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!

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.

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.

WEEK 7 –

  • Seed corn maggot  – Poor emergence may be a sign of underground feeding by seedcorn maggots, which are the immature stage of Delia platura. Plants are most susceptible at seedling stage. Host plants include: corn, green and broad beans, onion, brassicas, peas, pepper, potato, spinach, and beet.
    • SCM is especially attracted to newly-tilled soil with high organic matter / manure inputs.
    • They have multiple, overlapping generations per year. This image by U. of Illinois highlights how adults, eggs, and maggots may all be present at the same time.
    • If emergence is low, scout 2-ft row sections for seed damage and white, tapered maggots that look very similar to cabbage maggot. Both species favor cool conditions for egg-laying, but D. platura are more active as adults in warm weather.
    • There is a fascinating biological (fungal) control for SCM that alters the fly’s behavior:  It causes the flies to settle on tips of grain stems or high-up flowers and die, which increases dispersal of the fungus to spread farther.
  • Seed bugs – There have been recent complaints of high numbers of ‘small, flying insects’ in both urban and rural areas since mid-April. The bugs are 3-4mm with elongate bodies and wing covers with 4-5 veins. Experts agree that the taxonomy of this group is in need of a major revision, so they are usually referenced to genus level only.
    • More than half of all known Nysius species are from Hawaii, including the endemic wēkiu bug, that migrates to the summit of Mauna Kea each year.
    • Nysius spp. are seed predators and tend to be less selective then other, related  Lygaeidae. Extensive damage can occur in wheat, quinoa, canola, and sorghum. Occasional feeding can occur on ornamentals, other cereals, and tomatoes.
    • Similar to boxelder bugs, they are attracted to large, sunny, white buildings, which has led to nuisance reports by homeowners. Various Ask-an-Expert questions have been submitted, one of which I was able to identify last week as Nysius, probably N. raphanus. The high numbers we are seeing now is likely the result of overwintered nymphs maturing into active, winged adults. There are 4-7 generations per year.

WEEK 14:

    • 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.

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