Category Archives: sweet corn

Sap Beetles in Corn

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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.

Seed Maggot Problems

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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 blog post (Jan 25, 2021) – aka all about maggots on one page with link to a video by Dr. Nault, a SCM expert
  • Related 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.

Precision Ag Tools

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The definition of Precision Agriculture has evolved over 22 years and has more than a few associated acronyms (PA; SSCM=site-specific crop management; VRT=variable rate technology).

If one were to attempt to summarize the definition of PA: it involves awareness of growing conditions within a field and the use of technology as a decision support tool to maximize production efficiency while minimizing environmental impact of agricultural inputs.

We may be most familiar with PATs (Precision Agriculture Technologies) such as:

  • GPS-guided tractors or the use of
  • UAVs (unmanned aerial vehicles AKA “drones”) as imagery sensors or product applicators
  • Other PATs include robotic weeders and mechanized transplanters.
  • So many acronyms!

Check out The University of Sydney’s Australian Centre for Field Robotics promo video:

Resources closer to home include the UAS at OSU program, and a fellow Beaver blogger who has a great annotated resource list about Drones in Agriculture here. UAVs are even being used for restoration seeding efforts in Oregon rangelands.

Perhaps you’re not quite ready for autonomous tech. One simple and easy way to jump on the PA bandwagon is to use calibration tools. These are based on mathematical models of soil and crop parameters for a specific latitude, soil type, etc.. At the click of a button, they provide output estimates to help schedule irrigation, determine fertilizer needs, or predict harvest dates. These are in addition to the MANY mobile apps now available.

Another new trend (and a way to sneak in one last acronym) is for companies to offer SaaS: Software as Service, like our friends at Valley Agronomics.

As you go about planning and planting this year, why not give these PA tools a try. The program developers are usually very receptive to comments, as it helps them improve the models, or know that they are working adequately.

DISCLAIMER: Mention or links to any of the products or services on this page do not imply endorsement.
Computerized vision robot picker view of a mapping system to identify and target specific branches. credit: F. Moore
A grasshopper swarm detected by Nat’l Weather Service radar – Northern Montana, July 2021. View tweet

Pest Report – Week of Sept 11th

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WEEK 23 –
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.

Read the full report here: http://bit.ly/VNweek23 and subscribe on our homepage to receive weekly newsletters during field season.

BMSB in Veg Crops

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Tis’ the Season! According to a pest model for this region, the summer generation of brown marmorated stink bug (BMSB) adults start 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.

BMSB model for Corvallis, OR. 2017; based off Nielsen et al 2008, and available at uspest.org

 

 

 

 

 

 

 

 

 

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.

BMSB egg masses are usually laid on the underside of leaves in groups of 28 eggs – count em’ and see! 🙂 – Sweet corn, Corvallis OR, 8-Sept-2017 J. Green

FOR MORE INFO:

Wiman lab page – Oregon State University – Identification, monitoring efforts, and resource list

Neilsen et al., 2008 – Rutgers University – Developmental details

BMSB info for vegetable growers – great photos of injury, explanation of life cycle, etc.

Western Corn Rootworm

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rootworm photos title image

Western Corn Rootworm (WCR) is considered 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?!)

Regardless of the species, rootworm damage is similar: larvae chew on roots, which can cause lodging or goosenecking. Adult beetles attack foliage and can clip silk (corn) or chew on blooms (squash) or pods (beans) if populations are high enough.

poor tipfill of corn
Poor pollination during silking affects tip fill. This picture is from the Midwest, where WCR is a much bigger issue than it is in the PNW. PHOTO CREDIT: J. Obermeyer

Q: So why mention WCR if it’s not yet 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.

Also, the Oregon Dept. of Agriculture (ODA) asked us to conduct a preliminary distribution survey of D.  D. virgifera in the PNW, both in field corn and sweet corn. You can read more about that project here: http://bit.ly/CRWinOR

diagram of map showing range of western corn rootworm 2004 vs 2014
Expansion of WCR in 10 years. Based on C.Edwards and J. Kiss (Purdue Field Crops IPM) and A. Murphy (OSU, PNW 662)

RESOURCES:

  1. 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.
  2. 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.

Pest Report and Press Release

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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. This page shows how to identify corn earworm adult moths.
  • VegNet was featured in the July-Aug issue of OSU Linn & Benton Cty Extension’s Newsletter! Click photo to read the article.

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