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.
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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
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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.
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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!