilized with either 12 g (0.4 oz) of Apex 20N–4.3P–8.4K (20–10–10) CRF or 14 g (0.5 oz) of Apex 17N–2.2P–9.2K (17–5–11) CRF using similar fertilizer placement methods; and Snapshot 2.5TG (isoxaben + trifluralin) was applied at 0, 84, or 168 kg/ha (0, 75, or 150 lb/A). Containers were overseeded with creeping woodsorrel (Oxalis corniculata). Weed control improved with increasing herbicide rate. Across the three experiments, dibbling CRFs with no herbicide resulted in 85 to 97% weed control, while topdressing resulted in 19 to 85% and incorporating resulted in 55 to 88% control. With herbicides, dibbling fertilizer resulted in 89 to 99% weed control while topdressing resulted in 82 to 90% and incorporating 81 to 98%. Dibbling fertilizer resulted in greater shoot growth (growth index) of azalea (Rhododendron ‘Stewartsonian’), holly (Ilex crenata ‘Compacta’), lavender (Lavandula × intermedia ‘Grosso’), and wintercreeper euonymus (Euonymus fortunei ‘Emerald Gaiety’). In Expt. 3, incorporating CRFs resulted in higher root ratings than dibbling in lavender and euonymus. Though measurable differences in root and shoot growth were observed in all experiments, differences were economically unimportant.

Ornamental Grass Tolerance to Postemergence Grass Herbicides

Twelve ornamental grasses from the genera Calamagrostis, Cortaderia, Eragrostis, Erianthus, Miscanthus, Sorghastrum, Spartina, Panicum, and Pennisetum were evaluated for tolerance to the postemergence herbicides fenoxaprop-ethyl, fluazifop-P, and sethoxydim at 0.4 kg a.i./ha. Calamagrostis was uninjured by fenoxaprop-ethyl as measured by visual injury ratings, height, and foliage dry weight. Greenhouse studies evaluated the tolerance of three Calamagrostis cultivars to fenoxaprop-ethyl rates of 0.4 to 3.2 kg a.i./ha with no observed visual injury from any treatment. However, the expansion rate of the youngest Calamagrostis leaf was reduced linearly with increasing herbicide rates each day after application. The highest rate (3.2 kg a.i./ha) reduced the leaf expansion rate by 1 day and all other rates by 3 days after treatment. Leaf expansion rate differed between Calamagrostis cultivars at different times after herbicide treatment. Dry weight of Calamagrostis arundinacea `Karl Foerster' was reduced at 4 weeks after treatment but not at 10 weeks after treatment. Chemical names used: (±)-ethyl 2-[4-[(6-chloro-2-benzoxazolyl)oxy)phenoxy]propanoate (fenoxaprop-ethyl); (R)-2-[4-[[5-trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid (fluazifop-P); 2[1-(ethoxy imino)butyl]-5[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one (sethoxydim).

Soil as Herbicide Carrier for Italian Ryegrass (Lolium multiflorum) Control in Wheat (Triticum aestivum)

The efficacy of herbicides applied broadcast by hand with a soil carrier or sprayed with water carrier were compared for Italian ryegrass control in winter wheat in central Oklahoma. Italian ryegrass was controlled 77 to 100% with BAY SMY 1500, chlorsulfuron, and CGA-131036 applied with both carriers. Metribuzin applied POST with 187 L ha–1water was less phytotoxic to Italian ryegrass and wheat than with 200 kg ha–1soil. All herbicides applied with 200 kg ha–1silt loam soil as carrier at two locations controlled Italian ryegrass 96 to 100%. Increasing herbicide rate, soil carrier quantity, or broadcasting soil-carried herbicide in two directions rather than one did not significantly improve herbicide efficacy over that of conventional spraying.

The Influence of Terbufos on the Response of Five Corn (Zea mays) Hybrids to CGA-136872

Field experiments were established to investigate the influence of terbufos on the response of five corn hybrids to postemergence applications of CGA-136872. In 1987, Asgrow RX404, Dekalb DK656, Funk's G4673A, and Pioneer P3165 were tolerant to CGA-136872 when no soil insecticides were applied. In 1988, terbufos was applied at 1.1 kg ai ha-1in-furrow at planting. Injury was observed on all hybrids following CGA-136872 application in 1988. With the exception of Funk's G4307, all hybrids were tolerant to CGA-136872 in 1989 when no soil insecticide was used. When terbufos was applied in-furrow, injury increased with increasing herbicide rate for these hybrids.

Effects of Preemergence Herbicides on Soybean (Glycine max): Weed Competition

Glasshouse experiments were conducted to evaluate the effects of preemergence applications of metribuzin, pendimethalin, alachlor, and imazaquin on the competitive relationship between soybean and sicklepod, tall morningglory, or common cocklebur. An equal-ratio series design was employed where the proportion of species in a mixture remained constant and total plant density was varied. The ratio of soybean:sicklepod fresh weights was altered by alachlor and imazaquin while the ratio of soybean:tall morningglory fresh weights was altered only by imazaquin. The ratio of soybean:common cocklebur fresh weights was altered by metribuzin and imazaquin. Increasing herbicide rates resulted in higher soybean:weed fresh weight ratios and higher herbicide response coefficients.

Response of a young loblolly pine ( Pinus taeda) plantation to herbicide release treatments using hexazinone

In March 1980, a study was initiated on a site in the Piedmont of Alabama to examine the effect of hexazinone rate and formulation in releasing newly planted and 1-year-old loblolly pine in a dense stand of hardwoods (4.6 m 2 ha −1 groundline basal area, 17 100 rootstocks ha −1). Treatments included a factorial combination of three hexazinone formulations (1 cc 10% a.i. pellet, 1 2 cc 10% a.i. pellet, 20% a.i. granules) at three rates (1.12, 1.68, and 2.24 kg a.i. ha −1), plus an untreated control (10 treatments). Hardwood density following treatment decreased with increasing herbicide rate. Reduction in hardwood density was similar for the two pelleted formulations and lower for the granules. High rainfall amounts soon after application (13.2 cm within 10 days) appeared to have washed some herbicide from the granule-treated plots prior to uptake by hardwoods, possibly causing lower reduction of hardwoods relative to the pellets. Effects of treatment on pine mortality differed between newly-planted (interplants) and 1-year-old (original) pines. This is likely due to differences in root system development and overall size between the two classes of pines at the time of treatment, and associated differences in both the ability to compete with hardwoods for site resources and the likelihood of uptake of a fatal dose of hexazinone. Five growing seasons after treatment, mean pine size (height, groundline diameter, and dbh) differed among treatments for both interplanted and original pines, with size increasing with increasing hexazinone rate. Mean tree volume of pines was more strongly correlated with hardwood groundline basal area than with any other measure of hardwood density ( r = −0.61 for interplanted pines ( P < 0.001), r = −0.51 for original pines ( P < 0.001)) five growing seasons after treatment.

Toxicity and Site of Uptake of Soil-Applied Imazaquin in Yellow and Purple Nutsedges (Cyperus esculentusandC. rotundus)

Imazaquin {2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-3-quinolinecarboxylic acid} site of uptake and toxicity from soil application were investigated in yellow nutsedge (Cyperus esculentusL. #3CYPES) and purple nutsedge (C. rotundusL. # CYPRO). Imazaquin concentrations of 0.1 to 0.5 ppmw inhibited yellow nutsedge shoot emergence completely, while purple nutsedge shoots emerged at the lower concentrations. Herbicide placement above the tuber reduced shoot emergence and shoot and root dry weights of both species more than did placement below the tuber. Increasing herbicide rate increased the number of tuber buds that sprouted. Three-day-old nutsedge propagules absorbed14C-imazaquin from both rhizome shoots and roots and the herbicide moved both acropetally and basipetally in nutsedge propagules.