3 May 1996

Linseed in jeopardy

LINSEED crops will be at risk from flea beetle attack this spring, especially if cool, dry weather continues.

Although a high proportion of growers used insecticidal seed treatments this season, the risk of damage remains once crops have emerged.

Seed not treated with insecticide is especially vulnerable, says Des DSouza of agchem maker Agrevo. Growers may have to spray before the crop is fully established, as the pest can damage seedlings before they emerge.

Linseed can be treated with Decis (deltamethrin) – the product is approved for use on oilseed rape and can be used on linseed under the minor use extension arrangements. It should be applied at 0.5 litres/ha (0.35pt/acre) as soon as damage is seen. A repeat treatment may be needed, he adds.

Growers who have not used seed treatments should keep an eye on the crop "day by day", says Alan Lane, ADAS entomologist at Wolverhampton. "Scratch through the soil for emerging shoots. If damage is present act quickly."

Sprays may also be needed once treated seed crops have emerged, he advises. "Where populations are high continuous waves of the pest can attack the crop. Crops growing on moisture-deficient soils in cool conditions will be slow to establish. That is the worst scenario with flax flea beetle."

Any pyrethroid with an OSR recommendation can be used. In the warm, Gamma-HCH may be a better choice, he says.