Regional trapping in Tillamook county has been ongoing for 6 weeks. We’ve recently begun to incorporate GIS maps to make it easier for program leaders and participants to visualize ‘hot-spots’ of armyworm moth activity.
Of 15 total monitoring sites, positive trap counts this week are confined to a 5 mi2 area, centralized around Tillamook city limits. This type of pattern can only be visualized by mapping, and may help focus efforts for further scouting. Fun stuff!
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:
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].
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 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