Category Archives: squash

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.

Caution for Cucurbits

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This “CAUTION” post is similar to one I made a few weeks ago for cole crops; a quick way to highlight a potential problem, in hopes that consultants, gardeners, etc., will do some scouting to investigate if/to what extent they may be affected.

We saw, for the first time this season, some western striped cucumber beetle (Acalymma trivittatum) activity on both both weedy volunteer and cropped cucurbits.

This pest is of particular concern because it vectors bacterial wilt, a plant pathogen caused by Erwinia tracheiphila bacteria. Researchers now suspect that, rather than overwintering in the intestinal tract of adult beetles, the bacterium overwinters in the sap of alternate host plants (i.e. volunteer and weedy cucurbit species). The alternate host plants may not show symptoms of being infected, which can make management difficult.

As adult cucumber beetles feed, the beetles become infected with bacterial wilt, and then transmit it to crops. This infection can be direct (feeding on one host then another), or secondary (fecal contamination of already wounded tissue). Once the disease is established, it cannot be managed with pesticides, so ‘awareness’ of cucumber beetle activity levels, and subsequent control if necessary, is considered the best preventative tactic.

A few tips for scouting bacterial wilt in cucurbits:

    • Melons, squash, and cucumber are considered more susceptible than zucchini and watermelon, but all related plants (Cucurbitaceae) are at riska
    • Damage can occur quickly – scout 2-3X/week for beetle pressure and wilt symptoms
    • Symptoms can be immediate on some plants, and not occur until after fruiting on others
    • Leaves may look dull green, yellowing at leaf margins
    • Vines wilt during the day, but seem to recover at night
    • Quick diagnostic test (photos below): stems/vines are cut close to the crown, and a ‘stringy’ sticky substance appears when the two halves are pressed then pulled apart from each other. b

erwinia_knifecutting
1. make a clean, vertical cut close to the crown

2. push segments together then slowly pull apart

PHOTO CREDITS: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org

 

 

There is a great new eXtension article about biology and management of cucumber beetles in organic farming systems available at: https://beav.es/ZYJ (it’s ok – we’ll use a Beavs shortlink to promote WSU just this once…there’s some great people/research going on up there!)

 

aDISCLAIMER: regional differences in pathogen expression are likely, do not rely on literature from other areas
bDISCLAIMER: may not work for all species or all cases

 

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

Squash Bug season

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Squash bugs have an elongated body shape and striped abdomen. Eggs are red and laid in clusters. Nymphs are gregarious, and progress in color from light gray to dark.

Anasa tristis is one of the squash bugs common in the PNW.

This pest is notoriously hard to detect, because they can hide on the underside of foliage, on plant stems, near irrigation lines, or even under fabric mulch.

Squash bugs use their piercing-sucking mouthparts to feed on leaf tissue and inject their saliva, which causes wilting of leaf tissue and, depending on the species, vectors cucurbit diseases.

Damage tends to be localized but can occur quickly because nymphs are gregarious, and feed alongside adults. If left undetected, vines eventually wilt and die.

Squash bugs have been a problem this year in the southeastern U.S., as noted by this news article.

[2018] According to a laboratory-based estimate, nymphal instars may be present in July, with a possible 2nd generation of adults in early August (model source: GDD58 single-sine, Fargo and Bonjour, 1988).

** 2019 Degree-Day Model Update**:
Adults noted East of the Cascades: June 27th (see report)
Eggs (predicted with GDD model, Corvallis): June 1st
Nymphs (predicted with GDD model for Corvallis): July 17th
Adult 2nd gen. (predicted with GDD model for Corvallis): Aug 4th

FOR MORE INFORMATION
1 H. B. Doughty, J. M. Wilson, P. B. Schultz, T. P. Kuhar, Squash Bug (Hemiptera: Coreidae): Biology and Management in Cucurbitaceous Crops, Journal of Integrated Pest Management, Volume 7, Issue 1, January 2016, 1, https://doi.org/10.1093/jipm/pmv024

2 PNW Insect Management Handbook section

3 This page shows how to differentiate squash bug, BMSB, and others