Cutworm Central

As we endure the College World Series rain delay, let’s take time to learn about a different type of strike. (A segue stretch, I know)…

Mamestra configurata Walker, bertha armyworm, is native to North America and is a major pest of canola, so most published literature reports on damage and economic thresholds in Brassica rapa and B. napus, and some suggest that populations (in Canada) have gotten worse with the increasing acreage of rapeseed¹.

This species has been monitored for 20+ years via the VegNet program, and outbreaks in vegetable crops have been few and far between. However, as with any armyworm, scouting is KEY because when damage does occur, it happens quickly and usually on a large scale.

Larvae feed above-ground, on foliage and fruit of hosts from over 40 different families. Some of the documented hosts include:

Flax
Alfalfa
Fruit trees
Sugarbeets
Hops
Mint
Potatoes
Weeds: especially lambsquarters, Canada thistle, and sow-thistle

After group feeding on foliage as ‘baby’ caterpillars, mid-stage larvae spin silk threads that help disperse them on the wind, a few meters within a field, and voracious feeding begins.

SCOUTING for bertha armyworm involves leaf pulling and visual scans. As a scout crosses a field pulling and examining leaves, they should stop every ten leaves and scan for a plant or a small grouping of plants with a lot of holes in the leaves, then walk to that location and try to find larvae.

These patchy, hard-to-find areas of damage are called armyworm “strikes” [there it is].

Pheromone traps are used to monitor activity of adult bertha armyworm moths. The moths occur at low densities, but any detection of them in a trap is cause for prompt and careful field scouting.

MANAGEMENT
Natural enemies (predators, parasitoids, viruses) probably exert heavy levels of control on bertha armyworm, otherwise we would see more frequent outbreaks.

1. Dosdall, L.M. and B.J. Ulmer. 2004. Feeding, development, and oviposition of bertha armyworm on different host plant species. Environ. Ent. 33(3): p. 756-764.

2. Lamb, R. J., W. J. Turnock, and H. N. Hayhoe. 1985. Winter survival and outbreaks of bertha armyworm, Mamestra configurata on canola. Can.Entomol. 117: 727-736.

*Apamea* moths are flying now. Larvae are cutworm pests of grasses.

Apamea cutworms can be serious pests of grasses. There are a few different species that are common in this region. Two of them have fun common names.

A. cogitata, the thoughtful Apamea

and its more unfortunate contrary:

A. dubitans, the doubtful Apamea

The current activity of this common group of moths is not of direct concern. Rather, it is the active, overwintering larvae that are considered pests because they feed on grass roots. A. dubitans and A. cogitata are probably similar to the congeneric A. devastator, which only has 1 generation per year. I made a post about them in February.

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 daylength¹. The species we caught in traps this week (thoughtful and doubtful) are less well-studied. But I wager a guess that we could begin to see larvae in fields by about mid-September.

Fun fact: “cogitare” translates from Latin as “to think”. One of Francis Bacon’s most famous works “Cogitata et visa” (“Thoughts and Conclusions”) was written in 1612. In it, he posed that philosophy and science have common interests.

¹ Kamm, 1990. Biological observations of glassy cutworm in western Oregon. Pan-Pac.Ent. vol. 66

If you’ve followed this blog, you may know I have a penchant for word play and grammar jokes. So yes, here’s another one:

Black and Bluhm – in reference to Agrotis ipsilon (black cutworm) migration patterns and Wilbur L. Bluhm, emeritus OSU Extension agent who tracked the phenology of many ornamental plants in western Oregon for over 40 years.

Phenology is the study of periodic life cycle events and how they change from year to year. It is an armchair hobby of mine, and also has direct implications for crop pest monitoring. Plants and animals alike develop and progress through life cycle events (leaf out, molting, bud break, etc.) according to temperature.

When Spring arrives 20 days earlier than normal, the implications become even more important:

source: USA National Phenology Network, www.usanpn.org Jan1-Mar5

Black cutworm, like many crop pests, exhibits long-range migration behavior, and adult moths depend on nectar sources to literally fuel their journeys. A recent study¹ examined pollen load on A. ipsilon antennae and found that they are especially frequent visitors to flowering woody dicots like honeysuckle, hawthorn, hazelnut, alder, oak, maple, etc.

source: Univ. of Wisconsin Dept. of Bio.

According to Bluhm’s tracking² , most of the plant species mentioned above are, in general, blooming earlier than they used to here in Oregon. This obviously varies widely by year and by species, but bear with me…

If more floral resources are available, earlier, and insect development also is ‘ahead of schedule’, it stands to reason that moth flights could be affected.

The chart below shows peak flowering of three common woody species, and their phenology over the past few decades. I compared this to my dataset of black cutworm moth trap counts and found an interesting pattern:

graph — Phenology of flowering woody plants and increase in early season abundance of black cutworms. Black triangles indicate years when moth counts >0.5/day on April 30th. Datasources: W.Bluhm² and J.Green.

And now, just for fun..listen to this and ponder the potential relationship between black and bl[oom] !

¹ Liu, Y., et al. 2016. Host Plants Identification for Adult Agrotis ipsilon, a Long-Distance Migratory Insect. Int’l. J. Mol. Sci.,17(6).
² The Wilbur L. Bluhm Plant Phenology Study <http://agsci-labs.oregonstate.edu/plantphenology/>

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.

In July 2017, Willamette Valley grass seed loads were contaminated with a mix of many different species of caterpillars.

The summer of 2017 is proving to be quite the year for crop pest activity. A regional monitoring program called VegNet produces weekly activity reports for 10+ species that occur in this region.

Many of the pests monitored are moths. Adult moths lay eggs on host plants, eggs develop into caterpillars, and caterpillars damage crops.

Last month, there were widespread reports of cutworm and armyworms showing up in grass seed hopper bins and detected only as loads were being delivered. More info on that here.

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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Now that Fall has officially begun (Sept. 22nd), it’s time to start talking about potential for damage to fall and winter crops from Noctua pronuba, the winter cutworm.

According to limited data of N. pronuba activity in this region, there seem to be two flight periods – early spring (Mar-May) and now (Aug-Oct). Adult moths are easier to detect than larvae, and we are currently working on improving sampling techniques. Based on information from flight periods of adults, we can better estimate the potential for larval damage.

The widespread winter cutworm ‘epidemic’ of 2015 could have been one of two things: an unfortunate ecological fluke brought on by a combination of mild temperatures, moisture events, natural cyclical wave of predators, etc. or (gulp..) a sign of things to come.

We have found winter cutworm moths throughout the Valley and intend to increase sampling efforts over the next few weeks. Stay tuned and in the meantime, review these tips for scouting:

If possible, examine plants at dusk, dawn, or preferably at night, when cutworms would be actively feeding. For daytime scouting, look in the soil at base of plants, digging up to 2″ may be required.
Look for wide swaths of damage that may occur in a ‘feeding wave’ pattern – especially on large acreages. N. pronuba behaves like an armyworm, and true armyworm also has been noted in abundance this year. Click here to help distinguish between species.
Larvae are large, and marked with black dashes down each side of the back. The dashes occur on the posterior 2/3rds of the body. A white to cream diagonal pattern may be present on the sides of the body, depending on how old the larvae is. The ventral (belly) side of winter cutworm may be tinged with pink.
Adult moths are relatively large-bodied and have a unique coloration (see below). The orange-yellow hindwing is most noticeable if the moth is in flight; it ‘flashes’ out to the naked eye, as seen in this video:

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Winter cutworm is a new pest threat in this region. It has a wide host range and can be very destructive because it moves and feeds in large masses, similar to armyworms. As the name implies, cutworms are active during the winter, and therefore can affect perennial and fall-seeded crops including legume and grass cover crops, grasses grown for seed, ornamentals, vegetables, and grains.

Between November 2015 and February 2016, dozens of reports were made throughout Oregon and Washington, where there was suspected damage from winter cutworm, which is the immature, damaging stage of the large yellow underwing moth. Adult moths have been present in this region since 2001, yet there had never before been accounts of widespread damage being done by winter cutworm. In response, an OSU Extension publication was released (available here), and public presentations were made in Multnomah, Polk, Linn, Benton, and Douglas counties.

Large Yellow Underwing moths can be recognized by the distinct pattern and coloration on the hindwing. Photo credit: Merrill Peterson

Adult moths have been very abundant over the past few weeks. They are easily recognizable by their large size (~2″) and hindwing, which is bright orange-yellow and bordered by a thick dark band.

We are currently researching whether winter cutworm will be a problem again in the months to come.

For more information:

If you have seen this moth, please comment below or contact jessica.green(AT)oregonstate.edu.

“Winter Cutworm: A New Pest Threat in Oregon” (EM 9139) https://catalog.extension.oregonstate.edu/em9139

Cutworm Central

Damaging caterpillars of the PNW: updates and information

Striking out

Grass pest moths detected

Black n’ Bluhm: investigating the link between

If you’ve followed this blog, you may know I have a penchant for word play and grammar jokes. So yes, here’s another one:

Devastation Imminent

Large Yellow Underwings Found in Traps

Rise in field crop cutworm activity

Winter and also SPRING cutworm

Fall flight

Winter Cutworm Update

Contact Info