SEED TREATMENT does not guarantee protection against cabbage stem flea beetle, oilseed rape growers have been warned.

Conditions are favouring insect attack in young crops and growers must be aware of the threat from larvae hatching in October and November, according to Syngenta.

“With warm soil temperatures and now some rain, crops are growing very rapidly,” said the firm‘s Trials Manager, Tom Whitworth.

“Extension from the two leaf stage to six leaves will dilute imidacloprid seed treatment protection, leaving crops vulnerable to insect attack.”

While there may only be limited physical effects on vigorous plants from adult beetles at first, they will lay eggs until temperatures fall to freezing, Mr Whitworth advised.

“When the larvae hatch in October or November and burrow into stems, resulting yield losses could prove very costly.”

Reliable detection of Cabbage Stem Flea Beetle, in time for a tank-mix application with herbicide or fungicide, will provide cost effective control of a potentially serious pest, added David Green of ADAS.

In trials using Hallmark Zeon (lambda-cyhalothrin) at the threshold of five larvae per plant, gave an average yield response of 0.34t/ ha, at a cost of £3.50/ ha, he said.

For an interactive guide on manufacturer supported tank mixes, together with Crops commentary, go to our Tank Mix Guide 2004.