RAIN HITS APHIDES

Press, Volume XCIX, Issue 29222, 4 June 1960, Page 9

RAIN HITS APHIDES

Elements Help Farmers

A clear indication of the effect of heavy rain on aphid populations is available from the records of the sub-station of the Entomology Division of the Department of Scientific and Industrial Research at Lincoln.

Counts made on the day of the rail and rain storm on March 29 showed a mean population of 110 aphides per plant of rape and swedes. When a further count was taken in the following week on the same plots it was shown that the rain had reduced the average number of aphides per plant to only two. Aphid Mortality Mr A. D. Lowe, an entomologist of the sub-station staff, said this week that the practical significance of this result was that it indicated what had been suspected for some time—that intensive rain caused heavy mortality in aphid populations. Farmers would recognise that as being one of the main reasons for the downward trend in aphid populations as soon as the autumn rains came.

From a farmer’s point of view Mr Lowe said that the same truth applied at any other time so that heavy rain would be of significance at any time from early November to mid-March in keeping aphides at bay. In this jespect Mr Lowe said that there was a significant difference between Canterbury and other districts where there were periodic summer rains which kept the aphid populations down. Warmth or high temperatures were responsible for stepping up the reproductive rate of aphides provided that they did not cause plants to wilt. Irrigation Effect It was probable that border dyke type irrigation by helping to keep plants in good condition made them slightly more suitable as hosts for aphides. The significance of the effect of rainfall was being carefully watched by all workers at Crop Research Division who were interested in the various aspects of growing brassica crops, said Mr Lowe. \