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 often a peppering of holes particularly on salad leaves.
Quick facts
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 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). Most do not feed on garden plants or have a noticeable effect on them, a few species in the genera Phyllotreta and Psylliodes feed on brassicas and related plants. The small beetles are 2-3mm (about 1/10in) long, with 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 populations are large
- 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
- Adult flea beetles can be seen jumping off leaves when disturbed
- Root feeding by the grubs does not usually affect growth in home gardens
Management
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 using the methods in the non-pesticide section below. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.
Non-pesticide
- Growing susceptible crops under insect proof mesh may keep the beetles out
- Where possible tolerate populations of brassica flea beetles, on larger brassicas where outer leaves are discarded, these beetles usually have a limited effect on edible parts
- Encourage wildlife in the garden, such as birds, frogs and predatory ground beetles who will eat the larvae and sometimes the adult beetles
Pesticides
The RHS recommends that you don't use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.Where you cannot tolerate flea beetles, manage them using the information above as your first course of action.
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.
If you do decide to use pesticides, the shorter persistence products (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.
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
Always follow the instructions on the products. For edible plants, make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval.
Homemade products are not recommended as they are unregulated and usually untested.
Be aware that products such as Neem oil are not registered for use in the UK and we cannot advise on their use.
Plants in flower must not be sprayed due to the danger to bees and other pollinating insects.
- Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer). These have a largely physical mode of action. These pesticides although broad spectrum have a very short persistence and so may require reapplication to keep beetle numbers in check
- More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer). These products have long lasting action against insects including those that are beneficial
- A broad spectrum systemic insecticide (which is absorbed and transported through plant tissues and has contact action) containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles. Systemic pesticides are widely considered to be the most environmentally damaging, remain active for a long time and will kill beneficial invertebrates
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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