The first in a new series of Syngenta pest management guides has highlighted the danger of pollen beetle migrations into oilseed rape crops in the recent warm weather, according to its author, David Green of ADAS.

Recent warm weather will have triggered the rapid and long distance movement of pollen beetle into oilseed rape crops. The migration could not have come at a worse time for any backward or drought stressed crops at their most vulnerable green to yellow flower bud stages, warns ADAS entomologist, Green. Such crops cannot afford any further check from insect attacks and growers should interpret treatment thresholds accordingly, he adds.

Green provides growers with clear guidance on pest evaluation and treatment thresholds. If an invasion is suspected when a winter OSR crop is at the green to yellow bud stage, 20 plants should be beaten over a white tray and the number of shiny black beetles captured should be counted; more than 20 beetles per plant demands immediate treatment; if there are 5 to 15 beetles and the crop is still at the green bud stage, or at all backward, again treat with urgency, he advises. Only if beetle numbers are below 15 per plant with the crop well advanced towards flowering, or below five per plant at any growth stage, is spraying unnecessary.

When thresholds are breached and crops are sprayed at the green to yellow bud stage, follow-up treatment may be required if re-invasion occurs before the crop reaches full flowering.

The Syngenta guide to Summer Pests of Oilseed Rape is the first in a series of technical pest management guides written for growers by ADAS. For a copy of the free guide and to receive future copies, growers and agronomists can call Syngenta Technical Enquiries on 0800 1696058.