8 December 2000

Thin OSR stands might not pose big yield threat

THIN oilseed rape crops may not pose such a threat to yield as some growers fear.

If the trend to milder winters continues even the thinnest crops could compensate next spring, said ADAS expert John Spink of ADAS Rosemaund.

"Do not think they are a disaster. They have not lost much yield potential yet and if things go fairly well from here on they will not.

"Most years we spend all our time trying to convince growers that their crop canopies are too big. This year it is a case of convincing you that the crops you have will be alright."

Target plant population should be 25-30 plants/sq m, evenly spread. "If theyre in patches, that is not ideal." But even populations as low as 10plants/sqm have shown no yield penalty in trials at Nottingham University, he said.

Main reason for that is the ability of light to penetrate to lower pods, boosting seed number, improving pod retention and reducing lodging, ADAS works shows. In trials thinner canopies have yielded up to 0.3t/ha more than thicker ones, he noted.

Unless canopies are very thick avoid a spring triazole fungicide for growth regulation. "In smaller crops they can push the canopy size below the optimum and cut yield."

Low cost Autocast direct seeding from the combine could have a role, Mr Spink added. "If it establishes well then the extra growth from the early start can be controlled with mowing in spring, nitrogen rate and timing and the use of a growth regulating triazole."

One Notts grower in the audience reported good success with 40ha (100 acres) of Autocast rape mown last spring to control canopy growth. &#42

Thin rape stands might still yield well, says ADAS Rosemaunds John Spink. In trials open canopies give best results.