Hello, all. After this morning’s invited speaker talk (OPVC Annual Grower Meeting – see below for link to watch it), I thought it might be helpful to assemble some existing resources we have about Delia spp. maggots 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
…An uncommon phrase to hear in agriculture, but recent floods will have a dramatic effect and have already caused an estimated $12.5 billion dollar loss in the Midwest. Impacts include crop damage, inability to access fields to work ground or plant, and water contamination.
Here at home, the mainstem of the Willamette River and its tributaries (Long Tom, Mary’s, Callapooia) are in huge swells, with property flooding and road closures abundant. For current updates, check Benton and Linn County webpages or ODOT TripCheck.
From an insect pest point-of-view, the changes that may come about are uncertain, but I will be keeping a close ‘eye to the ground’. Flooding could cause mortality for some species (onion bulb mite, beetles, sawflies), promote growth in others (armyworms, mosquitoes), and have little effect on bugs that overwinter in sheltered areas (BMSB and ladybugs).
‘Twas a dreary day when I could finally get out to our research farm to assess damage to fields. However, our farm manager is resilient and those that have lived here longer say it’s “not that big of a deal”. I guess when you live in Oregon with 300 days of rain, you make your own mental sunshine.
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.
….Cutworms and armyworms, that is. Many studies report increased activity of these pests in years following record rainfall, and moisture dependency is common. This simply means that more eggs hatch if there is sufficient moisture in the soil.
For more info about cutworm ID, activity, and more,
Some species I have noticed on the rise over the past few years:
Spodoptera praefica is native to the Western U.S. It is considered a generalist feeder. Larval feeding causes extensive defoliation of leaves and also fruit damage. As the name implies, these worms are gregarious (feed in groups), and therefore can cause extreme damage.
Host plants include: alfalfa, asparagus, bean, beet, cabbage, carrot, corn, clover, lettuce, onion, ornamentals, pea, potato, wheat, and many others.
Apamea cogitata is considered a pest of grasses and grains (Poaceae). It is a cutworm, and has one generation per year, usually peaking in mid-July. This species is widespread in the Northwest. One of the identifying characteristics is a pink-hued fringe on the margins of the hindwing.