Stubble puts aphids in a holding pattern

But infected seed may still be major problem

Retention of stubble can reduce cucumber mosaic virus (CMV) spread in lupins by about 50 per cent compared with sowing into bare earth. That's the latest word from a GRDC- funded program at the WA Department of Agriculture aimed at practical management strategies to reduce CMV. Crop residues on the soil surface reduce the landing rates of incoming aphids which bear the virus. Stubble provides protection early in the season before lupins develop a canopy.

Trials were conducted on lupins sown at wide row spacing. Seeding rates of 40-80 kg/ha produced the same result. Researchers report that despite these advantages, retaining stubble did not significantly improve yields in the trials. They are now looking at infection levels in the harvest seed.

One half per cent infection? Don't sow!

A recent trial has shown that sowing seed with as little as 0.5 per cent CMV infection can provide a sufficient source of infection to result in yield losses of 16 per cent. Infection levels between 0.5 per cent and one per cent reduced yield by up to 19 per cent, while infection levels, up to five per cent caused yield reductions as high as 42 per cent. Researchers now say a safer recommendation would be to test seed and not sow with infection levels exceeding 0.01 per cent.

Stubbie also inhibits BYMV

Another trial, with bean yellow mosaic potyvirus on narrow-leafed lupins, showed that retaining stubble on the soil surface at seeding will assist in management of the virus, and that wide row spacing in the absence of retained stubble should be avoided.

New test for CMV in lupin seed

There's a new test for CMV in lupin seed.

The test, developed at Murdoch University with support from growers through the GRDC. uses a polymerase chain reaction assay and is more sensitive, more accurate and simple! than previous methods.

In 1992-93 the West Australian Department of Agriculture used the test on 1253 growers' samples, each of 1000 seeds.