28 April 1995

Sclerotinia tip for OSR crop

OILSEED RAPE growers should protect crops against Sclerotinia before petal fall. The aim is not just to preserve yield in the current crop, but also to reduce disease levels in future susceptible crops.

So says Huw Phillips of Kinross-based Scottish Agronomy. "All our main break crops like carrots, peas, potatoes and linseed are susceptible. But oilseed rape is the only crop in which the disease can be controlled successfully.

"Growers need to consider the long-term risk to keep their rotational options open. Spraying the rape crop will help to maintain a low or negligible level of infection in the rotation."

Mr Phillips believes a mix of 0.75 litres/ha (0.53pt/acre) of vinclozolin (Ronilan) and 0.5 litres/ha (0.35pt/acre) of mbc is the most cost-effective treatment, at about £25/ha (£10/acre).

Stephen Derbyshire, agrochemical manager for Cargill, reckons many growers are growing rape on the same fields as four years ago when the disease last caused severe problems.

Early petal fall

He believes growers should consider the risks at early petal fall before spraying. "The severity of the disease is weather related. If it is hot – above 20C (68F) – and humid in the crop, and the field has a history of disease, or is close to one that has, then it will very probably be worth spraying."

Further south, Herts-based Samco agronomist, Peter Taylor, reckons a mid-flower insurance spray is worthwhile. But he suggests growers match product to risk. Many can get away with mbc alone at 1 litre/ha (0.7pt/acre), he believes. "It is quite good on Sclerotinia and gives reasonable Botrytis control. And it is relatively cheap at about £8/ha." &#42