Robin Bond, C.H. Koger, D.H. Poston, T.W. Eubank, J.B. Blessitt, and V.K. Nandula. Mississippi State University, 82 Stoneville Road, P.O. Box 197, Stoneville, MS 38776
Glyphosate-resistant Italian ryegrass (Lolium multiflorium) has been confirmed in Australia. A population of Italian ryegrass exhibiting four-fold tolerance to glyphostate has been identified in Mississippi cotton (Gossypium hirsutum) production systems. Field studies were conducted in 2007 at an on-farm site located near Tribbett, Mississippi, to evaluate response of the glyphosate-tolerant Italian ryegrass to spring-applied burndown herbicide programs.
Treatments were arranged as a two-factor factorial within a randomized complete block design with four replications and the study was repeated. The first factor included a nontreated, Roundup Weathermax at 0.77 lb ae/A alone and in combination with Select Max at 0.046 or 0.068 lb ai/A, or Gramoxone Inteon alone at 1 lb ai/A. First factor treatments were applied just prior to Italian ryegrass anthesis. The second factor included a nontreated, Gramoxone Inteon at 1 lb/A, or Select Max at 0.046 or 0.068 lb/A applied after Italian ryegrass anthesis. Ammonium sulfate at 17 lb/100 gal was added to all Roundup Weathermax and Select Max treatments, and a nonionic surfactant at 0.25% v/v was added to all Gramoxone Inteon applications. Treatments were applied with a CO2-propelled backpack sprayer equipped with 11003 flat fan nozzles at a delivery rate of 15 gallons per acre. Italian ryegrass control was visually estimated 14 d after pre-anthesis treatments and 8, 24, and 35 d following post-anthesis treatments. After the last visual evaluation, biomass estimates were determined by harvesting all aboveground Italian ryegrass plant material from a 1 m2 area from each plot. Data from both studies were subjected to the SAS PROC MIXED procedure. Least square means were calculated and mean separation for treatments were produced at P≤0.05.
Italian ryegrass control 14 d after pre-anthesis applications was at least 93% with Gramoxone Inteon. No other treatment provided greater than 61% control. Only treatments containing Gramoxone Inteon as a pre- or post-anthesis treatment controlled Italian ryegrass ≥90% by 8 d after post-anthesis applications. Gramoxone Inteon followed by Select Max at 0.068 lb/A and Roundup Weathermax plus Select Max at 0.068 lb/A followed by Select Max at 0.068 lb/A provided 92 and 91% control, respectively, at 24 d following post-anthesis treatment. By 35 d after post-anthesis treatment, only Roundup Weathermax plus Select Max at 0.046 or 0.068 lb/A or Gramoxone Inteon followed by Select Max at 0.068 lb/A controlled Italian ryegrass ≥88%.
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