retention are less likely to be damaged by an infestation of aphids or the viruses they transmit according to new research supported by the GRDC. The research, through Agriculture WA and the Centre for Legumes in Mediterranean Agriculture, found aphid arrival in crops and the spread of aphid-borne viruses is greatly affected by the amount of stubble retained during seeding.
Aphids and the viruses they spread are major threats to lupin production throughout WA. Aphids can reduce crop yields by feeding on plant sap and indirectly by transmitting virus diseases. In 1988 losses caused by cucumber mosaic virus (CMV) were estimated to be as high as $10 million.
In trials at Badgingarra, the Chapman Valley and Avondale, Agriculture WA entomologist Francoise Berlandier with virologist Roger Jones and agronomist Annette Bwye found aphids were less likely to land on lupins and spread viruses when crops were planted early at 80¬100 kg/ha or where stubble mulch was present.
Denser seeding works
"Seeding early using narrow row spacings and a high sowing rate will help achieve a density of 45 plants/m2 which enables the crop canopy to close over at a faster rate than lower sowing rates," Ms Berlandier said.
"That shades out CMV and bean yellow mosaic virus (BYMV) infected plants, reducing the number of infected plants from which aphids pick up and transmit viruses. The high plant density also deters some species of aphids from landing in lupin crops."
So does stubble retention
"The stubble repels incoming aphids attracted to the pattern of bare earth and green plants by covering the bare earth with a reflective mulch. It is particularly beneficial in years when aphids arrive early and in wide row spaced crops which form closed canopies later than normal row spaced crops," said Ms Berlandier.
Added Dr Jones, "our trials have shown that CMV spread had been reduced by up to 50 per cent at one site where 2 t/ha of straw mulch had been retained. At another site straw mulch had reduced the spread of bean yellow mosaic virus by more than 50 pet-cent".
Both researchers said the findings should provide a bonus for farmers who have adopted stubble retention and encourage others to do so.
"In years when aphids arrive in crops early, many more growers could significantly cut their crop losses from CMV and BYMV by planting crops early at higher rates and retaining stubble at seeding," said Dr Jones.
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