winter « Cutworm Central

The common name ‘armyworm’ is added as an identifier based mostly on behavior. Larvae move in large groups, sometimes over quite impressive distances. In severe cases, a feeding wave can be seen, like the front line of an advancing Army.

Taxonomy (the science of grouping and naming organisms) can be equally important though. Of the 11 species of Spodoptera that are present in the U.S., 10 of them have armyworm as a common name. That is to say… Spodoptera = armyworm. There are of course armyworms from other genera, but we’ll have to explore that another time, or browse the blog here. Oddly, “true” armyworm is one example.

For many years since I’ve lived in Oregon, something has been bugging me. I’ve heard reports about “fall armyworm”, but all of my go-to websites list Spodoptera frugiperda as not occurring here: PNW moths (a huge NSF-funded, collaborative regional effort); nor MPG (moth photographers group which started as a hobby project and is now a great resource ran by Mississippi State); nor GBIF (an international network of biodiversity data). If you still don’t believe me and want to consult iNaturalist instead…we can’t be friends…but you’ll find the same thing – over 8,000 observations…none from Oregon.

Identification

Adult moths in the genus Spodoptera vary in size and wing patterning. Eggs are laid in large clusters and covered with a dense layer of scales from the female’s abdomen, giving the clusters a ‘fuzzy’ appearance (see examples).

Larvae have a black spot on either the mesothoracic segment (e.g. beet armyworm, S. exigua) or the first abdominal segment (e.g. fall armyworm, S. frugiperda)(see diagram). Patterning, stripes, color of the larvae all vary widely, even within populations. What S. frugiperda DOES have is four large, evenly colored tubercles (spots) arranged in a square on the dorsal side of abdominal segment A8. For GREAT pictures of them, please see reference #4. If it doesn’t have those four spots, it’s not fall armyworm. But caution here too… black cutworm has spots on A8 but they’re not in a square. Corn earworm has them in a square, but two of them are less prominent. Ok, I’m rambling and losing some of you, sorry :). My point is that…

I suspect that some of the reports of “fall armyworm” in the PNW have been from improper identification of larvae. If I’m wrong, please leave a comment so we can chat! There are MANY species of Noctuidae that can actively feed during the fall and winter. The photo below shows adult moths detected in pheromone traps during the same 2 days in late September 2022. All of them have larvae that feed in fall…but none of them are fall armyworm.

References

Early R, González-Moreno P, Murphy ST, and Day R. 2018. Forecasting the global extent of invasion of the cereal pest Spodoptera frugiperda, the fall armyworm. NeoBiota 40: 25-50. https://doi.org/10.3897/neobiota.40.28165
Sparks, Alton N. 1979. “A Review of the Biology of the Fall Armyworm.” The Florida Entomologist, vol. 62, no. 2, pp. 82–87. JSTOR, https://doi.org/10.2307/3494083
Passoa, S. 1991. “Color identification of economically important Spodoptera larvae in Honduras (Lepidoptera:Noctuidae)”. https://digitalcommons.unl.edu/insectamundi/414/
Zuefle, M. 2018. “Sweet Corn Larval Pest Identification”. NY State IPM Program. https://hdl.handle.net/1813/57328

…Over the past 2 weeks, I have started to detect Noctua pronuba in pheromone traps. There is a commercial lure available, and I have some of those deployed currently, but honestly, have just as good of luck tracking them as non-targets in other armyworm traps.

In 2017, there were 2 apparent activity periods, which matches with published estimates from U. of Idaho, one of the only other places in the country with a documented outbreak of winter cutworm. ~~Click here~~ to see an interactive comparison of trap catches between years, so far.

Keep in mind, these observations are NOT, at this time, part of a full-fledged sampling program for Noctua pronuba. Rather, I am mentioning adult flight because it is an indicator that there is POTENTIAL for winter cutworm activity starting about September 10th.

** Please review the OSU Extension publication for more info about host plants, history, biology, and identification of this species **.

AUGUST 2018 – EDITS to the original (FEB 2018) post

Ok, now that I’ve got your attention…

The subject line is a playful way to introduce you to Apamea devastator, although the damage it can do is no laughing matter.

This species overwinters as mature larvae, and I found some south of Corvallis just last week.

Larvae live underground, and feed on roots and the base of plant stems.

Host plants include:

Grass (pasture and seed)
Cereals
Corn
In outbreak years, feeding has been reported on: cabbage, lettuce, bean, beets, and radish

This pest is particularly fond of fescue, timothy, and bluegrass. Outbreaks have occurred in PNW fescue.

SCOUT IN SEPTEMBER AND OCTOBER by surveying grass fields for any sign of browning-off or slow growth. In herbaceous plants, the first sign of injury is often WILTING. Dig up the roots and search surrounding soil for translucent, large (3cm), greenish to white larvae with little to no body markings, except for the brown prothoracic shield just behind the head. Common name: glassy cutworm refers to the light, almost ‘glassy’ appearance, versus most other cutworms that have distinctive markings along the surface of the body (examples here).

Glassy cutworms have reddish-brown heads and a darkened plate just behind the head.

MANAGEMENT
It is important to realize that general predators can keep cutworms populations suppressed below damaging levels. Parasitoid pressure, however, may not be as effective for this species; a 1990 study from Oregon found that the cutworms matured almost to pupation before they were killed by parasitoids, thus feeding in the current season is not suppressed. Try to consider the impact on natural enemies before choosing to apply chemical controls.

If scouting reveals a need to make a treatment, consult the PNW Insect Management Handbook, and be sure your crop is listed on the pesticide label. Rain or irrigation may help move the product into the soil surface, which is important for this species.

TIPS FROM THE FIELD/LITERATURE:

This year (2018), I am catching A. devastator adult moths as non-targets in traps placed near cole crops. This could mean they are emerging from fields where they did early-season damage as larvae – because they feed on roots and stems, perhaps this is one of the factors contributing to the broccoli mystery. It also suggests that actual population numbers are higher than normal, because I usually do not see this species in my traps.
In fine fescue, damage from larvae tends to occur more on plants that are within 3 ft of a weedy grass.
In western Oregon, glassy cutworm (Apamea devastator) moths emerge in late June, peak in July, and larvae take 100-120 days to develop, depending on daylength
A. devastator has dangerous similarities to Noctua pronuba, the winter cutworm: both species have erratic outbreaks, and have caused damage to Oregon crops in previous years. Both overwinter as larvae, and have been documented feeding throughout the fall and winter. (E.G. THIS ORIGINAL POST – FEB 8th, 2018)

activity of moth flights

Adult moths have a busy forewing pattern and can be worn beyond recognition. Look for black triangles near the terminal edge of the forewing, and a kidney-shaped (reniform) spot outlined in white. Hindwings have a gray border and white fringe.

This week, there were Noctua pronuba moths found in traps throughout the valley. Although we are not specifically trapping for them at this time, their presence should be considered a cautionary tale. As we know from years past, where there is one, there are many.

This moth is easily recognizable by 3 main features:

Large size (± 2 inch wingspan)
Bright yellow hindwing that can only be seen in flight
Thick black border on hindwing

Adult moths are not a problem. In fact, they have been in Oregon for 15 years. However, in 2015 there was an outbreak of larval N. pronuba, common name: WINTER CUTWORM. Yes, these larvae are active (hence feeding) throughout the fall and winter months. They move in groups, like armyworms, and can be very destructive.

Scroll down for more information on winter cutworm, or comment below if you have questions or concerns. Thanks for reading.

The arrival of Spring brings with it opportunity to discuss Noctua pronuba and its potential to affect this year’s plantings.

The extremely WET winter and recent mild temperatures mean that cutworm pressure could be higher than normal this year.

As seen in the figure below, crop damage can occur throughout the winter, AND ALSO INTO SPRING.

To scout for damage, look for areas of clipped grass or missing seedlings. Dig to at least 2″ and sort through the soil. Or, investigate at night to catch cutworms in the act!

Winter cutworm spotted on hazelnut tree trunk near Newberg. DEC 2016 PHOTO CREDIT: Nik Wiman

Larvae will be feeding now, and they eat truly everything, including commercial grasses, home lawns, vegetable crops, and ornamentals. Most cutworms are subterranean but some can also climb up to feed on foliage. Certain species do this in vineyards, but until recently, we did not know if N. pronuba displayed this behavior:

Happy planting, and please feel free to CONTACT me with cutworm sightings or questions.

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Cutworm Central

Damaging caterpillars of the PNW: updates and information

Tag Archives: winter

Fall Armyworm or Just…Armyworms in Fall?

Identification

References

Large Yellow Underwings are on track

Devastation Imminent

Large Yellow Underwings Found in Traps

Winter and also SPRING cutworm

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