KILLING RAGWORT

Wairarapa Times-Age, 7 June 1940, Page 2

KILLING RAGWORT

trials at ruakura. USE OF SODIUM CHLORATE. ■Reporting to the last meeting of the Ruakura Farm Advisory Committee, Mr P. W. Smallfield, Superintendent of the Ruakura Animal Research Station, said that at the time of the previous committee meeting it had been planned to treat ragwort plants with 21. 5 and 10 grams of sodium chlorate per plant. Different groups of plants were to be treated at different seasons at Mamaku, Putaruru and Ruakura, and the instructors of the Fields Division were to carry out similar experiments in a number ot ragwort districts. No significant results, said Mr Smallfield were yet available from the Ruakura and Putaruru experiments. At Mamaku, treatments made in June and in August, 1939, had already shown 10 to 25 per cent regrowth from 10 grams of chlorate per plant. More regrowth has been obtained from smaller doses. Later applications had not yet had time for regrowths to appear. These results confirmed those from a 1938-39 Mamaku experiment in which sodium chlorate applications of I.’, grams and more per plant had given complete kills when the treatments were made during October to March. Treatments during April. to August had given regrowth even with doses of 10 grams per plant. • RESULTS AT PUTARURU. However, these results were contrary to those previously obtained at Putaruru where the best kills had been obtained from the winter treatments. Possibly the differences were due to the greater rainfall at. Mamaku. During the summer of 1939 at Ruakura an experiment was laid down to determine the effect of soil moisture and chlorate efficiency. Chlorate was applied to ragwort, when the soil was very dry and also to other ragwort plots which had been watered. The January treatments had given complete kills irrespective of the soil moisture or the quality of chlorate applied. Similar treatments in March had all given regrowth, again irrespective of soil moisture. Appaiently the seasonal variation had been greater than any effect due to difference in soil moisture.

In all the recent experiments owing to the larger quantities of chlorate required it was applied as a mixture consisting of 25 per cent chlorate and 75 per cent lime. Ten grams of sodium chlorate per plant is a very large dose and if applied as the usual 5 per cent lime chlorate mixture would represent nearly half a pound of mixture per plant. Published results of American experimental work indicate that soil fertility and high nitrate in particular has a depressing effect on the toxicity of sodium chlorate. This may partly explain the variable results obtained in the Waikato. Experiments have been laid down at Ruakura on ragwort plants in which nitrate content of the soil was artificially adjusted, so that at the time of application of sodium chlorate, various levels of nitrate obtained on the different plots.