Last fall’s winter cutworm outbreak

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

It started on October 1, 2007, as a routine email request from Norm Myers, MSUE Oceana county extension director, for information on the so-called winter cutworm, Noctua pronuba. Within a couple of days, we received reports of thousands of cutworms in yards and crawling on homes in Wexford County. Then we started to get reports of large swaths of alfalfa and rye fields being eaten in Oceana, Lake, Osceola, Mason, Cheboygan and Alpena counties. By the middle of November, things took a rather bizarre turn when we started getting reports about bulimic dogs and cats vomiting up wads of the cutworm that they had snacked on. Pets weren’t the only ones taking advantage of this bountiful food source. Duke Elsner, MSUE Grand Traverse County, sent us photos of box elder bugs, which are normally vegetarians, apparently feeding on the cutworms. Squirrels were also reported to have taken part in the feast.

The winter cutworm is brownish with two rows of black dashes along the back. The species overwinters as a larva and is known to feed on mild days throughout the winter. 

This bug was first discovered in North America in Nova Scotia in the late 1970’s. It is now reported to occur from coast to coast in southern Canada and the temperate United States. Its food plants include a wide variety of crops and vegetables: strawberry, tomato, potato, carrot, cabbage, beet, lettuce, grape and also grasses. Although larvae feed on many other cultivated and wild plant species, no economic damage had ever been attributed to this insect in North America before the outbreak in the northern Lower Peninsula last fall.

Rather than trying to retell the story, we think it would be far more interesting if we let the first responders tell it as it happened. Here are some excerpts from some of the e-mail we received from the extension educators who were waist deep in last fall’s outbreak.

October 1, Norm Myers, Oceana CED: “We had a big problem with cutworms getting in to homes and garages last fall. I have had a call from a chemical dealer already this fall and it sounds like the same problem, only this time it is at food processors.”

October 3, Sheri Pollington, MSU/E Wexford County: “This lady brought these in today and she said they are EVERYWHERE…she’s being overtaken by them. She doesn’t understand where they are coming from as she doesn’t have any trees close to her home. She says they are on her deck, driveway and the side of her house and there are hundreds and thousands of them.”

October 5, Norm Myers, Oceana CED : “I collected 100-plus from the floor of a young cherry orchard. The processor showed me one of his migrant houses where the insect had clustered in what were probably the millions before it was treated.”

October 8, Norm Myers, Oceana CED: “My first reports of this were from homeowners, but I have since had reports from orchardist where they were eating out the grass middles in cherry orchards. Today, I had my first report from a crops farmer, where they were eating a hay field. My suspicion is that it is the grass they are eating, but I haven’t seen the field so cannot say for sure. They act much like an armyworm, showing up literally in the millions and moving in mass from one area to another. I am a little concerned that they represent a threat to emerging winter wheat (which we have a lot of this year) if this is more than an outbreak in an isolated area.”

October 16, Jerry Lindquist, Osceola CED: “Here are some photos of the farm in Lake County that had winter cutworms that Howard identified on Friday. The farmer noticed them after he picked up some recently cut third-cutting round-baled hay and saw the larvae dropping out of the bales. This was during the 80 and 90 degree weather of a week ago. Once the field was cut, he noticed them moving in mass across the road and said the tractor tires were actually starting to spin because of the slippery larvae covered pavement.

Back at home he found more in another cut alfalfa field. The picture shows feeding damage on the edge of an adjoining field of alfalfa and volunteer oats that they started to move into. He said that within a day of moving into this field they reversed course and headed to his white plastic ag bags of stored silage and either died on the surface or disappeared. We had temperatures down to 28 degrees on Saturday night, so when I was there on Monday there were few live larvae still visible. I did notice a large flock of about 100 crows that seemed to be feeding in the cut hay fields on the remaining worms on Monday.

I am also getting reports of them in Osceola County showing up around home foundations.”
October 23, 2007, concerned homeowner, Kalkaska County: “I live in Fife Lake, Michigan and my home, garage and pole barn are being invaded by caterpillars. They are in the grass by the thousands. I feel like I’m in a "B" movie. What can be done about these bugs? They’ve eaten what was left of my hostas and we have ten acres of hardwoods. I would hate to see these guys kill my maples and beeches. What can I do?”

October 26, 2007, Norm Myers, Oceana CED:  “I have been hearing stories of Noctua pronuba feeding on cereal grains, but now I have proof. This is a rye field adjacent to an alfalfa field. The worms ate the alfalfa and moved into the rye. Fortunately, we got down in to the high 20s yesterday morning and there were very few worms left.

October, 2007, Jerry Lindquist, Osceola CED: “I got a rye call this morning as well. This was not as conventional as it was a rye field for wildlife viewing. The field was sown last fall and the headed rye was mowed down in August of this year to re-seed it. The field was not tilled this summer, so the cutworms emerged, fed in October and devoured the three acre field, and are now moving onto the homeowner’s lawn in a feeding wave.”

October 29, 2007, Duke Elsner, Grand Traverse County: “In my area there has been a lot of larval mortality in the last two weeks - they just crawl along and slow down, then sort of decay in place. Very soft, mushy corpses, and no sign of fungal sporulation on any I have seen so far. I am wondering if this is something viral?

I have attached some pictures of what certainly looks like a box elder bug feeding on one of the dead larvae. These were taken on my deck, where a number of larvae have died in recent days.”

October 31, 2007, Jim Breinling, Mason County: “This morning here in Mason County have worms still feeding on alfalfa field. Should the grower spray now? Wait until spring and scout? Pray or head south for the winter?”

November 12, 2007, Mary Dunckel, Alpena CED: “Three more occurrences in Alpena…
1. Two oat fields completely eaten last Wednesday.
2. I was in the veterinarian’s office Friday and while at the counter paying for my cat’s vaccination a woman came running in with a bag. She was completely frantic as her dog had just vomited up the contents of the bag. Yes, you guessed it….probably 40-50 noctua pronuba!
3. On Saturday, I did my usual fall cleaning of my goldfish pond and there they were again…sucked into the filter (lots of them).

These guys are everywhere.”

November 13, 2007, Jill O’Donnell, Wexford County: “Just thought you would like to know that our calls have picked up again concerning - Noctua pronuba. Most of my calls have been from homeowners. Any new thoughts on controlling this critter?”

November 14, 2007, Dr. Christina DiFonzo, MSU: “I just got off the phone with Paul Ponik, a Posen area farmer. He gave me a report of what the cutworm is doing and it is still very active. According to him, they seem to prefer alfalfa, leaves first, then stems. They went into a new seeding with oats and left that field soon after, so maybe they don’t like oats or something they give off. They went into his father’s lawn and seem to cut the grass off right at the soil level. He also believes that they are working under the soil surface as well. He is concerned that if they take down wheat like this, at the soil level or even below soil level, will the wheat come back from that? We know wheat grows back from winter grazing, but this is lower. Where is the growing point?

His father took a hand sprayer with Sevin to them Tuesday and seemed to kill them. It appears to Paul that there are two different hatches involved, with some larva being an inch long and others up to three inches in length. He timed their progress over a highway and clocked them at eight inches per minute.

During the day, they hide under corn stalks or leaves. They feed from about 4:00 PM to 4:00 AM. In the morning, they are as big and fat as this big man’s little finger. By afternoon, they have shrunk in size.

They are still moving. They have just entered a clover field.

He asks whether they will gnaw at alfalfa crowns, and whether they will work under the snow on wheat. What will happen to wheat if they eat below the soil surface? He hopes that maybe some Canadian scientists have learned some things to share with us.
So far, he is teaching me about this worm, but he prefers it be the other way around.”

November 15, 2007, Ben Bartlett, Cheboygan CED: “I’ve received confirmation that it’s in Otsego, Presque Isle and most recently – Cheboygan counties (on a lawn) have them in good numbers. They are primarily working on wheat fields up here. Some alfalfa as well, but they aren’t fond of orchardgrass. The questions that I can’t answer are;

1) What will the moths do in the spring? Stick around for another generation or fly off bugging someone else.
2)  No thresholds, but if they spray this fall, will it be useful only if they are actively feeding in this cold weather?
3)  Why do squirrels eat them? (just kidding, but the lawn owner observed squirrels getting their winter protein!)

November 16, Jerry Lindquist Osceola CED: “Here is another bizarre impact of the winter cutworm (Noctua pronuba) outbreak that has occurred in another area of the state, making it in my mind not just another freak occurrence. The report of a second dog getting sick by consuming winter cutworms has come in. A black lab in the Midland area, was vomiting blood, went off of food, and after a week was passing whole cutworms in her stool. The veterinarian diagnosed it as a potential parasite problem, sent a stool sample to Cornell’s Parasite Diagnostic Lab and they identified it as armyworm. The dog owner called me after our television news spot on cutworms, and I am quite sure cutworms are what the dog ate.

The dog owner from Midland County says now whenever the dog goes into their large lawn and adjoining two acres of un-mown turf, her nose is to the ground and she is in an aggressive hunting mode. These cutworms just showed up in Michigan for the first time in October. They are two to three inches in size and are fat. They can show up in numbers from a few, to a thousand in a lawn situation and seem to be quite widespread in the Northern Lower Penninsula.“

November 21, 2007 Jill O’Donnell, Wexford County: “I took the cutworm handout to the local vet offices so they would know the cutworm if they had any cases. Airport Animal Clinic said they had three cases of dogs eating the worms and becoming sick. John Amrhein said his cats were also eating the worms with the same results. “
To view a news video clip featuring Jerry Lindquist talking about the crop damage caused by winter cutworm, click here.

To view a news video clip of a Presque Isle County woman finding winter cutworms under the snow in her yard and watching them come back to life, click here.

Side view of cutworm.
Click to view more images of cutworms

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