28 May 1999

Doubts raised over anti-BYDV seed treatment

By Andrew Blake

AN anti-aphid cereal seed treatment launched last autumn may not be robust enough to prevent barley yellow dwarf virus in hot spots in the south, warns a farm management company.

But while French users get twice as much of the active ingredient applied to seed, the maker maintains the dose for UK conditions is sufficient provided drilling rate is not too low.

Secur, the imidacloprid fraction in two seed dressings from Bayer, was used on about 5% of all cereals sown last year by Velcourt, says technical director, Keith Norman. "In the east we have had no problems. But in a high BYDV pressure area, on one of our farms in Dorset, it is not controlling the disease properly."

The "isolated incident" is on nine fields of Beaufort wheat and four of Fanfare barley treated, respectively, with Sibutol Secur (bitertanol + fuberidazole + imidacloprid) and Raxil Secur (tebuconazole + triazoxide + imidacloprid) instead of relying on spraying. "The damage in the wheat is not as bad as in the barley where up to 7% of the area has BYDV foci."

The risk from the aphid-borne disease is very high on the farm, Mr Norman acknowledges. "The fields are in a wooded area in a valley with water meadows." Nearby fungicide trials, where autumn aphicide sprays were omitted, were almost wiped out by the disease.

"The pressure is incredibly high. Even three cypermethrin sprays have not been enough to control it and the seed treatment was better than nothing. If we had not used it there would have been no crop left. It is clear that where we have really intense pressure we shall need the back up of a spray."

Mr Norman believes the result might have been different had the concentration of imidacloprid in the dressing been the same as in France where growers get twice as much.

"It is a shame we have not got the same rates, because with its environmental benefits of not killing beneficials and avoiding LERAP, we thought it was the answer to a maidens prayer. We have been trying to get away from using cypermethrin."

The barley at Woodsford Farm, Dorchester was not sown until Oct and all at 145kg/ha, says farm manager John Midwood. But he admits the mid Sept-drilled wheat was, with hindsight, slightly at risk at only 120kg/ha.

"The label also says that in high risk areas we should look to over-spray. But the whole point of using the treatment was to ease our autumn workload and to avoid having to worry about buffer zones when spraying Category A aphicides. If we are going to have to spray as well we are not much better off. I am a bit disappointed."

It is interesting to note that where a spray was applied to a Regina headland in one mostly Fanfare field, BYDV in the main part of the field was generally quite low, he adds. "Perhaps the spray acted as a barrier."

"Our experience shows that the product is good but not entirely water-tight in extreme situations," says Mr Norman. "Maybe this southern fringe of England, which is more like France, deserves the higher rate, though I do not expect we shall get it." &#42