Sainfoin has Natural Tolerance to Glyphosate

Sainfoin Has Natural Tolerance to Glyphosate

Leonard M. Lauriault, Forage Agronomist, Francisco Contreras, Agronomist, Dawn M. VanLeeuwen, Agricultural Biometrician, and Rex E. Kirksey, Superintendent, New Mexico State University, Las Cruces, NM 88003

Natural herbicide tolerance to glyphosate in perennial forage legumes is highly desirable. In previous research (1), it was observed that sainfoin (Onobrychis viciifolia) appeared to be unaffected by glyphosate applications to interplot alleys. This article reports a follow-up study conducted in 2002 and 2003 at New Mexico State University’s Agricultural Science Center at Tucumcari, NM, USA (35.20°N, 103.68°W; elevation 4091 ft) to evaluate the effect of glyphosate applications on basal ground cover percentage of sainfoin.

The study was a factorial arrangement of glyphosate treatment [nontreated control or 2.5% glyphosate (4 lb/gal as isopropylamine salt) at 10 gal/acre + ammonium sulfate at 12 lb/100 gal applied to the same plots treated three times during 2002] and sainfoin variety (‘Renumex’ or ‘Remont’) with three replicates. Sainfoin (35 lb unhulled seed per acre) was drilled 30 August 2001, into a conventionally tilled seedbed formed into beds for furrow irrigation. In the first production year (2002), irrigations were applied to achieve field capacity only on 15 May and 7 June, after which irrigation water became unavailable. In spring 2002 and 2003, 22-104-44 lb N-P₂O₅-K per acre was broadcast. The glyphosate treatment was applied on 12 June, 19 July, and 9 August 2002, to maximize control of summer annual grasses and forbs as soon as sainfoin had recovered from biomass removal, which took place on 5 June, 9 July, and 7 August. When biomass was removed, the sainfoin was in full bloom in June and in rosette in July and August. Because the first harvest was taken before any glyphosate was applied and sainfoin yields were not measurable for subsequent harvests due the sainfoin’s growth stage, yield data was of no value, except that weed-free sainfoin yields for the first harvest in this study (0.37 ton/acre) were consistent to those in a similarly managed trial at this location (1). Percentage basal ground cover of sainfoin was visually rated prior to the first glyphosate application in 2002 and after initiation of spring growth in 2003. Basal ground cover data were analyzed as a 2 × 2 factorial of glyphosate treatment and cultivar with year as a repeated measurement using SAS PROC MIXED ANOVA (SAS Institute Inc., Cary, NC).

Multiple glyphosate applications did not reduce sainfoin basal ground cover compared to the nontreated control (65 and 63%, respectively) and there was no visible injury or significant interactions between glyphosate treatment and sainfoin variety or between these main effects and year. Basal cover percentage of sainfoin increased from 57% in 2002 to 71% in 2003 (P < 0.05), probably because of this species’ ability to increase plant size to thicken stands (2). Basal cover also differed (P < 0.02) between sainfoin varieties (80 vs. 48% for Renumex and Remont, respectively), likely due to varietal adaptation to this location.

This study is the first to demonstrate that sainfoin has natural tolerance to multiple applications of 2.5% glyphosate solution, applying 1 qt/acre of glyphosate containing 4 lb/gal isopropylamine salt of glyphosate, even within the same growing season. Because sainfoin basal cover increased after three glyphosate applications in one year, it is possible that applications could be made as needed with no negative consequence. Research is needed to evaluate the effects of glyphosate application during sainfoin establishment (3) and to establish the maximum glyphosate rate for crop safety because only one rate was used in this study, although it was a fairly high concentration for the purpose for which it was used. Finally, labeling to include sainfoin as a primary crop is needed before glyphosate should be applied to monoculture sainfoin.

Literature Cited

1. Lauriault, L. M., Kirksey, R. E., and VanLeeuwen, D. M. 2008. Perennial cool-season forage legume performance in diverse soil moisture treatments, Southern High Plains, USA. Bull. 796. Online. New Mexico State Univ. Agric. Exp. Stn., Las Cruces, NM.

2. Mowery, D. P., and Matches, A. G. 1991. Persistence of sainfoin under different grazing regimes. Agron. J. 83:714-716.

3. Moyer, J. R., Hironaka, R., Kozub, G. C., and Bergen, P. 1990. Effect of herbicide treatments on dandelion, alfalfa, and sainfoin yields and quality. Can. J. Plant Sci. 70:1105-1113.