16 October 1998

Seed treatment set to deliver in West Country

By Charles Abel

A NEW anti-BYDV seed treatment should help one Dorset grower overcome 6m buffer zone problems, protect the crop from planting and put an end to autumn spray day worries.

BYDV pressure around Frith Farm, Stalbridge is severe most years, says manager Ken Dunn. "Were surrounded by grass and we have a lot of hedges, so we get aphids whether it is a good year or a bad one."

Trial plots on the 167ha (413 acre) farm showed a 30% yield loss where barley received no autumn spray last year. "You could see the patches – it just looked awful."

This autumn all the winter barley will be sown with an anti-BYDV seed dressing, once conditions permit.

Main reason for the move is a desire to protect the entire field. "Six metre buffer zone restrictions mean we have to leave a lot of crop unprotected. We dont have a single field without a ditch and we do take the restrictions seriously," Mr Dunn comments.

This years 10ha (25 acres) of Regina winter barley will go in two fields surrounded by ditches which leave 1ha (2.5 acres) of the crop in 6m headlands. That could cause a £200 loss, assuming a 30% knock to the farms average malting barley yield of 6.5t/ha (2.6t/acre).

New seed treatment Raxil Secur (tebuconazole + triazoxide + imidacloprid) means the crop can now be protected right up to the field margin, notes farm agronomist Mike Rastall of Profarma.

It also means BYDV protection is independent of the weather. "We run a tractor mounted sprayer, so autumn spray days can be a real issue," says Mr Dunn.

The seed treatment is also considered safer than blanket sprays. "We dont know how useful beneficial spiders and insects are. But if you are going on early with a BYDV spray to beat the weather, the crop may barely have two leaves. You can be applying 90% of the spray to the soil, which can not be good."

But Mr Dunn still has two concerns. "Aphids have to feed on the crop to take up the insecticide from the seed treatment. Im convinced it wont be 100% effective at avoiding BYDV."

The £11.50/ha (£4.50/acre) cost is also felt to be high, equating to two pyrethroid sprays plus the cost of the second application. Sometimes a second spray is not needed, notes Mr Dunn.

To check the benefits of the seed treatment one bag of Raxil-only Regina will be sown for comparison this autumn.

Mr Dunn is also meticulous about stubble hygiene. "It helps minimise green bridge carryover. We dont waste a lot of corn through the combine, making sure settings are right to avoid volunteer problems. Good bushel weights help too. You really cant avoid grain loss if youve grown a thin sample."

If a field does need cleaning paraquat is the preferred option. "It makes the best job of weeds and kills the aphids too," notes Mr Rastall.

For winter wheat the BYDV strategy is two sprays for crops drilled before October, one spray for those sown in early October and a careful think for later sowings.

Each week Mr Rastall receives a report of aphid numbers and infectivity to guide decisions. If pressure is high a premium product such as lambda-cyhalothrin (Hallmark) or deltamethrin (Decis, Pearl Micro) is used. "Trials show they give an advantage." Where risk is lower cypermethrin (Ambush, Toppel) suffices.

BYDV TREATMENTS

&#8226 Beats 6m buffer zone.

&#8226 Protects seed from sowing.

&#8226 No more spray day worries.

&#8226 Environmental benefits.

&#8226 £11/ha cost.

&#8226 Is it 100% effective?

Resistance OK

Using Raxil Secur and Sibutol Secur cereal seed treatments is unlikely to increase the risk of aphids developing resistance to Gaucho, the sugar beet seed treatment containing the same insecticide, imidacloprid.

The aphids which affect cereals are different from those affecting beet, notes Brooms Barn entomologist Alan Dewar. The only small, but theoretical, risk concerns build up of the insecticide in the soil, he notes.

Imidacloprid is quite persistent, lasting up to 400 days, so could accumulate. Poor weed beet control in subsequent crops could expose beet aphids to the insecticide, increasing selection pressure. "But that is very much a theoretical risk. So far no resistance to imidacloprid has been found anywhere. If and when it is it may pay to have a rethink. But in the meantime I dont think growers should be concerned."