As part of AHDB-funded project FV 344a, "Combating Resistance to Aphicides in UK Aphid Pests", three DBM samples were tested by Rothamsted Research for resistance - from Lincolnshire, Suffolk and Scotland. All three samples tested resistant to pyrethroids.
Where pyrethroid-resistant caterpillars are present, growers are likely to get poor control from pyrethroid sprays. Some of the DBM population will probably be controlled by natural enemies including parasitoid wasps, recently found parasitising DBM at Warwick Crop Centre (AHDB project FV 440), so a selective insecticide is beneficial.
There are practical measures that can be used on a daily basis to prevent resistant strains of pests developing and to plan ahead for the forthcoming season.
AHDB fact sheet 01/13 outlines how the repeated use of insecticides, fungicides and herbicides, if not properly managed, can result in the development of resistant pest, pathogen and weed populations. It lists the known cases of resistance that may potentially cause problems in the control of a range of pests, diseases and weeds that commonly occur on horticultural crops in the UK and advises how to prevent resistant strains developing.
Although approvals change rapidly, the principles of resistance remain unchanged. Current approvals are displayed on the Chemicals Regulation Directorate website, or consult a BASIS-qualified adviser before deciding to apply any plant-protection products listed in this publication.
For more details on DBM, see http://horticulture.ahdb.org.uk/diamondback-moth.
For details on all AHDB Horticulture activity, see horticulture.ahdb.org.uk.