Flea beetles on brassicas and allied plants

Some species of flea beetle feed on the leaves of all brassicas and related plants, including rocket, radish, swede, turnip and wallflowers. The result is a peppering of holes that looks unsightly, particularly on salad leaves.  

Flea beetle (Phyllotreta sp.) on Turnip (Brassica sp.). Credit: RHS/Entomology.

Quick facts

Common name Flea beetle
Scientific name Various, mainly Phyllotreta and Psylliodes species on brassicas and allied plants
Plants affected Many plants in the brassica family, including cabbage, broccoli, sprouts, turnip, radish, salad rocket, wallflower and alyssum. Also nasturtium and Cleome
Main symptoms Small rounded holes in the foliage, especially on seedlings. Small beetles jump off the plants when disturbed
Most active Spring and summer

What are flea beetles?

There are more than 100 species of flea beetle in Britain, they are a subfamily of the leaf beetles (Chrysomelidae). A few species feed on brassicas and related plants. The mall beetles are 2-3mm (about 1/10in) long, with the enlarged hind-legs that enable them to leap when disturbed. The adults feed on the leaves and the larvae on the roots, the root damage does not usually affect crops in gardens.

Symptoms

  • Rounded holes are scalloped out of the upper leaf surface; often these do not go all the way through the leaf. The damaged areas dry up and turn pale brown
  • Seedling plants are particularly susceptible the growth of older plants is only checked if infestations are heavy
  • Several Phyllotreta and Psylliodes species can be responsible. These beetles are 2-3mm (about 1/10in) long, coloured black or metallic green or blue, some have a yellow stripe running the length of each wing case
  • Flea beetles can be seen jumping off leaves when disturbed
  • Root feeding by the grubs does not usually affect growth in home gardens

Control

Check susceptible plants frequently from spring onwards so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.

Non-pesticide control

  • Growing susceptible crops under insect proof mesh may keep the beetles out
  • Where possible tolerate populations of brassica flea beetles
  • Encourage wildlife in the garden, such as birds, frogs and predatory ground beetles who will eat the larvae and sometimes the adult beetles

Pesticide control

  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer). Several applications of these short persistence products may be necessary to give good control
  • More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
Follow label instructions when using pesticides. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number applications, spray interval and harvest interval

Plants in flower should not be sprayed due to the danger to bees and other pollinating insects

Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener

Downloads

Pesticides for gardeners (link downloads pdf document outlining pesticides available to gardeners)

Biology

  • Brassica flea beetles overwinter in leaf litter as adult beetles that emerge in mid-spring to feed on seedlings of brassicas and other host plants
  • In late summer there is sometimes a significant migration of adult beetles into gardens from brassica crops especially oilseed rape fields, when damage to mature plants can occur
  • The whitish brown larvae live in the soil and feed on the plants' roots, but this does not usually cause significant damage in gardens
  • Pupation takes place in the soil in mid-summer


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