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© 2007 Plant Management Network.
Accepted for publication 2 October 2007. Published 5 October 2007.

Influence of Selected Pasture Herbicides and Application Timings on Sericea Lespedeza Control

Kevin Bradley, Assistant Professor, Division of Plant Sciences, University of Missouri, Columbia 65211; and Robert A. Masters, Rangeland Scientist, Dow AgroSciences, Indianapolis, IN 46205

Corresponding author: Kevin Bradley. bradleyke@missouri.edu

Bradley, K., and Masters, R. A. 2007. Influence of selected pasture herbicides and application timings on sericea lespedeza control. Online. Forage and Grazinglands doi:10.1094/FG-2007-1005-01-RS.

Abstract

Field trials were conducted in 2004 and 2005 to determine the effect of various herbicides alone or in pre-mix formulations applied in the summer and autumn on sericea lespedeza [Lespedeza cuneata (Dumont) G. Don] control and density one year after treatment (YAT). In both years, triclopyr plus fluroxypyr, picloram plus fluroxypyr, and metsulfuron were applied at five application timings. In 2005, triclopyr was also applied at each of these timings. In both years, all treatments provided greater than 90% late-season sericea lespedeza control when applied at the early- or mid-vegetative stage of growth. All treatments except metsulfuron also provided greater than 80% late-season sericea control when applied at the late-vegetative or pre-bloom stage. There was no effect of application timing on sericea lespedeza stem density 1 YAT. Herbicide treatments reduced sericea lespedeza stem density from 53 to 86% when compared to non-treated control plots 1 YAT. Triclopyr, triclopyr plus fluroxypyr and metsulfuron provided similar reductions in sericea lespedeza stem density 1 YAT. These results indicate that, regardless of the application timing, similar sericea lespedeza control will be achieved 1 YAT with triclopyr, triclopyr plus fluroxypyr, and metsulfuron, which is contrary to current recommendations for this species.

Introduction

Sericea lespedeza (Lespedeza cuneata L.) is a perennial herbaceous legume native to eastern Asia. Sericea lespedeza was introduced into the United States in the late 1890s as a forage, and was also planted for erosion control on roadsides, strip mines, and rights-of-way (3,4,9). Since that time, sericea lespedeza has become a serious problem weed in pastures, hay fields, conservation reserve areas, roadsides, and rights-of-way. Sericea lespedeza has been designated as a noxious weed in Kansas and Colorado and is currently being considered for addition to the noxious weed list in Missouri.

Several factors contribute to the invasiveness of sericea lespedeza. First, many researchers have found that sericea lespedeza is poorly suited as a forage because plants quickly become unpalatable with maturity (5,10,13). Stitt (13) found that tannin levels in sericea lespedeza increased from 6 to 21% as height increased from 10 to 90 cm. For this reason, cattle only graze more palatable newly-emerged sericea lespedeza. In most instances, cattle will not graze the more mature stems later in the summer that ultimately will flower and produce seeds that shatter and contribute to ever increasing number of seeds in the soil seedbank. Sericea lespedeza is also a prolific seed producer. Guernsey (4) found that established plants can produce as much as 670 kg of seed per hectare annually while other authors have found that plants commonly produce about 1,000 seeds per stem (11).

Another factor that contributes to the competitiveness and spread of sericea lespedeza is its allelopathic properties. Kalburtji and Mosjidis (7) found that residues of sericea lespedeza plants reduced the germination, emergence, seedling growth, and biomass of rye (Secale cereale L.) and tall fescue (Festuca arundinacea Schreb.). Similarly, bermudagrass [Cynodon dactylon (L.) Pers.] biomass was reduced by as much as 17% when sericea lespedeza residue was added to the soil (6).

Based on research conducted in tallgrass prairies of Oklahoma and Kansas, two strategies are currently recommended for the control of sericea lespedeza with herbicides (1,8,11). First, good control has been achieved with applications of triclopyr [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid] when applied to vegetative sericea lespedeza in June or July. Second, good control also has been observed with applications of metsulfuron [2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] amino]sulfonyl]benzoic acid] applied to sericea lespedeza at early bud to bloom growth stages, which typically occurs in September or October. Since the time of these earlier experiments, however, several new prepackaged herbicide mixtures have been introduced onto the marketplace. Two of the most recent are triclopyr plus fluroxypyr [[(4-amino-3,5-dichloro-6-fluoro-2-pyridinyl)oxy]acetic acid], sold under the trade name PastureGard, and picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) plus fluroxypyr, sold as Surmount. Previous research has revealed that fluroxypyr also provides good control of sericea lespedeza (8), but little to no research has been conducted with these new fluroxypyr-containing prepackaged combinations. The objectives of this research were to evaluate short- and longer-term sericea lespedeza control in response to several application timings of triclopyr plus fluroxypyr, picloram plus fluroxypyr, triclopyr, and metsulfuron.

Materials and Methods

Separate field experiments were conducted in central Missouri at the Prairie Fork Conservation Area located in Calloway County, Missouri during the 2004 and 2005 growing seasons. Each year, field trials were established in conservation reserve areas that contained heavy infestations of sericea lespedeza. Tall fescue was the dominant grass in both experiments. The soil type at both locations in both years was an Armster cobbly loam (fine, smectic, mesic Mollic Hapludalfs).

All herbicide treatments (Table 1) were applied at 5 km/h with a hand-held CO₂-pressurized research backpack sprayer containing 8002 flat fan nozzle tips (Spraying Systems Co,. Wheaton, IL) that delivered 140 liter/ha. All treatments were applied at five distinct application timings; to early-, mid-, and late-vegetative stages during the summer, and to pre-bloom and full-bloom stages in the late summer and early fall. The average size and density of sericea lespedeza at the time of each application is recorded in Table 2. The average monthly temperature and total monthly precipitation for each sericea lespedeza growing season from 2004 to 2006 is recorded in Table 3.

Table 1. Pasture herbicides evaluated in the 2004 and 2005 experiments for the control of sericea lespedeza.

 ^x aAll treatments applied with a non-ionic surfactant at 0.25% v/v.

Table 2. Dates of herbicide applications and average sericea lespedeza height and stem density at each application date in experiments initiated in 2004 and 2005.

Table 3. Average monthly temperature and total monthly precipitation at each site from May through October during 2004, 2005, and 2006.

Treatments were arranged in a randomized complete block design and were replicated four times in the 2004 experiments and 3 times in the 2005 experiments. Individual plots were 3 by 5 m in size in 2004 and 3 by 12 m in 2005. Late-season sericea lespedeza visual control ratings and tall fescue injury ratings were taken each year at a time that corresponded to one month after the last herbicide application timing. Visual control ratings were based on a scale of 0 to 100, with 0 equal to the vigor and sericea lespedeza ground cover observed in the untreated control plots or no tall fescue injury and 100 equal to complete sericea lespedeza control or complete tall fescue death. Visual ratings of sericea lespedeza control were made during the season of treatment. To evaluate longer term control, sericea lespedeza stem densities were measured about one year after the last application timing (YAT). In each experiment, the total number of sericea lespedeza stems in two randomly selected 1-m² areas within each plot were counted and averaged to provide the mean density of sericea lespedeza stems per square meter.

All data were analyzed using the generalized linear model procedure in SAS (Version 8, SAS Institute Inc., Cary, NC) and means were separated with Fisher’s protected LSD at the 5% level. There was a significant treatment by year interaction for the within-season visual ratings and 1 YAT stem density; therefore, all results are presented separately by year. Additionally, there was a significant treatment by application timing interaction for the within-season visual ratings, but not for the 1 YAT sericea lespedeza stem density data. Therefore, all late-season treatment and timing combinations are presented, but 1 YAT density counts were averaged across application timings.

Tall Fescue Injury

Metsulfuron was the only treatment that resulted in any visual tall fescue injury in either year (data not shown). Regardless of application timing, metsulfuron caused no more than 15% visual tall fescue injury, which was usually in the form of stunting and/or seedhead suppression. Tall fescue that received early season applications of metsulfuron had fully recovered by the time of the within-season ratings. Other researchers have observed similar responses of tall fescue to metsulfuron (12). Metsulfuron has even been used to selectively control tall fescue in some types of turf (2).

Within-Season Sericea Lespedeza Control

In both years, greater than 93% within-season sericea lespedeza control was observed with either rate of triclopyr plus fluroxypyr when applied at the early-, mid-, or late-vegetative stages (Tables 4 and 5). Pre-bloom and full bloom stage applications of triclopyr plus fluroxypyr at 0.38 plus 0.13 lb/acre provided similar within-season control of sericea lespedeza as vegetative stage applications. Although little information has been published on this new prepackaged herbicide mixture, these results are contrary to previous research and current recommendations for sericea lespedeza control with triclopyr alone (8,11). Within-season sericea lespedeza control was more variable and did decrease with pre-bloom and full bloom stage applications of triclopyr plus fluroxypyr at the lower rate.

Table 4. Influence of herbicides and application timings on within-season sericea lespedeza control in the 2004 field experiment.

 ^x All treatments applied with a non-ionic surfactant at 0.25% v/v.

 ^y Means followed by the same letter are not significantly different, LSD = 0.05. LSD applies to all treatment by timing comparisons. Untreated controls not included in analysis.

Table 5. Influence of herbicides and application timings on within-season sericea lespedeza control in the 2005 field experiment.

 ^x All treatments applied with a non-ionic surfactant at 0.25% v/v.

 ^y Means followed by the same letter are not significantly different, LSD = 0.05. LSD applies to all treatment by timing comparisons. Untreated controls not included in analysis.

Although triclopyr alone was not evaluated in the 2004 experiment, greater than 90% within-season sericea lespedeza control was achieved with triclopyr in 2005, regardless of application timing. Control was slightly reduced with the pre-bloom stage applications. Excellent sericea lespedeza control with vegetative stage applications of triclopyr has also been reported by Altom et al. (1) and Koger et al. (8).

Vegetative stage applications of picloram plus fluroxypyr provided excellent within-season control of sericea lespedeza, but control generally decreased with pre-bloom or full bloom stage applications (Tables 4 and 5). Previous research indicates that 0.25 lb ai/acre picloram or less will provide poor control of sericea lespedeza (1); therefore, the results from this research indicate that the fluroxypyr component of this prepackaged mixture contributes much to the level of sericea lespedeza control achieved.

A similar, and even more dramatic response to application timing was observed with metsulfuron (Tables 4 and 5). In both years, metsulfuron provided greater than 90% sericea lespedeza control when applied at early- and mid-vegetative growth stages, but control decreased as the season progressed. Metsulfuron provided lower within-season sericea lespedeza control than other herbicide treatments when applied in the pre-bloom or full bloom stage of growth. These results are contrary to current application timing recommendations for sericea lespedeza control with metsulfuron and results from previous research (8,11). However, the lack of sericea lespedeza control with bloom stage applications of metsulfuron is most likely a reflection of the slow-acting nature of metsulfuron in comparison to the other herbicides evaluated. This became evident when 1 YAT sericea lespedeza stem density was measured in metsulfuron treated plots compared to plots treated with triclopyr and fluroxypyr (Table 6).

Table 6. Influence of herbicide treatments on sericea lespedeza stem density one year after treatment (YAT) in experiments initiated in 2004 and 2005.

 ^x All treatments applied with a non-ionic surfactant at 0.25% v/v.

 ^y Means followed by the same letter are not significantly different, LSD < 0.05.

Sericea Lespedeza Density One Year After Treatment

There was no effect of application timing on sericea lespedeza stem density 1 YAT; therefore all density counts were averaged across timings to display significant differences between herbicide treatments. In both years, all treatments reduced sericea lespedeza stem density 1 YAT compared to the untreated control (Table 6). In both years, similar sericea lespedeza stem densities were observed 1 YAT with applications of triclopyr plus fluroxypyr at 0.28 plus 0.09 lb/acre and 0.38 plus 0.13 lb/acre and also with metsulfuron at 0.015 lb/acre. In 2005 when triclopyr was included in the experiment, this treatment also provided similar sericea lespedeza stem densities as both rates of triclopyr plus fluroxypyr and metsulfuron. Picloram plus fluroxypyr resulted in higher densities of sericea lespedeza 1 YAT than any of the other treatments evaluated.

On a percentage basis, triclopyr plus fluroxypyr at 0.28 plus 0.09 lb/acre provided 62 to 76% sericea lespedeza stem reduction 1 YAT, whereas triclopyr plus fluroxypyr at 0.38 plus 0.13 lb/acre, picloram plus fluroxypyr at 0.17 plus 0.17 lb/acre, metsulfuron at 0.015 lb/acre, and triclopyr at 0.75 lb/acre provided a 73 to 86%, 53 to 67%, 71 to 74 %, and 71% stem reduction 1 YAT, respectively. These results are similar to those reported by Altom et al. (1) and Koger et al. (8), who observed the most consistent sericea lespedeza control 1 YAT with applications of triclopyr, but slightly lower and more variable control with metsulfuron. Additionally, Altom et al. (1) observed 0 to 74% sericea lespedeza stem reduction 1 YAT with applications of picloram at 0.25 lb/acre, which is consistent with the lower levels of sericea lespedeza control observed in these experiments with the picloram plus fluroxypyr prepackaged mixture.

Conclusions

The results from these experiments indicate that the triclopyr plus fluroxypyr prepackaged herbicide mixture provided as good or better within-season sericea lespedeza control and stem density reduction 1 YAT than metsulfuron or triclopyr, which are the herbicides currently recommended for sericea lespedeza control in most regions. Conversely, the results from these experiments also indicate that the picloram plus fluroxypyr prepackaged mixture will not provide as good of sericea lespedeza control 1 YAT as triclopyr plus fluroxypyr, metsulfuron, or triclopyr, but that similar levels of sericea lespedeza control will be achieved with this prepackaged combination during the season of treatment. Lastly, the results from these experiments indicate that similar longer-term sericea lespedeza control will be achieved with triclopyr, triclopyr plus fluroxypyr, and metsulfuron, regardless of the timing of application. This is contrary to current recommendations pertaining to the optimum timing of metsulfuron and triclopyr applications and will allow producers and land managers more flexibility in the management of sericea lespedeza infestations. As triclopyr, triclopyr plus fluroxypyr, and metsulfuron each control a different spectrum of weed species, the presence of other weed species and the cost of these herbicides should be considered before selecting a treatment for the control of sericea lespedeza.

Literature Cited

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2. Dernoeden, P. H. 1990. Comparison of three herbicides for selective tall fescue control in Kentucky bluegrass. Agron. J. 82:278-282.

3. Donnelly, E. D. 1954. Some factors that affect palatability in sericea lespedeza (Lespedeza cuneata). Agron. J. 46:96-97.

4. Guernsey, W. J. 1970. Sericea lespedeza, its use and management. U. S. Dep. Agric. Farmers Bull. 2245:1-29.

5. Hawkins, G. E. 1955. Consumption and digestibility of lespedeza sericea hay and alfalfa hay plus gallotannin. J. Dairy Sci. 38:237-243.

6. Kalburtji, K. L., and Mosjidis, J. A. 1993. Effects of sericea lespedeza root exudates on some perennial grasses. J. Range Manage. 46:312-315.

7. Kalburtji, K. L., and Mosjidis, J. A. 1993. Effects of sericea lespedeza residues on cool-season grasses. J. Range Manage. 46:315-319.

8. Koger, C. H., Stritzke, J. F., and Cummings, D. C. 2002. Control of sericea lespedeza (Lespedeza cuneata) with triclopyr, fluroxypyr, and metsulfuron. Weed Technol. 16:893-900.

9. Lynd, J. Q., and Ansman, T. R. 1993. Symbiotic tripartite nitrogen fixation effectual in eroded soil restoration with 20 year-age sericea lespedeza. J. Plant Nutr. 16:149-164.

10. McGraw, R. L., and Hoveland, C. S. 1995. The Lespedezas. Pages 266-271 in: Forages, 5th Ed. R. F. Barnes, D. A. Miller, and C. J. Nelson, eds. Iowa State Univ. Press, Ames, IA.

11. Ohlenbusch, P. D., and Bidwell, T. 2001. Sericea lespedeza: History, characteristics, and identification. Agric. Exp. Sta. and Coop. Ext. Serv. Pub. MF-2408, Kansas State Univ., Manhattan, KS.

12. Peters, T. J., Moomaw, R. S., and Martin, A. R. 1989. Herbicides for postemergence control of annual grass weeds in seedling forage grasses. Weed Sci. 37:375-379.

13. Stitt, R. E. 1943. Variation in tannin content of clonal and open-pollinated lines of perennial lespedezas. Am. Soc. Agron. J. 38:1-5.