Asparagus beetle is a widespread on asparagus during the summer months. It feeds on the stems and foliage. Extensive defoliation can weaken the plants and result in a poor crop in the following spring.
Scientific name Crioceris asparagi
Plants affected Vegetable asparagus, but not ornamental Asparagus species
Main symptoms Presence of adult beetles and grubs. Foliage is eaten and may dry up and turn brown
Most active May-September
What is asparagus beetle?
Asparagus beetle is one of about 250 species of leaf beetle (family Chrysomelidae) found in Britain, they range in size from 1 mm to 18 mm. The family contains many metallic and attractive species and all feed on plants (herbivores).
Both the colourful adult and grey larval stages of asparagus beetle eat the foliage of asparagus, they can also gnaw bark from stems, causing growth above the point of damage to dry up.
- The adult beetles are 6-8mm long (about 1/4in), they are black with six yellow blotches on their wing cases and a reddish thorax
- They can fly and so can reinvade asparagus patches from nearby and from places where it has overwintered
- The adult beetles and their grubs feed on asparagus foliage and bark
- If the bark around the stem circumference has been completely removed, the stem and foliage above dries out and turns yellow brown
Check asparagus 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, in the case of asparagus these are the only products approved for use on the crop in home gardens.
- Small populations are unlikely to affect cropping in subsequent years and can be tolerated
- Hand pick the beetles and larvae from plants when seen from late spring onwards
- Burning old stems at the end of the year may destroy some overwintering beetles
- Encourage wildlife in the garden, many animals including birds, frogs and predatory insects such as ground beetles and social wasps will eat the larvae and sometimes adult beetles.
Pesticide controlThe RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner
- Large plantings, where hand removal is not feasible, can be sprayed with organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer). These pesticides although broad spectrum have a very short persistence and so may require reapplication to keep beetle numbers in check.
- No synthetic insecticides are available to the home gardener for use on asparagus
- Plants in flower should not be sprayed to avoid harming bees and other 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
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
- Asparagus beetles overwinter as adults in sheltered places such as grass tussocks or piles of vegetation. They emerge in May and June and lay elongate black eggs that are attached by one end to the asparagus spears and foliage
- The adult beetles can fly and are very adept at locating patches of asparagus
- The creamy greyish-black larvae reach up to 10mm long (3/8in) when fully grown
- They pupate in the soil
- There are two generations between May and September
- In the autumn, adult beetles seek sheltered places where they overwinter
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