Control of Rushes in Tauranga County

New Zealand Journal of Agriculture, Volume 87, Issue 1, 15 July 1953, Page 20

Control of Rushes in Tauranga County

By

A. V. ALLO,

Instructor in Agriculture, Department of Agriculture, Tauranga

IN the last 3 years a number of experiments have been carried out in Tauranga County in an attempt to control rushes with hormone weedkillers. Much of the coastal country in the Te Puke district consists of a large area of partially drained swamp country of a peaty loam soil type that is fairly wet in winter and on many parts of which rushes grow in profusion. There are two main species of rush on the area, Juncus effusus and Juncus pauciflorus, the former being the soft rush eaten by stock in winter and the latter the wiry, hard rush which stock will seldom if ever touch. Trials have been conducted on both these species, and the areas selected ranged from very wet paddocks which are waterlogged throughout the winter to relatively well-drained country on which rushes are not so serious a problem. In all trials the most heavily infested portion of the field was selected for treatment, and the purpose was to find a method of treating rushes that would give a reasonable degree of control at an economic cost. After 3 seasons’ experimenting it is now considered that a large part of the answer has already been obtained, though it must be stressed that this is only an interim report.

It has been found that the first essential is to mow the rushes in November or early December and to spray the regrowth when it is 12 to 18in. high, usually 6 to 8 weeks later. Spraying of uncut rushes has given rather poor results, as also has the spraying of the stumps of freshly cut rushes. Of all the hormone weedkillers tried best results have so far been obtained from the use of ethyl ester of 2,4-D applied at the rate of 1-j to 21b. of acid equivalent per acre in 22 gallons of water; this was sprayed through 32 fan nozzles at a pressure of 401 b. per square inch, and the tractor speed was 2 miles per hour. On easy country where greater tractor speed is possible better control is obtained if the above rate of hormone is applied in 30 to 40 gallons of water per acre and low volume nozzles are used. This necessitates traversing the area twice and where possible the second application should be at right angles to the first. The use of the amine salt of 2,4-D at 21b. of acid equivalent per acre is also giving very promising results, though this material has been tried for only a season and final judgment cannot be passed on it until next spring, when the plots can be examined for

regrowth. Best results have been obtained on Juncus effusus', results from spraying of Juncus pauciflorus, though not so striking, are still very good. Farmers should not expect rapid results after spraying. The first symptoms are a browning of the tips of the leaves, usually showing up 2 to 3 weeks after spraying. This browning continues along the leaves, which after about 2 months show a distinct brown to black at the base of the plant. At this stage they pull out of the clump very readily, usually a sign that the plant will be killed. As a result of these experiments several farmers in the Te Puke district have sprayed areas themselves, and several have obtained from 60 to 90 per cent, kills of rushes. It is considered that hormone weedkillers offer a very promising means of controlling Juncus effusus and Juncus pauciflorus, but it must be stressed that they will give complete and permanent control only if drainage of the area is improved to permit excess water to get away. If the ground is still allowed to get very wet each winter, fresh seedlings will come away again and the control effected by the hormones will give only temporary relief.