Development of simple diagnosis program of damages by problematic exotic upland weeds

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Some exotic weeds have recently seriously infested crop fields in central Japan. In this study, 1) a field assessment method to visually evaluate the wheat yield loss by Italian ryegrass(Lolium multiflorum Lam.) was developed. 2) To understand the influence of tillage systems on the germination ecology and seedbank dynamics of naturalized Italian ryegrass, we compared the fate of the seeds after-ripened in the soil with that on the soil surface. The results suggest that the no-till system, which leaves many seeds on the soil surface, may promote rapid depletion of Italian ryegrass seeds through germination before wheat sowing in early winter. In contrast, seed burial by tillage may inhibit germination of the seeds, and form a large seedbank available to germinate during the wheat growing season. 3) The extent of post-dispersal weed seed predation in upland wheat fields was quantified. The seed predators in the field interior areas and the boundary strips were mainly invertebrates(crickets and carabid beetles) and vertebrates(rodents or birds). The results of this study suggest that predators make a substantial contribution in the depletion of post-dispersal seeds of Italian ryegrass in the wheat fields.