Diagnosis of Key Soil-borne Diseases affecting vegetables and small fruits

Zelalem Mersha State Plant Pathology Specialist

June 4th, 2013

The process of attempting to determine or identify a possible cause of a disease or disorder

The opinion reached by this process

Diagnosis

By the time plants are showing typical symptoms, it may be too late to handle the problem

• Scenario 1: Pre-emergence • Scenario 2: Post-emergence

• Acute and systemic • Soil line or surface contamination

Photo Credit: David Trinklein, MU Extension

Soil-borne diseases Diseases that are caused by

pathogens that survive in the soil matrix and in residues on the soil surface

Problems of roots or stems disrupting the uptake and translocation of water and nutrients from the soil.

Source: Agrios 2005

Soil-borne diseases Immediate symptoms: wilting, yellowing, stunting & also plant death.

Such symptoms could be a result of pathogen infection or stresses (cold weather, drought, nutrient deficiencies etc. )

Symptoms from diseases caused by pathogens could also be unique for one pathogen or a range of pathogens.

The Rhizosphere “The area around a plant root that is inhabited by a unique population of micro-organisms influenced by the chemicals released from plant roots” (Lorenz Hiltner, 1904)

The hot spot of microbial interactions influenced by root exudates

• Beneficial • Neutral • Pathogenic

The Rhizosphere

Source:http://www.nature.com/scitable/knowledge/library/the-rhizosphere-roots-soil-and-67500617

Rhizosphere & the microbes Beneficials

• Trichoderma series • Bacillus series • Lactobacillus series • Fluorescent Pseudomonas • Actinomycetes series • Rhizobium series • Mycorrhizae fungi series

Pathogens • Fungi (Fusarium, Verticillium,

Rhizoctonia, Sclerotinia, Aphanomyces)

• Oomycete (Pythium, Phythopthora)

• Bacteria (Pseudomonas, Ralstonia)

• Nematode (Meloidogyne)

• Virus

Diagnosis

Infectious or non-infectious?

• Non-living factors • drought, deficiency or toxicity • Freeze, wind, chemical injury • Overwatering, deep planting

• Non-contagious in nature • NO presence of disease signs • Patterned uniformly on

many plant species, plant parts or on a large area

• Effects are temporary if conditions

improve e.g. wilt

• Caused by living factors • Fungi, Oomycetes (water molds) • Bacteria, Virus or viroids • Mycoplasmas

• Contagious in nature – dispersal by wind, rain, mechanical, residue, man

• Presence of disease signs • Patterned locally to certain

plants or invade a localized area of the plant

• Effects on plants or plant parts are

permanent

Source: Dan Egel, Purdue University

Non-infectious Infectious

Which one?

Winter injury of turnip (Brasica rapa)

Phytotoxicity Tomato edema

• Walnut wilt of tomato (Juglone)

• Fungal (Rhizoctonia, Verticilium, Fusarium)

• Bacterial (Pseudomonas, Ralstonia)

• Oomycete (Phytium, Phythopthora)

Source: Agrios 2005

Non-infectious Infectious

Diagnosis - temporal

Source: http://whereplantsrock.files.wordpress.com/2011/03/starting-seeds.jpg

Pythium and Rhizoctonia (Cornell)

Pre-emergence

• Seed contaminated • Soil contaminated

Fusarium and Rhizoctonia (Florida)

Post-emergence • Pathogen comes in

contact with the plant at or near the soil surface

Diagnosis – temporal (When?)

• Weather • Nursery • High tunnel or field

• Seasonality

• Cycle • Crop history

• Management practice (events)

• Watering • Fertigation

Diagnosis: spatial

Source: Cary Rivard, Kansas State University

Spatial view of soil borne diseases

Pythium & Rhizoctonia damping-off (Pre-emergence)

Soybean cyst nematode

Source: Gregory Tylka, Iowa State University Source: Cary Rivard, Kansas State University

Sclerotinia lettuce head drop

Diagnosis – spatial (Where?)

• Location • On a plant/s in a nursery or field • Nearby counties, state, regional

• Climate • Soil type • Field history – keep the record

• Distribution • Random or aggregated vs. uniform • Hot spot in the nursery or field?

• Low or high spots • Field edges

Symptom (sign) & pathogen based diagnosis Symptom response of host to the

pathogen (Subjective)

Sign portion of the pathogen or its products (Objective)

PATHOGENS: seeds, soil, residues • Watermolds

• Pythium • Phythophthora

• Higher fungi • Rhizoctonia • Fusarium • Sclerotium • Macrophomina

Favorable ENVIRONMENT • Waterlogging • Sprinkle irrigation • Cold weather • Contamination • Shady area

Environment Pathogen

Plant

Damping offs

Source: David Trinklein, MU Extension

Underground, soil line or crown rots of seedlings leading to their early death Pre-emergence • Seeds and radicle rot under the soil • Poor & uneven stand of seedlings

Post-emergence: • Cotyledons may wither and die • Seedlings may fall over

Damping offs: water molds

Source: Kala Parker, NCSU

http://www.njha.org/projects_hortid_plantpropagation.html

Damping offs: water molds

http://www.pocketdiagnostic.com/ http://www.pocketdiagnostickits.com.au/

Damping offs: higher fungi

Wilts: Fungal (Verticillium) Wilting of the foliage & internal necrosis of the vascular tissue in the stem of the plant

Photo Credit: Macnab & Sherf, Identifying diseases of vegetables

Photo Credit: Sally Miller, Ohio State University

Wilts: Fungal (Fusarium)

http://lyonsfungiatlas.blogspot.com/

Photo Credit: Sally Miller, OSU Source: Dan Egel, Purdue University

Photo Credit: P. Champoiseau, University of Florida

Wilts: Bacterial (Ralstonia)

Crown and root rots

Decay of the crown area and the true root system

Pythium crown rot

Photo Credit: Macnab & Sherf, Identifying diseases of vegetables Pythium root rot

Rhizoctonia root rot

Fusarium root rot

Crown and oot rots - Phythopthora

Decay of the true root system - Blueberry

Crown and root rots (Phytophthora capsici)

Crown and root rots (Phytophthora capsici)

Virginia Cooperative Extension

Wire stem & head rot (Rhizoctonia)

University of Illinois IPM

University of Illinois IPM

Sclerotium blights: lettuce head drop

Springfield, Missouri

Marshall, Missouri

Southern blight of tomato: Sclerotium rolfsii

ENDOPARASITES

ECTOPARASITES

Root-lesion nematodes

Dagger nematodes

Root-knot nematodes

Reniform nematodes

Nematode damage

Source: http://www.docstoc.com/docs/114564773/March-29-2007

Nematodes: root knot

Source: Gregory Tylka, Iowa State University

Summary

Country-wide

Regional

State-wide

County level

Nursery (Spatial and temporal)

Farm (Spatial and temporal)

Symptom/sign based

Laboratory diagnosis

• Direct microscopy • Cellophane • Stereo microscope

• Moisture chamber

• Plating

• Field and laboratory kits • Agdia • ELISA

• Baiting technique

• Tissue • Fertigation

Plant Diagnostic Clinics in the Midwest

Iowa State University

University of Illinois

Kentucky University

University of Tennessee University of

Arkansas

Kansas State University

Midwest Vegetable Production Guide for Commercial Growers 2013. Dan Egel et al. Editors http://www.btny.purdue.edu/pubs/id/id-56/ (Book or available to download and print)

Plant Disease Diagnosis (APSnet)

Plant Diagnostic Clinics • University of Illinois, Iowa State University, Kansas State University • University of Arkansas, University of Tennesse, Kentucky University • University of Wisconsin, Purdue University

Lincoln University in Missouri – Cooperative Extension Programs

• Plant Pathology, Vegetable IPM, Innovative Small Farmers Outreach

University of Missouri Extension – Division of Plant Sciences (MU IPM Program) • Organic vegetable gardening, http://extension.missouri.edu/p/G6220 • Starting plants from indoors seeds, http://extension.missouri.edu/p/G6570) • Disease prevention in home gardens http://extension.missouri.edu/p/G6202 • Common Diseases in the home garden http://extension.missouri.edu/p/g6203

Missouri Department of Agriculture,

Missouri Botanical Garden

Useful Resources

Integrated Management of Watermelon Diseases at Carver Farm LU

Alternaria GSB Anthracnose

23.8 m

Plastic mulch

Cover crop mulch

No mulch

Plastic mulch

Cover crop mulch

No mulch

Plastic mulch

Cover crop mulch

No mulch

Calendar-based spray 30.8 m

Control (No spray) MELCAST-guided spray

• Mulching • Plastic • Cover crop

• Fungicide • Timing (MELCAST vs. Calendar • Mode of Action

MELCAST 2013 - Carver Farm, LU, JC - Clarkton - Hornersville - Kennett

Cucurbitaceae 1. Cucumis sativus (‘Straight eight’) 2. Cucumis sativus (‘SVR14763462’) 3. Cucumis sativus (‘SVR14784719’) 4. Cucumis melo 5. Cucurbita pepo 6. Cucurbita maxima 7. Cucurbita moschata 8. Citrullus lanatus 9. Ocimum basilicum

Demonstration

Pathogens • Sclerotinia rolfsii • Rhizoctonia spp. • Pythium ultimatum

Host Plants • Tomato (Heirloom and Hybrid) • Squash

Demonstration

Environment Pathogen

Plant

Sclerotinia rolfsii Rhizoctonia spp.

Tomato (‘Big Beef’ and ‘Cherokee’)

Squash (‘Dixie hybrid’)

Demonstration: Inoculation

http://www.prophyta.de/en/technology/sclerotinia-diseases/mode-of-action/

Demonstration: preliminary results

Observations and activities • Observation of Rhizoctonia and Sclerotinia growth on agar medium • Observation of growth performance differences between inoculated and non-inoculated plants • Observation of root growth of inoculated and non-inoculated plants • Cut and dissect stems and roots of inoculated and non-inoculated plants and record your observation (plant, stem, root appearances etc.)

• Disinfect hand, scissors and dispose all infected plants for autoclave-kill procedure

Acknowledgements • MU Plant Sciences Division

• Dr. Lee Miller • Dr. Jeanne Mihail • Dr. David Trinklein • Dr. Laura Sweets

• KSU Plant Pathology • Dr. John Leslie • Dr. Cary Rivard • Dr. Megan Kennelly

• Spenser Epple (LU)