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.
2019 Data and Maps from: the PRISM program, Oregon State University white=normal; yellow=slightly less; green=approx. 2X increase.