SPRAYING TO CONTROL NODDING THISTLE

Press, Volume XCVII, Issue 28530, 8 March 1958, Page 9

SPRAYING TO CONTROL NODDING THISTLE

Results Of Mid-Canterbury Trials

Trials to test the control of noddiifij thistle by hormone sprays and hormone-treated superphosphate, conducted this season on farms in the Ashburton county by the Department of Agriculture, had shown that, the thistles could definitely be killed by these means, although the cost at the moment was fairly high, said Mr C. P. Whatman, an instructor of the department, in a recent lecture to the agricultural section of the Mid-Canterbury district of Federated Farmers.

The farmer niQre or less com mi tied to annual spraying if lie wanted to control nodding thistle on his farm, and if the trials, which would be continued next season, could show that a 90 per cent, control of nodding thistle could be achhieved, farmers would probably be prepared to spend,money to do so, Mr Whatman said.

In its trials, the department had particularly investigated cheap methods of spraying and methods least detrimental to the existing sward. “Not only must we kill nodding thistle, but we must kill it cheaply; and more important still, we must kill it without danage to the sward,’’ Mr Whatman said.

Four weed-killing agents had been employed in the trials. They were the; organic chemicals MCPA, MCPB, 24D Amine; and hormonetreated superphosphate. From results so far, considering both effectiveness of thistle kill and lack of damage to pasture, MCPB was the treatment the department would recommend, Mr Whatman said.

Trials On Three Fanns The trials were conducted on the 'farms of Messrs D. Stewart (Rakaia), J. D. Cocks (Lismore), and L. R. Bagrie (Hinds). On each farm a paddock infested heavily with nodding thistle was subdivided into plots about two chains long by five yards wide. There were generally similar pasture conditions in each paddock. The paddock on the Rakaia farm contained a ryegrass and white clover pasture; at Lismore there was subterranean and white clover, with various grasses; and at Hinds subterranean clover was the dominant sward.

The three hormone sprays were applied at two different rates—.6lb and 1.21 b of acid equivalent an acre in each case. Treatments were given at two times—towards the end of May and about the middle of September. Further treatments were made by varying the amount of the hormone in the superphosphate. There were also plots treated with superphosphate alone, and untreated plots, as part of the investigations. “Summarising the result of the hormone spray trials, practically all the treatments were effective in killing nodding thistle,” Mr Whatman said. “The rate of ,61b was almost as effective as was 1.21 b. The rate of kill varied between the different materials used, but the final results did not vary very much.”

“Summarising the effect of the hormone-treated superphosphate, the light rate, equivalent to lewt an acre, was as effective as the heavy rate; and with the light rate, there is little damage to the clover owing to the superphosphate with the hormone, while later there is an additional response from the superphosphate,” Mr Whatman said. •. . “I stress that the kill from treated superphosphate was not spectacular—it was extremely patchy, and it was slow. We were very disappointed in it for a start, and • were rather surprised that it worked out so well as it did later in the season. But it was not nearly as attractive a kill as. that which resulted from the hormone' sprays.” Effect On Pasture “Another important -factor is the effect on the pasture—often hormone sprays give a complete kill of clover or a good thinningout of clover in the pasture,’* said Mr Whatman. “That must be a very serious factor in any treatments that we apply. It was very definite, particularly in the early spring, that the 24D Amine was far too damaging to the clovers. Even at the low rate of .61b acid equivalent an acre there was very considerable clover damage. “The subterranean clover plants very stunted and reddishcoloured with very little vigour, and the break-out of these plants during the spring was very greatly reduced. White clover suffered in much the same way—a distinct thinning-out, and reduction in vigour.

“The heavy rate of MCPA was harmful to almost the extent of the 24D Amine.

“The MCPB caused very little damage to clover, the ,61b being as effective as the 1.21 b on the thistles, so that from the points of view of thistle kill and lack of effect on the pasture. MCPB is the treatment we would recommend.

“The hormone-treated superphosphate did not cause great damage to the clover,” said Mr Whatman. “It appeared as if the amount of superphosphate in the mixture was sufficient to give the clover enough boost to combat the effect of the ■hormone. In the early stages there was very little response to the superphosphate as compared with the response to the untreated superphosphate, but. on the other hand, there was little or no damage to the clover as compared with the 24D Aminetreated plots. Later on, the superphosphate started to boost the growth of the plots—a delayed response, so that the superphosphate was not wasted. However, had it not been for the wet conditions during November and December we might have seen no result from the superphosphate at all.”

“One other point concerns the two applications in autumn and spring. There has been nothing very definite from that, except that there appeared to be just as good results from a single application in the spring as there was from an application in both autumn and spring.

“Present indications are that one can use .61b MCPB in the spring and get good results, or use lewt hormone-treated superphosphate to the acre and get satisfactory results,” Mr Whatman said.