USE OF D.D.T. ON FARMS

Press, Volume XCI, Issue 27629, 9 April 1955, Page 5

USE OF D.D.T. ON FARMS

Care Needed In Buying

UNEVEN MIXING CAUSES FAILURES

Some hints about the use of D.D.T. superphosphate to control grass grub and porina caterpillar are given in a Canterbury Chamber of Commerce bulletin prepared by Mr'K. M. Doull, lecturer in agricultural zoology at Canterbury Agricultural College. For routine treatment on all pastures where control for the full three years is required, Mr Doull recalls that the application should be 21b ppi D.D.T. per acre. For pastures on which control for, up to two years is required the rate should be 11b ppi D.D.T. per acre. These application rates can be obtained by using one or other of the two grades of D.D.T. super now put out by fertiliser manufacturers. One grade contains 261 b ppi D.D.T. per ton and when applied at IJcwt per acre gives a dosage of 2.11 b D.D.T. per acre. The other grade contains 401 b D.D.T. per ton and when applied at lewt per acre gives a dosage of 21b ppi D.D.T. per acre.

One important cause of failure has been poor mixing of D.D.T. and super, says Mr Doull. The amount of D.D.T. in each ton of super is small and thorough mixing is essential. Unfortunately some firms are using mixing plant which was not designed for this type of work. The result is that there is an uneven distribution of D.D.T. through the super* On analysis, samples taken from batches of D.D.T. super have been found to contain D.D.T. varying between one-fifth and eight times the desired amount. Until such time as suitable plant is in universal use, some weaknesses in mixing will continue to arise.

With the big increase in the use of D.D.T. several new agents have taken up importing this chemical. Unfortunately not all concerns handling D.D.T. have realised the significance of the words “ppi content.” Like most synthetic chemicals, D.D.T. as manufactured contains at least three different chemicals, all technically* alike m that they contain the same amount of hydrogen, chlorine and carbon, but which, owing to their chemical structure, have different biological properties. These different forms are known as isomers. The two main isomers of D.D.T. are the para-para isomer (ppi), which has strong insecticidal properties, and the ortho-para isomer (opi), which is of little value. Exact Amounts It is essential that everyone should know the exact amount of ppi D.D.T. m the product they are using. They can then adjust the quantity used to give the recommended 21b of ppi D.D.T. per acre. Mr Doull then gives five “do’s” and “donts” for farmers:

(1) Don’t drill D.D.T. super with seed. When drilled in, the insecticide is concentrated in the drill strips while the six-inch strips between them are untreated. Grubs and caterpillars can feed and grow in these untreated strips. In fact the caterpillars, feeding above the ground, can destroy the grass in the treated strips. (2) Do apply D.D.T. to short xiry pastures. To be effective the insecticide must reach the ground as soon as possible. If the grass is wet D.D.T. will stick to the foliage and once it has dried on. a lot of rain is needed to shift it down to the ground. Every endeavour must be made to have pastures grazed short and application must not be made until the grass is dry.

(3) Don’t spray D.D.T. on pastures. Low volume spray outfits with coarse nozzles are capable of putting on uc to 60 gallons per acre but even at this rate of application there is not sufficient spray applied to make the D.D.T. run off on to the ground. There is frequent blocking of. the . nozzles resulting in uneven distribution. (4) Do not use a spin top-dresser. The D.D.T. super is a simplfe mechanical mixture and the violent action of the spinner tends to separate the two components. The D.D.T. being in very small light particles is not thrown very far and this results in uneven coverage. (5) Do make regular use of D.D.T. Experience has shown that best results are obtained if D.D.T. is used as an insurance against attack. If each pasture is treated during its second winter and again every third or fourth year thereafter it will be continually proofed against attack. In other words farmers should incorporate the use of D.D.T.-super into their normal farming routine. If one-third or onequarter of the pastures are treated each year there should be no further trouble from grass grub or porina. AERIAL TOPDRESSING Mr Arthur Shand, Island Hills, writes:— When aerial topdressing pilots such as the late Keith Ballagh have done so much for our hill country with phosphates and clovers. I feel I must reply to Mr Sim of Carew, who has set alight some doubts about the future of their careers without much more use of lime in the hills. Most of our South Island hill country is stony and rocky. The distintegration of these stones, rocks and rubble acts similarly to lime on the plains in keeping acidity from the soil. Molybdenum in a minute quantity added to the first sowing of superphosphate also assists. Oversowing with clovers is the “must” on hill country. The clovers in their turn are stimulated by the phosphates to produce nitrogen.

If Mr Sim would come and allow me to show him somp steep hill country sown as above mentioned, I feel sure his one regret would be that it was not possible to get a header harvester to gather the red clover seed that has already set. All will not be well with either plains, hill farmer or fertiliser factory if the bombing starts again. The topdressing pilot will be a part of our guardian force for the next 100 years, whether it be checking erosion, returning fertility to our already depleted bills or dropping supplies and equipment where needed in either war or peace.