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Anthony (Tony) Keinath,

Professor of Plant Pathology

Clemson Coastal REC, Charleston

Sustainable Disease Management for Vegetable Growers

Organic Richland IPM Workshop, Sep. 13, 2012

Today’s Outline What causes diseases on plants?

The disease triangle shows that disease is an interaction between ___, ___, and ___.

5 groups of pathogens

How is disease managed?

5 control strategies

Management of specific vegetable diseases

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The Disease Triangle: Disease is an Interaction

Host Plant

Environment

Disease

Pathogen

fungi,

water molds,

bacteria,

viruses,

nematodes

Rain, dew, fog;

Temperature

Sunlight

Wind

Disease Triangle for Phytophthora Blight

Host Plant Phytophthora

Environment

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3 Powdery Mildews (Fungi)

3 Downy Mildews (Water Molds)

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Damping-Off, Root and Crown Rots Damping-off

Pre-emergence

Post-emergence

Seed rot (extreme case)

Root rot, crown rot on older plants

Soil fungi Pythium (most common)

Rhizoctonia

Use transplants Older plants have stronger cell

walls = resistant

3 Bacterial Diseases

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Cercospora leaf spot (fungal) (left) and bacterial blight (right) on turnip greens

Which leaf is infected by a fungus and which by a bacterium?

Bacterial Diseases “The Essentials”

Need specialized tests to ID bacteria

Worse in wet weather

Generally difficult to control

Copper is the only effective material available to organic growers.

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Virus Diseases

Virus Diseases General symptoms are distorted growth or irregular

yellowing

Can be confused with herbicide injury

Many viruses spread by insects

Aphids, whiteflies, thrips

Need specialized tests to ID viruses

Difficult to control

Tomatoes with resistance to ToMV, TSWV See Reimer Seeds (reimerseeds.com)

Summer squash with resistance to mosaic viruses See Harris Seeds (harrisseeds.com)

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Root-Knot Nematode Primary symptoms—galls

Secondary symptoms— Yellowing Stunting

MANY hosts Mainly dicots

Parsley family

Okra

Use marigolds to control by starving young ‘todes

Use resistant tomato and So. pea cultivars

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The Importance of Plant Disease Prevention

Post-harvest

Crop management

At-planting decisions

Pre-plant soil preparation

5 General Control Strategies

Avoidance

Protection

Resistance

Eradication

Exclusion

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What is EXCLUSION?

Keeping a pathogen out of a disease-free area, e.g., a garden, a county, a country.

Quarantine of affected areas

What to do: Use disease-free

transplants Be careful when saving

seed Don’t move or spread

infested soil Clean equipment purchased

from other states

How Pathogens Are Spread

Wind

Splashing rain

Moving water/soil

Insect vectors

Infected plants/parts

Transplants

Seeds

Tubers

Contaminated tools, hands, shoes

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What is ERADICATION?

Eliminating or destroying a pathogen after it is established

Remove plants that carry a pathogen

Sanitation is a VERY Important Eradication Method

Difficult to achieve 100%

eradication

Eradication may have negative

side effects, e.g. fumigation

Examples of Eradication

Remove diseased plants or parts --including roots.

Clean contaminated tools.

Grow marigolds to eradicate root-knot nematodes.

Eliminate wild radish (host for cole crop pathogens)

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What is the Difference Between…

Resistance

Genetic ability of a plant to defend itself from pathogens

Opposite is susceptible

Resistance is (usually) the most effective strategy.

Tolerance

“Ability of a plant to endure disease without serious damage or yield loss”

Sometimes used by seed companies to mean “a low level of resistance”

Heirloom varieties may have tolerance

What is PROTECTION?

Placing a barrier between the plant and the pathogen to prevent infection.

Spray fungicides

Identify diseases to select the best fungicide.

Most effective when applied before plant is infected.

Especially organic-approved fungicides

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Common Vegetable Fungicides

Conventional Organic and Biofungicides

Protectants Chlorothalonil

Mancozeb

Copper

Sulfur

Systemics Strobilurins (e.g. Quadris,

Cabrio)

Tebuconazole and related

Group 3 fungicides (e.g.

Monsoon)

Potassium phosphites

Copper

Sulfur

Potassium bicarbonate

Serenade

Root-Shield

Organocide (5% sesame oil + 92% fish oil)

Neem oil

Who Decides What Fungicides Are “Organic”?

Organic Materials Review Institute (OMRI)

Reviews products against the National Organic Standards

National Organic Program (NOP)

Part of USDA, Agricultural Marketing Service

National Organic Standards Board National List of Allowed

and Prohibited Substances

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NOP The National List of Allowed Synthetic Substances

As plant disease control:

1) Coppers, Fixed

2) Copper Sulfate

3) Hydrated Lime

4) Hydrogen Peroxide

5) Lime Sulfur

6) Oils, Horticultural

7) (fruit only)

8) Potassium Bicarbonate

9) Elemental Sulfur

10) (fruit only)

11) (fruit only)

What is AVOIDANCE? Preventing contact between

pathogen and host to prevent disease.

Includes modifying the environment to make it less favorable for disease.

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Avoidance Techniques

Don’t grow RKN-susceptible plants in summer.

Stake tomatoes to prevent fruit rots.

Raise beds to prevent damping-off.

Don’t wet leaves when watering.

The Disease Triangle: An Aid to Management

Host Plant

Environment

Disease

Pathogen

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General Cultural Practices

Reduce leaf wetness

•Drip irrigation •Increase row/plant spacing •Avoid edges of woods •Row orientation

Improve soil drainage

• Raised beds • Subsoil • Add organic matter

• Compost • Cover crops

Controlling Downy Mildews Reduce leaf wetness

• Increase row/plant spacing • Avoid edges of woods

Cole crops • Late planting date • Resistant broccoli, cabbage • Potassium phosphite

Cucurbits • Early planting date • Tolerant: ‘Aladdin’ pumpkin, C. maxima, C.

moschata • Fungicides

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Controlling Powdery Mildews Biopesticides

• Organocide • Potassium bicarbonate

Sulfur

• Do not apply at 90ºF.

Resistant summer and winter squash and pumpkin cultivars from Harris Seeds

English pea—early planting date

Powdery and downy mildew on the underside of a pumpkin leaf.

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Controlling Tomato Diseases Early blight

• Resistance • Increase row/plant spacing • Fungicides • Serenade for organic production

Southern blight • Deep plowing • Grafting

• ‘Big Power’

Bacterial spot

• Avoid fall planting • Increase row/plant spacing • Copper sprays

Bacterial spot on tomato fruit and foliage. Note copper residue on fruit.

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Sustainable Disease Management

Use organic soil management

• Cover crops • Crop rotation • Compost

Use as many cultural practices as possible to

• Exclude, • Eliminate and • Avoid disease.

. Check plants weekly for problems

Identify diseases to select the best control method.

• Bacterium or fungus? • Water mold or true fungus?

Apply least toxic fungicide when needed