Selective herbicides for establishing weed‐free grass: The effect of mixtures and sequences of herbicides, including ethofumesate and methabenzthiazuron

Summary Two field experiments compared various sequences of ethofumesate, methabenzthiazuron and mecoprop, and mixtures of metamitron, ethofumesate and methabenzthiazuron for their control of Poa annua L. and Stelluria media (L). Vill. during the establishment of autumn‐sown perennial ryegrass ( Lolium perenne L.). In experiment 1 pre‐emergence treatments required a second, post‐emergence spraying to give complete control of P. annua . Grass seedlings reappeared in early spring following ethofumesate treatment, but populations built up earlier where methabenzthiazuron had been used. The most successful treatment was ethofumesate at 1.4 kg a.i. ha −1 followed by 0.7 kg a.i, ha −1 in spring. Methabenzthiazuron at 0.8 kg a.i. ha −1 followed by ethofumesate at 0.7 kg a.i. ha −1 in December was also effective. Methabenzthiazuron at 1.6 kg a.i. ha −1 damaged ryegrass but was effective as a secondary treatment at lower doses in spring. Most treatments controlled S. media satisfactorily, but this sometimes increased the yield of P. annua . Metamitron greatly reduced tiller numbers of P. annua in experiment 2, especially when sprayed with methabenzthiazuron. Only treatments which included ethofumesate controlled S. media adequately but there was no advantage in combining this herbicide with any other for controlling P. annua .