Non-Thrips Arthropods Impacting Onions

Stuart Reitz Malheur County Extension

Oregon State University

Onion Thrips

Onion Maggot and Seedcorn Maggot Adults

M. Storey

Bugwood.org

Onion Maggot / Seedcorn Maggot

• Historically, most damaging insect pest

• Multiple generations –first most damaging

• Onion maggot emerges earlier, but seed corn tends to be more damaging

By Rasbak at Dutch Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3219061

Univ. Minnesota

Cornell University

Factors Affecting Maggot Damage

• Cool soil temperature • Excessive moisture • Favor slow seed

germination and seedling emergence

• Increase susceptibility to maggot infestation.

Maggot Management

• Cull Disposal

Sean Ellis

Maggot Management

• Delay Planting to allow soil to warm

• Seed Treatments – Neonicotinoids– Spinosad

• At Plant Treatments– Lorsban (Chlorpyrifos)

• Control of adults - difficult

Tim Waters

Wireworms

Wireworm Biology

• Multiyear lifecycle• Feed on germinating seeds, roots and young

seedlings• Patches in row sections are missing• When soil temperatures rise to about 50° in the

spring, wireworms move towards surface• Hot, dry weather of about 78° - wireworms burrow

into soil (over three feet). • Cereal crops are highly susceptible to wireworm

infestation

Managing Wireworm

• Seedbed – Good seedbed for faster germination

– Go over minimum seeding rate

• Planting Time– “Problem” fields – plant later

Chemical Management

• Fumigation – Telone (Dichloropropene, Chloropicrin) may help

• Lorsban (Chlorpyrifos)

• Seed Treatments (Neonicotinoids)

Bulb Mites

• Wide host range

• Feeding on outer layers of tissue allow pathogen entry.

• Cool, wet weather leads to greater damage.

• Survive in soil on crop residues

• Rapid plant back fosters population growth and damage

Bulb Mites• Allow plant residues to

breakdown

• Avoid successive onion crops.

• Flood irrigation or heavy winter rains.

• Fumigation –Metam Sodium (Vapam)

University of Minnesota

Spider Mites

Spider Mites

Spider Mites

• Large infestations –late July - September

• Disperse from Neighboring Fields• Corn, mint, sugarbeets

• Abamectin (Agri-Mek)• 30 Day PHI

Sven Spichiger

Sven Spichiger

L. Donovall.

Allium Leafminer

• European species

• Currently ONLY in Pennsylvania, New Jersey, New York

• Can mine into bulb

Serpentine Leafminers

• Liriomyza trifolii

• Wide host range

Natural Enemies

Bugological

Diglyphus

Leafminer Parasites

• Parasites can control leafminer

• Parasitoids highly susceptible to many broad spectrum insecticides

• Pyrethroids, carbamates

Leafminer Management

• Abamectin (Agri-Mek or other formulations)

• Cyromazine (Trigard)

• Spinetoram (Radiant) / spinosad (Entrust or Success)

• Azadirachtin (Aza-Direct or other formulations)

Salt marsh caterpillars on onionAmy Ivy

Beneficial Insects

Summary• Pests – not just thrips!

• Accurate identification

• Below Ground Pests– Cultural Controls– Preventative Insecticide Treatments

• Foliar Pests– Many are Secondary pests– Avoid flaring populations with pyrethroids, Lannate

applications late in the season

Pest Management Plans

• Pest Management Strategic Plan for Dry Bulb Storage Onions in the United States. 2013. Howard Schwartz et al. http://www.ipmcenters.org/pmsp/pdf/USonionPMSP.pdf

• An Integrated Pest Management Strategic Plan For Treasure Valley Onions; Oregon and Idaho. 2017. Katie Murray, et al. https://ipmdata.ipmcenters.org/documents/pmsps/Onion_IPMSP_June_2017.pdf