3 May 1996

Thrips hit East Anglia

THRIPS have hit beet, bean and pea crops in Norfolk and may be affecting crops across a wider area, reports the latest Virus Yellows bulletin from Brooms Barn research station in Suffolk.

The tiny (2mm) pests are hard to see and their feeding has been confused with frost damage. Close examination reveals black tips on young growing points between the cotyledons and clearing soil from the hypocotyl reveals a blackened stem, similar to that seen with blackleg.

Alan Dewar of Brooms Barn believes the thrips are cabbage thrips and may be more abundant in crops after brassicas, including oilseed rape, and linseed. They have short wings, cannot fly and probably over-wintered in the soil.

Dr Dewars advice is to spray crops immediately if any damage as described above is seen on any plants. If more than half the plants are affected he suggests re-drilling.

Although there are no specific recommendations for thrip control in sugar beet, some products used for other pests will also control thrips, he notes.

Pyrethroids like deltamethrin (Decis), deltamethrin and heptenohpohs (Decisquick), cypermethrin (Ambush) and lamda-cyhalothrin (Hallmark) are likely to give good control.

Organophosphates such as dimethoate, pirimiphos-methyl and chlorpyriphos are also effective but hit non-target organisms harder, he adds.