University of Maryland Extension

Asparagus Beetle Damage Greater This Season

Author: 
Dr. Gerald Brust, IPM Vegetable Specialist

April 2010

I have seen and gotten calls about greater amounts of common asparagus beetle feeding damage to asparagus this spring than normal. As the name implies the common asparagus beetle, Crioceris asparagi, is the asparagus pest most frequently seen in the field and causes most of the damage (Fig. 1). Adult beetles are ΒΌ-inch long with oval-shaped bodies and are bluish-black with six cream colored spots on their backs. Adult spotted asparagus beetles are reddish-orange with twelve black spots. The larvae of both species are slug-like with visible heads and legs. Common asparagus beetle larvae are light gray with a black head, while spotted asparagus beetle larvae are orange.

Common asparagus beetle adults overwinter in sheltered locations such as under loose tree bark or in the hollow stems of old asparagus plants. Adults appear as the asparagus spears are emerging. The beetles lay numerous dark brown, flat, oval-shaped eggs on end in rows on the spears or ferns (Fig. 2). The eggs hatch within a week. The larvae migrate to the ferns to start feeding. They feed for about two weeks and then fall to the ground to pupate in the soil. About a week later, adults emerge to start another generation, feeding on the ferns for the remainder of the growing season.

Feeding on the spears by adults can cause browning, scarring (Fig. 2) and may cause asparagus spears to twist into a shepherd's crook shape (Fig. 3). When the ferns appear the common asparagus beetle larvae and adults will feed heavily, which can weaken the plant and reduce the plant's ability to provide nutrients for the following season. Numerous eggs of the common asparagus beetle laid on the spears can make the asparagus unmarketable.

Start scouting plants after asparagus plants emerge and continue throughout the growing season. The best time to check for asparagus beetles is in the afternoon when they are most active. If 10% of plants have adult asparagus beetles or >20% of spears have eggs management is needed.

The following chemicals can be used to control beetles and larvae: carbaryl, malathion, and permethrin (all have a 1-day PHI). Sanitation practices, such as elimination of plant residue in and around the asparagus field will decrease the number of overwintering sites available to adults. The parasitic wasp Tetrastichus asparagi, parasitizes asparagus beetle eggs and can sometimes provide up to 70% control. Lady beetle larvae and other predators may also be active, and will consume both eggs and larvae.

Fig. 1 Common asparagus beetle adult

Fig. 2 Asparagus beetle eggs and asparagus damageFig. 3 Asparagus beetle damage to spear

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