Flea beetles on brassicas and allied plants

Flea beetles feed on the leaves of all brassicas and related plants, such as rocket, radish, swede and turnip. The result is a peppering of holes that looks unsightly, particularly on salad leaves.  Some ornamental plants, such as wallflowers are also damaged.

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

Quick facts

Common name Flea beetles
Scientific name Various species, mainly Phyllotreta and Psylliodes species on brassicas and allied plants
Plants affected Many plants in the brassica family, incl. cabbage, broccoli, brussels sprout, 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 April to May and August

What are flea beetles?

Some species of flea beetle are pests of: brassicas and related plants. The adults feed on the leaves and the larvae on the roots. These small beetles are 2-3mm (about 1/10in) in length, with the enlarged hind-legs that enable them to leap off plants when disturbed.

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 to damage by the adult beetles and the growth of older plants can also be checked if infestations are heavy
  • Several Phyllotreta and Psylliodes species are responsible. These beetles are 2-3mm (about 1/10in) long, coloured black or metallic green or blue, and some have a broad yellow stripe running the length of the wing cases
  • Flea beetles can be seen jumping off leaves when disturbed
  • Root feeding by the grub stage does not usually affect growth

Control

Non-chemical control

  • Ensure rapid germination and development of seedlings so that they grow through this vulnerable stage quickly
  • Keep plants watered during dry spells and avoid sowing into cold soil
  • Covering seedling plants with insect proof netting (e.g. Enviromesh) will reduce damage by excluding the adult beetles

Chemical control

  • On food plants ensure that the crop is listed on the pesticide label and that all instructions are followed, particularly those on harvest interval, spray interval and maximum number of applications. 
  • Brassicas can be sprayed with the systemic insecticide thiacloprid (e.g. Provado Ultimate Bug Killer Ready To Use), deltamethrin  (e.g. Bayer Provado Ultimate Bug Killer), lambda-cyhalothrin (Westland Resolva Bug Killer) or pyrethrum (e.g. Py Spray Garden Pest Killer, Bug Clear Gun for Fruit & Veg)
  • Only one application of thiacloprid is permitted on leafy brassicas during the growing season or two (in some cases three) applications of deltamethrin or lambda-cyhalothrin can be used. The organic pesticide pyrethrum is not restricted in numbers of applications and could be used up to one day before eating the produce

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

  • Flea beetles overwinter in leaf litter as adult beetles that emerge in mid-spring to attack the seedlings of brassicas and other host plants
  • In late summer there is sometimes a significant migration of adult beetles into gardens from 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
  • Pupation takes place in the soil in mid-summer

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