26 October 2001

Phoma surge threatens OSR yields

AS predicted in farmers weekly earlier this autumn phoma levels have rocketed in oilseed rape, prompting disease experts to urge early treatment of crops across the south and east.

Growers in the west and south-west, where dry conditions have delayed the onset of the fungus, have been warned to keep an eye on crops.

Phoma levels in monitored fields at ADAS Boxworth shot up from 1% plants infected to 50% in just a week, reports ADAS oilseed specialist Peter Gladders.

The key worry is the timing, he says. "Usually we are into November before the phoma explosion occurs, and its development is very dependent on temperature. The mild conditions mean the disease is now growing rapidly down the stem.

"Normally we recommend spraying at 10-20% plants infected, but I would say bring that nearer to 10% now."

Latest readings from ADAS Terrington, in Norfolk show 40% of plants are infected while this figure stands at 12% for High Mowthorpe in Yorkshire.

Growers should be looking for a chemical with kickback as well as protective activity when spraying, advises Dr Gladders. He advocates a standard half rate, which means 0.25 litres/ha of Plover (difenoconazole) or 0.4 litres/ha of Punch C (carbendazim + flusilazole). "And consider repeating this in early December."

This is the third year in succession that phoma has come into the crop early. Last year, when levels were not as high, a fungicide application gave a 0.75t/ha yield response in Apex, says Dr Gladders. The disease causes stem canker in the spring, resulting in lodged crops. &#42