Wheatgrowers Should Remember Aphids

Press, Volume C, Issue 29500, 29 April 1961, Page 6

Wheatgrowers Should Remember Aphids

Farmers who are growing wheat this year should bear in mind the

recommendation of scientists that to escape the autumn flight of cereal aphids wheat should not be sown before mid-May, but if it is sown earlier than this a particularly keen watch should be kept on the crop in the autumn as well as in the spring so that if aphids are detected a spraying programme can be followed.

Mr A. D. Lowe. an entomologist of the Lincoln sub-station of the Entomology Division of the Department of Scientific and Industrial Research, said this week that the aphid commonly found on wheat in New Zealand was of importance both as a pest and carrier of cereal yellow dwarf virus. Its correct name was Rhopalosiphum padi. but as it was the only aphid so far on cereals in any numbers in New Zealand it had already become known as the cereal aphid. This insect lived on all cereals and many grasses. It was active throughout the year with flight periods in Canterbury in April to midMay and from mid-Septem-ber to mid-October. The population, both winged and wingless, was made up of female insects which gave birth to living young immediately on landing on host plants at a rate determined by factors such as temperature.

Aphids landing on autumnsown wheat last year were shown to have increased to 200 per plant by October 8, indicating a high rate of increase in the spring. Flights in the late autumn were from grasses of all kinds to newly emerging cereals, and in the spring there were further flights to spring-sown cereals, the aphids leaving these crops as they ripened off to return to grasses where they spent the autumn.

Mr Lowe said that the

recommended action to combat the aphids and the virus they carried was to plant wheat after mid-May to avoid the main autumn flight and to keep a watch for aphids.

and where they were seen in autumn or spring to apply a suitable insecticide. Materials available and likely to be beneficial were Rogor 40 applied at 16 fluid ounces to the acre and Metasystox applied at 12 fluid ounces to the acre. The cost per acre for these materials was from 17s 6d to 20s. They could be combined with weed sprays where the materials were compatible. Mr Lowe said that little was known about the incidence of virus and its relation to the level of aphid infestation. but a small trial at Lincoln last year showed that where aphids were controlled even as late as October less virus was evident at harvest and an increase in yield amounting to not less than 10 per cent, and probably nearer 20 per cent, was obtained from one spraying. Winged Aphids The winged aphids, which are about l-Bth of an inch long and greenish black in colour, give rise to young which when fully grown are not much bigger than a pin head being l-20th of an Inch across. They have no wings and are represented by a dark spot often seen on the under side of the flag. Mr Lowe said that when aphids could be seen by the farmer it was time to spray. If precautions were taken to protect Aotea against the aphid-virus complex, Mr Lowe said that there was every chance that its high yielding characteristics would be restored and within its high yield there was plenty of room tor aspraying programme. Mr Lowe said that work on sampling of greenfeed crops for aphids had already begun and both the Crop Research Division and the Department of Agriculture proposed Io undertake an extensive series of trials as well as a good deal of biological work on the aphid in the coming season. With the Increased area now being put into wheat the aphid was bemz given a good chance to build up. said Mr Lowe, and it might be that spraying for the aphid would become a standard practice in growing wheat