15 September 1995

Aphicides are better by half

A GRAPHIC demonstration of green bridge carryover of BYDV is highlighted in an aerial photograph from Cyanamid.

The picture shows a West Country field of winter barley earlier in the year. Before drilling, half was treated pre-harvest with glyphosate (against onion couch) and the other half sprayed with paraquat – in this case as Scythe.

Although both halves were subsequently affected by aphid-borne BYDV, because neither was sprayed with an autumn aphicide, the area after glyphosate (left) was hit much harder.

Cyanamids Roger Allen believes this was because the paraquat-treated half lost its aphid-appeal relatively quickly as the weeds became desiccated. By the time the field was ploughed there were fewer turned under than in the glyphosate-treated half where the weeds stayed green longer.

BYDV is a big problem in the west, especially after grass and weedy stubbles, he points out.

"Even when youve ploughed the aphids down they seem to be able to move back up to infect the young plants over a long period," he adds. This means infection can often take place between aphicide sprays.

The photograph highlights the importance of an autumn aphicide programme. "It is essential to use a pyrethroid in following cereal crops where there is a threat of BYDV transmitted by aphids living on the green bridge," says Mr Allen. &#42

Neither half of this winter barley field escaped BYDV, but speedier green bridge destruction on the right may have helped reduce infection.