WEEK 24 – Cabbage maggots are one of the most challenging pests for brassica growers. They tunnel through root tissue and increase the risk of exposure to plant pathogens Read this cabbage maggot page, which includes more info on biology and how to sample for them. Another late season pest is diamondback moth. Many sites are listed as "n/a" this week, because fields have been harvested and traps are being removed.
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WEEK 23 – Corn earworm flights have been consistently high, and scouting this week revealed late stage larvae, pupal exit holes, and newly-emerged adults that will lay eggs within 3-5 days. This diversity makes control difficult, and scouting is recommended. Spotted cucumber beetles do become active in the fall, but levels this year are about 500% higher than historical norms.
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It’s….BMSB Season! According to a pest model for this region, the summer generation of adults started appearing this week. This pest is very mobile, and will move into fall crops readily. I caught a glimpse of an egg mass in sweet corn today (photo below), and nymphs are expected to peak within the next few days.
Bell pepper, sweet corn, and tomato are all considered desirable hosts. Symptoms include sunken kernels, whitening on fruits, and spongy tissue. Rather than re-invent the wheel, I decided to direct you to some GREAT resources (see list below) for BMSB ID and management in vegetables.
FOR MORE INFO:
Wiman lab page – Oregon State University – Identification, monitoring efforts, and resource list
WEEK 20 – Diamondbacks continue to hatch; corn earworm flight; beneficial insect tracking. Perhaps most importantly: we found 5 Large Yellow Underwing Moths (the adult phase of winter cutworm)in traps this week. More information is available here.
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All this talk about crop PEST insects should not go unaccompanied by at least a brief mention and applaud for those silent heroes, the BENEFICIALS!
Biological control by generalist predators can be quite effective at mitigating pest insect populations, depending on the circumstance.
Two of the most common predators that we see in vegetable crops are ladybird beetles (ladybugs) and lacewings. I decided to track activity of these two groups this year, just to see if any activity patterns would be evident.
Ladybugs and lacewings can be passively sampled with yellow sticky traps. Although, for a more detailed study, one would want to incorporate sweep net sampling, increase trap numbers per acre, etc.
The convergent lady beetle (Hippodamia convergens) is a native species. They overwinter as adults, mate, and then lay eggs in the spring. A study from Corvallis using field-collected H. convergens found that 228 growing degree-days (above a threshold) are required for development from egg to adult, and that this heat-unit requirement is rather consistent throughout North American populations (Miller 1992 Env. Ent. 21).
The graphs above show a clear pattern of increased activity (adults on sticky cards) beginning around late June-early July.
Sure enough, the peak in adult ladybug activity correlates with published heat-unit requirements, and is confirmed by a degree-day model and online phenology tool (uspest.org, check it out!)
Cool! But what does all this mean? Well, it suggests that passive sampling is a good way to estimate ladybug phenology, and could provide us with comparative data on predator activity differences between years.
Perhaps more importantly: recognize that while it takes ~230GDD to detect ADULT ladybugs, the larvae are predacious too and have been busy in your fields and gardens all spring!!
WEEK 18 – Diamondback moths are exploding, and I try my hand at interactive maps!
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We monitor for cabbage loopers because they are pests of brassica crops. Feeding can occur on a wide variety of vegetable hosts including: beet, celery, cucumber, lettuce, pea, pepper, snap bean, spinach. Not all hosts are suitable for complete development of the insect, but feeding is feeding, from a grower or gardener’s perspective.
Plants, like insects, are ectotherms, which means that their rate of development depends on external conditions. Sure, most companies put ‘days-to-harvest’ on the seed packet, but we all know that is just an estimate, and can vary widely by region. It’s greatly influenced by temperature; especially if we encounter variations from the ‘normal’ levels of heat and/or rainfall.
Faculty at OSU Extension’s Small Farms Program and the Integrated Plant Protection Center have developed an online, predictive tool to help guide grower decisions and crop planning. The resource is called CROPTIME, and it provides models for a few of the crops grown in Oregon, with aims to develop 50 models (vegetables and weeds) eventually. Here is a 9-minute video that describes how to use the program.
This tool can greatly aid vegetable growers in estimating regional, temperature dependent phenology for a specific variety. For instance:
Broccoli Harvest Estimates - 2017
This information is collected from an online prediction tool, Croptime, from Oregon State University. The program is free to use and publicly available. Planting dates and varieties can be adjusted by the user and models are available for broccoli, sweet corn, cucumber, and sweet pepper.
*Estimates are accurate for W. Oregon only, these particular values are based off weather data near Keizer, OR.
50% head initiation
For more information, visit http://smallfarms.oregonstate.edu/croptime
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.