Q What is asparagus beetle?

A Asparagus beetle (Crioceris asparagi) feeds on asparagus and can be a severe problem if allowed to build up.

Caption: Look out for adult asparagus beetles from late spring

Q What does asparagus beetle look like?

A This handsome red, yellow and black pest is slender and 8mm long. It's easy to spot, unlike its dull-grey-green, caterpillar-like grubs. You might also notice the brown eggs on the spears. They are flask-shaped and laid on end in groups in June.  

Q Could I mistake asparagus beetle for anything else?

A The adults are very distinctive, but you might think they are a ladybird at a casual glance.

Q What damage do asparagus beetle do?

A Only asparagus is affected. The adults and larvae graze on the foliage, sometimes completely stripping the plants of leaves. This weakens the plants and could reduce the crop.

Q When should I expect asparagus beetle?

A The adults shelter over the winter in the soil, under stones and in old plant debris. In late spring, usually after the cutting season is over, they lay eggs on the plant's foliage. After about a week the larvae hatch and eat the foliage for about two weeks. They then form 5mm pupae in the soil, which last for another two weeks, when the adults emerge.

This cycle is repeated with up to three generations before the foliage dies down in late autumn. The adults can fly and infest other gardens.  

Q Can I spray asparagus beetle?

A Often they are only a minor nuisance, and you can pick off enough beetles and larvae by hand on a small patch to prevent them from doing much harm. Some experts suggest that spraying is needed if 10% of the foliage has been eaten or if more than half is infested with larvae.

If you think larvae are sufficiently numerous, apply an insecticide containing pyrethrum, such as Scotts Bug Clear Gun for Fruit & Veg or Py Spray Bug Killer. You need to make sure all the foliage gets covered as pyrethrum does not travel around the plant. Further sprays may be needed as more larvae emerge.

Q How can I reduce the chances of an asparagus-beetle attack next year?

A Getting rid of the beetles' overwintering sites will help keep their numbers down. Clear away, shred, compost or burn old fern at the end of the year. Remove plant rubbish, stones, planks and any other cover that beetles could use around the asparagus plot.