Marissa Schuh, IPM Extension Educator, mschuh@umn.edu and Annie Klodd. Originally published 2022, updated in 2025.
As asparagus grows and gets picked, asparagus beetles are showing up as well. There are two beetles we see in asparagus, common and spotted asparagus beetle. We generally hear the most about the yellow, black, and red common asparagus beetle. These guys are tricky to manage, read on for the answers to common questions we get about these pests from growers.
The Midwest Vegetable Production Guide can be used to quickly find options that work in asparagus beetles and have a shorter PHI. Options with shorter PHIs are:
There are organic products with asparagus beetles on their label, but their efficacy is a mixed bag. As mentioned above, Entrust has asparagus beetles on the label, but in Michigan field trials, it didn't reduce adult beetles or number of eggs compared to the areas where no pesticides were used. Pyganic also has asparagus beetle on the label, and in field trials reduced the number of eggs found (but to a much lesser extent than the conventional products). Pyganic did not meaningfully reduce the number of adults found.
If you are seeing high numbers of beetles in ferns later this summer, you could treat them. A threshold is 50-75% of ferns infested. Tread carefully, as flowering asparagus ferns are attractive to bees, so these applications have to be timed carefully.
As asparagus grows and gets picked, asparagus beetles are showing up as well. There are two beetles we see in asparagus, common and spotted asparagus beetle. We generally hear the most about the yellow, black, and red common asparagus beetle. These guys are tricky to manage, read on for the answers to common questions we get about these pests from growers.
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Common asparagus beetles feed on spears and ferns. Photo: Whitney Cranshaw, Colorado State University, Bugwood.com |
Do I actually need to spray?
The threshold for asparagus beetles are:- 5-10% of plants are infested with adults or larvae.
- 2% of spears have eggs.
Asparagus beetle eggs are laid single-file in a line. Photo: Annie Klodd, UMN Extension.
What do I spray?
Using insecticides in spring asparagus is a challenge because of the constant picking. Any product that you use needs to have a short Pre-Harvest Interval (PHI). This varies with each product. Some products have 30 or 60 day PHIs, meaning they cannot be used until harvest has wrapped for the year.The Midwest Vegetable Production Guide can be used to quickly find options that work in asparagus beetles and have a shorter PHI. Options with shorter PHIs are:
If asparagus beetles are a recurring problem, it is also important to check the label for maximum application limits. For example, Sevin XLR Plus has an application rate of 1-2 qts. per acre, with the label stating that you cannot use more than 5qts per year or more than 5 applications to the same asparagus spears/ferns in a year. Again, the Midwest Vegetable Production Guide outlines this information in a concise way.
How do I get the most out of my spray?
Unfortunately, asparagus beetles are most active on warm sunny afternoons. This means the times when we want to be out picking are also the best window of time to make pesticide applications. If you are seeing significant damage, sacrifice a picking to ensure that the most beetles possible are contacting your spray.How often do I spray?
Two tricky things about spraying asparagus beetles are that1) new spears are constantly emerging.
2) asparagus beetles remain active the entire season, except for a brief period in June.
New spears are not protected by insecticides that were sprayed prior to their emergence. After applying your first spray, scout the crop regularly to see if asparagus beetles or eggs appear again. If infestation reaches the action threshold (5-10% of spears are infested, or 2% of spears have eggs), it is time to spray again. Rotate insecticide modes of action to stay under the maximum allowable rates for each insecticide.
New spears are not protected by insecticides that were sprayed prior to their emergence. After applying your first spray, scout the crop regularly to see if asparagus beetles or eggs appear again. If infestation reaches the action threshold (5-10% of spears are infested, or 2% of spears have eggs), it is time to spray again. Rotate insecticide modes of action to stay under the maximum allowable rates for each insecticide.
Can I do stuff later this year to prevent next year’s asparagus beetle?
Once we are done picking and letting a patch fern out, asparagus beetle is still hanging around. They continue to feed on ferns and build their populations, and research has found majority of asparagus beetles overwinter in fields. Research in Michigan looked at different ways of managing ferns in the fall and spring, and found that rotary mowing ferns in the spring and fall reduced common asparagus beetle populations on farms.If you are seeing high numbers of beetles in ferns later this summer, you could treat them. A threshold is 50-75% of ferns infested. Tread carefully, as flowering asparagus ferns are attractive to bees, so these applications have to be timed carefully.
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