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.
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.
We have received many emails this week about ‘home invasions’ of odd-looking bugs. In each case, the culprits were boxelder bugs. Although easily recognized as adults, the partially mature phase (nymphs) can be unfamiliar.
Nymphs and adults aggregate in large groups, especially on light-colored homes with a warm-facing side. The concern for damage on ornamental or fruit trees is low. Rather, these are considered a nuisance pest. The sheer and sudden numbers of them is what causes calls to come in.
If you read this title and wondered “where are weeks 1 thru 6?” .. you need to subscribe! Weekly reports are sent directly by email, but sometimes there is so much happening, I have to do a mid-week update via blog. This is one of those weeks!
The cabbage looper outbreak continues, with trap counts averaging 1000 times higher than normal. Yes, you read that right.
12-spot beetles. You see ’em, you know ’em, but did you know they can be devastating underground pests? The pictures below were taken this week on spinach for seed and seedling spinach (yes, there’s a difference).
As adults, beetles chew on foliage, flowers, fruit, corn silks, etc.
As larvae, grubs chew on and tunnel through roots.
For more info about 12-spots, click here; or branch out a bit and learn about the whole rootworm complex that plagues regional growers and gardeners.
Spring is a critical time to assess wireworm populations because when soil temperatures warm to 50°F, larvae begin to migrate up within the soil column and seek underground plant tissues to feed on. Root crops are most commonly damaged, but chewing on seeds, seedlings, and fruit also have been reported.
I am coordinating a pitfall trapping effort to determine if non-native adult click beetle species are present in western Oregon (contact me if you’d like to participate). To monitor your own fields, bait stations are recommended, because they are a better indicator of actual, larval (wireworm) pressure.
I will post a more detailed pest profile page in the coming weeks, but for now:
For more information, click the link to read a publication by Nick Andrews et. al re: Biology and Nonchemical Mgmt. in PNW potatoes.
2-may-19 update: the PEST PROFILE PAGE is ready, and has more details about how to monitor, ID, etc.
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.
…the slimy worm-looking things covering the sidewalks around campus this week. They are the immature form of craneflies, commonly known as leatherjackets.
I’m hoping it’s not too late to save our campus lawns, but by the time this kind of damage is apparent, insecticides may not be effective. By mid-May, the leatherjackets will pupate then hatch into adults. Adults are harmless (other than a nuisance).
Maintaining grass health is the best defense against craneflies. Monitoring should be done from January to March, when larvae are feeding underground. More information is available at: http://whatcom.wsu.edu/cranefly/Index.htm
Participating in the OSU Extension Open House last night was fun and rewarding (thanks, staff!!). I enjoy outreach events and inevitably learn something from interacting with the public.
Yesterday’s conversations led to today’s topic: “Problems with my PEAS”
In the span of two hours, three different citizens came to me wondering why their early-planted peas are being “attacked by an unidentified marauder” (direct quote).
All 3 inquiries were similar and there were some important clues present: leaves are being damaged from the edge inward (chewing mouthparts); not cut off at soil level (cutworm); nothing obvious when scouting at night.
WEEK 0: Spring has sprung and we need field sites. Broccoli plantings will be starting soon, cooperating growers are encouraged to contact me to reserve their spot. Cutworms and armyworms are likely going to be a problem this year.
Many have been spotted already, even on campus sidewalks (see below)! This species is especially fond of ryegrass and orchardgrass, and outbreaks have occurred in western Oregon.
So..why did the caterpillar cross the road? Because it overwinters as a partially mature larvae and peristaltic searching mobility increases when ambient temperatures exceed 10°C, of course!
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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.
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.
FOR MORE INFO:
Wiman lab page – Oregon State University – Identification, monitoring efforts, and resource list
WEEK 16 – Two types of rootworm are now widely present in the Valley. See this page to learn how to ID and differentiate between them. Another, third species, may be on its way. Western corn rootworm has been moving westward since 2004.
Read the full report here: http://bit.ly/VNweek16 and subscribe on our homepage to receive weekly newsletters during field season. Thanks!