Asparagus Beetle
Crioceris asparagi
The main pest of asparagus, this small, handsome beetle and its dark grubs chew the spears and later the ferny foliage. Spear feeding leaves brown scars and bent, shepherd-crook tips, and a heavy fern infestation weakens the crowns for next year.
🔎 How to spot it
The common asparagus beetle is a quarter-inch, blue-black beetle with a red thorax and cream-yellow blocks edged in red on its wing covers; the spotted asparagus beetle is reddish-orange with twelve black spots. The dark gray, hump-backed grubs feed on the ferns. The clearest early sign is the eggs: tiny dark eggs glued on end, standing straight out from the spears like little pegs.
🥀 Damage it causes
Adults and larvae chew the spears and the fern foliage. Feeding on emerging spears causes brown scarring and bent, shepherd-crook tips that make them unmarketable, while heavy summer feeding on the ferns can defoliate them and starve the crown, weakening the crop the following year. The eggs on the spears, though harmless, also make them unappetizing.
🛡️ Prevent it
Cut and remove all the old ferns at the end of the season and clear nearby debris, since the adults overwinter in that material and in sheltered spots around the bed. Harvest spears cleanly and frequently during the cutting season, which removes eggs and larvae along with the spears and denies the beetles a foothold.
🧯 If it is already here
Handpick the adults, larvae, and the standing dark eggs into soapy water; on a backyard bed, daily picking during harvest keeps the beetle well in check. Treat the ferns only if half or more are infested, using spinosad or another approved product. Conserve the tiny parasitic wasp that attacks asparagus beetle eggs, a major natural control.
💡 Good to know
Frequent, clean harvest is itself a control, because picking the spears carries off the eggs and young larvae before they can mature. A small parasitic wasp (Tetrastichus) destroys a large share of the eggs, so preserving it by avoiding broad-spectrum sprays is well worth it.
🌱 Plants it attacks
4 plants in the library can be attacked by this pest
For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.