Western Corn Rootworm (WCR) is considered is the most important corn pest in the U.S.1 . Most of this damage occurs in the Midwest, where corn acreage dominates the landscape. Over the last 50 years, farmers have used cultural, genetic, and chemical control strategies to lessen the effect of WCR and protect yields.
In comparison, the PNW produces a very small amount of corn (<5% of all regional farmland). Therefore, western corn rootworm has not been a problem for us so far2, and growers are much more accustomed to 12-spots (which is a western variant of the southern corn rootworm – confused yet?!)
Life histories are similar: larvae chew on roots, adult beetles attack foliage and can clip silk if populations are high enough. This interferes with pollination and can lead to poor tip fill.
Q: So why mention WCR if it’s not a problem here? A: This species is worth monitoring because it has been moving westward for the past 10+ years, and could become more abundant if corn production increases in the PNW. Yellow sticky traps are great passive sampling tools for many pests, so in short…might as well.
Gray, M. E., Sappington, T. W., Miller, N. J., Moeser, J., & Bohn, M. O. (2009). Adaptation and invasiveness of western corn rootworm: Intensifying research on a worsening pest. Annual Review of Entomology 54: 303-321.
Murphy, A., Rondon, S., Wohleb, C., and S. Hines. (2014). Western corn rootworm in eastern Oregon, Idaho, and eastern Washington. PNW Extension Publication 662. 7 pp.
WHAT: An epidemic of various cutworms and armyworms is occurring in grass seed fields in the Willamette Valley, and has led to severe contamination of harvested seed. The problem went unnoticed until fields were being cut, and high numbers of caterpillars were present in hopper bins and loads brought to seed cleaners.
WHY: Outbreaks occur every decade or so, and most experts agree that extensive fall and winter moisture is a major contributing factor. This is because, for many species of cutworms and armyworms, there is moisture dependency. This simply means that more eggs hatch if there is more rainfall, irrigation, etc.. In fact, my first-ever tweet was about this very topic! Additionally, cool, wet springs are detrimental for beneficial insects such as parasitoids and predators that usually keep cutworm and armyworm populations in check.
WHICH: In grass and pasture crops specifically, there tends to be a ‘species complex’ of related Lepidopteran pests all present at the same time, which can make identification difficult. Furthermore, coloration of larvae can vary extensively between individuals. Coloring can be influenced by population levels, host plant feeding, etc. From a management standpoint, this may not seem important because the pests can usually be treated as a group. However, in order to better understand the biology and develop predictive monitoring tools for the future, species identification is key.
The following results have yet to be confirmed by DNA barcoding, but they are based off morphological characteristics, regional history and activity records, and comparison with published literature. So far, I have determined the presence of at least 3 species:
Dargida procinctus – olive green cutworm. Light and dark larval forms, specialist feeding on grasses (Poaceae), and particularly prefers tall coarse grasses such as orchard grass and ryegrass. Outbreak occurred in 1980 Willamette Valley, and may be part of the Dargida species complex affecting E. OR and WA wheat growers (wheat head armyworm).
Mythimna unipuncta – true armyworm. A common pest, outbreak occurred in 2015. Adults are most common in late summer, but spring migrations are possible. Larvae are recognizable by alternating stripes of light/dark on the sides of the body, and dark netting on the eyes.
Spodoptera praefica – Western yellowstriped armyworm. This species is native to the western US, and closely resembles S. ornithogalli. This is a species of interest, I have been tracking it since 2015, more info to come. Wide host range.
HOW to scout for and manage: Unfortunately, the damage is done for the current harvest, but continued scouting is recommended. Sort through windrows and get down to the soil surface, where frass (evidence of larval feeding) will be notable (see figure below). Sweep netting is ineffective. Also be aware that harvest / bailing may cause any remaining armyworms to move out of the field to surrounding weedy areas, vegetable crops, etc. Try to examine field edges at night, and apply border treatments if necessary. I have noticed signs of biological control on a number of larvae, which could help mitigate populations.
FOR MORE INFORMATION: Consult the PNW Insect Management Handbook, and this pest alert put out by OSU Extension.
As one of Oregon’s top 5 commodities, the fact that grass seed harvests are having an insect problem is a big deal.
Over the past few weeks, seed has been arriving at the cleaner with high incidences of contamination by an unknown caterpillar. Wheat processors also are affected.
Based on timing and just a few photos, I have a good guess about what this is. Looking forward to getting some samples ASAP!
As in..not quite the attention-grabbing, human-adored, delightful critters known as butterflies, but we are here today to petition that moths are just as important!
National Moth Week celebrates the beauty, life cycles, and habitats of moths. “Moth-ers” of all ages and abilities are encouraged to learn about, observe, and document moths in their backyards, parks, and neighborhoods. National Moth Week is being held, worldwide, during the last full week of July (which isJULY 22-30th this year). NMW offers everyone, everywhere a unique opportunity to become a Citizen Scientist and contribute scientific data about moths. Through partnerships with major online biological data depositories, NMW participants can help map moth distribution and provide needed information on other life history aspects around the globe. More information can be found here.
Search the map to find an event near you, but I will tell you – we are the only one in Oregon so far! We hosted a booth at the Farmer’s Market to get the word out, and it was a huge success. There is also a moth walk planned for July 22nd, co-sponsored by Oregon State Arthropod Collection (OSAC) and Greenbelt Land Trust. More info here. UPDATE: EVENT FULL!
Better yet, create your own backyard mothing event! This document has some great tips on how to view and photograph moths. Then comes the fun part! Upload your findings to iNaturalist.org or a similar service. You do not need to be able to identify the species, others will help!
Good Luck, Have Fun, and Thanks for Your Help promoting and documenting this important group of insects!!
The 2nd generation of 12-spot beetles has emerged, and activity will likely remain high through September. Sweep ﬁelds with a sweep net to accurately assess population levels. Take a minimum of four samples (ten arcs of the net per sample) from different parts of the ﬁeld. Beetles tend to concentrate on ﬁeld edges. At this time of year, adult beetles are pests within snap bean and squash fields. They feed on folliage and developing pods.
There has been a boom of adult diamondback moths detected in pheromone traps. Development will be rapid under warm temperatures. Intensify field scouting so that treatments can be applied to avoid contamination.
Read the full pest report HERE and subscribe to receive alert updates.
WEEK 13: Early earworms; diamondback overlap – FULL REPORT HERE
Diamondback Moths are one of the smallest crop pest moths one is likely to encounter, but damage can be extensive. Part of the problem is their capacity to reproduce quickly, which leads to population buildup in a very short time. This is temperature-dependent and if not monitored, can catch growers off guard.
Corn Earworm is normally considered a late-season pest, but trends so far this year suggest a pattern similar to 2014, which resulted in a boom of moths in August, just as corn is silking. Larvae feed on corn silks and burrow into the ears. The resulting damage and frass (insect poop!) can cause delays in processing, or reduction of fresh-market value.
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