Climatic factors affecting herbicidal activity of sodium trichloracetate in different soils : a thesis submitted to the University of New Zealand in partial fulfillment of the requirements for the degree of Master of Agricultural Science (Horticulture)

Abstract

Trichloracetic acid (TC A) has long been known as a protein precipitant, but it was not until 1947 that research workers in the U.S.A. found it to be an effecive grass killer. Immediately it was subjected to a considerable amount of ex­perimentation, but it is only since 1950 that any trials have been conducted with this herbicide in New Zealand. Most of this early research was of an observational or emperical nature, and the results obtained were often in­consistent. However, it was soon determined that there was little downward translocation of T C A when foliar applications were made, and that for maximum kill it was essential for the herbicide to come into contact with the grass roots. Best control of couch (Agropyron repens .L.), for example, has been obtained when the TC A was sprayed on the upturned sod and light rain fell within a few days after application. Before commerical usage of any newly developed herbicide is recommended on agricultural land it is desirable to know the fate of that herbicide when applied to the soil, whether it will persist and be cumulative so that subsequent crops will be effected, if a short period of residual activity can be expected, or if the compound is rapidly dissipated. To this writer's knowledge, no attempt had been made in New Zealand to undertake a quantitative study of the effects soil type, temperature and rainfall have on the rate of inactivation and distribution of T C A when applied to the soil. Such an investigation therefore seemed pertinent, and more especially because results of similar studies overseas were not in full agreement. The published reports showed that both chemical and biological tests had been employed to determine the concentra­tions, or relative amounts of TC A in the soil, but in no instance had the two methods been employed for the one experi­ment. It was therefore considered that in a future investigation some useful purpose would be served by a comparison of results obtained by both tests. [From Introduction]