Pest insects in brassica crops: cabbage whitefly
Learn about the life cycle and monitoring of the cabbage whitefly, an increasingly important pest of kale and Brussels sprout crops.
Cabbage whiteflies overwinter as adult females on brassica crops, including oilseed rape, and certain species of weed (eg sow-thistle). These females lay eggs in early spring once the temperature rises. Some of the females disperse to new crops, probably quite locally, before laying eggs. The eggs hatch into larvae that soon attach themselves to the foliage – these are known as ‘scales’. The larvae feed on the plant and develop into pupae, which produce a new generation of adults. It appears that multiplication on the host is a key factor influencing the size of infestations, but there may also be further movement of adults (read the report from the project CP 091 Biology of cabbage whitefly for more information). There is a period in the autumn when at least some female cabbage whiteflies migrate to new hosts.
The cabbage whitefly is an important pest of brassicas, mainly as a contaminant.
Monitoring and forecasting
Research has shown that when cabbage whiteflies migrate, particularly in the autumn, they fly sufficiently high to be captured in the Rothamsted suction traps. However, this information is not available to growers on a weekly basis. Adult cabbage whiteflies can also be captured on sticky traps, particularly yellow ones. Regular crop walking is important to identify developing problems. A PhD study at the University of Warwick and funded by AHDB (CP 091) showed that D° sums can be used to indicate when the next generation of adults will emerge within a crop.
Non-chemical control methods
There are no established non-chemical methods for reducing the overall population of cabbage whitefly. The species appears to be attacked by few predators. PhD project CP 091 found that there is a native species of parasitoid wasp that attacks whitefly. In subsequent AHDB projects FV 406 and FV 406a, efforts were made to rear and release the wasp to manage field infestations. However, it was not possible to demonstrate the efficacy of the method convincingly, and the wasps are difficult and potentially expensive to rear. CP 091 showed for the first time that cabbage whitefly can be infected with a naturally occurring fungus that may, on occasion, lead to considerable mortality within an infestation. In CP 091, the fungus led to considerable mortality of adults in the autumn. Fine mesh netting used to exclude cabbage root fly may also exclude adult whitefly if the mesh size is sufficiently small.
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