USE OF SIMAZINE AS A PREVENTATIVE WEED CONTROL HERBICIDE FOR BIRDSFOOT TREFOIL

Abstract

Simazine at 0.8, 1.1, 1.6 and 2.2 kg/ha (active) was applied in October of each of three years to an established stand of Empire birdsfoot trefoil infested with grass. These rates were used alone and with an original application of each of 1.1 kg/ha paraquat and a mixture of 3.4 kg/ha dalapon + 1.1 kg/ha 2,4-DB (active). In addition, 1.1 kg/ha simazine (active) was applied in October to a new sowing of Empire birdsfoot trefoil. This rate was used alone and where each of 4.5 kg/ha dalapon, 1.1 kg/ha 2,4-DB or their mixture had been applied at the third true leaf stage of trefoil development earlier in the establishment year. The purpose of these trials was to determine the effect of simazine on the yield of birdsfoot trefoil and on the control of grass and broadleaf weeds. Simazine at 0.8, and 1.1 kg/ha applied in the fall of each year had no deleterious effects upon the yield of Empire trefoil. At the 1.6- and 2.2-kg/ha rate, a reduction in yield did occur after the second, but did not occur after the third, annual application of simazine.Although the grass proportion in old stands of trefoil was reduced to 10% or less by initial application of 1.1, 1.6 and 2.2 kg/ha of simazine, an increase up to the 30% level occurred after the second application at the 1.1- and 1.6-kg/ha rates. This grass proportion was maintained by a further application at these rates. Only the 2.2-kg/ha rate of simazine maintained the grass proportion below 10% of the yield. The original reduction in the proportion of grass was improved and subsequently maintained at a level of 25% or below where simazine was used at any rate in conjunction with an initial application of a mixture of dalapon and 2,4-DB. Combination of paraquat and simazine resulted in a trefoil stand reduction and low trefoil yields.A preventative weed control system using simazine is discussed. The program involves the initial use of a mixture of 3.4 kg dalapon and 1.1 kg 2,4-DB per hectare on new seedlings or on established stands. This is followed by an annual October application of 0.8 to 1.1 kg/ha (active) simazine.