Bayer CropScience - Pestspotter - Cabbage stem flea beetle

Pest: Cabbage stem flea beetle

Identification
The adult beetles are blue-black, 3 - 4.5 mm long. When disturbed the adults `jump` using specialised hind legs. The creamy white larvae have numerous dark spots on the back and are up to 7 mm long. They have a dark brown head, three pairs of legs and a dark plate at the tail end.

Symptoms
The adults feed on both the cotyledons and the young developing leaves giving the distinctive `shot-holing`. Where crops are growing slowly severe damage and even plant loss can occur. Normally the damage caused by the larvae is economically more important. These can penetrate and mine into the older petioles and from here migrate into the stem of the plants and then on to damage the growing point.

Life Cycle
During the summer the adults become inactive and move to cool shaded places before returning to feed on brassica plants in the autumn. After a few weeks eggs are laid from which larvae emerge, these tunnel into the petioles of brassica plants throughout the winter into spring depending on weather conditions. From late autumn the larvae migrate to the soil to pupate. The adults hatch from these pupae in summer. Adults can also overwinter in hedges and other sheltered areas, emerging in late spring to feed on leaves and pods. There is one generation per year.

Large numbers of adults have been seen crawling across trailers at harvest, but they do not cause any damage to the harvested crop.

Importance
The cabbage stem flea beetle is widespread in the UK and northern Europe. The damage caused by adult CSFB feeding gives rise to the `shot-holing` symptoms which affects the cotyledons and early leaves, resulting in stunting and poor plant vigour. If severe the damage can kill the seedlings even before they emerge. Seed treatments such as Chinook and Modesto can give useful reductions in damage, but in very severe attacks a pyrethroid spray may also have to be applied. If adult CSFB attack continues into the autumn then crops should be monitored for larval presence and where necessary a pyrethroid insecticide should be applied.

Threshold

Consider applying an early pyrethroid spray if adults have eaten :