Asparagus Miners

After investing time and garden space to asparagus, one of the last things you want to see is something attacking your spears. Originally from Europe, this tiny fly is now found everywhere asparagus grows. While asparagus miners do not cause serious damage, they can carry a disease that will.

Adult asparagus miner (Morri362) CC BY 3.0

Asparagus miner description and lifecycle

You won’t see the early life stages of asparagus miners. Whitish eggs are only 1/1000” in diameter and laid under the epidermis, at the base of asparagus stalks. Slightly larger larvae (15/1000”) are also white and tapered at both ends, with black mouth hooks. After feeding, they will grow to 1/5” in length before pupating. Pupae are dark brown and flattened and can be up to 17/100” long. These pests overwinter in the pupal stage, either in the soil or in stalks.

Asparagus miner pupa, late instar, early instar from left to right (Morri362) CC BY 3.0

Adult flies are small (1/10”), shiny black and somewhat humpbacked. They have clear, tapered  wings. They appear most often in May and again near the end of the summer.

Damage caused by asparagus miners
​
Damage is usually seen during the fern growth stage. As they feed, asparagus miners burrow a meandering pattern just below the surface. This feeding behavior can result in girdling, which causes chlorosis. More often, the damage is mostly cosmetic.

The real problem associated with asparagus miners is that they are vectors for Fusarium root and crown rot. If you see bright yellow discoloration or wilting in your asparagus plants, it may be that asparagus miners have brought Fusarium root and crown rot to your asparagus bed. In that case, both the affected plant and the surrounding soil should be removed and thrown in the trash.

​Controlling asparagus miners

Generally, parasitic wasps keep asparagus miners in check. If a heavy infestation occurs, remove the fern growth at the end of its season and throw it in the trash. Insecticides are not effective.

​Now you know.