How do I deal with asparagus beetles?
Q: I am having trouble with little black bugs on my heads of the asparagus / any suggestions?
— Nick from the Mahoning Valley
A: I have the same problem! When my husband and I built our house, the first items we planted were asparagus roots. We had both been reared on asparagus, mostly wild, so this idea was exciting. Within a couple years we began seeing the wonderful tips, and then more.
We have a 4-foot-by-15-foot bed of 20 plants that yielded about four bushels this year.
A couple years back, I started seeing little rows of black eggs on my spears. I didn’t have an issue, but this year I decided to research them. These rows of eggs are evidence of the asparagus beetle, feasting, mating and laying eggs on my asparagus. Yuk!
There are two kinds of asparagus beetles:
• The common asparagus beetle (Crioceris asparagi) is the most prevalent, most damaging. The adult has a 1/4-inch body, is bluish black, a metallic blue head, with 6 creamy yellow spots on its back. It has long antennae.
• The spotted asparagus beetle (Crioceris duodecimpunctata) adult is reddish-orange with two black spots.
Both life cycles are similar. The larvae of both are slug-like, with visible heads and legs. The common asparagus beetle larva is light gray with a black head hatching from brown-black rows of eggs. The spotted asparagus beetle larva is orange and hatches from rows of greenish eggs. They eat the spears and stems leaving them brown and curled over.
Adults live through the winter in sheltered debris and soil — so fall cleanup can help reduce populations.
When the spears emerge in the spring, the common asparagus beetles emerge to feed. They mate, lay eggs, and larvae hatch after one week, move to the spears and ferns to feed. They eat for two weeks, fall to the ground and turn into pupae in the soil.
After one week, the adults of the next generation emerge and begin feeding. As they eat, they mate and reproduce until the growing season is over.
The spotted asparagus beetle emerges later in mid-May and is gone by the end of July. The greenish eggs hatch to orange larvae that feed on asparagus berries.
If the beetles and their larvae feed enough on plants, they can weaken the asparagus reducing the nutrients for the next season. This also can lead to fusarium (fungus) that target weak plants.
The best way to prevent them is to clean up all debris around your plants as well as old tops after berries are red and mature. Then pick them off if you get them in spring.
I choose to handpick the adults in the afternoon (the time of most activity) and deposit them in hot soapy water. If I find eggs on my harvest, I scrape them off with my fingernail and rinse well.