THE REACTION OF TRIFOLIUM REPENS (L.) IN GRASSLAND TO 2,4‐D, MCPA AND MIXTURES OF 2,4‐D AND MCPB

Summary. Eight experiments were carried out on a range of pasture lypes under different management and in different years to lest the reaction of white clover ( Trifolium repens in grasstand to doses of up to 4 lb/ac of the herbicides MCPA‐sodium or‐potassium and 2,4‐D‐amine. The initial effect of the treatments was to reduce the amount of dover in the sward, the size of the reduction varying greatly from field to field for any one dose. In general, the higher the dose, the more severe was the depression of the clover 1 month after spraying. Both herbicides at 2 and 4 lb/ac caused substantial depressions on some of the fields. The growth of the treated clover was examined during the year following spraying. The ability of the clover to recover from the initial depression varied considerably in the different fields; on some, recovery started in the year of spraying and on others in the following year. Quick recovery was usually associated with a high initial resistance but there were fields in which the clover showed contrasting rates of recovery following similar depressions. The experiments produced no clear‐cut evidence as to why the initial resistance and speed of recovery varied in different fields. In one experiment the effects of MCPB‐sodium and 2,4‐D‐amine on white clover were compared separately and in a series of mixtures. An examination made 6 weeks after spraying showed that MCPB at up to 8 lb/ac had no significant effect on the clover, whereas 2,4‐D at 1 lb/ac caused a 22% reduction. Mixtures containing up to 0.37 lb 2,4‐D and up to 6 lb MCPB caused no reduction while those containing 0.75 lb 2,4‐D and 4 lb MCPB were not significantly different from 1 lb 2,4‐D alone. Reaction de Trifolium repens (L.) en prairie au 2,4‐D, au MCPA, et aux mélanges de1, 2,4‐D et de MCPB