Nematodes in Vegetable Crops

Inga Zasada - USDA-ARS Research Plant Pathologist and NematologistHannah Rivedal - OSU HAREC Plant Disease Diagnostician

What you should take away from our presentation...

• Biology of important nematodes in PNW vegetable production• Occurrence of nematodes in specific vegetable crops• Management of nematodes in vegetable crops• Sampling recommendations for laboratory submissions

Introducing Nematodes• Most abundant multi-cellular animals on the planet• Unsegmented aquatic roundworms• Occur in many environments: soil, freshwater, marine, animals

Plant-parasitic Nematodes

10%

Animal Nematodes

15%

Free-living Nematodes

25%

Marine Nematodes

50%

This is what you see…

But how do you interpret this information?

This is what we see…

How do nematodes feed on plants?

All plant-parasitic nematodes

have a protrusible spear

Stylet

Where do nematodes feed on plants?

Sedentaryendoparasite

Migratoryectoparasite

Migratoryendoparasite

Picture from Kathy Merrifield

Pictures from Nemaplex

Widely prevalent nematodes in the PNW

Also of interest in vegetables – Ditylenchus (stem and bulb nematode)

Data from 38,022 diagnostic soil samples from the PNW from 2012-2016

Root-knot Nematode

Vegetable hosts:Carrot, lettuce, onions,

parsnips, cabbage, cucumber, tomato, etc...

Species in the PNW:M. hapla

M. chitwoodiSedentary endoparasite

From MacTode

Pictures from ipcnet.org

Symptoms: Root galling and branching, reduced yield, wilting

Most damaging nematode in the

PNW

Picture from Kathy Merrifield

Symptoms:Lesions on roots, excessive rooting,

reduced yield, stunting

Root lesion Nematode

Most prevalent nematode in the PNW

Migratory endoparasite

Species in the PNW:P. penetransP. neglectus

P. thorneiPictures from Nemaplex

Stubby root Nematode

Stunt Nematode

Migratory endoparasite

Reported hosts in PNW:Onion, corn, potato, alfalfa, wheat,

mint, beet

Impact of this nematode on vegetables in the PNW is NOT KNOWN

Paratrichodorus allius is an important parasite in onion

Densities as low as 4 nematodes/250 cc soil

can cause damage (Ingham)

Picture from Nemaplex

Picture from MacTode

Picture from MacTode

Pin Nematode

Spiral Nematode

Migratory ectoparasite

Impact of this nematode on vegetables in the PNW NOT KNOWN

Even when present at high densities this nematode does not cause damage

Picture from Nemaplex

Picture from MacTode

Picture from MacTode

Stem and bulb nematode

Picture from Agriculture Canada

Migratory endoparasite

Two species found in the PNW:Ditylenchus dipsaci and D. destructor

Picture from MacTode

Reported hosts in PNW:Onion, garlic, strawberry, alfalfa

What nematodes are of concern in vegetables?

Veggie Crop Plant-parasitic NematodeOnion Stem and bulb, root lesion, stubby root, root-knotCarrot Root-knot, root lesion, stubby rootSweet corn Root lesionPea/bean Root-knotAsparagus Root lesionMelon Root-knot, root lesion, stubby rootPepper Root-knot, root lesionTomato Root-knot

Information from UC IPM Management Guidelines and PNW Disease Handbook

Little “threshold” information for PNWNematode Mean population densities in

PNW (per 250 cc soil)Root-knot 240Root lesion 256Stubby root 29Stunt 98Pin 462Spiral 171

Data from 38,022 diagnostic soil

samples from the PNW

Nematode Mean population densities in PNW (per 250 cc soil)

Root-knot 107Root lesion 393Stubby root 30Stunt 102Pin 250

Nematode Mean population densities in PNW (per 250 cc soil)

Root-knot 103Root lesion 86Stubby root 25Stunt 27Pin 288

Nematode Management

Challenges with Nematode Management

• Nematode Lifestyle• Mobility out of zone of activity• Broad host range• Diagnostic challenge• Longevity

• Fumigation Regulations/Registration• Methyl Bromide no longer available• Buffer zones• Registered products

• Costs• Financial• Time• Space

Host Resistance• What it is

• Host plants with genetics that kills or disrupts nematode lifecycle

• Why it works• Avoids infection altogether• Reduces nematode population in roots

• Variations• Grafting onto resistant rootstock

• Drawbacks• Not effective for migratory nematodes• Time consuming to ID genes

From MacTode

Crop Rotation

• What it is• Rotating a field out of a susceptible crop

for multiple growing cycles

• Why it works• Reduces pathogen population in the soil

• Drawbacks• Host range of the nematode matters!• Rotation crops may not be economically

viable

Susceptible Crop

Trap Crop

Nonhost Crop

Resistant Host

Fallow

Green Manure

Biofumigation

• What it is• Growing a Brassica crop that is chopped and

incorporated into the soil

• Why it works• Isothiocyanate - natural volatile compound

produced by chopping Brassica crops

• Drawbacks• Variable concentration of isothiocyanate• Variable tolerance of nematodes• Timing

Courtesy: P.P. Reddy

Courtesy: Cavendish Farms

Soil Solarization

• What it is• Passive heating of soil covered with plastic mulch

• Why it works• Increases soil temperature to kill juveniles and

eggs• Best in shallow soils/shallow distribution of

nematodes

• Drawbacks• Requires the heat of summer to be effective • Takes field out of production• Expensive

Courtesy: University of California

Courtesy: HGTV.com

Integration of Management Strategies

• Combining chemical, cultural and biological control, can achieve reduction in nematode damage and may help control other pathogens or improve soil fertility

• Requires an understanding of:• Nematode Biology• Control Mode-of-Action• Cost• Nematode Populations

Sampling for Nematodes

• Considerations• Goal of sampling

• Current population in soil• Identification of disease

problem• Leadtime

• Able to implement control measures

Courtesy: MacTode

Sampling for Nematodes – Population Assessment

• Timing • After harvest or before planting, with enough lead

time to implement management• Adequately moist soil

• What to bring• Random sample of soil from field of interest

• Nematodes not evenly distributed - plan to sample whole fields

• Break large fields into manageable sections• Collect 15-20 soil cores/shovels per section/field

• 6-12” cores, collect samples from previous rows• Mix thoroughly and submit at least 1 pint• Keep cool on way to submission

Courtesy: MacTode

Courtesy: Spectrum Analytic

Sampling for Nematodes - Diagnostics

• Timing• In growing season, symptoms present

• What to bring• Soil and affected roots/plant material

• Samples from around/within affected area and healthy area

• 6-12” cores - depending on roots of crop• Photos of pattern in field

• What a diagnostic clinic will want to know

• Symptoms• Pattern/Distribution• Cultivar• Field Inputs

Courtesy: MacTode

Nematology Labs in PNW

• University Labs• OSU Nematode Testing - bpp.oregonstate.edu/bpp/nematode-testing-service• U of I Nematode Testing – Parma Research and Extension Center, Parma, ID

• Private Labs• Northwest Agricultural Consultants – nwag.com/lab-services• Agnema - sites.google.com/view/agnema/home• Western Laboratories, Inc. - westernlaboratories.com/• A&L Labs – http://www.al-labs-west.com/

• Diagnostic Clinics• OSU HAREC Plant Clinic - blogs.oregonstate.edu/harecppath/services/• WSU Pullman Plant Clinic - plantpath.wsu.edu/diagnostics/

Takeaways

• A diversity of nematodes are present in the PNW

• Threshold data is not yet robust for PNW Vegetable Crops

• Management of nematodes is complicated and requires information and integrated techniques