Flea beetles on brassicas and allied plants

Some species of flea beetle 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 can also be damaged.

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?

Some species of flea beetle can damage 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  be 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 broad yellow stripe running the length of the wing cases
  • Flea beetles can be seen jumping off leaves when disturbed
  • Root feeding by the grubs 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. 
  • A wide range of brassicas can be sprayed with the contact pyrethroid insecticides deltamethrin (e.g. Bayer Provado Ultimate Fruit & Vegetable Bug Killer), lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), cypermethrin (e.g. Py Bug Killer) or pyrethrum (considered organic e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer (also contains fatty acids))
  • Two (in some cases three) applications of cypermethrin, deltamethrin or lambda-cyhalothrin can be used per crop and there is a 7 or 14 day harvest interval. The organic pesticide pyrethrum is not restricted in number of applications and could be used up to one day before eating the produce
  • Plants in flower should not be sprayed due to the danger to pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

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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