Flea beetles

Picture credit: W.S. Cranshaw, Colorado State University

There are many species of flea beetle and not all of them are pests in the garden. However, some species of flea beetle like to attack brassicas (particularly radishes, turnip, swede and salad leaves like rocket). They are also partial to flowers such as wallflowers and stocks.

Flea beetles are small shiny dark brown-black beetles 2-3mm long that are able to jump in a similar fashion to fleas (hence the name)

The adult beetles graze on the leaves making small holes while the larvae of the beetle can also eat the roots, although the latter causes little damage. Holing of leaves can sometimes be as much as fifty percent of the leaf. This will have a serious impact on the health of the plant. If it is a young plant, then it may well be killed by this damage. Adult plants can be weakened render-ing them liable to other pests and diseases,

Is this the same pest that nibbles around the edge of my broad beans?

No, those are bean weevils. Flea beetles make tiny holes all over the leaf as opposed to weevils that chip away around the edges of leaves. Weevils tend to attack just peas and beans rather than brassicas too.

Should I be worried and what action should I take?

Firstly this depends on the level of the infestation. Often plants do survive and it doesn’t significantly affect your crops.Keeping the area tidy over winter (to remove debris as possible overwintering sites) and promoting biodiversity in general can help control populations. Some species of wasps and flies are parasites of the flea beetle so are an effective biological control. A range of flowering plants will increase the biodiversity on your plot.

If the beetle is becoming more of a problem then try the following control methods:

1. Apply nematodes which help control the larvae in the spring.
2. Dust plants with diatomaceous earth, wood ash or garden lime. These materials help dehydrate the hard exoskele-ton (shell) of the beetle.
3. Rotate planting groups—don’t plant brassicas in the same bed. Try to keep gaps of at least two years.
4. Use bought or homemade sticky traps. Petroleum jelly or lard can be used on white or yellow plastic sheets.
5. Cover crops with environmesh or similar.
6. Keep the soil moist—for example using a mulch around the crops—flea beetles like hot, dry soil.
7. Plant a sacrificial crop close to your precious plants to draw in the beetles—they love radishes and mustard so these work well in conjunction with the methods discussed above
8. If you are happy to use non-organic methods that there are insecticides available on the market that will kill flea beetles.