The effect of low doses of paraquat and dalapon on two sward types based on Lolium perenne (perennial ryegrass) and Trifolium repens (white clover)

Blood, T.F.

Weed Res 4(4): 359-61


Accession: 014733888

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The possibility of the selective removal of undesirable grasses from a sward by herbicidal doses sub-lethal to ryegrass and clover but lethal to the weed grasses was investigated in 2 field experiments. Paraquat at 2, 4, 2+2 (June 1963 and April 1964), 4+4 (April and June 1963), 6 and 8 pounds per acre or dalapon at 2 and 4 pounds per acre, each in 20 gal/ac+ a wetting agent, were applied on 10 April 1963 to a ryegrass/clover ley sown in 1961 and heavily infested with Poa trivialis, and also to an old permanent pasture. The species present in the permanent pasture were Poa trivialis 2.3%, Holcus lanatus 2.8%, broad-leaved weeds 6.7%, Agrostis spp. 17.3%, Festuca rubra 38.7%, L. perenne 57.7% and T. repens 25.7%. Botanical analyses of the treated ley in the autumn showed that all treatments except dalapon at 2 pounds per acre significantly reduced the amount of P. trivialis present. All treatments especially paraquat at 6 pounds per acre and 4+4 pounds per acre, tended to increase the proportion of rye-grass, but did not affect that of the white clover present. With the permanent pasture, no significant differences were observed between the composition of the treated and untreated plots. This may have been due to the greater variability of the permanent pasture compared with the evenly distributed sward of the ley and to the low proportion of the herbicidally susceptible weed grasses P. trivialis and H.