Studies on the selectivity of herbicides alachlor and trifluralin

In order to gain information on the general and specific selectivity of the herbicidesalachlor and trifluralin, two field experiments (one in summer and one in winter) and several glass house experiments were conducted. Throughout the experiments both herbicides gave good control of a wide range of annual grassy weeds. The perennial grass, Paspalum paspalodes was resistant. Trifluralin (1.12 kg/ha) failed to control members of the family Compositae, especially palinsoga parviflora and §onchus oleraceus. Bumex acetosella_was the most resistant plant to alachlor at the rate of 2.24 kg/ha. In the experiments on Specific selectivity, using trifluralin at rates of 1.12 kg/ha, 0.56 kg/ha, 0.28 kg/ha 33% two closely related Amaranthus_spp.(A. powellii and A. hybridus) were used. In all but one of the experiments A. powellii was shown to be less Susceptible to trifluralin than A. hybridus. This difference in susceptibility of the 2 species is ascribed to quicker germination and faster growth in the bigger—seeded A. powellii_with consequent lowering of concentration of trifluralin in the susceptible parts of the seedlings. In addition simple experiments on the influence of temperature on germinatiOn of the two fimaranthus sppl_were carried out. A;M29Wellii germinated more rapidly than A. hybridus_at all temperatures except the lowest (22°C). At the highest temperature (43°C), germination of A. hybridus 3 days. At 45°C there was no germination of either species