Pest Focus: Flea Beetle

If you have noticed tiny black beetles crawling over your brassica plants this month then flea beetle could be the cause. These tiny bugs are around 3mm long, and, true to the name, jump off affected foliage once they are disturbed. Colour variations include metallic green and blue, as well as a yellow stripe running down the length of the wing case, depending on the species you are dealing with. Their larvae are small, creamy-coloured grubs with a brown head and a pair of legs. Crops that are affected include Brussels sprouts, cabbage, turnips, broccoli, radishes and some salad leaves. You may also find this pest on your nasturtiums.

Symptoms include round holes on the surface of the leaves (they often do not penetrate the entire thickness of the foliage, but brown patches develop in those areas), the black adults visible on plants and the grubs feeding on the roots. Young seedlings are particularly vulnerable to attack, so watch these edibles closely for signs of infection. Organic control methods are limited, but you can protect seedlings by growing them in a greenhouse or polytunnel and planting them out when they have matured past the stage where they are most tempting to this pest. Insect-proof netting is another option for growers who do not have the option of under cover cultivation. Insecticides are available but these should only be used in extreme circumstances – these should be products that are suitable to use on edible plants, too.

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