Much room for improvement

Press, Volume CXI, Issue 32720, 24 September 1971, Page 13

Much room for improvement

There is still much room for improvement of mechanical applicators for spreading granular insecticides. This was one of the main points made at a field day held at Rangiora airport last week by the Canterbury committee of the Weed and Pest Control Society. Much of the afternoon was spent inspecting the work of a number of applicators used by chemical Aims for spreading granular insecticides. To indicate the spread that the machines were achieving, the tractors, with spreaders attached, straddled a number of trays containing sheets of white paper covered with paste. This gave the visitors the opportunity to inspect the evenness of spread. On eye appraisal, there was no obvious criticism. The true efficiency of the machines, however, was brought sharply into focus by Mr K. R. Humphries, of the Agricultural Engineering Institute at Lincoln. He outlined the methods being used by the institute for measuring the evenness of distribution, adding that it was quite a problem simulating ground conditions in a laboratory. From the outset, he warned that tarpaulin testing by manufacturers was not satisfactory, because the granules would fling much further than they would on pasture. The aim of the laboratory tests was to find the point of most even distribution, which was known as the co-efficient of variation.

Mr Humphries then produced some figures showing that some machines are far from the ideal. One of the machines which had been demonstrated had a 30 per cent variation of spread. Instead of putting oh, say, 101 b to the acre, it would be' putting on only 71b.

On the other hand, a helicopter hopper had performed weß—it had a variation Of only 5 per cent. This was a good laboratory performance. Mr Humphries. said the basic cause for the wide variations of distribution with ground machines was that in most cases they were gravity fed, with distribution by a spinner. '' The talking-point of the demonstration was provided by a Piper Pawnee aircraft, which swept in low over the markers to release its load. To get an indication of the evenness of spread, a roll of white newsprint was spread across the target area. As with previous demonstrations, tins was liberally coated with paste. When account is taken of wind resistance created by an aircraft travelling at more than 80 miles an hour, compared with the ground machines at a bare two miles and a half an how, the evenness obtained was quite remarkable. The field day programme was designed for the benefit of agents handling various brands of insecticides, or as the president of the Canterbury committee (Mr A. D. Lowe) termed it—“for the people between the manufacturer and the user.”