The experiments that appear in this work were conducted at Paine Experiment Station during the seasons 1948-1949; 1949-1950; and 1950-1951.
They have beeo carried out onwheat.
1°- Hand weeding; total and partial compared to an unweeded check in order to determine the effect of the weeds upon the yield.
2°- Comparison of different iormulations of 2,4-D and MCP (2-metil-4-chlorophenoxyacetic acid).
3°- Application of different rates of 2,4-D amine salt indifferent stages of growth of the wheat.
Trial number one gave increases of yield between 19,5 and 58,1% with partial weeding and with total weeding the increases were from 22,3 to 70%.
In the experiment number two the general effect of the weedkillers, were appreciated but differences as between the various herbicides were not significant. Having three years results of experiments with different formulations of 2,4-D and MCP, it is possib1e to recomendany of its formulations for selective work in appropiated rates.
In trial number three we got good results with the applications of the weed killer as much in increasing the yield of wheat as in controlling the weeds when it was sprayed either in constant or higher rates than 287,5 grs. per Ha. of 2,4-D acid equivalent. There was tendency toward increased yields with higher rates. The best dates of application were first and second except in 1950, due to variations inclimatic conditions. In the last date of applications just before heading the highest rates had a depressive effect onthe wheat.
The results obtained in these three seasons experiments show the great depressive effect oí the weeds upon the yield of the wheat and indicate the advantages to use selective weed killers in this crop in order to control broadleaf weeds.
Different formulations of 2,4-D, rates and dates of application were studied; 2,4-D compounds did not show significant differences in its action. The best dosages varied between 500 and 800 grs. of acid e

1 Ingeniero Agronómo del Depto. de Investigaciones Agrícolas