WHEAT SOWING ADVICE

Press, Volume CIX, Issue 31984, 10 May 1969, Page 9

WHEAT SOWING ADVICE

AVER the last two growing " seasons, the question of aphides in wheat has become a little more complicated by the appearance of the grain aphis on heads of wheat late in November, says Mr A. D. Lowe, an entomologist of the Entomology Division of the Department of Scientific and Industrial Research at Lincoln. Though severe damage has been done to some crops by this aphis, its occurrence in no way alters the advice given by the aphid-virus committee over the last few seasons in relation to sowing date. This advice is aimed at avoiding the incidence of barley yellow dwarf virus in wheat crops by sowing wheat, where possible, after June 1.

It is now well known that this virus can reduce yields, and hence profits, considerably, and that it gets into the plant by the feeding of the cereal aphis (a different species from the grain aphis) on the young plants. Cereal aphides develop the winged form during April and May, and fly from grasses on to available green crops at any time up to-the end of May. About one year in 10, they may even fly during June. But in the main—abput 80-per cent of the time —flights will be finished by the first week in June at the latest. Hence wheat sown after the end of May, and emerging no earlier than midJune, will not be above ground when the aphis is landing. So it is still true that you can “avoid yellow dwarf virus by late sowing.” The virtue of this system is that it is based on prevention, not cure, and so it costless to the grower.

There are of course some farmers who do not find this

advice acceptable. Experience has told them that wheat must be sown on their particular farm earlier than the end of May. One inquiry received recently at the Entomology Division of D.S.I.R. was from a grower who wished to gq on an overseas holiday towards the end of May.

His question was what sort of risk did he take if he sowed wheat before May 20. The answer is relatively simple—-there is a slightly greater risk than sowing after the end of May. Fortunately, this risk can be taken provided one other precaution is observed. Where wheat is sown earlier than the end of May, it must be inspected carefully during the winter to see if aphides are present. If they are, , the application of any good aphicide will remedy the trouble-. Thls step' can be taken at any time before mld-September and

still be effective. Some growers have been able to keep application costs down by using an insecticide when boom spraying for weeds. Farmers who find the presence of a second aphis in wheat a confusing issue may ignore the question of the grain aphis at this time of the year. As far aa is known at present, this is a spring problem, not an autumn one.

The important, thing with the autumn-sown wheat crop is to sow after the end of May in order to have the best possible chance of avoiding barley yellow dwarf virus. If you cannot Sow as late as that, then it will be necessary to inspect for aphides, and take measures to control! them if they are present. Separate advice will be given in , the spring for growers .who are troubled with the grain aphis.