This beetle is one of the major pests of asparagus in the garden and damage is caused by both the larva and adult insect.
Both stages of this insect feed on asparagus stems and the resulting damage will turn the stem brown/dead above the point of feeding
This weakens the plant and if the insect is not controlled, plant death will happen.
How do you know you’ve got this pest?
You’ll see the beetle or larva on the stem of the plant.
The stem/fern will go brown and die.
Note the larva tend to emerge from overwinter in plant debris/mulch in May and June and you’ll see feeding damage from that point onwards.
What Can You Do To Control This Pest?
- Burn old stems at the end of each garden year. This will eliminate overwintering stages.
- Handpick the beetles and larvae when seen on the plants from late spring onwards. Drop into a pail of soapy water.
- Remove all egg sacs from asparagus spears. Adult beetles will lay a new clutch every 5 days or so.
- You have to check your asparagus plants every second day to catch these creatures before they get to damage levels (adults will fly in from wild asparagus or neighboring gardens.)
- Larger plots can be sprayed with pyrethrum based sprays where these sprays are legal. Check your local garden centers for available sprays. Note that spraying with pyrethrum during flowering stages should not be done to avoid killing bees that pollinate/work the asparagus flowers.