Kevin Ong, PhD. Associate Professor and Extension Plant Pathologist Director – Texas Plant Disease Diagnostic Laboratory College Station, TX

Basic Plant Pathology Disease ID and what not.

What is a PLANT DISEASE?

Any alteration of a plant that interferes with its normal appearance, function, or value and renders it unfit for its normal use.

TWO kind of disease

•  Infectious – Transmissible from plant to plant – Caused by biotic (pathogenic) agents

•  Non-infectious – Disorder caused by unfavorable physical

environmental (physiogenic) effect

What can make plants sick?

Baudoin, A.B.A.M. 2007. The Plant Disease Doughnut, a Simple Graphic to Explain what is Disease and what is a Pathogen. The Plant Health Instructor. DOI: 10.1094/PHI-T-2007-1221-01

Plant Disease Central Concepts

CONCEPT #1: Disease triangle

•  Three factors:

PATHOGEN (disease causing agent)

DISEASE

The Disease Triangle

PATHOGEN (disease causing agent)

Susceptibility Susceptibility Susceptibility

Disease Occurs

Disease

CONCEPT #2: Disease Cycle

Overseasoning/ Overwintering

Management

Management

Management

Infection

Host

Reinfection

Management

Management

Glossary – the language

Sign and symptoms Symptomology

SIGN The pathogen (or parts of) can be visually

observed on the host plant.

SYMPTOM External or internal reaction or alteration of a plant due to the

disease

Sign or Symptom?

Urediospores

Teliospores

Symptomology •  Anthracnose

–  Describes an appearance as dark, sunken leaf, stem, or fruit lesions.

–  Typically describe symptoms made by fungi

Ivy- Colletotrichum

Nandina

euonymus

Ash- Gnomoniella

Symptomology

•  Blight –  Characterized by

general and rapid killing of leaves, flowers, or stems.

Rose-Botrytis

Red cedar -Phomopsis Oleander - Rhizoctonia

Forsythia-Sclerotium

Symptomology •  Canker

–  A necrotic, often sunken lesion on a stem, branch, or twig of a plant. Sycamore-Discula

Holly

Symptomology

•  Chlorosis –  Yellowing of

normally green tissue due to chlorophyll destruction or failure of chlorophyll formation

Rose-iron chlorosis

Symptomology •  Dieback

–  Progressive death of shoots, branches, and roots generally starting at the tip.

Rhododendron-Phytopthtora

Podocarpus-Botryodiplodia

Symptomology •  Gall

–  A swelling or overgrowth produced on a plant.

–  Gall is plant tissue

Rose-Agrobacterium

Azalea-Exobasidium

Pine-Cronartium

Symptomology •  Leaf spot

–  A self-limiting lesion on a leaf.

Photinia-Entomosporium

Rose-Diplocarpon

Ivy-Xanthomonas

Symptomology •  Mildew

–  Used to describe fuzzy growth on plants.

–  Typically refers to mycelium and spores of fungi that are observed.

Euonymous-Oodium

Crape myrtle-Erysiphe

Rose-Peronospora

Symptomology

•  Ringspot –  Circular area

of chlorosis with a green center.

Orchid-freeze

INSV

Symptomology

•  Rosette –  Short, bunchy

habit of plant growth.

Rose rosette (UT-Knoxville)

Rose-unknown

Symptomology

•  Scab –  A roughen, crust-like

disease area on the surface of a plant organ.

Apricot-Cladosporium

Symptomology

•  Scorch –  Burning pattern on leaf

margins. –  Typically would indicate

water deficiency problems.

Sycamore-Xylella

Oak-Ceratocystis

Symptomology

•  Shot-hole –  Holes on

leaves.

Cherry laurel-Xanthomonas (UT –Knoxville)

Symptomology

•  Stunting –  Result of

reduced plant growth.

Cotton-Sting nematode

Symptomology •  Wilt

–  Loss of rigidity and drooping of plant parts generally caused by insufficient water in the plant.

Azalea-Cylindrocladium

Rose-Verticillium