2010 Volume 55 Issue 3 Pages 174-182
A field assessment method to visually evaluate the wheat yield loss by Italian ryegrass (Lolium multiflorum Lam.) was developed. This survey was conducted in soybean-wheat rotational fields during 2004 to 2007 at Toyozumi, Fukuroi city, Shizuoka Prefecture, Japan. In June of each year, Italian ryegrass infestation levels for each field were visually rated according to six grades, and wheat and weed yield were quantified. Visual grading of ryegrass infestation was a reliable predictor of the relative wheat yield loss and weed abundance (plant density and dry matter). Ryegrass density and dry matter correlated with wheat yield loss;the relationship was described with a quadratic hyperbolic regression curve. Wheat yield loss up to 20% was regressed at weed densities of 8 to 12 plants m-2. Our results suggest that visual estimation of weed infestation is easy and effective for regional assessment of weed monitoring, crop loss and economic damage.
