Soil type and the parameters associated with it (water holding capacity, %OM, etc.) could be important as we continue to investigate armyworm population dynamics. The Web Soil Survey is a useful, interactive tool that is freely available to all.
We are trying to discern why certain sites in our Tillamook trapping effort have 10-20X the amount of armyworm moths detected.
We know that when there is abundant soil moisture, more eggs are laid, and more eggs hatch, which increases the risk for damage by larvae.
Sites less than 5 miles apart have similar pasture management but very different trap counts.
In low-lying areas like coastal Oregon, the distance to the water table might vary between fields
I encourage you to check out the Web Soil Survey tool (link above) and do some “digging” around – there’s a wealth of information available!
Predicting cutworm and armyworm pressure is difficult. But without predictive tools (monitoring of adult moths, crop scouting, and detection of larvae), cutworm and armyworm attacks are only noticed too late, when the most severe damage has already been done.
Here are some factors that affect activity levels:
Cyclic booms and busts of pest population levels affect the balance of natural enemy regulation, which is one reason why we seem to have ‘bad’ cutworm and armyworm (and looper!) years followed by years where populations seem more normalized.
Some of the cutworm and armyworms we have in this region arrive each year as long-range migrants from southern latitudes. Weather patterns such as el Niño and la Niña can affect migration patterns.
Another predictor of risk is winter moisture level, both locally and in areas where moths overwinter. These, and other abiotic factors contribute to cutworm and armyworm survival and potential damage each year.
Wet Winter = Worms
Okay, so the equation isn’t quite that simple, but we do know that armyworm outbreaks tend to be worse after years with excessive rainfall from Sept-March. Due to recent trends, we will be researching WHY outbreaks happen and if we can better predict them. Stay tuned… (and tell your friends to subscribe for updates!).
Armyworm species, in particular, exhibit moisture dependency. This simply means that the percentage of egg hatch is greater if there is abundant soil moisture. Our regional precipitation was relatively normal from January-March (below, left), but 200% wetter than normal in April (right), and the flooding in May could affect egg hatch as well.
Maps courtesy PRISM program, Oregon State University white=normal; yellow=slightly less; green=approx. 2X increase
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)
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).
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)