Grass Grub Chemical Kills Birds

Press, Volume CIX, Issue 31984, 10 May 1969, Page 10

Grass Grub Chemical Kills Birds

Birds—basicallysea birds—have been killed after feeding on paddocks in Mid-Canterbury treated with 20 per cent parathion granules against grass grubs. The chemical was being used in the course of field assessment. Confirming this week that this had happened, a spokesman for a chemical company said that it had decided to restrict further application of this material until it had determined exactly what had happened. But he added that because of the toxicity of the material to birds and also its persistence in the top soil there seemed little possibility of using it for control of grass grubs.

The company spokesman said that under field assessment a chemical was applied under restricted conditions

under the supervision of the manufacturer. His firm and also the Department of Scientific and Industrial Research had been conducting small-scale trials with the material for three years and it had been found to be quite successful against grass grubs that were resistant to DDT. The bird deaths, he said, had followed the broadcasting of the materia] over larger areas and it was something that had not been expected or foreseen, but sometimes something like this happened during field assessment The chemical, he said, had been applied for many years as an emulsion without bird

deaths and it had also been used at a lower rate in field scale trials against a weevil pest of hew sown pastures, catoptyes, in the Rakaia and Pendarves districts, again without harm to birds.

The chemical used In the most recent field trials against grass grub had been applied to paddocks containing inserts that birds might feed on.

As soon as dead birds were noticed he said that they had contacted the Wildlife Division and other appropriate authorities and after consultation it had been decided to restrict further application of the chemical. His company was now only recommending its use after drilling on bare ground, with the insecticide subsequently being worked into the soil with a light harrowing.

It had started trials with the Wildlife Division to determine whether this was a case of secondary poisoning or not. He said these trials were rather late to get much data, but his company was inclined to the view that it was secondary poisoning. The question was whether the birds had absorbed the poison through the skin of their feet or had ingested it with dead insect* that had been killed by the material.

Freshly killed birds, he said, had been found 10 days I after treatment of an area and after 160 points of rain had fallen. This indicated that the chemical was too toxic to use for topical application to pastures at the rates used. The material had been used in granule form at rates of 21b to 31b to the acre of active

ingredient and these appeared to be border line levels for birds. However, birds had been killed where the 21b rate was used and this was the minimum rate that could be applied for control of grass grub. The chemical appeared to be reasonably insoluble and did not move readily through the soil.

As many as 50 birds had been found on a paddock the morning after treatment, but .in other cases there had only been one and in some cases none at all. It appeared that where birds had not been killed they had not been feeding on that paddock and it seemed that there was no way

of knowing whether birds would feed a particular paddock or not.

The company representative said that in relation to total bird numbers the deaths had not been large. They had basically been confined to the Carew district, with some deaths also having ocr-rred in a small area at the Rakaia mouth.

Fortunately, he said, his company had alternative chemicals that could be used instead of the 20 per cent larathion granules. Diazinon n Gesapon 80 E.C. at two pints to the acre applied in the rain was just as good and was 20c an acre cheaper than 31b of 20 per cent granules. Application in the rain was essential to ensure that the material penetrated into the soil.

Gesapon SG, a granular formulation of 5 per cent active ingredient of diazinon, could also be applied at 401 b to the acre before rain, but the cost here was $B.BO an acre, compared with $6.27 for Gesapon 80 E.C.