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ARS Home » Southeast Area » Stoneville, Mississippi » Crop Production Systems Research » Research » Publications at this Location » Publication #201940
Title: Differential Response to Glyphosate in Italian Ryegrass (Lolium multiflorum) Populations from Mississippi

Author
item NANDULA, KIJAY - DREC - STONEVILLE, MS
item POSTON, DANIEL - DREC - STONEVILLE, MS
item EUBANK, THOMAS - DREC - STONEVILLE, MS
item Koger Iii, Clifford
item Reddy, Krishna

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2006
Publication Date: 4/1/2007
Citation: Nandula, K.K., Poston, D.H., Eubank, T.W., Koger III, C.H., Reddy, K.N. 2007. Differential Response to Glyphosate in Italian Ryegrass (Lolium multiflorum) Populations from Mississippi. Weed Technology 21:477-482.

Interpretive Summary: The intense use of glyphosate and continued adoption of glyphosate-resistant crops without rotation with non-glyphosate-resistant crops has increased the selection pressure to evolve resistance in certain weed populations. To date, eleven weed species have evolved resistance to glyphosate. Scientists from Delta Research and extension Center, Mississippi State University and USDA-ARS, Southern Weed Science Research Unit and Crop Genetics and Production Research Unit, Stoneville, MS have characterized two Italian ryegrass populations from Mississippi, Tribbett and Fratesi, suspected to be tolerant to glyphosate. A third population from Mississippi, Elizabeth, known to be susceptible to glyphosate, was included for comparison. Plants were treated with glyphosate at 0, 0.11, 0.21, 0.42, 0.84, 1.68, 3.36, and 6.72 kg ae/ha to determine GR50 rate. GR50 (herbicide dose required to cause a 50% reduction in plant growth) values for the Tribbett, Fratesi, and Elizabeth populations were 0.66, 0.66, and 0.22 kg/ha, respectively, indicating that both Tribbett and Fratesi populations were 3-fold more tolerant to glyphosate compared to the Elizabeth population. Alternative chemical control options exist for managing these populations. However, timing, economics, prevailing weather conditions will determine effective management of Italian ryegrass populations. This is the first report of glyphosate-resistant Italian ryegrass populations from glyphosate-resistant cotton and glyphosate-resistant soybean crop situation.

Technical Abstract: Two Italian ryegrass populations from Mississippi, Tribbett and Fratesi, were suspected to be tolerant to glyphosate. A third population from Mississippi, Elizabeth, known to be susceptible to glyphosate, was included for comparison. Plants, 10- to 15-cm-tall (3 to 6 leaves, 2 to 3 tillers), were treated with the isopropylamine salt of glyphosate at 0, 0.11, 0.21, 0.42, 0.84, 1.68, 3.36, and 6.72 kg ae/ha. GR50 (herbicide dose required to cause a 50% reduction in plant growth) values for the Tribett, Fratesi, and Elizabeth populations were 0.66, 0.66, and 0.22 kg/ha, respectively, indicating that both Tribbett and Fratesi populations were 3-fold more tolerant to glyphosate compared to the Elizabeth population. These three populations were also treated with diclofop at 0, 0.13, 0.25, 0.5, 0.75, 1, and 2 kg ai/ha when plants were 8- to 10-cm-tall (2 to 3 leaves, 2 to 3 tillers). Diclofop GR50 values for the Tribett, Fratesi, and Elizabeth populations were 0.25, 0.28, 0.21 kg/ha, respectively, indicating similar tolerance to diclofop in the three populations. Response of all three populations at two growth stages, 8- to 10-cm-tall and 15- to 20-cm-tall, to clethodim rate (0, 0.02, 0.03, 0.05, 0.06, 0.08, 0.09, and 0.13 kg ai/ha) was measured. Clethodim GR50 values for the Tribett, Fratesi, and Elizabeth populations at the small growth stages were 0.016, 0.023, 0.014 kg/ha, respectively, and at the large growth stage were 0.04, 0.034, 0.02 kg/ha, respectively. Alternative chemical control options, mesosulfuron, clethodim, nicosulfuron + rimsulfuron, glufosinate, and paraquat, are available for managing glyphosate-resistant Italian ryegrass, depending on weed growth stage and prevailing weather conditions among other factors.