The effect of insecticide treatment on the establishment and growth of Italian ryegrass under different sowing conditions

Italian ryegrass, Lolium multiflorum Lam., cv. RvP., was broadcast in spring on to fine and coarse seedbeds at seed rates of either 2 or 20 kg ha^-1. Each of the four combinations of sowing condition was either left untreated or treated with fungicide or insecticide. The establishment of the sown species and of weeds under each regime was measured and their relative contribution to dry matter assessed in four cuts during the sowing year. Seed rate affected weed invasion and yield more than seedbed condition. Insecticide treatment increased the establishment and yield of ryegrass and its contribution to total herbage yield under all four sowing conditions. The fungicide treatment had no effect. The improvements caused by insecticide treatment were associated with a reduction in the level of infestation by shoot flies, Oscinella spp. (Diptera: Chloropidae): the effect of a single treatment in April was still detectable in October.