Asparagus beetle
A small metallic blue-black beetle with yellow marks whose adults and grey grubs chew asparagus spears and ferns.
Also known as: Common asparagus beetle
Symptoms and identification
Spears have scarred, brown, chewed patches and bend over, and ferns are stripped. Small dark eggs stand upright on spears and stems, and plump grey grubs with black heads feed on the foliage.
Causes
Adults overwinter in plant debris and hollow stems, emerge in spring when spears appear, and lay eggs on them. Larvae feed for 2 to 3 weeks and several generations occur in warm years.
Organic treatment
Hand-pick adults, larvae and eggs, or knock them into soapy water. Ladybirds, lacewings and small wasps are natural predators, so avoid broad-spectrum sprays.
Prevention
Cut and remove all old ferns in late autumn or winter to remove shelter, and cut spears often during harvest so that eggs do not hatch. Keep the bed free of weeds.
Chemical treatment (use with care)
Use an insecticide labelled for asparagus beetle, following the label, and take care not to spray during harvest.