Beetle Damage On Your Asparagus?
Small black beetles on the tips of your spears? Asparagus looking chewed? Could be beetle damage. What it is and what to do.
What is it?
Crioceris asparagi (asparagus beetles) and crioceris duodecimpunctata (spotted asparagus beetles) injure asparagus plants throughout the growing season. They are especially problematic in new shoots emerging in the spring.
What does it look like?
The beetles vary is color from a spotted reddish orange to a bluish black. You may also note humpbacked orange or slate gray colored grubs around infested plants. Often there are shiny black specks on spear tips and the tips may also be chewed or scarred looking. The beetles are relatively small, about 1/4 inch, and can usually be found chewing on the tips from the moment new growth emerges through to adult fern growth.
How does it manifest?
Asparagus beetles feed on the tips of asparagus spears as grubs and adults. This injures the shoots, ferns and stems which starves the root system of food normally manufactured in the foliage, which provides fuel for necessary growth. Once this has begun, the plant becomes starved and will not grow healthy foliage the following year, which could result in stunted or crooked spear growth.
What can you do about it?
Your best bet is to apply a pyrethrins containing insecticide at the first sign of damage. As long as beetles and grubs can be seen feeding, continue to apply the insecticide at 3 day intervals. In late fall, you should also treat the adult fern growth so that beetles cannot overwinter on the ferns and reinfest the following years crop of asparagus.