Scout Fields for Western Corn Rootworm Beetles

On the Lookout

Recently, we have seen Western Corn Rootworm Beetles on the rise. While it’s nothing to get overly alarmed about, it’s important to always be aware and think about how you are managing pests on your farm. 

The rise can be attributed to a few different factors. First, it’s a hot dry summer. There was a bad case of Corn Rootworm was in 2012, the last year that we had a significant drought. While most of our readers in our area have gotten adequate rainfall this year, areas just west of us are experiencing a moderate drought. Another reason for a rise in Corn Rootworm is because less BT corn has been planted. This can be attributed to a drop on commodity prices (farmers are less likely to invest in more expensive hybrids) and consumer pressure for Non-GMO corn has turned farmers away from using such hybrids. 

Where are they?

Western Corn Rootworm Beetles can be selective in the fields that they chose to impact—some are more prone than others. Issue Prone Areas include:
•    Later Maturing Hybrids
•    Replanted portions
•    Fields that were delayed developmentally
•    Fields with late season weeds (the beetles like to hang out in them and lay their larvae)
•    Fields adjacent to weedy soybean fields (for the same reason as the previous bullet point)
•    Soybean fields with heavy late season volunteer corn

However even if you do not have fields that would be considered “issue prone” it is still important to scout and be on the look out for them.

The Western Corn Rootworm (WCR) Beetle is what you would be looking for at this time of year. Earlier in the season, you would have been looking for this pest in its larval (worm) life stage. However now they have evolved into its adult form and become a beetle. The WCR Beetle 

I Have Them, Now What?

Spraying Western Corn Rootworm after they have evolved to the beetle life stage is most likely too late. This is simply trying to fix a problem that has already occurred—the damage is done. There are still action steps that can be taken to ensure insect pressure numbers do not increase, for as we all know the lifecycle of insects only continues with new generations. 

There are very limited number of foliar insecticides that will take care of the Western Corn Rootworm Beetle simply because they do not have enough of a residual affect. This is why a single insecticide application—even those that are well timed—may not be enough. It would take multiple applications to eradicate the issue and that could become very costly. However, depending on the stage the corn plant is in, it may be necessary to make some kind of application to prevent silk clipping. WCRW Beetles feed on the silks (known as silk clipping). Missing silks cause the kernel to abort or not form, which can lead to several ear abnormalities. However, if pollination has already occurred, we do not recommend treatment. 

Having a clean field is another way that you can manage insect populations. The Western Corn Rootworm Beetle especially loves waterhemp. Uncontrolled weeds can become the perfect breeding ground so if you are looking to disrupt their life cycle—or prevent them from ever becoming an issue—taking care of weeds can become a critical step.

Further Action

Adult control of Western Corn Rootworm Beetle should always be a last resort to save your crop. The best way manage this insect is to manage it long before it ever becomes an issue. This can be done through Insect Pest Management (IPM)
IPM can include management such as:
•    Scouting
•    Rotating host crops
•    Rotating hybrids
•    If using non-BT corn—be sure to use a soil applied liquid or granular insecticide
•    Avoid layering same Active Ingredient in soil applied and foliar insecticide
•    Switch management tactics year to year
•    Avoid “Kitchen Sink Approach” (throwing everything at it and hoping something works)

Want to know more about Western Corn Rootworm Beetle and what you can do to control it? Contact your Centra Sota agronomist to set up some scouting.