Plants affected
Vegetable asparagus, not ornamental types.
Symptoms
Both 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.
Cause
The adult beetles are 6-8mm long, black in colour with six yellow blotches on their wing cases and a reddish thorax.
The beetles emerge from the soil in late spring (May and June) and lay black eggs on the asparagus spears and foliage. The creamy greyish-black larvae are up to 10mm long when fully grown, after which they go into the soil to pupate. There are two generations between May and September.
Control
Burn old stems at the end of the year to destroy overwintering beetles. Hand pick the beetles and larvae from plants from late spring onwards.
Large plantings can be sprayed with pyrethrum (Py Spray Garden Insect Killer, Doff All in One Bug Spray, Scotts Bug Clear Gun for Fruit & Veg or Gem Stop Bugs). If the plants are in flower, spray at dusk to avoid harming bees.