Western Bean Cutworm Catches are Climbing

Aug 04, 2020

Before I talked about the WBC trap data, I want to thank everyone who set up a trap this year and are entering their data into the network. Despite COVID-19, there are more than 1000 WBC traps in the system! That is a record and helps us figure out what the flight patterns are.

Now for the trap results. We are just entering into Week 10 of trapping. Western bean cutworm trap catches have definitely increased over the last few days. The dashboard from the Great Lakes and Maritimes Pest Monitoring Network indicate that the majority of the larger catches are coming from southwestern Ontario though some traps in Bruce and Peterborough counties have also had significant trap catches this week. Highest moth catch in the last 7 days was in Thamesville with 440 moths while one near Aylmer was not far behind at 435 moths. I only have two days of data for this week (Week 10) so I do expect more data to come in the next few days from last week’s monitoring. Expect trap catches could even be higher than that.

What does the data show? We are not at peak flight yet. Michigan seems to also be climbing in catches. Here in Ontario, we have a week or two to go still yet. So even though the corn crop is reaching the right time for a fungicide application for ear mould protection, adding an insecticide now is likely premature. Thankfully, the corn crop did get in earlier than last year. So some of the moths might not choose corn to lay their eggs in (sorry dry bean growers). Or in those areas where most of the corn is at very similar growth stages, there could be a dilution effect, where moths go to several fields in the same area to lay eggs instead of choosing just one or two. Unfortunately, dry beans are very likely going to be equally attractive now that we are in what is typically Week 10 of WBC trapping. We see that already when we compare trap counts by crop. In 2019, peak flight was this week (Week 10) for southern counties while counties in central and eastern Ontario didn’t peak until Week 11 and 12 (next week and two weeks from now).

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Video: Spring 2026 weather outlook for Wisconsin; What an early-arriving El Niño could mean

Northeast Wisconsin is a small corner of the world, but our weather is still affected by what happens across the globe.

That includes in the equatorial Pacific, where changes between El Niño and La Niña play a role in the weather here -- and boy, have there been some abrupt changes as of late.

El Niño and La Niña are the two phases of what is collectively known as the El Niño Southern Oscillation, or ENSO for short. These are the swings back and forth from unusually warm to unusually cold sea surface temperatures in the Pacific Ocean along the equator.

Since this past September, we have been in a weak La Niña, which means water temperatures near the Eastern Pacific equator have been cooler than usual. That's where we're at right now.

Even last fall, the long-term outlook suggested a return to neutral conditions by spring and potentially El Niño conditions by summer.

But there are some signs this may be happening faster than usual, which could accelerate the onset of El Niño.

Over the last few weeks, unusually strong bursts of westerly winds farther west in the Pacific -- where sea surface temperatures are warmer than average -- have been observed. There is a chance that this could accelerate the warming of those eastern Pacific waters and potentially push us into El Niño sooner than usual.

If we do enter El Nino by spring -- which we'll define as the period of March, April and May -- there are some long-term correlations with our weather here in Northeast Wisconsin.

Looking at a map of anomalously warm weather, most of the upper Great Lakes doesn't show a strong correlation, but in general, the northern tiers of the United States do tend to lean to that direction.

The stronger correlation is with precipitation. El Niño conditions in spring have historically come with a higher risk of very dry weather over that time frame, so this will definitely be a transition we'll have to watch closely as we move out of winter.