CONTROL MEASURES

Wairarapa Times-Age, 20 August 1940, Page 9

CONTROL MEASURES

, CALIFORNIAN THISTLE PREVENTION OF SEEDING. AN INFORMATIVE BULLETIN. Except in certain districts where the local body has declared otherwise, states a bulletin issued by the Canterbury Chamber of Commerce, Californian thistle is legally a noxious weed throughout New Zealand. Under the Noxious Weed Act, continues the bulletin, inspectors can enforce cutting during the flowering period to prevent seeding. This law is seldom fully enforced as the land most severely infested is frequently the river beds and other waste lands, and these areas cannot easily be cut. The result is that they produce an annual crop of seed in comparison with which the seed produced on individual farms is small.

The farmer, however, usually cuts his thistles before they flower to protect the rest of his farm. This does not keep the land free from seed unless his neighbour’s plants and those on waste areas nearby are also cut. In crops which are harvested for seed, especially grass and clover, the thistles cannot usually be prevented from maturing. These will then occur as an impurity in the line of seed. Even a trace of thistle seed in a line can be responsible for widespread distribution of the weed. For this reason, a careful examination of the purity certificate should be made. Californian thistle, if present,, will be described under the name of Circium arvense.

KILLING BY CULTIVATION. The principle underlying the method of killing the weed by cultivation is starvation by destroying all new shoots before they develop leaves. Each and every new set of shoots appearing through the ground should be cut off immediately. In this way the reserves in the underground stems are used up and the plant ultimately dies from exhaustion. Californian thistle ceases to be a trouble in areas sown in lucerne and cut for hay for several years in succession. The reason for the suppression of the thistle under such treatment is similar to that under cultivation. The regular cutting 3-4 times a year tends to exhaust the weed. It cannot keep pace with the lucerne m ih, endeavour to produce the new leases. It becomes partly smothered and grows weaker and weaker. USE OF SODIUM CHLORATE. The weed can be eliminated by the use of sodium chlorate. This is more effective when applied in the late autumn when the thistles are dying down. During the preceding summer they should be prevented from seeding either by cutting or previous dusting with chlorate. At the time of treatment it is advisable to cut the thistle; if they are more than six inches high it loses its effectiveness. If the soil is hot and dry the chlorate decomposes, and it is also less effective on deep silty, or swampy soils. The chlorate may be sprayed on in a 5 per cent solution with water, i.e., 51b. to 10 gallons at the rate of SOO--400 gallons an acre, or the powder may be applied dry at the rate of 2cwt. an acre or equivalent to about joz. a square yard. When large areas are to be treated it can be mixed with carbonate of lime to help with the even distribution of the dry powder and applied through a lime sewer. ISOLATED PATCHES. Very small isolated patches of thistle may be killed by placing salt licks or rubbing posts on the patch. Straw stacks may also be built on small patches provided the straw more than completely covers the area. On land that is too poor for costly treatment the establishment of plantations is an effective means of control. Certain diseases are known to attack Californian thistle, such as rust, which affects the plants in the autumn. In some areas the thistle, after growing strongly for several years, dies out of its own accord for reasons that are not known.

On land capable of growing good pasture, improved pasture manage-

ment is a very effective means of reducing the rigour of the thistle. The competition by strong growing grasses and clovers associated with the heavy trampling and breaking of the stems by stock combine to weaken the weed considerably.