Time Now To Look For Aphides

Press, Volume CVIII, Issue 31760, 17 August 1968, Page 10

Time Now To Look For Aphides

The Aphid and Virus Committee recommends all wheat growers to examine their autumn-sown crops now for the presence of aphides.

These insects are about a tenth of an inch long, dark green in colour with reddish blotches on the hind end. At this stage of the year they are usually wingless, and will be found sheltering at the base of plants, either feeding on the undersurface of the leaves or on the white basal portions. It is necessary to dig up several plants with a trowel and the whole clump should be thoroughly inspected for aphides. A number of trowel samples should be taken from different parts of the field and each checked for aphides. If any aphides are found then the crop should be treated before September 1. Trial data has shown that treatments of autumn-sown crops during July and August are likely to be of more benefit than those applied later.

The earlier recommendations with respect to sowing date in relation to aphis infestation still apply. Wheat sown before May 1 will be infested with aphides every

year Crops sown between May 1 and 15 are likely to be infested and should receive a careful check for aphides Wheat sown between May 15 and 31 could emerge after the flights have ceased but there could be some risk to those crops which emerged before the middle of June. Wheat sown after June 1 will almost certainly avoid the problem of aphides and cereal yellow dwarf virus.

The cereal aphis'is easily killed and spraying with any recommended aphicide at standard rates usually gives 100 per cent control. The use of granular insecticides on crops sown after June 1 is not warranted at this stage. Where crops also require spraying for annual weeds, such as wild turnip, the weed control chemical and insecticide can be applied in the one operation. The concentrated chemicals should not be mixed but added separately to the spray tank while it is being filled with water. However, the insecticide spray should be applied before the end of August, and not delayed until weed spraying can be completed later in September.

It is usually necessary to apply insecticide separately, particularly where perennial weeds such as Californian thistle are a problem, since these are seldom through the ground until the end of September or early October. This is too late for aphis control in autumn-sown wheat. The precautions with respect to stage of growth of crop for weed control should be observed. This applies par-

ticularly to early spraying where, In general, the crops should be beyond the fiveleaf stage before applying MCPA or 2-4 D. Because of adverse weather this season, many crops may be sown in August and these can be regarded virtually as spring-sown crops. Recommendations and advice regarding control of cereal aphides in these crops will be given in mid-September as spring flights do not begin until this date.

The grain aphis (light-green in colour), which infested the heads of wheat in many areas of Canterbury last season, has been found over-wintering in cereal greenfeed. This aphis may be a problem in the coming season and, if necessary, advice about control measures will be given at a later date.