The natural enemy of my enemy is my friend! We start seeing increased activity of beneficial insects this time of year. Everyone can identify a ladybug, a select few know what a lacewing looks like, but did you know that certain flies, beetles, and even yellowjackets also help to regulate pest populations?

CLICK TO VIEW a newly revised OSU Extension publication about natural enemies

READ RELATED POSTS here on the blog

and GO OUT and look on crops, wildflowers, and weeds (especially wild carrot right now) to see these “good guys” in action!

Doesn’t seem possible but we are in week 7 of the 2021 monitoring season. It has been a slow and rather uneventful start, compared to recent years, but predictions of extreme summer heat and drought could change that.

  • Data tables are available for week 6 and week 7
  • Looper levels remain VERY low
  • An early (Apr-May) boom of cabbage white butterfly means greenworms could be present in gardens and fields – scout accordingly
  • Aphid scouting will once again be part of VegNet’s regional monitoring effort. See the aphid profile page for more info
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Three years ago, my field season was so affected by yellowjackets (FIG. 1) that I decided to find out what I could learn about them. Their abundance, activity, what influences populations, etc. It was actually harder than I thought to find information! This was noted by a 2018 paper , where the team investigated 908 published papers over almost 40 years and yep – less than 3% of them were wasp-related (FIG. 2).

Despite the importance of both taxa, bees are universally loved whilst wasps are universally despised.”

Seirian Sumner et al., 2018
Continue reading

While none of us have a crystal ball, especially in agriculture, I thought it might be fun to offer some thoughts / warnings of how this year might look for insect pests of vegetables. I predict* ……

  • “Flea beetles will be rampant.” In the spring, adult flea beetles emerge from overwintering, and are already causing some problems in radish. We’ve been told by both local and regional sources that it’s going to be a hot and dry summer = flea beetles’ favorite weather. I suggest early and often scouting in brassica crops. Starting now, begin to scout weedy areas around fields. Once the crop emerges, or shortly after transplanting, focus efforts on field edges. It may be necessary to scout daily – yes, daily. Be aware that these insects are easily disturbed (they jump), sticky traps placed ~10″ off the ground can help assess activity – place them near edges. You’ll recognize the distinctive ‘pitting’ on cotyledons and true leaves. Check stems for signs of damage as well, just above the soil surface. For more information, see the flea beetle pest profile page.

  • “Wireworms are a cryptic foe we should get to know.” They are a common problem in grass and potato production. Adult click beetles do not live for very long and do not cause damage. Larvae (wireworms), on the other hand, live for 2-6 years and damage can be extensive. Before planting, especially if you are coming out of a grass rotation, take my advice and place a few bait traps to assess larval activity. Instructions and more information is available at the wireworm pest profile page.

  • “Every other year, cabbage loopers cause fear.” Ok, I admit, this one is just a stretch to fit the rhyme scheme. However, it is true that in the Willamette Valley, we have had major looper outbreaks in 2017 and 2019… so 2021 is a possibility. Trap count data will be available soon.

* PLEASE NOTE: these are merely educated guesses. In fact, part of the fun of monitoring insects is that they are truly so unpredictable!

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I mentioned in last week’s newsletter that the Oregon Dept of Agriculture (ODA), Washington State Dept of Agriculture (WSDA), and Washington State University (WSU) are all active in their efforts to prevent and detect Japanese beetles in the region. Remember:

  • This Thursday, April 1st, at 9am, WSU/WSDA is offering a webinar. Click here to register and learn more.

Also be sure to check out the OSU Extension publication that includes information on identification, life cycle and scouting, damage, control measures, and how to report a suspected Japanese beetle. EM 9158    Published April 2017 4 pages https://catalog.extension.oregonstate.edu/em9158

Please help us get valuable information about chlorpyrifos 

  • Restrictions on the use of chlorpyrifos and the complete revocation of its registration are underway.
  • An ODA specialty crop block-funded project involves a cross-commodity collaboration to identify viable options as alternatives to chlorpyrifos.
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After this morning’s invited speaker talk (OPVC Annual Grower Meeting), I thought it might be helpful to assemble some existing resources we have about Delia spp. in the PNW. Browsing these links could help you better prepare for the planting season. Also feel free to leave a comment with any specific concerns or impact you’ve experienced. Thanks to Dr. Nault for a great presentation this morning!

  • ** VegNet alert – late June 2020 – Seedcorn maggot issues reported/confirmed in snap bean and parsnip
  • ** Pest profile page – Seedcorn maggot species complex, literature
  • ** Pest profile page – Cabbage maggot overview, ID, management
  • Temporal trends – late July 2018 – Temporal trends and species complex info
  • Scouting report – mid Oct 2020 – Maggot complex found in stored onion
  • Research report (pdf) – 2016 maggot trial in direct-seeded radish, chlorpyrifos alternatives
  • VegNet alert – May 2018 – Poor emergence, general info seedcorn maggot
  • U. of Mass. factsheet – Seedcorn maggot
  • Dr. Brian Nault, lab site – Cornell Entomology (pdf) – Delayed planting to help manage onion maggot

Root maggots are creamy white to yellow, opaque, and legless. They are tapered; blunt posterior end. Determining species is difficult and requires examination with a microscope.

Root Maggots of the PNW – Overview

Delia species (Diptera: Anthomyiidae). Small (5-8mm) flies – black, brown or grey – the immature phase are called maggots – they feed on root and sometimes stem tissue – identification technical and difficult* – often referred to as a rootfly ‘complex’. Adults do not cause damage. Eggs are laid at the base of plants. Maggots tunnel into tissue which causes direct damage and also increases the risk of infection by plant pathogens..
D. radicum: Cabbage maggot
Our most familiar regional issue. Adults prefer cool weather and maturing (4-7 leaf) brassica plants to lay eggs. Flight period well-documented and can be useful for predicting timing of egg-laying pressure.
HOSTS: weedy mustards, broccoli, cauliflower, etc.
.
D. platura: Seedcorn maggot
Attracted to organic matter and decay. Sometimes worse in fields that have been cover cropped to increase N. Often a secondary pest (invades after initial decay of tissue due to other factors). Active earlier than other species.
HOSTS: many, but especially large seeded vegetables like corn, peas, dry beans, snap beans
.
D. florilega: Bean seed maggot
Nearly indistinguishable from D. platura, often occur together.
HOSTS: association is broad, but mostly a problem in turnips, radish, canola
.
D. planipalpis: Western radish maggot
Similar in appearance to D. radicum, but different leg hair arrangement.
HOSTS: radish and canola (verified in literature); also probably other crucifers
D. antigua: Onion maggot
A major problem in onion production. Many good resources available.
HOSTS: onions, garlic, chives, etc.
.
D. floralis: Turnip maggot
Similar in appearance to other species; different leg hair arrangement.
HOSTS: turnip and radish
* Link to ID guide (Savage et al. 2016) but beware, it involves counting and measuring hairs on adult fly thoraces and legs – good times!

When people talk about beetle pests in corn, they’re usually referring to damage that occurs below the soil level. For many species, including western corn rootworm, wireworms, and white grubs, the common name refers to the immature stage that attacks corn roots underground.

So, when i saw this beetle-looking-larvae feeding ON developing kernels this week, I was intrigued and confused. And “well, maybe I was a little bit… ‘concerned'” [obscure movie quote, congrats if you know it ;)]

Look in maturing ears with loosened husks or bird damage. They’re pretty good at camouflage, eh? For a closer view, watch this video.

Coleoptera: Nitidulidae are small, oval to elongate beetles with clubbed antennae and shortened elytra (wing covers). Feeding habits vary, but adults tend to feed on fresh or decaying organic matter. Because of this, they are often called fungus or pollen beetles (e.g. Meligethes aeneus in brassica, canola, and clover production). Aethina tumida, the small hive beetle, is another example.

The specimen I found near Scio is probably Carpophilus lugubris, a N. American native and known pest of sweet corn.

  • Can be a problem in both processed and market corn, because larvae feed within the ear and damage is not always visible until after husking.
  • Beetles are most attracted to ears damaged by rodents, birds, deer, etc. or when harvest operations leave lower ears – can become a reservoir.
  • May have correlation with volatiles expressed by the plant after attack by corn earworm
  • Common in stored grains and nuts; feces can contaminate dried fruits
  • Larvae develop for ~ 3 weeks then pupate in the soil, adults can live up to 300 days, 1 generation/year
  • NOTE: Dusky sap beetles can also cause damage in TOMATOES, STRAWBERRIES, and other soft fruits – just don’t have time to elaborate on that today!
  • UPDATE: sap beetle found in large numbers contributing to onion rot – OCT 2020. Access the scouting report.

Growers and field reps throughout the region have been noticing issues with seed maggots. Similar to root maggots, these are the immature form of a certain type of fly (Diptera: Anthomyiidae: Delia spp.).

There are three species, in particular, that can be devastating in vegetable crops. The first, cabbage maggot (D. radicum) is well-known and tends to infest brassicas only. Use this link for more info on cabbage maggot.

“Seedcorn maggot” is the common name for what is actually a complex of two species – D. platura and D. florilega. “Bean seed fly” is another commonly used name for adults. These two species are remarkably similar, both as larvae and adults. For adult flies, color is variable and one must examine leg hair length and placement. Maggots are indistinguishable, even by experts.


Complaints so far have come from parsnip and snap bean fields, but dry beans, corn, peas, and squash growers should take note. If emergence is low, scout 2-ft row sections. Look for damage to seeds and white, tapered maggots. Maggots are legless and have a blunt posterior.

Learn More About Seedcorn Maggot:

  • PNW Handbook Sections
  • Related VegNet blog post (May 18th, 2018)
  • PHOTOS ABOVE ADAPTED FROM: Savage, J., Fortier, A-M., Fournier, F., Bellavance, V. 2016. Identification of Delia pest species (Diptera: Anthomyiidae) in cultivated crucifers and other vegetable crops in Canada. Canadian Journal of Arthropod Identification No. 29: June 29, 2016. doi:10.3752/cjai.2016.29
  • Brooks, A. R. 1951. Identification of the Root Maggots (Diptera: Anthomyiidae) Attacking Cruciferous Garden Crops in Canada, with Notes on Biology and Control. Can. Entomol. 83(5): 109-120.
  • Higley, L. G. and L. P. Pedigo. 1984. Seedcorn Maggot (Diptera: Anthomyiidae) Population Biology and Aestivation in Central Iowa. Environmental Entomology. 13(5):1436-1442.