How do I manage asparagus beetles?


How do I manage asparagus beetles?


Two closely related insect pests, the asparagus beetle and the spotted asparagus beetle, occasionally attack asparagus plantings in Iowa. When asparagus shoots appear in spring, these beetles emerge from their sheltered, overwintering locations to chew on the tips and spears. Beetle-damaged shoots are disfigured, scarred, and brown in color, making them unappealing. After the last harvest of the season, asparagus beetles feed on the fern-like growth. Significant defoliation weakens plants, reducing spear production in the following year. 

Both species of the asparagus beetle are oval-shaped and about 6 mm (.25 inch) long. The asparagus beetle is brilliant, metallic blue-black, with six large, square, yellowish spots. The spotted asparagus beetle is reddish orange with 12 black spots. The beetles lay eggs on asparagus shoots. Larvae of the asparagus beetle are dark green to gray, black-headed, grub-like, and about 6 mm (.25 inch) long. Larvae feed on the shoot tips and foliage. Larvae of the spotted asparagus beetle are similar in size and appearance to larvae of the asparagus beetle but orange in color. They bore and feed on the berries of the asparagus.

Keeping weeds and debris out of asparagus plantings reduces sites for adult beetles to overwinter. A prompt and complete harvest also helps prevent the establishment of larvae. Handpicking may be an appropriate control if the asparagus planting is small and only a small number of beetles are present. Populations of the spotted asparagus beetle larvae can be reduced by gathering and destroying infested berries. 

Encouraging natural predators can significantly reduce asparagus beetle populations.  Lady beetle larvae and a specific species of parasitic wasp feed on the larvae.  Eliminate pesticide use to encourage these beneficial insects, as pesticides kill beneficial predators, parasites, and pests.  Natural and domestic predators (ducks, chickens) can help slow population buildup during the summer. 

Several insecticide dusts or sprays can be applied to spears or foliage when significant numbers of adults or larvae are present (more than 50% of spears with larvae on them). Check the label to be sure the product is labeled for use on asparagus to control asparagus beetle.  Also check carefully the number of days required to wait between insecticide application and harvest.  Effective pesticides often have active ingredients such as malathion, carbaryl, pyrethroids, pyrethrins, neem, and spinosad.

Last updated on
May 16, 2024