Browsing by Author "Hagood, Edward Scott Jr."

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    Allelopathic effects of ferulic, gallic, and vanillic acids on corn (Zea mays L.)
    Abdaoui, Fatima El (Virginia Tech, 1991-01-03)
    Studies on the activity of femlic, gallic, and vanillic acids on germination and growth of corn (Zea mays L.), radish (Raphanus sativus L.), and peanut (Arachis hypogaea L.) showed that the inhibitory effects of these acids were concentration and growth variable dependent. Ten days after treatment, significant reduction in percent germination of the three species occurred with higher phenolic acid treatments, except that gallic acid did not significantly inhibit peanut germination. Among the growth parameters investigated, root elongation and dry weight were more affected than either germination or shoot length and dry weight. Radish and corn were more sensitive than peanut. In two-combination experiments, the interactive effects of phenolic acids on corn germination and shoot growth were generally not significant, indicating an additive effect. Femlic acid, generally, antagonized higher concentrations of vanillic or gallic acids on corn root length and dry weight, suggesting a differential uptake of phenolic acids by corn roots or a limited uptake of gallic and vanillic acids in the presence of ferulic acid. In a soil system, higher and repeated phenolic acid treatments were required to bring about inhibition of corn growth than those which were effective in petri dishes. All levels of the synthetic auxin, 2,4-D (2,4-dichlorophenoxyacetic acid) were effective in reversing the inhibitory effects of 1 mM ferulic acid on corn root length when these two acids were applied in combination. No 2,4-D treatment counteracted 10 mM of ferulic acid. All levels of 2,4-D combined with 1 mM ferulic acid and the mixture of 0.1 nM 2,4-D with 10 mM ferulic acid were antagonistic for corn shoot length. No significant interactions were obtained on corn germination or seedling growth when 2,4-D was combined with gallic acid. Using manometric techniques, no inhibitory effects of ferulic or gallic acids observed on 02 consumption of germinating corn seeds. Ferulic acid did not interfere with water uptake of corn seeds during imbibition and germination. These findings indicate that the phytotoxicity of these acids observed on corn germination and seedling growth are not due to their interference with water uptake and respiratory activity of germinating seeds.
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    Assessing Drift and Lateral Mobility of Flazasulfuron and Trifloxysulfuron Sodium
    Jester, Jennifer Lynn (Virginia Tech, 2009-12-04)
    Flazasulfuron is one of the newest sulfonylurea (SU) herbicides to be registered for use in the fine turf industry. Flazasulfuron is safe for use on bermudagrass (Cynodon dactylon), and zoysiagrass (Zoysia japonica) yet controls several grass, broadleaf, and sedge weeds. In fine turf, flazasulfuron controls cool-season grasses such as tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) without harming warm-season grasses. Although SU herbicides like flazasulfuron bring several potential benefits to turfgrass markets, there are also several concerns related to using these herbicides in turfgrass areas. For many plant species, SU herbicides can cause phytotoxicity or death at less than 1 g ai/ha-1indicating small quantities of active ingredient are required to cause problems if herbicide moves in the environment. Herbicide moves to nontarget plants either after it has been applied via lateral relocation or during application via spray drift. Trials were conducted to evaluate flazasulfuron and trifloxysulfuron sodium tracking, runoff and drift in turfgrass environments. Field trials were conducted at six locations across the US to evaluate effects of irrigation, herbicide treatment, nontreated buffer distance, and time of tracking on creeping bentgrass (Agrostis stolonifera) putting green response to dislodged herbicide residues. Although average turf injury did not exceed 2%, significant differences were noted when treated plots were irrigated prior to tracking. In addition, putting green injury was negatively correlated and normalized difference vegetative index was positively correlated with increasing buffer distance. Data indicate the importance of post treatment irrigation to reduce lateral relocation of SU herbicides like flazasulfuron and trifloxysulfuron sodium in turfgrass. In other studies, herbicides were applied to turfgrass on 7 to 11 % slopes and perennial ryegrass injury was assessed at various distances down slope following an irrigation or rainfall event. Herbicide movement in runoff water was indicated by perennial ryegrass discoloration as much as 18 m below treated plots when excessive herbicide rates were applied to saturated soils. Based on perennial ryegrass injury, flazasulfuron at the rates tested was equivalent or more mobile than trifloxysulfuron sodium and equivalent or less mobile than pronamide when subjected to irrigation or rainfall soon after application to saturated soils. To assess spray drift, a bioassay based on corn height reduction was conducted and corn plants were exposed to potential spray drift in field conditions using conventional turfgrass spray equipment. A sprayer was operated when wind speeds were between 6.4 and 9.6 km h-1 and sentry plants were placed various distances between 0 and 30 m down wind. Wind speeds and direction were confirmed with anemometers and neutrally-buoyant balloons. Herbicide drift was not detected beyond 4.6 m downwind of either herbicide application. Data suggest a 5- to 8-m nontreated buffer area should sufficiently protect neighboring cool-season turfgrasses and other plants against flazasulfuron drift, runoff, and tracking as long as product is not applied to saturated soils and irrigated prior to traffic.
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    Characterization of Acetolactate Synthase-Inhibiting Herbicide-Resistant Smooth Pigweed and Corn Weed Management Programs Utilizing Mesotrione in Combinations with Other Herbicides
    Whaley, Cory Miller (Virginia Tech, 2005-03-01)
    Repeated use of acetolactate synthase (ALS)-inhibiting herbicides in recent years has resulted in the selection of 89 weed species resistant to these herbicides. One management strategy that can eliminate or slow the development of resistance is applying mixtures of herbicides with different modes of action. This research involved the characterization of ALS-inhibiting herbicide-resistant smooth pigweed (Amaranthus hybridus L.), as well as investigations on weed management programs in corn (Zea mays L.) utilizing mesotrione, a triketone, in mixtures with other herbicides. ALS-inhibiting herbicide-resistant smooth pigweed biotypes were collected from fields in Virginia, Delaware, Maryland, and Pennsylvania to evaluate response to ALS-inhibiting herbicides and to determine the molecular mechanisms of resistance. Sequencing of the ALS genes from these biotypes revealed two amino acid substitutions known to confer resistance, Ala122 to Thr and Ser653 to Asn, and one that has not been previously reported in plants, Asp376 to Glu. The smooth pigweed biotype with an Asp376 substitution displayed resistance to four classes of ALS-inhibiting herbicides that included imidazolinone (IMI), sulfonylurea (SU), pyrimidinylthiobenzoate (PTB), and triazolopyrimidine sulfonanilide (TP) chemistries. Transformation of this smooth pigweed ALS gene into Arabidopsis thaliana confirmed that the Asp376 substitution is responsible for the resistance. Other biotypes that had a substitution at Ala122 exhibited resistance to an IMI herbicide, little to no resistance to SU herbicides, and increased sensitivity to a PTB and a TP herbicide, whereas, biotypes that had a substitution at Ser653 exhibited high-level resistance to an IMI herbicide and lower resistance to PTB and SU herbicides. Experiments were also conducted to investigate the effectiveness of mesotrione in preemergence (PRE) and postemergence (POST) corn weed management programs in Virginia. Mesotrione applied PRE in mixtures with S-metolachlor and atrazine controlled common lambsquarters (Chenopodium album L.), smooth pigweed, common ragweed (Ambrosia artemisiifolia L.), and morningglory (Ipomoea spp.) species when a timely rainfall followed application. POST applications of mesotrione controlled common lambsquarters and smooth pigweed, but common ragweed and morningglory species were not always controlled. Common ragweed and morningglory species were controlled by mesotrione in a mixture with atrazine POST. Large crabgrass [Digitaria sanguinalis (L.) Scop.] and giant foxtail (Setaria faberi Herrm.) control was generally better when the ALS-inhibiting herbicides nicosulfuron plus rimsulfuron or rimsulfuron plus thifensulfuron plus atrazine were applied in a mixture with mesotrione. Mixtures of mesotrione with other POST herbicides in a total POST program produced corn yields comparable to standard PRE followed by POST weed management programs.
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    Characterization of the Mechanism of Resistance of a Johnsongrass (Sorghum halepense) Biotype to Selected Graminicides in Virginia and Response of Mugwort (Artemisia vulgaris) to Specific Herbicidal and Cultural Control Strategies
    Bradley, Kevin Wayne (Virginia Tech, 2000-04-26)
    Johnsongrass [Sorghum halepense (L.) Pers.] and mugwort (Artemisia vulgaris L.) are both rhizomatous perennial weeds that are capable of rapidly colonizing a variety of different environments. Separate experiments were conducted throughout Virginia from 1996 to 1999 to determine more effective methods for reducing infestations of these perennial weeds in the future. Field and greenhouse experiments conducted on a resistant johnsongrass population discovered in New Kent County, Virginia revealed that this biotype exhibits low levels of resistance to the aryloxyphenoxypropionate (APP) herbicides quizalofop-P and fluazifop-P and the cyclohexanedione (CHD) herbicide sethoxydim. Additional laboratory experiments revealed that resistance is not due to differential absorption, translocation, or metabolism of the APP and CHD herbicides in the resistant vs. the susceptible biotype. However, acetyl-coenzyme A carboxylase (ACCase) assays revealed that resistance to the APP and CHD herbicides is conferred by an overproduction of the ACCase enzyme in the resistant compared to the susceptible johnsongrass biotype. In field experiments conducted on mugwort infestations discovered in several counties throughout Virginia, 100% mugwort control was achieved with standard application rates of picloram at 4 months after treatment (MAT), and also greater than 70% mugwort control was achieved with the higher application rates of clopyralid, glyphosate, and dicamba at 4 MAT. However, all other herbicides evaluated in these experiments provided less than 65% mugwort control at 4 MAT, even at exceptionally high use rates. Additionally, the results from these trials revealed that sequential herbicide applications and sequential mowings prior to herbicide application are both effective mugwort control strategies.
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    The Control of Various Bermudagrass Cultivars in Tall Fescue Utilizing Fenoxaprop & Fluazifop
    Johnson, Michael Dale (Virginia Tech, 2000-04-24)
    Bermudagrass (Cynodon dactylon (L). Pers.) is considered to be one of the most difficult to control grass weeds in turf throughout the U.S. Recent breeding efforts have produced much more desirable bermudagrass cultivars, and therefore its use has increased. Ironically, as bermudagrass use becomes more popular it poses even greater difficulties to the turf manager. The need to control these warm season turfgrass species, without causing injury to other desirable turfgrass species, is one of the most intractable problems a turf specialist encounters. Herbicides previously used to selectively control bermudagrass such as siduron and oxadiazon have proven to be of only minimal efficacy or to induce significant injury to other desirable turfgrasses. Tests conducted in 1993, 1994 and 1995 have indicated that fenoxaprop plus fluazifop (Horizon 2000R) controlled bermudagrass effectively. Six bermudagrass (Cynodon dactylon) cultivars and tall fescue (Festuca arundinacea) were used in the susceptibility studies. Visual control and cover ratings were taken at two-week intervals until ten weeks after the final treatment. Sequential applications of labeled rates of fenoxaprop or fluazifop alone only temporarily controlled bermudagrass shoots. Horizon 2000 applied at 0.40 kg ai/ha in three sequential applications proved effective in controlling bermudagrass rhizomes and stolons. From results of previous studies and research conducted here it has been hypothesized that synergistic effects of fenoxaprop on fluazifop allow both differential control of various bermudagrass cultivars and increased tall fescue tolerance to these herbicides.
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    Control, Assessment and Glyphosate Resistance of Palmer Amaranth (Amaranthus palmeri S. Wats) in Virginia
    Ahmed, Amro Mohamed Aly Tawfic (Virginia Tech, 2011-08-08)
    Glyphosate resistant crops were rapidly adopted by farmers since their introduction in 1996 and currently, greater than 90% of cotton and soybean crops are glyphosate resistant. Glyphosate has been an effective mean for controlling Palmer amaranth, however overreliance on glyphosate based systems resulted in weeds that can no longer be controlled with glyphosate. Palmer amaranth resistance to glyphosate has been confirmed in ten US states including Virginia's bordering neighbor North Carolina. The objectives of this study were to i) determine the spread of Palmer amaranth and evaluate awareness among farmers and agribusinesses of herbicide resistant weeds in Virginia; ii) determine the efficacy of commonly used cotton and soybean herbicides programs for Palmer amaranth control; and iii) conduct greenhouse experiments to quantify the level of glyphosate resistance in a Greensville County, Virginia population. Using a communication network of Virginia county extension agents and crop advisers, Palmer amaranth was found in 15 Virginia counties. A survey was conducted to evaluate awareness of herbicide resistance and management of weeds in Virginia. Ninety percent of producers had fields planted to Roundup Ready® crops for each of the last 3 years. One hundred percent of the responders claimed awareness of the potential for weeds to develop resistance to glyphosate, but when asked about how serious they consider weed resistance to herbicides, the responders average rating was of 7.9 (on a scale of 1 to 10 where 1 is "not at all serious" and 10 is "very serious" ). Eighteen percent of the responder population claimed no awareness of glyphosate resistant weeds documented in Virginia. Herbicide efficacy experiments were established in soybean and cotton fields infested with Palmer amaranth. In soybean, experiments were established in a field where Palmer amaranth was not adequately controlled with glyphosate in the previous year. Glyphosate applied at 0.87 + 0.87 + 1.74 kg ae ha⁻¹ at 1, 3, and 5 weeks after planting (WAP) provided 82 to 85% control in 2009, but only 23 to 30% control in 2010, a hot and dry year. Glyphosate applied after preemergence (PRE) herbicides improved control to 90 percent. Programs that included s-metolachlor + metribuzin applied preemergence and followed by glyphosate + fomesafen applied postemergence provided the best control (93%) at 8 WAP. Glufosinate based herbicide programs provided greater than 85% control when applied alone, and control increased to 95% when preceded by PRE herbicides. Many conventional control systems integrating different modes of action provided more than 80% control at final evaluation of Palmer amaranth in 2009 and 2010. In soybean, the most consistent and effective program was flumioxazin applied PRE followed by chlorimuron + thifensulfuron, which provided 99 and 82% control at final evaluation in 2009 and 2010, respectively. Cotton fields were heavily infested with Palmer amaranth, but control with glyphosate had historically been good. Glyphosate applied early postemergence, late postemergence, and late post-directed provided more than 95 percent control at final evaluation of Palmer amaranth. Preemergence applications of fomesafen, fluometuron, or pendimethalin + fomesafen provided 77 to 99 percent early-season control and control was complete with an additional postemergence glyphosate application. Glufosinate applied at 0.45 kg ha⁻¹ at 1 and 3 WAP or applied at 0.45 kg ha⁻¹ following a preemergence herbicide provided greater than 95% control. Greenhouse experiments confirmed Palmer amaranth resistance in a population collected from Greensville County, Virginia. In the first experiment, the resistant biotype's I₅₀ value (rate necessary for 50% inhibition) for dry weight was 1.47 kg ae ha⁻¹, which is 4.6 times greater than the susceptible biotype and 1.7 times the recommended use rate of glyphosate. For fresh weight, the I₅₀ value of the resistant biotype was 1.60 kg ae ha⁻¹, 4.7 times that of the susceptible biotype of 0.34 kg ae ha⁻¹. In the second experiment, the I₅₀ value for the susceptible population could not be determined because all glyphosate rates resulted in complete control. However, the resistant population required 1.01 and 1.30 kg ae ha⁻¹ of glyphosate to reduce the fresh and dry weight by 50%.
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    Differential Response of a Virginia Common Lambsquarters (Chenopodium album) Collection to Glyphosate
    Hite, Grace Ann (Virginia Tech, 2008-04-29)
    The purpose of this research was to evaluate a common lambsquarters (Chenopodium album) collection from Westmoreland County, Virginia, which exhibited a differential response to glyphosate treatments as compared to most other common lambsquarters. Plants from this site that survived glyphosate applications were collected in both 2002 and 2004. Greenhouse studies were conducted on F1, F2, and F3 progeny from this collection and compared to a wild type collection from Montgomery County, Virginia. Evaluations were conducted on these plants treated with a range of glyphosate rates. F1 progeny of the Westmoreland plants from both 2002 and 2004 collections showed reduced response to glyphosate relative to the Montgomery collection. Vigor reduction of F1 progeny from three 2004 Westmoreland source plants with 0.84 kg ae/ha of glyphosate ranged from 66 to 85% at 28 days after treatment (DAT), compared to 89% for the Montgomery collection. Evaluation of four Westmoreland F2 common lambsquarters lines derived from 2002 collections indicated significant differences in glyphosate sensitivity. Fifteen F2 lines were generated from 2004 collections from each of three Westmoreland source plants and from the Montgomery source. For the least sensitive Westmoreland source, vigor reduction ranged from only 24 to 36% across F2 lines in response to 1.68 kg/ha of glyphosate at 28 DAT, relative to 55 to 100% for the Montgomery source. I50 estimates for fresh weight reduction were 0.91 and 0.32 kg/ha, for these sources, respectively. Sequential treatments of 0.42, 1.26, and 1.68 kg/ha applied at three-week intervals to the least susceptible 2004 Westmoreland F2 line resulted in only 37% vigor reduction and no mortality among 360 treated plants. Growth chamber studies were also conducted on the F2 progeny of these sources to determine if differential growth responses occur in noncompetitive environments and in the absence of glyphosate treatment. Generally, few differences were observed among the Westmoreland and Montgomery collections in growth parameters including height, leaf number, leaf area, leaf size, shoot weight, and reproductive output. However, significant differences were observed with regard to root weight, root length, and root density. In germination studies, it was determined that the Montgomery source had significantly faster and greater seed germination than the Westmoreland source. The susceptibility of F3 seedlings to glyphosate varied significantly with respect to F2 parent line and glyphosate rate. Mortality of 100% was observed in F3 seedlings from the Montgomery source in response to the 3.36 kg ae/ha glyphosate rate, while no mortality was observed in Westmoreland F3 seedlings in response to this glyphosate rate.
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    Double-crop corn (zea mays) weed control in Virginia
    King, Steve Russell (Virginia Tech, 2000-04-25)
    Double-crop production of corn (Zea mays L.) for grain following the harvest of small grain is not currently practiced in Virginia. Historical precipitation and evapotransportation data indicate that delayed corn planting could result in a higher probability of moisture during critical periods of crop development. Double-crop corn may also reduce economic risk as two crops would be harvested in the same year. Field experiments were conducted in three Virginia locations in 1998 and 1999 to determine the herbicide inputs required for double-crop corn production relative to those required in full-season no-till corn production. Experiments were conducted in a split-plot, randomized complete block design with cropping system as the main plot and herbicide treatment as the subplot. Herbicide treatments included combinations of nonselective herbicides for no-till establishment and/or preemergence residual herbicides and/or selective postemergence herbicides in both production systems. Glyphosate-tolerant corn was planted in all experiments and postemergence glyphosate treatments were also evaluated. In each experiment, dependent variables included weed control by species evaluated throughout the season, as well as weed biomass and corn yield evaluated at the end of the growing season. Generally, nonselective herbicides were not required in the double-crop system where atrazine was applied as a preemergence treatment, or where selective postemergence treatments were applied. Where a significant proportion of the infestation was comprised of perennial species, however, atrazine treatments were not sufficient in the double-crop system. Postemergence glyphosate treatments provided excellent broad-spectrum weed control in this situation. In heavy annual grass infestations, postemergence glyphosate treatments provided superior weed control to preemergence treatments alone, and equivalent weed control to treatments in which both preemergence and postemergence herbicides were applied. Corn yield response to weed control and cropping system variables varied significantly between the 1998 and 1999 growing seasons. Where adequate late-season rainfall was received, economic return from small grain and corn crops in the double-crop system was higher than the return in the full-season system, particularly in infestations where the double-crop system allowed significant reduction in herbicide input.
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    Effect of postemergence johnsongrass control on MCDV and MDMV incidence and severity in field corn
    Eberwine, John Wright (Virginia Tech, 1996-04-05)
    In the summers of 1989 and 1990, researchers in Va. and Md. began to observe lateseason reductions in com vigor in areas treated with nicosulfuron or primisulfuron for postemergence johnsongrass control. Symptoms observed included chlorosis, reddening of the leaves and shortening of the internodes. The nature and time of symptom expression were consistent with those caused by maize chlorotic dwarfvirus (MCDV) and maize dwarf mosaic virus (MDMV) infection of com. It was hypothesized that postemergence johnsongrass control increased the incidence and severity of MCDV and MDMV in virus-susceptible corn hybrids due to increased feeding by vectors of these viruses on treated corn. Field experiments were conducted in 1991 and 1992 to evaluate the effect of postemergence johnsongrass control with broad casted nicosulfuron, postemergence directed imazethapyr, mechanical control and no control on virus disease incidence and severity in a virus-susceptible ('Southern States 565') and a virus-tolerant ('Southern States 844) corn hybrid. Visual injury evaluations taken 10 weeks after treatment showed that the virus-susceptible com hybrid sustained significantly more injury, averaged across johnsongrass control methods, than did the virus-tolerant corn hybrid. Within the virus-susceptible com hybrid, where johnsongrass was controlled, regardless of method, significantly more injury was observed relative to the nontreated check. Further, averaged across johnsongrass control treatments, the virus-tolerant corn hybrid yielded significantly higher compared to the virus-susceptible com hybrid. Experiments conducted in 1993 and 1994 utilized cages as a means of preventing insect movement from the infected johnsongrass to the crop. Blackfaced leafhopper evaluations suggested that the cages significantly reduced leafhopper movement from the infected johnsongrass to the corn, however complete exclusion was not achieved. Results of corn tissue assays showed that MCDV and MDMV were being transmitted, however no treatment differences were detected. Two experiments were conducted in 1994 to analytically test the hypothesis and to determine the time course of MCDV and MDMV double infection of corn tissue. Johnsongrass control treatments evaluated included broadcast nicosulfuron and no treatment. Postemergence johnsongrass control increased MCDV and MDMV incidence 9 to 21 days after treatment. Further, significantly more double infections of MCDV and MDMV were observed 14 to 21 days after treatment in experimental units receiving the nicosulfuron application.
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    Effect of Temperature and Chemical Additives on the Efficacy of the Herbicides Glufosinate and Glyphosate in Weed Management of Liberty-Link and Roundup-Ready Soybeans
    Pline, Wendy Ann (Virginia Tech, 1999-03-25)
    The introduction of herbicide resistant crops offers producers many more options for weed control systems. These crops allow environmentally safe, non-selective herbicides to be used as selective herbicides, broadening the spectrum of weeds controlled, while not harming the crop. As these crops are very new on the market, investigation of their performance under various environmental conditions as well as in various weed control programs is needed. Liberty-link ® soybeans are resistant to the herbicide glufosinate, because of the incorporation of a gene encoding phosphinothricin acetyl-transferase (pat), which is able to detoxify glufosinate. Roundup-Ready ® soybeans are transformed with an altered, non-sensitive form of 5-enolpyruvylshikimate- 3-phosphate synthase (EPSPS), which confers glyphosate resistance. Field and greenhouse studies were conducted to determine the efficacy of glufosinate and glyphosate on annual and perennial weeds. Also to determine whether the use of ammonium sulfate (AMS) or pelargonic acid (PA), a 9-carbon fatty acid, as additives of glufosinate or glyphosate would increase their efficacy, while maintaining their safety on the transgenic soybeans. Three annual weeds: common lambsquarters, giant foxtail, sicklepod, as well as two perennial weeds: common milkweed and horsenettle were included in studies. Uptake, translocation, and metabolism of 14C-glufosinate + AMS or PA, were studied in the five weeds in order to determine the basis for their differential weed sensitivity to glufosinate, and the effect of the two additives. The effect of temperature on Liberty-Link ® and Roundup-Ready ® soybeans after application of glufosinate or glyphosate was investigated. Injury was quantified by measuring chlorophyll content of herbicide treated soybean trifoliolates. Uptake, translocation, and metabolism studies of 14C-glufosinate and 14C-glyphosate in transgenic soybeans were conducted to determine the potential cause for the observed temperature-dependent sensitivity. Since glufosinate is a synthetic analog of a naturally occurring bacterial toxin, it was tested for possible bactericidal activity on the soybean pathogen Pseudomonas syringae. Greenhouse and field-studies showed that the 5 weeds responded differently to glufosinate and glyphosate. Common milkweed was the most tolerant to glufosinate and common lambsquarters to glyphosate while giant foxtail was the most sensitive species to both herbicides. Some interactions between AMS or PA and glufosinate or glyphosate were also observed. Uptake and translocation studies showed that AMS increased the uptake of 14C-glufosinate in some weeds, whereas PA had only minimal effects on absorption and translocation of glufosinate. Metabolism of glufosinate was detected only in common lambsquarters. A rate dependent loss of chlorophyll in Liberty-Link ® soybeans treated with glufosinate was observed that was greater at 15° C than at 25° or 35° C. Metabolism studies showed a decrease in the rate of glufosinate metabolism 3 hours after treatment in Liberty-Link ® soybeans grown at 15° C versus 25° C. Conversely, chlorophyll loss in glyphosate-treated Roundup-Ready soybeans was greater at 35° C than at 15° or 25° C. Translocation studies showed a significantly greater percentage of absorbed 14C-glyphosate translocated to developing meristems at 35° C than at 15° C in Roundup-Ready® soybeans. Glufosinate concentrations of 1 mM and higher significantly inhibited the growth of Pseudomonas syringae (L-529) in liquid media cultures. Typical field use rates of glufosinate also reduced the number of live P. syringae on Liberty-Link® soybean leaves. Overall, the results of this research show that annual and perennial weeds differ in their sensitivity to glufosinate and glyphosate. Additives such as AMS and PA may enhance the efficacy of glufosinate on perennial weed species, and glyphosate in most weeds. Differences in weed sensitivity to herbicides and effects of additives can in most cases be explained by differences in absorption or metabolism. Variable temperatures may affect the engineered resistance of transgenic soybeans to the herbicides glufosinate and glyphosate. The herbicide glufosinate has some bacteriocidal activity on P. syringae. Nomenclature: Glufosinate, 2-amino-4-(hydroxymethylphosphinyl) butanoic acid; Glyphosate, N-(phosphonomethyl)glycine; PA, pelargonic acid (nanoic acid); AMS, ammonium sulfate; giant foxtail, Setaria faberi Herrm.; common lambsquarters, Chenopodium album L.; sicklepod, Cassia obtusifolia L.; horsenettle, Solanum carolinense L.; common milkweed, Ascleipias syriaca L. pat, phosphinothricin acetyl transferase; EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase.
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    Efficacy and selectivity of the herbicide rimsulfuron in potatoes [Solanum tuberosum], transplanted tomatoes [Lycopersicum esculentum], and transplanted peppers [Capsicum annum]
    Ackley, John A. (Virginia Tech, 1994-04-06)
    Rimsulfuron {N-[[ 4,6-dimethoxy-2-pyrimidinal)amino ]carbonyl]-3-( ethylsulfonyl)-2-pyridinesulfonamide} is a new sulfonylurea herbicide under development by E.I. Dupont de· Nemours & Company Inc. for preemergence and postemergence grass and broadleaf weed control in Solanaceous vegetable crops. The efficacy and selectivity of rimsulfuron were determined in potatoes, transplanted tomatoes, and transplanted peppers in field studies in 1991, 1992, and 1993. Treatments included rimsulfuron and metribuzin alone and in combination in potatoes and tomatoes, rimsulfuron alone in peppers, and sequential applications of rimsulfuron in tomatoes and peppers. Application timings included preemergence and postemergence in potatoes, while only post-transplant applications were evaluated in tomatoes and peppers. Preemergence applications of rimsulfuron controlled weeds if rainfall was received within a few days following application. Control was often greater in potatoes and tomatoes than in peppers. These differences likely relate to more frequent rainfall events in potatoes and tomatoes than in the later-planted peppers.
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    Egyptian Broomrape (Orobanche aegyptiaca Pers.) and Small Broomrape (Orobanche minor Sm.) Parasitism of Red Clover (Trifolium pratense L.) in Vitro
    Morozov, Ivan Vladimirovitch (Virginia Tech, 1998-05-13)
    Broomrapes, Orobanche spp., are holoparasites that affect the growth of a variety of broadleaf crops. One of the distinct characteristics of the family Orobanchaceae is the lack of chlorophyll, and hence inability to synthesize their own food. Broomrapes subsist on the roots of the host plant from which they derive the carbon, water, and nutrients needed for further growth. Parasitism as such leads to yield reductions, and in case of heavy infestations, complete crop failure. Among other plants parasitized by broomrapes are several legumes, some of which are also the world's most economically important crops. As part of their unique biology, legumes provide an ecological niche for diazotropic soil bacteria, which belong to the family Rhizobiaceae. In return, the host plant receives fixed nitrogen from the nodules, specialized structures produced on the roots of most legume plants upon inoculation with bacteria. Orobanche spp. germination depends on the presence of chemical stimulant in host root exudates. It has been reported that inoculation of some legumes resulted in greater infestation by parasitic weeds. In addition, bacterial nodules were assumed to provide a place for broomrape invasion of host legume. Furthermore, infestations were observed to be more intense in aerobic conditions when rhizobia are most active. It is possible that production of the stimulant could be correlated with the infection of roots with Rhizobium, and that the nodules formed on the roots could play a role in broomrape parasitism; however, others have not confirmed this. Studies were conducted to investigate the possibility of interaction between Orobanche spp. attack and Rhizobium nodulation in legumes. Seed germination, number of parasitic attachments, as well as the morphology of two broomrape species, small broomrape (Orobanche minor Sm.) and Egyptian broomrape (Orobanche aegyptiaca Pers.), were studied. O. minor showed a greater percent seed germination, and formed a greater number of attachments on red clover (Trifolium pratense L.) inoculated with Rhizobium leguminosarum bv. trifolii in comparison with non-inoculated plants. However, the addition of the inoculum did not appear to enhance O. aegyptiaca seed germination or the number of its attachments on the host roots compared with the controls. Morphological observations of O. minor attachments on red clover suggest that parasitic attachments were not situated over the bacterial nodules, but perhaps involve parasite-induced enzymatic degradation followed by mechanical protrusion of host plant root cortex, possibly utilizing host plant-rhizobacteria interactions as well.
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    Environmental influence on postemergence chemical control of crabgrass (Digitaria spp.) in turf
    Chism, William John (Virginia Tech, 1990-05-16)
    The influence of environment on efficacy of postemergence herbicides was quantified. A three-fold approach included: first, use of field test sites to select an herbicide sensitive to environmental conditions; second, quantify herbicide responses to temperature, moisture, and morphological conditions; and third, conduct laboratory research to determine if differential uptake, translocation, or metabolism would account for these responses to the environment. Section one of the research was designed to determine if field research can be used to detect herbicides sensitive to environmental influences. Herbicides compared were: imazaquin, BAS 514 and tridiphane to fenoxaprop-ethyl (the cool-season herbicide standard) for postemergence control of large crabgrass (Digitaria sanguinalis) in Kentucky bluegrass (Poa pratensis) and bermudagrass (Cynodon dactylon) turf. BAS 514 was significantly influenced by variable environment. Section two of the research studied control of southern crabgrass (Digitaria ciliaris) by BAS 514 as influenced by morphological and physiological factors. BAS 514 efficacy was influenced by crabgrass growth stage, air temperature, and irrigation level. Flowering crabgrass plants were the most tolerant, while preemergence and true-leaf stages were the most sensitive. Plants held at soil moisture levels near saturation and 25° C were the most sensitive to BAS 514. BAS 514 was not effective against plants grown at low moisture levels and 15° or 35° C. Section three of the research compared the uptake, distribution, and metabolism of ¹⁴C BAS 514 in southern crabgrass and Kentucky bluegrass plants, a sensitive and non-sensitive species. Foliar applied BAS 514 was rapidly absorbed by both species. Uptake and partitioning was similar in both species from 0.5 to 32 h, but different at 128 h, with bluegrass more uniformly distributing the herbicide. Metabolism of BAS 514 was low with only 3% metabolism in both species. Uptake, distribution, and metabolism apparently are not involved in differential sensitivity to BAS 514. Field research can be used to select an herbicide sensitive to environmental influences. Temperature and soil moisture influenced the herbicidal activity of BAS 514. Uptake, translocation and metabolism did not appear to influence selectivity of this herbicide.
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    Evaluation And Characterization of Herbicide Resistance In Italian Ryegrass (Lolium multiflorum Lam.) Biotypes To Diclofop-methyl And Alternative Management Options
    Morozov, Ivan Vladimirovitch (Virginia Tech, 2004-03-29)
    Italian ryegrass (Lolium multiflorum Lam.) is a competitive weed in small grain production areas throughout the northwestern and southeastern US. In small grains, Italian ryegrass has generally been controlled with postemergence treatments of diclofop, or diclofop-methyl, a member of the subfamily of the aromatic carboxylic acid family, the aryloxyphenoxypropionates. The first incidence of diclofop resistance in Italian ryegrass was reported in Virginia in 1995. Experiments to characterize diclofop resistance in several Virginia biotypes of Italian ryegrass included the following objectives: (1) evaluation of the presence of diclofop resistance in several Italian ryegrass biotypes collected across Virginia, (2) evaluation of alternative herbicide efficacy for diclofop resistant Italian ryegrass control, and (3) characterization of the aryloxyphenoxypropionate (APP) resistance mechanism in resistant Italian ryegrass biotypes. The response of 32 biotypes to diclofop collected from various locations statewide with varying histories of diclofop applications confirmed diclofop resistance in Virginian Italian ryegrass populations. At 4-times the label-recommended application rate, only 50% of biotypes previously exposed to diclofop in a cropping situation were adequately controlled versus 94% of the biotypes not previously treated with diclofop. Tralkoxydim provided the most effective control of four of the biotypes. No postemergence treatment effectively controlled one biotype previously exposed to diclofop applications. Effective preemergence herbicide treatments for Italian ryegrass control in the greenhouse included acetochlor (two formulations) and flufenacet plus metribuzin. In the field, flufenacet plus metribuzin resulted in excellent Italian ryegrass control, little crop injury, and acceptable barley yields. Acetyl-coenzyme A carboxylase (ACCase) assays and herbicide absorption, translocation, and metabolism studies were conducted to investigate resistant mechanism(s) to two APP herbicides, diclofop and quizalofop. ACCase assays indicated no differences in enzyme activity between the two biotypes of Italian ryegrass evaluated. Furthermore, no significant differences in the specific activity of ACCase were detected between the two biotypes in the absence of diclofop. [14C]Quizalofop-P absorption, translocation, and metabolism did not differ between resistant and susceptible Italian ryegrass biotypes. Lack of a significant biotype effect suggests that differential metabolism does not explain the differential response to diclofop treatments observed in the herbicide dose-plant response experiment.
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    Evaluation of novel techniques to establish and transition overseeded grasses on bermudagrass sports turf
    Mittlesteadt, Tyler Lee (Virginia Tech, 2009-04-29)
    Most professional turf in Virginia is comprised of bermudagrass (Cynodon dactylon L.) or (Cynodon dactylon x C. transvaalensis Burtt Davy) as a monoculture in summer and overseeded with perennial ryegrass (Lolium perenne L.) (PR) in winter, during bermudagrass dormancy. Two transitions are required in an overseeding program, fall establishment of PR and spring control of PR. During each transition, turf quality suffers as one grass dies or enters dormancy while another grass is promoted to fill voided areas. Field studies at various locations in Virginia were conducted to investigate methods of improving spring and fall transition. Bermudagrass green cover in August was influenced by duration of PR competition variably between three bermudagrass cultivars. For example, "Midiron", "Patriot", and "Riviera" bermudagrass required 218, 139, and 327 cumulative growing degree days at base 18.3 C (GDD) to reach 95% cover. Bermudagrass biomass was also positively correlated with increasing duration of noncompetitive GDD. Total nonstructural carbohydrates were not correlated to duration of PR competition. Novel application methods were invented and tested at Virginia Tech. Drip, sponge, and strip application methods were used to create patterns of PR control using selective herbicides. Controlling a portion of PR with these methods maintained acceptable turfgrass quality throughout the spring transition and improved bermudagrass cover 12 to 20%, speeding transition by 20 or more days. Efforts to improve PR establishment in dense bermudagrass suggest chemicals that injure existing bermudagrass can improve PR establishment, but cause unacceptable turf discoloration. Mechanical methods to disrupt the bermudagrass canopy had less effect on PR establishment than chemical treatments.
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    Evaluation of Weed Control and Crop Tolerance With Postemergence Herbicides in Sethoxydim-Tolerant Corn
    Ashley, James Elton Jr. (Virginia Tech, 1998-04-27)
    Field experiments were conducted in 1995, 1996, and 1997 at six locations to evaluate strategies for the use of sethoxydim-tolerant hybrids in Virginia corn production. The specific objectives of this research were to evaluate the effect of graminicides including clethodim, fluazifop-P, quizalofop-P, and sethoxydim, and method of application, on crop tolerance and bermudagrass (Cynodon dactylon L.) control; to evaluate the effect of sethoxydim in combination with broadleaf herbicides on crop tolerance and bermudagrass control; to evaluate sethoxydim-based herbicide programs for annual grass and broadleaf weed control; and to determine the response of sethoxydim-tolerant corn hybrids to these graminicides in the absence of the competitive effects of weeds. All experiments were conducted using a randomized complete block design with four replications. Individual plots consisted of 4 corn rows 7.6 meters in length in which the two inner rows received treatment and the two outer rows served as borders. All applications were made with a CO2-pressurized backpack sprayer delivering 210 L/ha of water at 220 kPa using flat fan spray tips. The dependent variables evaluated included crop response to herbicide treatments, weed control by species, and corn yield. All data were subjected to analysis of variance and appropriate mean separation techniques at the 0.05 significance level. Excellent bermudagrass control was obtained from postemergence broadcast or postemergence directed applications of sethoxydim, fluazifop-P, quizalofop-P, clethodim, and fluazifop-P plus fenoxaprop. Broadcast applications of fluazifop-P and both broadcast and directed applications of clethodim caused significant crop injury, however. Combinations of sethoxydim with bentazon, bentazon plus atrazine, flumiclorac, and halosulfuron resulted in reduced bermudagrass control relative to that control afforded by sethoxydim alone. In experiments to evaluate control of annual species including smooth pigweed (Amaranthus hybridus L.), common lambsquarters (Chenopodium album L.), giant foxtail (Setaria faberi Herrm.), ivyleaf morningglory (Ipomoea hederaceae L. Jacq.), jimsonweed (Datura stramonium L.), large crabgrass (Digitaria sanguinalis L. Scop.), and a perennial, yellow nutsedge (Cyperus esculentus L.), excellent broad spectrum control was achieved with sethoxydim in combination with bentazon, bentazon plus atrazine, nicosulfuron, or primisulfuron. Crop tolerance to these treatments was excellent. In experiments to evaluate sethoxydim-tolerant hybrids and susceptibility to graminicides, no rate of sethoxydim caused significant injury to any hybrid tested. Tolerance of these hybrids to a 1X rate of quizalofop-P was also demonstrated, although 4X and 8X rates of fluazifop-P and quizalofop-P caused significant injury. Clethodim at all rates of application caused significant crop injury. Differential responses to graminicides among hybrids were noted.
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    Gray leaf spot of corn: yield loss and evaluation of germplasm for resistance
    Carter, Michele R. (Virginia Tech, 1992-06-06)
    Gray leaf spot (GLS) of corn (Zea mays L.), caused by the fungus Cercospora zeaemaydis (CZM) (Tehon and Daniels) has increased in incidence and severity with increasing use of no-tillage and continuous corn practices. This disease can be yield limiting. Corn hybrids were evaluated under natural disease pressure for three years (1989, 90, and 91) at two locations (Montgomery and Wythe Co., VA). Yield losses ranged from 2127.4 kg/ha (Wythe Co., 1991) to 4242.2 kg/ha (Wythe Co., 1990). It was estimated that 77% of the variability in yield was due to GLS. Fungicides were evaluated for the control of GLS over three years on a susceptible hybrid, Pioneer Brand 3320. All fungicides, with the exception of mancozeb, provided significant control over nontreated check in all years. Benomyl, propiconazole and terbutrazole were the most effective fungicides. As much as 93% of the variablilty in yield was attributed to blighting. Reduction in blighting also increased the kernel weight. The toxin, cercosporin, produced by CZM was evaluated for its ability to elicit differential responses in corn germplasm by three methods, ie., vein inoculation, root, and shoot uptake. No consistant differential reponses were found with vein inoculation, but 31-day old plants were significantly more sensitive to the toxin than 21-day old plants, as measured by lesion width. Root and shoot uptake of the toxin by inbred germplasm produced lesions that resembled those produced by CZM in the field. Microscopic, yellow fluorescing crystals were found associated with necrotic tissue from toxin-treated inbreds. Significantly more injury occurred to toxin-treated inbreds exposed to light than to darkness. By chromatographic analysis, 407.1-1076.7 ng of toxin/g of tissue was recovered from leaf lesion extracts of plants exposed to light. Five inbreds (B73, H99, Va59, NC250a, and NC264) showed consistent and differential responses to the toxin. H99 and NC250a showed differential responses to the same concentration of toxin, thus suggesting that some germplasm are more sensitive to the toxin than others. Tests using the toxin as a means to identify resistant germplasm did not provide reliable predictions of germplasm response to CZM in the field.
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    Growth Analyses and Patterns of Cross-Resistance in Four Imidazolinone-Resistant Smooth Pigweed (Amaranthus hybridus) Populations
    Poston, Daniel Hasford (Virginia Tech, 1999-09-28)
    Studies were conducted in 1996 through 1999 to: (1) evaluate the responses of one imidazolinone (IMI)-susceptible (S) and four -resistant (R1, R2, R3, and R4) smooth pigweed populations to various acetolactate synthase (ALS)-inhibiting herbicides, (2) determine the mechanism of resistance, and (3) evaluate the relative growth and competitiveness of each population. Field studies were conducted in 1996 near Marion, MD, in a field with a history of repeated imazaquin use. Smooth pigweed control with IMI herbicides was < 8 percent, but control with sulfonylurea (SU) herbicides ranged from 73 to 99 percent. Follow-up greenhouse studies were used to confirm IMI resistance in the Marion, MD smooth pigweed population (R4) as well as three others (R1, R2, and R3). R populations were 730- to 1350-fold more tolerant to imazethapyr than the S population. Based on resistance ratios, all R populations displayed low-level cross-resistance to chlorimuron and negative cross-resistance to thifensulfuron, pyrithiobac, and cloransulam-methyl with R2 being the most sensitive of the R populations to pyrithiobac and cloransulam-methyl. Absorption, translocation, and metabolism of ¹⁴C-cloransulam-methyl in S and R2 populations were generally similar. Three metabolites of cloransulam-methyl with ratio of front (Rf) values approximately 0.83, 0.65, and 0.45 were isolated. The metabolite with a 0.83 Rf value increased over time as the parent molecule decreased indicating that it plays a major role in cloransulam-methyl metabolism in smooth pigweed. The other metabolites did not change significantly over time and never represented more than 5 percent of the extracted radioactivity. The identity of these metabolites has not been determined. Using enzyme assays, it was determined that IMI resistance in R populations was due to an altered ALS that was no longer susceptible to inhibition by these herbicides. ALS from S, R1, and R2 populations responded similarly to chlorimuron and thifensulfuron, but reductions in enzyme activity by chlorimuron and thifensulfuron were significantly greater for R3 ALS than for S, R1 or R2 ALS. ALS from R2 and R3 was significantly more sensitive to inhibition by pyrithiobac compared to S ALS. Based on resistance ratios, R2 and R3 ALS were also more sensitive to inhibition by cloransulam-methyl than S ALS. Negative cross-resistance to thifensulfuron, pyrithiobac, and cloransulam-methyl in some R populations at the whole-plant level can be explained by increased sensitivity at the enzyme level. Under noncompetitive conditions in the greenhouse, S produced 17, 23, 25, and 44 percent more biomass than R1, R2, R3, and R4 populations, respectively. S plants were also taller than R plants 17 and 21 d after planting (DAP) and displayed a faster initial rate of leaf area increase compared to all R populations. The net assimilation rate of S was significantly higher than R2 and R3 populations 24 DAP. R3 and R4 populations had significantly less chlorophyll per g of plant tissue compared to S; therefore, reduced growth in some R populations compared to S may be linked to chlorosis that generally appears early in seedling development. Biomass production in the field under competitive conditions was similar for all populations using both monoculture and mixed populations. For this reason, the differences in growth observed in the greenhouse in the S population may not confer a competitive advantage over R populations in the field.
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    Herbicide-based Weed Management Systems for Potato (Solanum tuberosum) and Wheat (Triticum aestivum) and Growth and Reproductive Characteristics of Smooth Pigweed (Amaranthus hybridus)
    Bailey, William Anthony (Virginia Tech, 2002-08-09)
    Integrated weed management involves the utilization of weed biology principles to develop effective and economical control strategies. This research involved investigations of herbicide-based weed management programs in potato (Solanum tuberosum L.) and winter wheat (Triticum aestivum L.) as well as investigations of the biological characteristics of smooth pigweed (Amaranthus hybridus), a troublesome species in many crops. Sulfentrazone is an herbicide registered for use in soybean [Glycine max (L.) Merr.] and tobacco (Nicotiana tabacum L.) that may also have potential for use in potato. In field experiments, potato tolerance to preemergence (PRE) applications of sulfentrazone at rates up to 0.21 kg/ha was similar to that from the registered herbicides metribuzin, metolachlor, or metribuzin plus metolachlor PRE. Potato generally did not tolerate sulfentrazone applications to foliage. Sulfentrazone effectively controlled common lambsquarters (Chenopodium album L.) at rates as low as 0.11 kg/ha and also controlled several annual grasses at higher application rates, but was slightly less effective on jimsonweed (Datura stramonium L.) and ineffective on common ragweed (Ambrosia artemisiifolia L.). Potato tuber yield and grade from sulfentrazone PRE applications was similar to yield of potato treated with registered herbicides. Laboratory research was also conducted to determine the mechanism of sulfentrazone selectivity between potato (a tolerant species), common lambsquarters (a sensitive species), and jimsonweed (an intermediate species). After 48 h root exposure to [14C] sulfentrazone, absorption by common lambsquarters was nearly two-fold that of jimsonweed and three-fold that of potato. Both weed species also exhibited nearly a two-fold increase in sulfentrazone translocation from roots to shoots compared to potato. Since the site of action of sulfentrazone, protoporphyrinogen oxidase, is located in shoot tissue, translocation to shoots is essential for sulfentrazone toxicity. Therefore, the proposed primary mechanisms of selectivity between these species are differential root absorption and differential translocation. Experiments were also conducted to investigate the potential of the experimental herbicide AE F130060 03 for Italian ryegrass (Lolium multiflorum Lam.) control in winter wheat. In laboratory research, foliar absorption of AE F130060 03 in Italian ryegrass was at least three times that in wheat. Additionally, herbicide metabolism was greater in wheat, particularly in wheat treated with the herbicide safener AE F107892. In field experiments, AE F130060 03 was as effective as diclofop-methyl for control of diclofop-sensitive Italian ryegrass and more effective than diclofop-methyl and all other herbicides tested for control of diclofop-resistant Italian ryegrass. Although wheat injury from AE F130060 03 was greater than from other herbicides, wheat recovered and yields were not affected. Postemergence AE F130060 03 applications controlled Italian ryegrass from emergence until the end of tillering, but applications made to four- to five-tiller Italian ryegrass resulted in the least amount of new Italian ryegrass emergence following application. To further define the utility of AE F130060 03 in winter wheat, ten wheat cultivars adapted to Virginia were evaluated for tolerance to AE F130060 03. Biomass production between cultivars was not influenced by AE F130060 03 application in the greenhouse, although slight yield decreases due to herbicide application were found in FFR 518, Coker 9663, AgriPro Patton, and VA98W593 under weed-free conditions in the field. Greenhouse, growth chamber, and field experiments were also conducted to investigate growth and seed production of one imidazolinone-susceptible (S) and five -resistant (R1, R2, R3, R4, and R5) smooth pigweed biotypes. Although the S biotype produced more total biomass than four of the five R biotypes, R4 displayed a more rapid growth rate at 3 to 5 wk after planting and a faster germination rate than S and all other R biotypes. Seed production in R4 was similar to S and greater than in all other R biotypes. Early rapid growth in R4 did not translate into increased biomass accumulation compared to S at the conclusion of the experiments.
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    Impact of Sulfonylurea Herbicides on Seeded Bermudagrass Establishment and Cold Temperature Influence on Perennial Ryegrass Response to Foramsulfuron
    Willis, John Benjamin (Virginia Tech, 2008-10-31)
    Advancements in cold tolerance of seeded bermudagrass and introduction of sulfonylurea herbicides have given turf managers new tools. Seedling bermudagrass response to sulfonylurea herbicides applied before or soon after seeding has not been characterized. Field observations have indicated that variability exists among sulfonylurea herbicides used for perennial ryegrass control. Objectives of the conducted research were to evaluate sulfonylurea herbicides for safety and utility while establishing seeded bermudagrass, and to elucidate variability in perennial ryegrass control with foramsulfuron. Field experiments were conducted in Blacksburg, VA to assess turfgrass and smooth crabgrass response to flazasulfuron, foramsulfuron, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron-sodium, applied 1 and 3 weeks after and before seeding. Herbicides applied 3 weeks after seeding (WAS) were generally more injurious than when applied 1 WAS. Foramsulfuron, metsulfuron, and sulfosulfuron are safe to apply 1 and 3 WAS, causing no reduction in turf cover. Herbicides applied before or after seeding injured bermudagrass in the following order from most to least injurious: flazasulfuron = trifloxysulfuron > rimsulfuron > metsulfuron = sulfosulfuron > foramsulfuron. Flazasulfuron and trifloxysulfuron-sodium are not safe to use within 3 weeks of seeding, while foramsulfuron and metsulfuron can be used anytime before or after seeding bermudagrass. Flazasulfuron, foramsulfuron, and trifloxysulfuron-sodium were evaluated for perennial ryegrass control as affected by environment. Among environmental variables collected soil temperature averaged 7 DAT correlated best with perennial ryegrass response of the three tested products. Soil temperatures below 18 C perennial ryegrass reduced control 9 WAT from 78 to 31% for foramsulfuron while flazasulfuron and trifloxysulfuron-sodium efficacy were not significantly affected. Temperature dependence on perennial ryegrass control can be ranked from most to least as follows; foramsulfuron > trifloxysulfuron-sodium > flazasulfuron. Studies were conducted to determine absorption and translocation of 14C flazasulfuron when applied to perennial ryegrass roots or foliage. Roots treated with 14C flazasulfuron absorbed 41% of recovered 14C while 25% of 14C moved from treated roots to foliage. It appears root absorption is an important component of flazasulfuron efficacy since most of the absorbed 14C remained in treated leaves and root absorbed 14C moved rapidly to foliage.