Rose-grain aphid widespread in Canterbury cereal crops

Press, 26 November 1982, Page 21

Rose-grain aphid widespread in Canterbury cereal crops

An aphid new to the South Island has recently been discovered in cereal crops in mid-Canterbury. It is rose-grain aphid, scientifically known as Metopolophium dirhodum. The first indication that rose-grain aphid was present in Canterbury came late last year when D.S.I.R. entomologists obtained a single specimen during routine trapping studies. No field infestations of the aphid could be found at that time.

Early this month the aphid was reported from an oat crop near Lincoln, according to Dr Ken Somerfield, an entomologist with the M.A.F. Plant Health Diagnostic Station, Lincoln.

Subsequent surveys by D.S.I.R. and M.A.F. personnel have shown that the aphid is fairly widespread in ceredl crops in an area which includes Lincoln, Johns Road (Christchurch), Darfield, Norwood, Lakeside, and just north of Ashburton, and it is likely to be more widespread than this.

-The aphid is at present most abundant in oat crops, but it is also present in wheat and barley. Confirmation of the identification of rose-grain aphid in Canter-

bury was provided by Mr R. G. Sunde, Plant Health Diagnostic Station, Auckland. The first record of rosegrain aphid in New Zealand was made late last year when 44 speciments were obtained from a trap being operated at Mangatawhiri. 50km south of Auckland. Information is currently being obtained from various sources on the effect of rosegrain aphid in cereal crops. One report- from England states that under trial conditions a 7 per cent loss of grain resulted from rosegrain aphid infestation. By comparison, in the same trial grain aphid (Sitobion avenae — present in New Zealand) caused a 14 per cent yield loss. Similarly, rose-grain aphid was found to cause a lowering of grain protein, though this was less than caused by grain aphid. In England and Europe rose-grain aphid infests cereals during the growing 1 season, and then in autumn 1 moves on to rose plants where it overwinters until I the following spring. It then ; moves back on to cereal ; crops. In New Zealand, where 1 winters are generally milder, I rose-grain aphid may behave 1

in a similar way to cereal aphid (Rhopalosiphum padi) and it may possibly overwinter on grass (graminaceous) hosts. However, this is at present only a hypothesis with no field evidence to support it. Current advisory opinion is that application of insecticide for rose-grain aphid may in general not be worthwhile this season. Farmers who normally apply ' insecticide against grain aphid will probably also control populations of rose-grain aphid in their crops. Next season the situation should be observed regularly and a possible earlier buildup of the aphid watched for. Early autumn-sown cereals should also be regularly checked next year. The recommended threshold for spraying these crops in the Northern Hemisphere is much lower to prevent introduction of barley yellow dwarf virus into the crops. Rose-grain aphid transmits barley yellow dwarf virus, and has also been recorded as transmitting other viruses. The D.S.I.R. hopes to conduct further studies on virus transmission by this aphid locally.