Cucumber Beetle Boom: What Now?

Author: Marissa Schuh, Integrated Pest Management Extension Educator, University of Minnesota Extension. Reviewed by Natalie Hoidal.

Vegetable growers across Minnesota are reporting issues with cucumber beetles right now, with many expressing that they’ve never had beetles quite this bad.  Crops are now flowering and we are well into the growing season, which puts a limit on what control options we have available.

Cucumber beetles’ talents include defoliating cucurbits, spreading bacterial wilt, and copulating. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Cultural Controls

We are out of the window where things like reducing overwintering spots and trap crops can be implemented.  If cucumber beetles are an issue right now, it might be worth making a note to think about what kind of cultural controls could be integrated into your farm practices.  Break out the 2022 calendar and give yourself a reminder.

Physical Controls

Netting is being removed to allow for pollination, which unfortunately gives cucumber beetles access to crops.  Physically removing beetles is possible in smaller plantings, though their numbers can often be overwhelming.

Chemical Controls

Chemical controls give growers their best shot at managing cucumber beetles at this point in the season, though they have to be chosen and applied carefully.

Application Timing

Key in all the products, organic or not, is to do what you can to avoid spraying pollinators and exposing them to pesticides.  Even products that do not kill bees right away can be brought back with bees to the hive, which hurts hive health. Try to make applications before 8 am or after 6pm as bees are most active in the morning, and squash flowers close later in the day. 

The other consideration is if a spray is necessary at all.  Vine crops are most susceptible to cucumber beetle feeding when they are in the 1-3 leaf stage, which cucurbits should be out of at this point in the season.  Some vine crops, like pumpkin and cucumber, can tolerate a fair amount of leaf feeding.  A defoliation level of 25% can be used as an action threshold when deciding if spraying for cucumber beetles is necessary.  This is true of both conventional and organic products, both can hurt pollinators!

While cucumber beetle feeding is unsightly, the leaf in the foreground isn’t at 25% defoliation. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

Product Selection

For organic growers, options are somewhat limited and a mixed bag in terms of results (which I am sure is coming as no surprise).  Kaolin clay (Surround) works best when used preventatively. If you have some vine crops on your farm that cucumber beetles haven’t found or are only feeding on in low numbers, these are good candidates for kaolin clay.  

In situations where higher populations of cucumber beetles are present, products that combine pyrethrins and neem (azadirachtin) (Azera) work best.  The combination gives you two different active ingredients to knock back beetles.  Pyrethrin can also be used, though it isn’t always effective.  Growers have had good luck with pyrethrin and spray water with a pH of 5.5-7.  If you have hard water, it might be worth looking into organic acidifiers, as having spray water in the right pH range is important in getting sprays to be effective.  Spinosad has also performed well in some trials. Check the label of the product you are thinking of using for specific bee precautions.

For conventional growers, there are more options available.  See the Midwest Vegetable Production Guide for options. Remember to rotate chemistries to manage potential resistance issues.

If you are more of an audio learner, tune into next week’s Vegetable Beet Podcast for a 30 minute discussion on organic cucumber beetle management. The show streams at 11:30 on Wednesday July 1st.  It will also be posted and you can find it wherever you listen to podcasts by searching for the Vegetable Beet.