A study of the susceptibility to Dalapon of four common pasture grasses : a thesis presented at Massey Agricultural College in part fulfilment of the requirements for the degree of Master of Agricultural Science in the University of New Zealand

Abstract

One of the more important developments of recent years in New Zealand agricuture has been the introduction of herbicides selective against grass species. Originally intended for the control of grass weeds in arable crops these herbicides have proved capable of being utilized in many other aspects of farming practice, the most spectacular of which is 'chemical ploughing'. This popular name has been coined to describe the process whereby pastures may be improved with the aid of herbicides on land which cannot succesfully be cultivated by conventional means. Extension of this technique to land which is only accessible to the aeroplane is being investigated by Blackmre (1958) and the preliminary reports suggest that 'chemical ploughing' may be a useful aid to aerial top-dressing and oversowing. Every new development, however striking, must satisfactorily blend with or replace existing practice before it becomes generally accepted. Many problems of practical application require solution before recommenbdations can be made to farmers and there are at present under investigation in field trials throughout the country. At the same time a thorough knowledge of the properties of the herbicides and the factors affecting their efficiency under a wide range of field conditions is essential. Where herbicides are applied to a mixed population of plants, as in a pasture, it is desirable to know, within fairly narrow limits, the tolerance of each constituent species. The experiments reported in this thesis were undertaken to investigate the susceptibility of some common pasture species to dalapon, the most important of the selective grass-killing herbicides involved in 'chemical ploughing' and associated techniques.