On The Hills

Press, Volume XCVII, Issue 28701, 26 September 1958, Page 9 (Supplement)

On The Hills

Sweet brier, manuka and matagouri also occur on hill country, while blackberry, broom, hawthorn and tutu constitute problems in some localities. In higher rainfall areas, bracken fern and ragwort are encountered and can be successfully controlled.

Some work on the chemical control of bracken fern is proceeding, but pasture improvement and management remains the first choice for fern control. The use of hormone weedicide allied with pasture improvement is successful in ragwort control. Thistles, especially variegated thistle and winged thistle, periodically infest hill country areas, these infestations usually following the opening up of pasture cover following drought. Honpone weedicides are Useful in removing the competitive effect of the thistles and allowing the reestablishment of a pasture cover. Some aerial spraying of thistles is Aerial /praying of gorse has been widely publicised but results haAe been variable. However, applied at the correct stage-4)f growth and in such a way.'that spray coverage is satisfactory will kill gorse. Complete coverage is difficult to achieve by aerial application. >Nassella Tussock By. far the greatest threat to this class of land lies in the spread of nassella tussock. This aggressive native of South America thrives on a variety of soils, is most competitive on soils subject to summer drought, and is well adapted for seed dispersal by means of' wind.

The fact that Canterbury experiences a dry climate with frequent north-west winds during the summer season means that conditions in this province favour the natural of nassella.

The resemblance of nassella tussock to some native species is probably one of the principal reasons why the weed was not recognised as a threat until just prior to World War 11. The war intervened and it was not until 1946 that the Nassella Tussock Act setting up the North Can-

terbury and Marlborough Nassella Tussock Boards, was passed. By this time, nassella had demonstrated its habit of becoming the completely dominant species and as it is unpalatable to sheep the future of sheep grazing on large areas of North Canterbury was jeopardised. Some afforestation was carried out and grubbing gangs were employed for scattered • infestations but no progress with the re-establishment of pasture on nassella infested hill country was made until the production of selective grass-killing chemicals during the last six or seven years. Major Problem Experimental work has shown that the tussock can be killed by chemicals and pasture species established in its place. Once pasture has been re-established the problem of maintaining a sufficiently vigorous cover to suppress the regeneration of nassella is one which must be faced. The Marlborough infestation of about 500 acres has now all been treated with herbicide and pasture establishment is proceeding. North Canterbury on the other hand has several thousand acres of dense tussock and many more thousands of acres less heavily infested and the task of control is a major one. The Department of Agriculture is pressing on with its programme of research work while the North Canterbury Nassella Tussock Board is intensifying its efforts along such avenues of control as the employment of rangers and grubbing gangs, the aerial application of weed-killer over extensive areas for seed control, and at heavier rates to certain blocks of tussock for the purpose of killing existing nassella prior tb* pasture establishment.

The possibility of planting some of the heavily-infested areas in trees is also being investigated. On a per acre basis, nassella control is expensive but to obtain a true picture the cost of control must be viewed against the background of the vast areas of farm land which could be involved if the spread of the weed was to remain unchecked.