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© 2007 Plant Management Network. Wild Oat (Avena fatua L.) Control With Reduced Rates Of Postemergence Herbicides Krishona B. Martinson, Assistant Extension Professor, Beverly R. Durgan, Professor, and Jochum J. Wiersma, Assistant Professor, University of Minnesota, St. Paul 55108 Corresponding author: Krishona B. Martinson. bjork026@umn.edu Martinson, K. B., Durgan, B. R., and Wiersma, J. J. 2007. Wild oat (Avena fatua L.) control with reduced rates of postemergence herbicides. Online. Crop Management doi:10.1094/CM-2007-0219-02-RS. Abstract Application rates of postemergence herbicides in wild oat infested spring wheat and barley were evaluated at Crookston, MN and Fargo, ND in 2002 and 2003 for weed control, crop injury, crop yield, and net economic return. Fenoxaprop, flucarbazone, clodinafop, tralkoxydim, and mesosulfuron were applied to 3 to 4 leaf wild oat at ½, ¾, and 1× labeled rates. Wild oat control, crop injury, crop and wild oat biomass, and grain yields were taken. Although there were differences between visible wild oat control, biomass reduction, crop yield, and net economic return (NET) of individual herbicide applications, reduced rates did not consistently result in less control or NET of wild oat compared to full rates. In some cases the ½× rate resulted in a greater NET compared to the ¾ and 1× rates. Introduction Wild oat (Avena fatua L.) is responsible for reductions in crop yield, increases in cleaning costs, and lowering of grain grade and quality (7). Weed surveys were conduced in 1978, 1979 (3), and 2000 (12) found that wild oat occurred in 66% of the surveyed fields in 1978, 60% in 1979, 32% in spring 2000, and 41% in summer 2000 (3,12). Zollinger et al. (12) concluded that lower occurrence of wild oat may be due to adequate control from several effective herbicides registered since 1979. Some herbicides are effective at controlling wild oat and preventing grain loss (1). Barton et al. (1) and Spandl et al. (8) observed that wild oat control increased as herbicide rate increased. Even though reduced herbicide rates decrease weed control, Spandl et al. (8) and Barton et al. (1) agree that reducing herbicide rates generally did not influence grain yields or net economic return. Stougaard et al. (9) found that excellent wild oat control was sometimes achieved with reduced herbicide rates, but there was no consistent relationship between wild oat growth stage and the level of control from a particular herbicide or rate applied. Reducing herbicide rates may be desirable, but the impacts on wild oat control, grain yield, and net economic return may be jeopardized. Thus, the objective of this study was to evaluate wild oat control with several new and recently introduced postemergence herbicides applied at 1×, ¾×, and ½× of labeled rates in hard red spring wheat and barley. Field Studies in Minnesota and North Dakota Field plots were established in 2002 and 2003 at Crookston, MN and Fargo, ND in areas managed for natural populations of wild oat. Average populations of wild oat were 748/m² at Crookson in 2002, 277/m² at Fargo in 2002, 1,376/m² at Crookston in 2003, and 751/m² at Fargo in 2003. The hard red spring wheat variety ‘2375’ and ‘Lacey’ barley, were seeded at 101 and 94 kg/ha, respectively, in 3- by 5-m plots at Crookston, MN. ‘Oxen’ hard red spring wheat was seeded at 101 kg/ha in 3- by 9-m plots at Fargo, ND; barley was not evaluated in Fargo. The experimental design was a randomized complete block with three replications at each location. Seeding, herbicide application, and evaluation dates are presented in Table 1. Table 1. Dates of field operation at Crookston and Fargo in 2002 and 2003.
x WIOA = Wild oat. Clodinafop, fenoxaprop, flucarbazone, tralkoxydim, and mesosulfuron were applied to 3 to 4 leaf wild oat at ½, ¾, and 1× of labeled rates. The 1× rates were fenoxaprop, 94 g a.i./ha; flucarbazone, 30 g a.i./ha; clodinafop, 56 g a.i./ha; tralkoxydim, 208 g a.i./ha; and mesosulfuron, 3 g a.i./ha. 2,4-D ester at 280 g a.i./ha and nonionic surfactant at 0.25% v/v were applied with flucarbazone, and Destiny methylated seed oil at 2,256 g/ha was applied with mesosulfuron. Clodinafop and tralkoxydim were applied with their pre-packaged adjuvants, DSV at 782 g/ha and Supercharge at 0.5% v/v, respectively. At the time of this study, the manufacturer of flucarbazone recommended applying 2,4-D ester with flucarabazone to increase crop safety. All treatments were applied with water at 94 liter/ha. A backpack sprayer with 11001 flat-fan nozzles and tips using 207 KPa of air pressure was used to apply all treatments. Nontreated plots were included for comparison. All plots were treated with bromoxynil at 280 g a.i./ha at the 2 to 3 leaf stage of wild oat to control broadleaf weeds. Wild oat control and crop injury were visually rated in comparison to the untreated plots at 7, 14, and 21 days after treatment (DAT) and heading, where 0% equaled no control or injury and 100% equaled complete wild oat control or crop death. Crop and wild oat biomass samples were taken after plants headed by clipping all plants from two 0.1-m² quadrats. Samples were then separated into crop and wild oat biomass samples and dried. Biomass dry weights were used to calculate the percent reduction in biomass from each treatment relative to the untreated control. Grain yields were determined by harvesting a 1.4- by 5-m strip through the center of the plot with a small plot combine. Grain was dried, and yields were adjusted to 13% moisture on a per-hectare basis. Herbicide costs used to calculate net economic return (NET) were based on 2003 prices (5). Costs of fenoxaprop, flucarbazone, clodinafop, tralkoxydim, and mesosulfuron were $34.25, $28.74, $32.32, $28.96, and $27.18/ha, respectively, for the 1× rate. Nonionic surfactant, crop oil concentrate (COC), 2,4-D Ester and Destiny were priced at $1.90, $2.37, $1.98, and $7.54/ha, respectively. A one-pass herbicide application fee of $12.35/ha was used for all herbicide treatments (6). Minnesota market prices in September of 2003 were $0.126/kg for wheat and $0.108/kg for barley, and were used to calculate NET. Net economic return was calculated using the following formula: NET = [(grain yield × crop market price) — (cost of herbicide program + herbicide application fee)] (8). No attempt was made to estimate dockage as a result of the presence of foreign material in the grain. Analysis of variance (ANOVA) was computed for all traits measured, assuming all effects, except replicates, as fixed. Means were separated using Fisher’s Protected LSD at the 5% level of significance. Herbicide Application Rate, Yield, and NET in Wheat Data were combined over years for each location as no year interaction and/or heterogeneity of error had been detected when combining the data. Wheat injury and wild oat control data presented in Table 2 represents ratings observed at wheat heading (21 to 36 days after treatment). Herbicide rate did not result in wheat injury at either location (Table 2). At Crookston, the highest level of visible wild oat control was 99% (clodinafop ½×) (Table 2). Treatments that did not differ from this value were flucarbazone at all rates, clodinafop ¾× and ½×, tralkoxydim ¾×, and mesosulfuron 1× and ½×. The lowest level of visible wild oat control was fenoxaprop ½×. Tralkoxydim ½× was the only treatment that did not differ from fenoxaprop ½× (Table 2). At Fargo, the highest level of visible wild oat control was 91% (clodinafop ½×) (Table 2). Treatments that did not differ from this value were fenoxaprop 1× and ½×, flucarbazone ¾× and ½×, clodinafop 1× and ¾×, and mesosulfuron ½×. The lowest level of visible wild oat control was 53% (tralkoxydim ½×). This treatment had less visible wild oat control than all other treatments. Table 2. Wheat injury, wild oat control, biomass reduction, grain yield and net economic return (NET) in wheat at Crookston, MN (CRK) and Fargo, ND (FRG).
x Wheat injury and wild oat control ratings observed at wheat heading (21 to 36 days after treatment). At Crookston, the highest level of wild oat biomass reduction was 100%, (clodinafop ¾×, tralkoxydim 1×, mesosulfuron 1×) (Table 2). Treatments that did not differ from this value were all rates of flucarbazone, clodinafop ½×, tralkoxydim ½×, and mesosulfuron ¾× and ½×. The lowest level of wild oat biomass reduction was 78% (fenoxaprop 1×). Treatments that did not differ from this value were fenoxaprop ½× and tralkoxydim ¾×. At Fargo, the highest level of wild oat biomass reduction was 96% (tralkoxydim 1× and ¾×) (Table 2). Treatments that did not differ from this value were fenoxaprop 1×, flucarbazone 1×, and all rates of clodinafop. The lowest level of wild oat biomass reduction was 60% (tralkoxydim ½×). The only other treatment that did not differ from this value was fenoxaprop ½×. At Crookston, the highest wheat yield was 3,800 kg/ha (clodinafop 1×) (Table 2). Treatments that did not differ from this value were flucarbazone 1×, clodinafop ¾× and ½×, tralkoxydim 1×, and mesosulfuron ½×. The lowest wheat yield was 3,300 kg/ha (fenoxaprop ½×, flucarbazone ¾×, tralkoxydim ¾×). Treatments that did not differ from this value were fenoxaprop 1× and ¾×, flucarbazone ½×, tralkoxydim ½×, and mesosulfuron 1× and ¾×. At Fargo, the highest wheat yield was 1,600 kg/ha (fenoxaprop ½×). This was the only treatment greater than the untreated wheat yield of 1,300 kg/ha (Table 2). All other treatments were not different from the untreated wheat yield and ranged from 1,200 to 1,500 kg/ha . At Crookston, the highest NET was $444/ha (clodinafop ½×) (Table 2). Treatments that did not differ from this value were clodinafop ¾× and ½×, tralkoxydim 1×, and mesosulfuron ½×. The NET was $379/ha (flucarbazone ¾×), and treatments that did not differ from this value were all rates of fenoxaprop, tralkoxydim ¾×, and mesosulfuron 1× and ¾×. All treatment NETs were greater than the untreated, indicating that the use of a herbicide at any rate was more profitable than not using a herbicide at all. At Fargo, the highest NET was $168/ha (fenoxaprop ½×) (Table 2). However, the untreated NET was not different from this treatment, or flucarbazone 1× and ¾×, clodinafop ¾× and ½×, tralkoxydim ¾×, and mesosulfuron ½×. In some cases, applying a herbicide (fenoxaprop 1× and ¾×, flucarbazone ½×, clodinafop 1×, and mesosulfuron ¾×) resulted in less NET than applying no herbicide at all. The reduced rates of clodinafop (¾× and ½×) were the only herbicide treatments to provide significant, consistent control of wild oat, wheat yield, and NET across locations. Herbicide Application Rate, Yield, and NET in Barley Barley was evaluated only in Crookston in 2002 and 2003. Barley injury and wild oat control data presented in Table 3 represents ratings observed at barley heading (21 to 36 days after treatment). Barley injury, wild oat biomass reduction, barley yield, and NET were combined over years. However, wild oat control data were not combined due to a year interaction and will be presented separately for 2002 and 2003 (Table 3). Table 3. Barley injury, wild oat control and biomass reduction, grain yield, and NET at Crookston, MN combined over 2002 and 2003
x Control data presented separately for each year due to a year × treatment interaction. y Barley injury and wild oat control ratings observed at barley heading (21 to 36 days after treatment). Although minor (<5%), visible barley injury occurred with flucarbazone 1×, and mesosulfuron 1× and ½×, as well as all rates of clodinafop and tralkoxydim (Table 3). All other treatments resulted in no visible barley injury compared to the untreated control. Some level of barley injury was expected, since flucarbazone, clodinafop, and mesosulfuron are not labeled for application in barley. However, minor injury occurred with both labeled and non-labeled herbicides. In 2002, the highest level of wild oat visible control was 99% (clodinafop 1×) (Table 3). Treatments that did not differ from this value were fenoxaprop 1×, flucarbazone ¾×, all rates of clodinafop, and tralkoxydim ¾×. The lowest level of wild oat visible control was 74% (fenoxaprop ½×). Treatments not differing from this value were fenoxaprop ¾×, mesosulfuron ¾×, and tralkoxydim ½×. In 2003, all treatments provided either 98 or 99% visible wild oat control. Several herbicide treatments gave 99 to 100% wild oat biomass reduction (Table 3). The lowest level of wild oat biomass reduction was 82% (fenoxaprop ½×). The only treatment that did not differ from this value was clodinafop ½×. The highest barley yield was 3,800 kg/ha (flucarbazone ¾×) (Table 3). Treatments that did not differ from this value were fenoxaprop ½×, and flucarbazone 1×. The lowest barley yield was 3,100 kg/ha (clodinafop ¾× and ½×, and tralkoxydim ¾×). The highest NET was $365/ha (fenoxaprop ½×), while the lowest NET was $286/ha (clodinafop 1×) (Table 3). However, neither NET was different from the untreated control ($316/ha), indicating that not applying a herbicide was as profitable as applying any rate of the herbicides investigated. Barton et al. (1) found barley net return was greatest when half or full herbicide rates were applied to 290 wild oat plants/m², and that net return increased as wild oat populations increased. In our studies, average populations of wild oat ranged from 748 to 1,376/m², significantly higher than the wild oat density investigated by Barton et al. (1). There was no difference in NET based on years (i.e., different wild oat densities) in our study, however different densities were not necessarily evaluated. No herbicide (labeled or non-labeled for barley) provided significant, consistent control of wild oat, barley yield, and NET across years. Reduced Rates Can Be Profitable Reduced rates were generally as profitable, or more profitable, than 1× rates of the herbicides investigated. These results agree with Barton et al. (1), who found that NET was greater for ½× rates than 1× rates or the untreated control. However, our results indicated that not applying a herbicide can sometimes result in a higher NET, as was the case for barley and wheat at Fargo. These results also agree with Stougaard et al. (9) who found that excellent wild oat control was sometimes achieved with reduced rates, but there was no consistent relationship between wild oat growth stage and the level of control from a particular herbicide or rate applied. These results are contrary to Spandl et al. (8) who stated that grain yields and net economic return were generally greater in herbicide treated plots than in the untreated control. Another potential benefit of using reduced herbicide rates is the possibility of reduced selection pressure and decreased incidence of herbicide-resistant weeds. Beckie and Kirkland (2) found that the percentage of resistant individuals in a population is directly proportional to selection pressure or effective kill after multiple herbicide applications. However, this study found reduced herbicide rates did not always result in less effective kill (i.e., control). In fact, the reduced rates of clodinafop were the only herbicide treatments that provided significantly high control of wild oat in wheat across locations. Drawback to Reduced Wild Oat Control There are drawbacks to reduced wild oat control, whether from reduced rates, ineffective full rate applications, unfavorable weather conditions, and/or poor crop stands. Less control of wild oat may lead to greater seed production and weed seed density in the soil in subsequent years (11). As a result, competition between future small grain crops and wild oat may be greater, potentially resulting in yield loss and reduced NET. Although we did not count number of seeds or measure seed returned to the soil, uncontrolled wild oats did produce seed and potentially returned seeds to the soil. Wille and Thill (11) concluded that the advantage of using reduced rates may diminish if the wild oat seed bank is allowed to increase in subsequent years. Stougaard et al. (9) suggests, and we agree, that there is a risk in recommending early applications (i.e., before a majority of the wild oat has emerged) of reduced rates until the interaction among wild oat growth stage, emergence patterns, and environment can be more completely understood. Wild oat that emerge after the herbicide application, and remain uncontrolled, may cause a reduction in yield and increase the soil seed bank. Conclusion The reduced rates of clodinafop (¾× and ½×) were the only herbicide treatment to provide statistical, consistent control of wild oat, wheat yield, and NET across locations. There was not a consistent relationship or pattern of wild oat control from a particular herbicide or rate investigated in barley. Although there were differences between visible wild oat control, biomass reduction, crop yield, and NET of individual herbicide applications, reduced rates did not consistently give less control of wild oat or NET compared to full rates. In some cases the ½× rate actually resulted in a greater NET and wild oat control compared to the ¾ and 1× rates. In wheat at Crookston, all treatment NETs were greater than the untreated check, indicating that the use of an herbicide at any rate was more profitable than not using an herbicide at all. However, in barley, NET from all treated plots were not different from the untreated control, indicating that not applying an herbicide was as profitable as applying any rate of the herbicides investigated. This probably reflects the greater competitive ability of barley against weeds compared to that of wheat (4). Whether using full or reduced rates, herbicides should be considered as just one component of an integrated weed management system (10). Various cultural practices including spring and fall cultivation (1), crop rotation, increasing crop seeding rates(1), herbicide rotation, delayed seeding, and fallow are strategies that can be used in combination with reduced herbicide rates to effectively control wild oat. Acknowledgments The authors acknowledge Jim Cameron and Mark Ciernia for technical assistance, Drs. Kirk Howatt and George Kegode for academic support, and the Minnesota Wheat Growers for partial funding of the project. Literature Cited 1. Barton, D. L., Thill, D. C., and Shafii, B. 1992. Integrated wild oat (Avena fatua) management affects spring barley (Hordeum vulgare) yield and economics. Weed Technol. 6:129-135. 2. Beckie, H. J., and Kirkland, K. J. 2003. Implication of reduce herbicide rates on resistance enrichment in wild oat (Avena fatua). Weed Technol. 17:138-148. 3. Behrens, R., and Strand, O. E. 1979. Survey of wild oat and other weeds in small grains in Minnesota. Univ. of Minn. Ext. Serv., St. Paul, MN. 4. Dew, D. A. 1972. An index of competition for estimating crop loss due to weeds. Can. J. Plant Sci. 52:921-927 5. Durgan, B. R., Gunsolus, J. L., Becker, R. L., and Dexter, A. G. 2003. Cultural and Chemical Weed Control in Field Crops. Univ. of Minn. Ext. Serv. Bull. BU-3157-F., St. Paul, MN. 7. Sharma, M. P., and Vanden Born, W. H. 1978. The biology of Canadian weeds. 27. Avena fatua L. Can. J. Plant Sci. 58:141-157. 8. Spandl, E., Durgan, B. R., and Miller, D. W. 1997. Wild oat (Avena fatua) control in spring wheat (Triticum aestivum) and barley (Hordeum vulgare) with reduced rates of postemergence herbicides. Weed Technol. 11:591-597. 9. Stougaard, R. N., Maxwell, B. D., and Harris, J. D. 1997. Influence of application timing on the efficacy of reduced rate postemergence herbicides for wild oat (Avena fatua) control in spring barley (Hordeum vulgare). Weed Tech. 11:283-289. 10. Thill, D. C., O’Donovan, J. T., and Mallory-Smith, C. A. 1994. Integrated weed management strategies for delaying herbicide resistance in wild oats. Phytoprotection (Suppl.) 75:61-70. 11. Wille, M. J., and Thill, D. C. 1997. Wild oat (Avena fatua) density and imazamethabenz dose affects wild oat seed production. Weed Sci. Soc. of Am. Abstr. 37:12. 12. Zollinger, R. K., Ries, J. L., and Hammond, J. J. 2003. Survey of Weeds in North Dakota. N. Dak. Ext. Serv. Publ. ER-83. Fargo, ND. |
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