Tackling asparagus beetle after harvest

Zsofia Szendrei<szendrei@msu.edu>, Michigan State University Extension, Department of Entomology - July 21, 2025

Learn what to do when asparagus beetles become problematic on the fern after harvest.

Skeletonized looking asparagus fern plants, caused by asparagus beetle feeding. — Asparagus beetles can skeletonize the fern, taking the photosynthetically active surface off the plants. Plants turn brown, and the lack of cladophylls indicates heavy feeding damage. Photo by Zsofia Szendrei and Ben Werling, MSU.

Asparagus beetles cause the most economic damage during harvest when they feed on spears and lay eggs. However, if large beetle populations are not managed after harvest, they can also cause serious damage to the fern. Both adult beetles and their larvae feed on the fern’s cladophylls—tiny leaf-like structures—and strip away the green tissue from the stems. This feeding reduces the plant’s ability to photosynthesize to build up energy reserves for the next season’s harvest. The last generation of beetles in the fern will also overwinter in fall, emerging in spring to cause harvest season issues. Good fern season management can reduce the number of beetles overwintering within and around fields.

Illustration of the life cycle of an asparagus beetle. — Asparagus beetles are active from the time that spears start emerging from the ground until the fall when fern declines. There are two to three overlapping generations of beetles during the summer months with both adults and larvae actively feeding on the fern. Illustration by Zsofia Szendrei, MSU.

What can growers do?

Non-chemical controls

To help reduce beetle numbers for the following growing season, mow the fern in late fall and again in early spring. This practice helps by removing or breaking down the stalks that adult beetles use as overwintering shelter, lowering their survival through the winter.

Labeled insecticides and notes on their use

There are at least seven insecticide active ingredients (AIs) from five modes of action (MOA) labeled for asparagus beetle management during the fern season (Table 1). Check current labels to keep track of recent changes. See the below notes for efficacy data from a 2024 on-farm trial by the Michigan State University Vegetable Entomology Lab.

Table 1. Insecticides labeled for asparagus beetle control during the fern season, their mode of action number (MOA), application rates, and the total number of applications allowed during the season at the highest rate.

Example tradenames	AI	MOA	Formulated rate/ac	Season total apps at high rate
Carbaryl 4L	Carbaryl	1A	1-2 qt	5
Perm-Up 3.2 EC	Permethrin	3A	2-4 fl oz	4
Assail 30 SG	Acetamiprid	4A	2.5-5.3 oz	2
Radiant SC	Spinetoram	5	4-8 fl oz	3
Entrust	Spinosad	5	2-4 fl oz	3
Dimethoate 4E	Dimethoate	1B	1 pt	2
Lannate LV	methomyl	1A	1.5-3 pt	5

Carbaryl plus Permethrin: Good efficacy against asparagus beetles and grubs in a 2024 Michigan State University (MSU) trial. Efficacy against beetles was equal to acetamiprid in this trial. This tank mix also has activity against Japanese beetle and tarnished plant bug.

Acetamiprid: Good efficacy against asparagus beetles and fair efficacy against grubs in a 2024 MSU trial. Japanese beetle, tarnished plant bug and asparagus aphids are also on the label.

Spinetoram: Fair efficacy against asparagus beetles and good efficacy against larvae in a 2024 MSU trial.

Spinosad: Fair efficacy against asparagus beetles and good efficacy against larvae in a 2024 MSU trial. Approved by the Organic Materials Review Institute.

Visit us at Michigan State University Vegetable Entomology Lab and Michigan State University Extension for more information.

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