Pacific Northwest Vegetable Extension Group

of Washington State University, Oregon State University, and University of Idaho

Photo Gallery of Vegetable Problems

Onion/Allium

General Onion/Allium Disease and Pest Management

Onion Disease Guide - A Practical Guide for Seedsmen, Growers and Agricultural Advisors. Published by Seminis Vegetable Seeds, Inc.’s Plant Health Department.

Pest Management Strategic Plan for Dry Bulb Storage Onions in the United States
SCRI Project Updates Talks and Publications, Allium Net.
Onion ipmPIPE Brochure

Onion ipmPIPE Diagnostic Pocket Series

Bacterial Diseases
Foliar Fungal Diseases
Bulb Growth Stages of Onion
Onion Insect Pests

Soil-Borne Diseases
Storage Fungal Diseases
Storm Damaged Onions
Virus Diseases

Onion Disease Risk Assessment

Thrips & Iris yellow spot virus (IYSV) Forecast
Bacterial Disease Forecasts
Fungal Disease Forecasts

(Click on photos to enlarge)
 


Diseases

Disease: Bacterial soft rot
Pathogen: Bacterial species

Photo of Bacterial soft rot on onion

Internal symptoms of bacterial soft rot of onion bulbs.

Internal symptoms of bacterial soft rot of onion bulbs.

Internal symptoms of bacterial soft rot of onion bulbs.

Bacterial soft rot on onion Internal symptoms of bacterial soft rot of onion bulbs.

Photo Source: G.Q. Pelter

Photo Source: Lindsey du Toit, Washington State University

On-Line Resources:

Bacterial Diseases, Onion ipmPIPE Diagnostic Pocket Series


Disease
: Basal rot
Pathogen: Botytis allii and Fusarium roseum

Photo of Basal rot on onion
Photo Source: G.Q. Pelter

On-Line Resources:

Onions, Garlic: Basal rot, Washington State University Hortsense

Storage Fungal Diseases, Onion ipmPIPE Diagnostic Pocket Series

Disease: Black mold
Pathogen: Aspergillus niger

Black mold on an onion. Sporulation of the black mold pathogen, Aspergillus niger, beneath the outermost dry scale of an onion bulb. Severe black mold beneath the outer dry scales of an onion bulb. Black sporulation of Aspergillus niger along the veins of the outer, dry scales of an onion bulb.
Black mold on an onion. Sporulation of the black mold pathogen, Aspergillus niger, beneath the outermost dry scale of an onion bulb. Severe black mold beneath the outer dry scales of an onion bulb. Black sporulation of Aspergillus niger along the veins of the outer, dry scales of an onion bulb.
Photo Source: G.Q. Pelter
Photo Source: Lindsey du Toit, Washington State University

Sporulation of the black mold fungus, Aspergillus niger, on an onion seed plated onto Kritzman and Netzer’s agar medium (the medium results in a dark brown color to the pathogen spores, which are black on most other agar media and on onion bulbs).
Sporulation of the black mold fungus, Aspergillus niger, on an onion seed plated onto Kritzman and Netzer’s agar medium (the medium results in a dark brown color to the pathogen spores, which are black on most other agar media and on onion bulbs).
Photo Source: Lindsey du Toit, Washington State University

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Onion (Allium cepa) – Black Mold

Storage Fungal Diseases, Onion ipmPIPE Diagnostic Pocket Series

 

Disease: Diseases of storage garlic

See: Diseases of Storage Garlic (Oregon State University)


Disease: Downy mildew
Pathogen: Peronospora destructor

Leaf dieback caused by severe downy mildew (Peronospora destructor) in an onion bulb crop with secondary colonization of the downy mildew lesions by the fungus that causes Stemphylium leaf blight (Stemphylium vesicarium). Two onion leaves on which sporulation of the downy mildew pathogen, Peronospora destructor, appears as if soil is adhering to the leaves compared to healthy leaves (lower two leaves). Microscope image of antler-shaped sporangiophores and lemon-shaped sporangia of the onion downy mildew pathogen, Peronospora destructor. Photo source: Lindsey du Toit, Washington State University. Bright yellow, elongated lesions on scapes infected with downy mildew in an onion seed crop. Photo source: Lindsey du Toit, Washington State University. Yellow to pale-green lesions caused by downy mildew on scapes in an onion seed crop. Note the ‘dirty gray’ appearance in the center of two of the lesions as a result of sporulation of Peronospora destructor.
Leaf dieback caused by severe downy mildew (Peronospora destructor) in an onion bulb crop with secondary colonization of the downy mildew lesions by the fungus that causes Stemphylium leaf blight (Stemphylium vesicarium). Two onion leaves on which sporulation of the downy mildew pathogen, Peronospora destructor, appears as if soil is adhering to the leaves compared to healthy leaves (lower two leaves). Microscope image of antler-shaped sporangiophores and lemon-shaped sporangia of the onion downy mildew pathogen, Peronospora destructor. Photo source: Lindsey du Toit, Washington State University. Bright yellow, elongated lesions on scapes infected with downy mildew in an onion seed crop. Photo source: Lindsey du Toit, Washington State University. Yellow to pale-green lesions caused by downy mildew on scapes in an onion seed crop. Note the ‘dirty gray’ appearance in the center of two of the lesions as a result of sporulation of Peronospora destructor.
Photo Source: Lindsey du Toit, Washington State University

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Onion (Allium cepa) – Downy Mildew

Foliar Fungal Diseases, Onion impPIPE Diagnostic Pocket Series

Onions, Garlic: Downy mildew, Washington State University Hortsense
 

Disease: Fusarium basal rot
Pathogen: Fusarium species

Photo of Fusarium basal rot on onion Photo of Fusarium basal rot on onion Fusarium basal rot of onion bulbs of the cultivar Gunnison caused by Fusarium oxysporum f. sp. cepae. Fusarium basal rot of onion bulbs of the cultivar Gunnison caused by Fusarium oxysporum f. sp. cepae.
Fusarium basal rot Fusarium basal rot of onion bulbs of the cultivar Gunnison caused by Fusarium oxysporum f. sp. cepae.

Photo Source: G.Q. Pelter

Photo Source: Lindsey du Toit, Washington State University

Fusarium basal rot of onion bulbs of the cultivar Gunnison caused by Fusarium oxysporum f. sp. cepae.
Fusarium basal rot of onion bulbs of the cultivar Gunnison caused by Fusarium oxysporum f. sp. cepae.
Photo Source: Lindsey du Toit, Washington State University

 

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Onion (Allium cepa) – Fusarium Basal Rot

Storage Fungal Diseases, Onion impPIPE Diagnostic Pocket Series
 

Disease: Iris yellow spot (IYS)
Latin binomial: Iris yellow spot virus (IYSV)
Host Crops: Primarily Allium spp., particularly bulb onion (A. cepa), but a range of common weed species in onion crops has been identified as potential symptomatic and asymptomatic hosts.

Photo of iris yellow spot virus lesions on onion Photo of iris yellow spot necrotic lesion in bulb onion crop Photo of iris yellow spot symptoms on onion scapes Aerial photo of iris yellow spot virus in onion seed crop
Close-up of iris yellow spot lesions in an onion bulb crop. Necrotic lesions on the lower leaves of an onion plant. Iris yellow spot symptoms on the scapes (seed stalks) in onion seed crops. Aerial photo showing a gradient in severity of iris yellow spot in an onion seed crop. Symptoms were most severe on the left side of the field, reflecting the direction of migration of the vector of iris yellow spot virus (IYSV), onion thrips, from the adjacent field that was planted to an onion seed crop the previous season. Because of the biennial nature of onion seed crops, the overlap in crops between sequential seasons results in a ‘green bridge’ effect, with movement of the vector and, therefore, IYSV from seed crops drying down for harvest to seedlings of the next season’s crops planted in close proximity.
Photo Source: Lindsey du Toit, Washington State University Photo Source: Fred Crowe, Oregon State University Professor Emeritus

On-Line Resources:

Iris yellow spot virus: An Emerging Threat to Onion Bulb and Seed Production

Susceptibility of storage onion cultivars to iris yellow spot in the Columbia Basin of Washington, 2004, L.J du Toit, Washington State University and G.Q. Pelter, Washington State University

Pacific Northwest Plant Disease Management Handbook: Onion (Allium cepa) – Iris Yellow Spot
 

Disease: Neck rot
Pathogen: Botrytis allii and Botrytis aclada are the two primary species that cause neck rot of onion, although as many as six species of Botrytis can infect various Allium spp.
Host Crops: Onion (Allium cepa) and other Allium spp.

Photo of neck rot of onion Photo of neck rot of onion Photo of neck rot of onion
Photos of neck rot of onion
Photo Source: Jordan Eggers, Oregon State University
Photo of neck rot of onion Photo of neck rot of onion Photo of neck rot of onion
Photos of neck rot of onion Severe neck rot of onion with abundant, dark sclerotia beneath the outer dry scales of the bulb.
Photo Source: Jordan Eggers, Oregon State University Photo Source: Lindsey du Toit, Washington State University

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Onion (Allium cepa) – Neck Rot

Important New York Vegetable Diseases: Onion Neck Rot, Vegetable MD Online, Cornell University

Botrytis Neck Rot of Onion, EB1359, Washington State University Extension

Onion neck rot, The Royal Horticultural Society

Detection and Identification of Botrytis Species Associated with Neck Rot, Scape Blight, and Umbel Blight of Onion, Plant Management Network

A Real-Time, Quantitative PCR Seed Assay for Botrytis spp. that Cause Neck Rot of Onion, Plant Disease, The American Phytopathological Society


Disease: Root rot
Pathogen: Trichodorus and Pythium

Photo of Root rot on onion
Photo Source: G.Q. Pelter

On-Line Resources:

Disease: Pink root
Pathogen: Phoma terrestris (Pyrenochaeta terrestris)
Host Crops: Primarily onion, but some strains of the fungus are pathogenic on barley, cantaloupe, carrot, cauliflower, cucumber, eggplant, pea, corn, millet, muskmelon, oat, pepper, ryegrass, sorghum, soybean, spinach, squash, sweet corn, tomato, and wheat.

Photo of onions showing symptoms of pink root Photo of onions showing symptoms of pink root Photo of symptoms of pink root on onion Photo of symptoms of pink root on onion
Patches of stunted onions caused by pink root. Stunted onion plants with premature leaf dieback as a result of pink root (right) compared to a healthy plant (left). Mild (left) vs. severe (right) symptoms of pink root infection on mature onion plants. Closeup view of onion roots infected with pink root, showing the distinct, dark pink discoloration and collapse of infected roots.
Photo Source: Carrie Wohleb, Washington State University Photo Source: Lindsey du Toit, Washington State University

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Onion (Allium cepa) – Pint Root

Soil-Borne Diseases of Onion, Colorado State University Extension

UC Pest Management Guidelines: Onion and Garlic Pink Root, UC IPM Online, University of California


Disease: Rhizoctonia stunting (also known as ‘Mallee’ in Australia after the Mallee region of South Australia, where the disease was first documented in that country)
Causal agent (Latin binomial): Rhizoctonia spp., particularly Rhizoctonia solani (various anastomosis groups, including AG 8). The fungi colonize the roots of winter cover crops planted preceding onion bulb crops. The cover crop is killed with a herbicide application in spring, around the time that onion seed is planted, to provide a physical barrier to protect emerging onion seedlings from wind- and sandblasting on the sandy soils typical of many fields in the Columbia Basin of central Washington and northcentral Oregon. Herbicide is applied to the cover crop to prevent the cover crop from competing with the onion crop. However, this enables Rhizoctonia spp. to colonize the dying roots and crown tissue of the cover crop, building up inoculum that can then colonize onion seedlings.
Host Crops: Onion, pea, cereals, other crops.

Photo of large patch of stunted onion plants in the Columbia Basin of Washington/Oregon, caused by Rhizoctonia. Photo of how severely stunted patches may be visible through harvest, as observed in this photo onion-rhizoctonia-stunting-3 onion-rhizoctonia-stunting-4
Large patch of stunted onion plants in the Columbia Basin of Washington/Oregon, caused by Rhizoctonia. Patches of stunted plants usually remain visible until the onion canopy closes fully. Severely stunted patches may be visible through harvest, as observed in this photo. Onion plants sampled from within a stunted patch (left) compared to plants sampled from an adjacent, healthy area of the field (right). Close up view of the ‘spear-tipping’ effect of onion roots on seedlings sampled from a stunted patch caused by Rhizoctonia.
Photo Source: Tim Paulitz, USDA ARS, Pullman, WA. Photo Source: Lindsey du Toit, Washington State University
onion-rhizoctonia-stunting-5 onion-rhizoctonia-stunting-6
Closeup, microscope view of dark-brown hyphae of Rhizoctonia growing on an onion seedling. Infrared, aerial photo of an onion bulb crop in the Columbia Basin of Washington showing areas of stunted patches (red = healthy crop canopy).
Photo Source: Lindsey du Toit, Washington State University

On-Line Resources:

Stunting of Onion in the Columbia Basin of Oregon and Washington Caused by Rhizoctonia spp. Plant Disease 97:1626–1635.

Effect of timing of glyphosate application to a winter wheat cover crop on stunting of spring-sown onions caused by Rhizoctonia spp. in the Columbia Basin of Washington, 2012, Plant Disease Management Reports 7:V046, 2013.

Efficacy of fungicides to manage onion stunting caused by Rhizoctonia spp. in the Columbia Basin of Oergon and Washington, 2011–2012, Plant Disease Management Reports 7:V047, 2013.

Yield responses of three onion cultivars to stunting caused by Rhizoctonia spp. in the Columbia Basin of Oregon and Washington, 2012. Plant Disease Management Reports 7:V048, 2013.

Rhizoctonia Seedling Blight of Onion and Pea Crops in the Columbia Basin, WSU 2011 Onion Field Day report, Soap Lake, WA, 26 Aug. 2011

Rhizoctonia Seedling Blight of Onion Crops in the Columbia Basin, WSU 2012 Onion Field Day report, Connell, WA, 30 Aug. 2012

Onion Stunting Caused by Rhizoctonia: Management and Economic Importance in the Columbia Basin of Oregon and Washington, Proceedings article from 2012 National Allium Research Conference, Las Cruces, NM, 12–14 Dec. 2012


Disease: Rust
Pathogen: Puccinia allii (= Puccinia porri)
Host Crops: Onion and garlic.

Photo of rust on onion tops Closeup of rust on onion tops Closeup of rust on onion top Closeup of rust on onion top
         
Photo Source: Seth Lewis, WSU NWREC Vegetable Pathology program Photo Source: Johnny Stark, WSU Puyallup PIDL
Photo of rust on onion tops
 
Photo Source: Johnny Stark, WSU Puyallup PIDL

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Onion (Allium cepa) – Rust

Diseases of onion and garlic ( Allium sepa and Allium sativa ) in Arizona: Garlic Rust, University of Arizona

UC Pest Management Guidelines: Onion and Garlic Rust, UC IPM Online, University of California

Prediction of Disease Infection of Welsh Onions by Rust Fungus Based on Temperature and Wetness Duration, IEEEXplore


Disease: Onion Smut
Pathogen: Urocystis colchici (= Urocystis cepulae)

Photo of Smut on onion Photo of closeup view of immature and mature smut sori. Closeup view of onion smut sori on the cultivar 'Red Label'. Photo of a smut pustule splitting on an older leaf in the field. Photo of stunting of onion plants infected with smut.
  Closeup view of immature and mature smut sori. Closeup view of onion smut sori on the cultivar ‘Red Label’. A smut pustule splitting on an older leaf in the field. Stunting of onion plants infected with smut.
Photo Source: D.A. Inglis Photo Source: Lindsey du Toit

On-Line Resources:

Onion Smut, Identification & Management of Emerging Vegetable Problems in the Pacific Northwest. Pacific Northwest Vegetable Extension Group.

Pacific Northwest Plant Disease Management Handbook: Onion (Allium cepa) – Smut

Efficacy Testing of Onion Seed Treatments in the Greenhouse and Field. Acta Hort. 631 in 2004 by McDonald et al.

Onion disorder: Smut. University of Wisconsin extension bulletin
 

Disease: White rot
Pathogen: Sclerotinia cepivorum
Host plants: Garlic, onion, and other Allium spp.

Photo of white rot on onion Title Title Title Title
White rot on onion. Stunted plants in an onion seed crop caused by the white rot fungus, Sclerotium cepivorum. Symptoms of white mold on plants from an onion seed crop include stunting, leaf chlorosis and dieback, and soil adhering to mycelium of the pathogen, Sclerotium cepivorum, on the bulbs and necks. Symptoms and signs of white mold on an onion plant cut lengthwise through the bulb to reveal a rot extending into the bulb, and dark, pinhead size sclerotia of the pathogen, Sclerotium cepivorum. White rot on a garlic plant.
Photo Source: G.Q. Pelter
Photo Source: Lindsey du Toit, Washington State University.
     

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Onion (Allium cepa) – White Rot

Onions, Garlic: White rot, Washington State University Hortsense

Soil-Borne Diseases, Onion ipmPIPE Diagnostic Pocket Series

Insect/Mite Pests

 

Common name: Bulb mites/eriophyid mites

Latin binomial: Aceria tulipae, an eriophyid mite, appears most commonly associated with damage to garlic in storage. Various bulb and eriophyid mites can feed on garlic cloves and bulbs of other Allium spp.

Host crops: Various Allium spp. as well as other plants or decaying organic matter. Severe infestations can cause desiccation of bulbs, and mites can vector garlic-rotting fungi.

Damage to garlic cloves caused by eriophyid mite feeding. Damage to garlic cloves caused by eriophyid mite feeding. Damage to garlic cloves caused by eriophyid mite feeding.
Damage to garlic cloves caused by eriophyid mite feeding.
Photo Source: Lindsey du Toit, Washington State University

Online Resources:

http://www.science.oregonstate.edu/bpp/Plant_Clinic/Garlic/eriophyids.htm

http://ecoport.org/ep?SearchType=pdb&PdbID=16129

Moth balls (the kind used to keep moths out of stored woolen sweaters) can help control mites in seed garlic, but should not be used for garlic that will be consumed.

Disease: Seedcorn maggot
Pathogen: Delia platura
Host Crops: Many vegetable crops including snap, kidney, and lima beans, onion, corn, turnip, pea, cabbage, and cucurbits. They cause the most damage in spring to newly emerging seedlings.

Photo of seedcorn maggot damage to onion Photo of seedcorn maggot larvae Photo of seedcorn maggot fly on soil Photo of seedcorn maggot fly
Onion seedlings damaged by seed corn maggot larvae, with the larvae (white) and a pupa (brown) shown in relation to the size of a paper clip and damaged onion seedlings. Seedcorn maggot larvae. Seedcorn maggot fly on soil. Seedcorn maggot fly.
Photo Source: Lindsey du Toit, Washington State University Photo Source: Tim Waters, WSU Extension Educator for Benton and Franklin Counties


On-Line Resources:

Pacific Northwest Insect Management Handbook: Vegetable crop pests – Seedcorn maggot

Seed Corn Maggot. VegEdge, University of Minnesota

Seed Corn Maggot. UMass Amherst

See Diseases, pests, and other problems common to many vegetables: Seedcorn maggot


 

Common name: Two-spotted spider mite
Latin binomial: Tetranychus urticae (= T. bimaculatus = T. telarius).
Host crops: Numerous species of low-growing plants as well as a wide range of shrub and tree species. Normally not a significant pest of onion crops in the Pacific Northwest.

Photo of mite feeding injury on onion leaves Close up of spider mites Two-spotted spider mite adult and eggs on a potato leaf. Eggs of the two-spotted spider mite, Tetranychus urticae.
Mite feeding injury on onion. Mites are found in the small depressions or pockets in the onion leaves. Close-up of mites and eggs. Two-spotted spider mite adult and eggs on a potato leaf. Eggs of the two-spotted spider mite, Tetranychus urticae.
Photo Source: Carrie Wohleb, Washington State University Extension Educator Photo Source: Silvia Rondon, Oregon State University


On-Line Resources
:

Pacific Northwest Insect Management Handbook. Chapter: Vegetables, Section: Common Pests of Vegetable Crops: Spider mite

Pacific Northwest Insect Management Handbook. Chapter: Supplement 1: Mite ID, Section: Common Mite Pests and Predators – pt. 1
 

Common name: Thrips, including western flower thrips, onion thrips, and other species.
Latin binomial: Various thrips including Frankliniella occidentalis (western flower thrips) and Thrips tabaci (onion thrips). The latter is also a vector if Iris yellow spot virus (IYSV).
Host crops: Numerous plant species including many vegetables such as basil, broccoli, cabbage, cauliflower, cucumber, onion, potato, pumpkin, squash, tomato and watermelon.

Photo of adult Western flower thrips Photo of immature Western flower thips
Adult western flower thrips are minute (less than 1/8 inch long) narrow-bodied insects that range from straw to dark yellowish-brown in color. Their four wings are very narrow and characterized by long fringed hairs. Immature western flower thrips resemble the adults but are smaller, wingless and translucent yellow in color. There are multiple generations per year and thrips may invade vegetable fields when alternate flowering plants dry up in the summer or when an adjacent host crop is harvested.
Photo Source: Michael Bush, WSU Extension, Yakima, WA

On-Line Resources:

Pacific Northwest Insect Management Handbook. Chapter: Vegetables, Section: Onion pt. 2.

Onion Thrips, Washington State University Extension Fact Sheet, FS126E.

Vegetables: Onions, Garlic: Onion thrips, Washington State University Hortsense.

Western Flower Thrips Thysanoptera: Thripidae Frankiniella occidentalis,

Onion and Garlic Thrips, UC IPM Online, University of California

Life Cycle of Onion Thrips (Thrips tabaci)

See Diseases, pests, and other problems common to many vegetables: Western flower thrips.
 

Common name (of damaging stage): Wireworm (adults are called click beetles or snapping beetles)
Latin binomial: Ctenicera spp. and Limonius spp. Several kinds of wireworms are in the Pacific Northwest. Wireworms causing the most damage in irrigated areas are the Pacific Coast wireworm (Limonius canus), the sugar beet wireworm (L. californicus), the western field wireworm (L. infuscatus), and the Columbia Basin wireworm (L. subauratus). The Pacific Coast and sugar beet wireworms are the most common. Where annual rainfall is <15 inches, the Great Basin wireworm (Ctenicera pruinina) may be a problem, especially when irrigated crops are grown on sagebrush or dry wheat land. This species usually disappears after a few years of irrigation, but may be replaced by Limonius spp. which are favored by moist conditions. West of the Cascades, other wireworm species are pests, including Agriotes spp.
Host crops: All crops are susceptible to wireworm, but this pest is most destructive on beans, carrot, corn, grain, onion, potatoes, spinach seed crops, and other annual crops in the PNW.

Photo of wireworm damage to onion bulb Photo of wireworms in soil around onion roots Photo of wirwirm in soil near onion roots Photo of field of onions showing wireworm damamge closeup of wireworm
         
Photo Source: Tim Waters, WSU Extension Educator Photo Source: Gary Pelter, WSU Extension Educator Emeritus Photo Source: Tim Waters,
WSU Extension Educator
Photo Source: Lindsey du Toit, Washington State University
Wireworms feeding on an onion plant in a bunching onion (CFC = cepa fisutlosum cross) seed crop. A click beetle of the species Agriotes obscurus, the larvae of which are wireworms. A click beetle of the species Limonius californicus, the larvae of which are wireworms. A click beetle of the species Limonius canus, the larvae of which are wireworms.
Wireworms feeding on an onion plant in a bunching onion (CFC = cepa fistulosum cross) seed crop. A click beetle of the species Agriotes obscurus, the larvae of which are wireworms. A click beetle of the species Limonius californicus, the larvae of which are wireworms. A click beetle of the species Limonius canus, the larvae of which are wireworms.
Photo Source: Lindsey du Toit, Washington State University Photo Source: Oregon State University – Oregon State Arthropod Collection.

 

On-Line Resources:

Pacific NorthwestInsect Management Handbook: Vegetable crop pests – Wireworm.

Managing Wireworms in Vegetable Crops. Ontario Ministry of Agriculture and Food

Wireworms. VegEdge, University of Minnesota.

Wireworms & Click Beetles. Washington State University.

Wireworm Field Guide - A guide to the identification and control of wireworms, Syngenta Crop Protection Canada, Inc.

Wireworm Biology and Nonchemical Management in Potatoes in the Pacific Northwest, N. Andrews, M. Ambrosino, G. Fisher, and S.I. Rondon, Pacific Northwest Extension Publication no. PNW607

See Diseases, pests, and other problems common to many vegetables: Wireworm.
 

Weeds

Common Name: Dodder
Latin binomial:Cuscuta spp.
Plants affected: Dodder is a parasitic plant that feeds on many other plant species. Dodder cannot photosynthesize, but produces haustoria that penetrate the host plant to absorb water and nutrients. Small, white to cream flowers are produced.

Dodder (back) and nutsedge (front) in an onion bulb crop. Stems of a dodder plant in an onion bulb crop. Note the haustoria (protrusions) that the dodder forms to attach to and penetrate onion leaves. A severe infestation of dodder in an onion bulb crop. Note the clusters of small, white flowers.
Dodder (back) and nutsedge (front) in an onion bulb crop. Stems of a dodder plant in an onion bulb crop. Note the haustoria (protrusions) that the dodder forms to attach to and penetrate onion leaves. A severe infestation of dodder in an onion bulb crop. Note the clusters of small, white flowers.
Photo Source: Lindsey du Toit, Washington State University

Online Resources:

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7496.html

http://www.colostate.edu/Dept/CoopExt/4DMG/Weed/dodder.htm

http://pnwhandbooks.org/plantdisease/pathogen-articles/pathogens-common-many-plants/parasitic-plants-oregon

http://pnwhandbooks.org/weed/horticultural/vegetable-crops/onions


Common name
: Yellow nutsedge
Latin binomial: Cyperus esculentus (Cyperaceae)
Plants affected: Any annual crop; the most seriously affected crops include onion and other plants with a light canopy and narrow range of herbicides available for use.

Photo of loseup view of a yellow nutsedge plant/flower. Photo of severe nutsedge infestation in an onion crop Nutsedge in an onion bulb crop.
Closeup view of a yellow nutsedge plant/flower. Severe nutsedge infestation in an onion crop. Nutsedge in an onion bulb crop.
Photo source: Lindsey du Toit, Washington State University

On-Line Resources:

Yellow Nutsedge. Identification & Management of Emerging Vegetable Problems in the Pacific Northwest, Pacific Northwest Vegetable Extension Group.

Diseases, pests, and other problems common to many vegetables: Yellow Nutsedge.
 

Abiotic Problems

Problem: Basal plate splitting, basal plate blow-out
Causal agent: Uneven irrigation of onion fields increases the incidence of this disorder. If the soil is repeatedly over-irrigated, dried, and over-irrigated again, onion bulbs are likely to develop split basal plates. The wounding provides an opportunity for secondary microorganisms and bulb mites to colonize the bulbs.

Photo of basal plate splitting on onion Photo of basal plate splitting on onion Photo of basal plate splitting of onion
     
Photo Source: Toni Grove, Whidbey Island Master Gardener Photo Source: Jenny Glass, Washington State University Plant Diagnostician

On-Line Resources:

Abiotic Problem: Onion internal dry scale
Cause: The exact cause of onion internal dry scale remains to be verified, but the problem is most prevalent and severe in onion bulb crops harvested after summers with extreme periods of heat stress, e.g., in 2014 and 2015 in the Columbia Basin of Washington/Oregon and the Treasure Valley of Oregon. Several dry, internal, fleshy scales in the developing bulb collapse in the upper part of the bulb, either partially or completely. The dry scales can readily be colonized by bacteria, fungi, or yeasts which may lead to development of bulb rots.

Title Title
Symptoms of internal dry scale in onion bulbs of diverse cultivars grown in the semiarid PNW in 2014 and 2015 Colonization of internal dry scales of onion bulbs by Fusarium proliferatum (upper left), bacteria (upper right and lower left photos), and a yeast (lower right photo)
Photo Source: Lindsey du Toit, Washington State University, and onion growers in the Columbia Basin Photo Source: Lindsey du Toit, Washington State University

Online Resources:

Internal Dry Scale and Associated Bulb Rots of Onion. A common problem was observed in the 2014–2015 season and the 2015–2016 onion-growing season on red, white, and yellow cultivars—internal dry scale. Careful monitoring of crop moisture demand to increase our understanding of onion physiology, particularly close to harvest, will help in the development of effective management practices to reduce the impact of internal dry scale on this important region of onion production.

Herbicide Injury

Problem: Herbicide injury

Causal agent: Onion and other Allium spp. can be injured by herbicides, e.g., as a result of drift of herbicides from nearby crops, from residual carryover effects when onions are planted into soil treated with herbicides from a previous crop, or from direct contact injury.

Injury to an onion seed crop as a result of drift of the herbicide Roundup (glyphosate) from an adjacent field. Note the stark, chlorotic (yellow) band across the scapes and the necrotic (dead) band of tissue at the ends of some of the leaves, indicating the stage of growth of the crop at the time the drift occurred. Injury to an onion seed crop as a result of drift of the herbicide Roundup (glyphosate) from an adjacent field. Note the stark, chlorotic (yellow) band across the scapes and the necrotic (dead) band of tissue at the ends of some of the leaves, indicating the stage of growth of the crop at the time the drift occurred.
Injury to an onion seed crop as a result of drift of the herbicide Roundup (glyphosate) from an adjacent field. Note the stark, chlorotic (yellow) band across the scapes and the necrotic (dead) band of tissue at the ends of some of the leaves, indicating the stage of growth of the crop at the time the drift occurred.
Photo Source: Onion seed crop grower

Online Resources:

Herbicide Symptoms, University of California, Division of Agriculture and Natural Resources

Herbicide Modes and Action and Symptoms on Plants, Richard Smith, Farm Advisor, University of California Cooperative Extension.


Our pages provide links to external sites for the convenience of users. WSU Extension does not manage these external sites, nor does Extension review, control, or take responsibility for the content of these sites. These external sites do not implicitly or explicitly represent official positions and policies of WSU Extension.

WSU Mount Vernon NWREC, 16650 State Route 536, Mount Vernon, WA 98273-4768, 360-848-6120
Contact Us: Lindsey du Toit and Carol Miles