Controlling common asparagus beetle during harvest season

Benjamin Werling<werlingb@msu.edu>, Michigan State University Extension, and Zsofia Szendrei<szendrei@msu.edu>, Michigan State University, Department of Entomology - May 26, 2020

Common asparagus beetle egglaying during harvest can cause major financial loss; get updated on products available for control.

Asparagus beetles on spears — Common asparagus beetles on spears during harvest. Photo by Ben Werling, MSU Extension.

Sources of beetles during harvest

In late summer, larvae of common asparagus beetle, called grubs or “slugs,” hatch from eggs and feed in fern. They then pupate in the soil and develop into an adult beetle. As winter approaches, these beetles seek out overwintering sites to protect them from cold weather, including loose bark in logs and trees surrounding asparagus fields, as well as hollow asparagus stems. As it warms up in spring, beetles emerge from overwintering sites ready to feed, mate and lay eggs during the asparagus harvest season.

Asparagus beetle control during harvest

Here are some suggestions from MSU Extension that may help control asparagus beetles during harvest:

Time sprays to have fresh insecticide residue on spears in the afternoon. Research at the University of Minnesota found adult beetles were most abundant in fields from 1:00-5:00 p.m., compared to morning hours. Having fresh insecticide residues on spears during this time could maximize the chances of beetles contacting them and dying.

Apply insecticides on warm, sunny days. Asparagus beetles are typically not active during cold weather. Unfortunately, this is also the time it is easiest to fit in insecticide applications. However, if beetles are not active, contact with insecticide may be limited. Applying insecticides during warm, sunny days may increase the number of beetles coming into contact with insecticide residues.

Control asparagus beetles in the fern season. This year’s beetles come from last year’s fern, making fern-season control important. Experience suggests problems during harvest can be reduced when beetles are kept in check the previous season. Some growers have even used later-than-normal insecticide applications in late summer to early fall with the goal of reducing the overwintering population’s size.

Consider banded applications to keep rates up and reduce cost. Asparagus beetles contact insecticides on the spears. Some growers apply insecticides in a band over the row by placing plug tips in nozzles that would hit between rows. This reduces application cost by lowering the broadcast rate, while keeping the rate in the band high.

Labeled products and notes on their use

There are at least five insecticide active ingredients (AIs) from four modes of action (MOA) with one-day preharvest intervals (Table 1). Generic forms exist and are labeled for all products. Note, methomyl, chlorpyrifos and permethrin are restricted use, and chlorpyrifos requires applicators to wear respirators.

Table 1. Conventional insecticides with one-day preharvest intervals labeled for asparagus beetle control during asparagus harvest, their mode of action number (“MOA”), application rates, number of applications allowed during harvest at the highest rate, and minimum days allowed between applications.
Tradename	AI	MOA	Formulated rate/ac	#apps at high rate	Retreatment interval
Carbaryl 4L	carbaryl	1A	1 qt.	3	3
Lannate LV	methomyl	1A	1.5-3 pt.	5	5
Lorsban 4E	chlorpyrifos	1B	2 pt.	1	na
Perm-up	permethrin	3A	2-4 fl oz.	4	7
Assail 30SG	acetamiprid	4A	2.5-5.3 fl oz	2	10

Carbamates (1A): Carbaryl has been a grower standard for years. During harvest use the cheapest formulation available since spears are frequently harvested, there is little benefit from the extended residual activity advertised for Sevin XLR Plus. If cost is a concern, consider a banded application to keep the rate in the treated area at 1 qt. Lannate is also labeled, but past research showed it was no better than carbaryl. Given this, and the fact it is the same mode of action, there may be little incentive to use methomyl instead of carbaryl.

Growers are concerned about resistance to carbaryl. In 2018, we placed asparagus beetles from an Oceana County problem population in cages with spears. At least for this population, carbaryl was still killing beetles.

Study on asparagus beetles showing control and 1 qt./ac — In 2018 asparagus beetles from a single Oceana County population were exposed to spears treated with no or 1 qt/ac carbaryl. After 72 hours, there was significantly higher mortality and less egglaying in cages with treated spears. Photo by Benjamin Werling, Michigan State University Extension

Organophosphates (1B): Chlorpyrifos (e.g., Lorsban) has a one-day preharvest interval, however only one preharvest application is allowed. This means the label would prohibit use during harvest if the typical application was made for cutworms in early spring.

Pyrethroids (3A): Permethrin (e.g., Perm-Up) has also been used, but some growers feel it is not as effective at controlling adult beetles compared to larvae. This has led to a preference for conserving this product for the fern season, where it can also be used for Japanese beetle and tarnished plant bug management.

Neonicotinoids (4A): Acetamiprid (e.g., Assail) is a newer product that some growers tried in 2018. Limited experience and research suggests it is effective, though it is not clear it is any better than carbaryl. It does offer a unique mode of action.

Organic products: Pyganic and Grandevo are labeled for asparagus beetle control during harvest, however we are not aware of any direct experience with their efficacy.

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