The seasonal response of Italian and hybrid ryegrasses to the control of frit fly, Oscinella frit

SUMMARY In years of relatively high frit fly activity the control of all generations produced increases averaging 0×44 t d.m. ha ‐1 in annual yield of Italian and hybrid ryegrass. A cutting programme designed to make the sward especially vulnerable to frit fly attack did not increase the total annual effect of pesticide treatment but accentuated the periods at which damage occurred. The annual yield increase was almost entirely obtainable by controlling the second and third frit fly generations, but even one treatment for this purpose was of doubtful economic justification. The prospect of augmenting the response to control of later‐occurring pests, such as leatherjackets or eriophyid mites, by including the part of the frit fly response which is recoverable by the same treatment, was a more probable justification for pesticide usage. There was some evidence that a Westerwold and a hybrid cultivar suffered more damage than an Italian ryegrass cultivar, but pesticide treatment did not improve the persistence of any cultivar.