16 November 2001

Root fly poses most significant danger to cauliflower crop

CABBAGE root fly has been the biggest problem in producing some excellent samples of organic cauliflower at Coswinsawsin, says farm manager Paul Harris.

Garlic-based sprays every eight days helped but proved nowhere near as effective as fleece, a fine mesh covering preventing the fly reaching the crop. But fleece is expensive and has to be removed for hoeing and replaced afterwards.

Trials next year may include garlic granules, and onion- or garlic-related plants grown in the brassica modules. Closer planting may also be tried so that even if some plants are lost, the ground will be covered more quickly to reduce risk of fly attack.

Early spring crops lost up to 40% of their plants through root fly, says Mr Harris.

Good weed control has been achieved by inter-row hoeing, starting as soon as the plants are big enough not to be buried and continuing every seven to eight days until the leaves are being damaged.

Charlock and runch proved very competitive and some hand-weeding, at £75-100/ha (£30-40/acre) each time, was required in September.

With conventional cauliflowers making 18-22p/head for 2000-2200trays/ha (800-900/acre), the organic crop earned 65p a head for about 1000 trays/ha (417/acre). "So we do need that extra price," says Mr Harris.

Sourcing organic brassica seed of varieties suitable for west Cornwall is difficult, he adds.

Paul Harriss inter-row hoeing at Camborne, Cornwall, kept on top of weeds to produce these fine samples of organic caulis.