Field Identification
A leaf-feeding leaf beetle specialized on asparagus. Adults are metallic blue-black with red or yellow markings; larvae are soft, gray-green grubs that chew spears, ferns, and cladophylls. Heavy feeding weakens crowns, reduces spear size, and leaves sticky frass that makes harvest unpleasant. From temperate zones to warm-summer regions across the Americas (roughly zones 3–13 where asparagus is grown), scout from spear emergence through fern fill—damage is often worst where the same crowns are stressed by drought or repeated cutting.
Adults are about 1/4 inch (6 mm) long with a rounded, shiny body; spotted asparagus beetle (Crioceris duodecimpunctata) is orange with black dots and targets berries. Eggs are dark, glued singly on their sides along spears or ferns. Larvae have a dark head and four instars before dropping to pupate in soil. Field ID is the combination of spear scarring, dark eggs, and slug-like larvae on ferns.
How to Deal With It
Organic Control Methods
Neem (azadirachtin) or spinosad can suppress larvae when applied to ferns and tender spears with thorough coverage; insecticidal soap targets young larvae on contact. Re-treat after rain and rotate materials to avoid thinning beneficial populations. Pyrethrin-based products offer a short-residual knockdown for adults when label timing allows and bees are not foraging.
Generalist predators including lady beetles (Coccinellidae), lacewing larvae (Chrysopidae), minute pirate bugs (Orius spp.), and ground beetles (Carabidae) consume eggs and larvae; small parasitic wasps attack eggs and larvae where present. Maintaining flowering insectaries near the bed supports these allies through the fern season.
Cut or snap spears close to soil during harvest to remove eggs before they hatch; destroy old ferns after frost where regulations allow to reduce overwintering sites. Avoid excess nitrogen that pushes lush, attractive growth; irrigate evenly so crowns stay vigorous without succulent flushes. Rotate new asparagus plantings away from heavily infested beds when replanting.
Hand-pick adults and larvae into soapy water during cool mornings; flick adults into a wide jar when they cluster on spears. Light row cover over young crowns can exclude adults during peak flight if edges are sealed daily during harvest windows.
Scout weekly from first spear through full fern, focusing outer rows and windward edges. Remove adjacent wild asparagus if it harbors early flights. Keep records year to year—populations build when cleanup is skipped and the same site is pushed for maximum spear count without recovery time.
Let Nature Handle It
Natural Enemies
- Lady Beetles (Coccinellidae)
- Lacewing larvae (Chrysopidae)
- Parasitic Wasps (Hymenoptera)
- Ground Beetles (Carabidae)
Threat Map