1 March 1996


BEWARE of potential insect damage to spring oilseed rape in hot dry seasons. That is one clear message from trials at Velcourts new demonstration site at George Farm, Stamford, Lincs.

Spring rape is very much the "poor relation" of winter rape, according to technical director Keith Norman. For the third year in the companys demonstration the gross margin of the spring crop was lower in 1995 – by up to £340/ha (£138/acre), he notes.

Pollen beetles are normally seen as the biggest pest threat to the spring crop. But last seasons unusual weather brought a bigger one, namely mealy cabbage aphids in June.

"They came in very quickly and were soon established," says Mr Norman. Flower buds in untreated plots became distorted and pods infested. The yield loss was "dramatic". Unsprayed Spok gave just 0.2t/ha (1.6cwt/acre) against 1.9t/ha (15cwt/acre) when treated with Aphox (pirimicarb).

The turnip rape Kova was similarly hit, giving only 0.4t/ha (3.2cwt/acre) untreated, but 1.7t/ha (13.5cwt/acre) where the pests were controlled.

"Dont underestimate the effects of pests in hot dry years," warns Mr Norman.