Insecticides And Residues In Produce

Press, Volume CVI, Issue 31071, 28 May 1966, Page 9

Insecticides And Residues In Produce

(By

A. D. LOWE

Residues in primary produce in New Zealand—meat, milk, butter and cheese—occupied the attention of about 50 scientists at the annual conference of the Entomological Society in New Plymouth last week.

The president, Mr A. J. Reeves, of Ivon Watkins-Dow, New Plymouth, took for his presidential address the subject, “Insecticides and World Production,” and concluded that the interests of both farmer and consumer were best served by a sober recognition of insecticides as a necessary part of the “chemicalisation” of farming. Such an attitude put these materials in their right perspective and gave force to the conclusion that there is little evidence for panic statements about their dangers to human welfare, he said.

“We must conform to certain standards," said Mr Reeves, “but at the same time let us see these materials as tools that work for our wel-

Insect Problem fare, not against it.” Dr. A. T. Johns, Assistant Director-General of Agriculture, addressed the conference on insect control in relation to primary production. He found it difficult to place an economic figure on damage attributable to insects since this varied from crop to crop and from year to year. He emphasised the damage to wool and hides and general thriftiness by animal pests and noted that animal dips cost farmers in excess of £lm annually. Pasture pests not only did direct damage—they altered the composition of pastures, thus reducing production, put land out of production during re-sowing or withholding periods, and generally decreased yield or carrying capacity. While refraining from naming an over-all figure to cover insect damage in New Zealand farming, Dr. Johns said: “figures ranging from £lsm to £3om have been named as the annual potential loss due to grass grub alone in the absence of chemical control. Whatever the correct figure, it is large by any standard, and is likely to increase as we increase carrying capacity, particularly as we sow introduced grasses in the tussock uplands.” Insect control cost horticulturists £Bm annually in a

£4om industry and this fact suggested it would be worthwhile to undertake research in the economics of pest control.

Dr. Johns said the greatest problem in New Zealand agriculture today was the finding of an effective method of control of grass grub. “We hope,” he said “that It will be found before resistance to DDT reaches the stage where DDT is no longer an economic proposition.” Mr D. A. Watkins presided over a symposium on the specific topic of residues. He introduced the superintendent of agricultural chemicals, Mr F. B. Thompson, who spoke of the factors leading to legislative control of pesticides in this country. Conditions were virtually dictated by New Zealand’s overseas customers, he said, and had their origin in the rejection of New Zealand meat in the United States because of the presence of B.H.C.—a material for which the tolerance was “nil" in that country.

Many people now regarded “nil” tolerances as a concept impossible of achievement and not necessary, said Mr Thompson, but regulations now in force would probably not be lifted for some time, and then only gradually as more and better information became available.

Speaking of dairy produce as one product affected, Mr Thompson stated four principles that were involved. (1) We must observe the limits set by our customers. (2) There is not much margin for error in application of pesticides in this field as “nil” tolerances are the order in most countries. This may be modified in the future but tolerances will never be high because of the large daily intake by most humans of these items—milk. butter and cheese.

(3) On the local scene, there is some slight increase of residues in dairy produce at certain times of the year, the cause of which is not yet fully understood. (4) Present thinking is that periods of four weeks withholding may not be sufficient in dairying areas during periods of slow growth and they may need extending in order to protect the individual farmer’s products.

Mr Thompson cited this case to show how the system of regulating worked and was aimed primarily at protection of the farm produce from suspicion at the buyer’s end. The actual chemical techniques used to detect residues in meat and other produce were outlined to the conference by Mr H. V. Brewerton of the Chemistry Division of the Department of Scientific and Industrial Research, Wellington. He said that low residues were extremely widespread in this country and that the equipment and personnel available should have the confidence of all involved in this question. Mr D. Harrison, a chemist of Wallaceville Animal Research Station, outlined the routine sampling of meat at freezing w’orks and the various experiments carried out by the Department of Agriculture to examine the methods of application of insecticides. By and large success had attended the adoption of regulated practices, especially the suspension of the use of dieldrin dips, and the application of DDT dust to pasture. A few extreme cases of residues over recent times had been traced to suspected breaches of the regulations. With-holding times and new preparations were constantly under review and there was no doubt that residues had been greatly reduced by the use of pelleted materials on pastures and the enforcement of specified with-holding periods. The whole procedure, now in force for about five years had reduced residues which grossly exceeded allowable levels to a situation where intolerable residues were now an exception, though minor levels still persisted and continuous vigilance and further work were both necessary to protect the country’s export trade.