Master Gardener Training Plant Pathology Greg Church, Ph.D. County Extension Agent – Horticulture, Plant Pathologist http://collincountygardening.tamu.edu Go to http://collin-tx.tamu.edu Click Publications, then Master Gardener Training Download Plant Pathology Information
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Master Gardener Training Plant Pathology Greg Church, Ph.D. County Extension Agent – Horticulture, Plant Pathologist .
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Fungal Diseases• Most of the common diseases occurring on landscapes
are caused by fungi.• 85% of plant diseases caused by fungi.• Majority of fungi are saprophytic.• Characteristics of fungi– Absorb nutrients– Multi-celled– Radial growth as tubular filaments– Reproduce and survive as spores– May “overwinter” as sclerotia, rhizomorph or spores.
Images from the Plant Management Network Image Collections.
Diagnosis of fungal diseases
• Presence of visible fungal structures– May be observed unaided or with
magnification.
• Can usually be cultured on artificial media for identification– Exceptions: obligate parasite such as rust
and mildew fungi.
FungiDamping-off Pythium sp.
Fungi
Alternaria Petal Blight of Rose
Fungi Dollar spot of turfSclerotinia homoeocarpa
Fungi
Blackspot of roses
Fungi• Entomosporium leaf
spots
Fungi
• Powdery mildew
Rose
Lilac Crape myrtle
Crape myrtle
Fungi
• Rust
Apple
Cedar
Chrysanthemum
Fungi
• Brown patch-Rhizoctonia
Fungi• Take-all- Gaeumannomyces
Bacterial diseases
• Characteristics of bacteria– Absorb nutrients– One-celled
(prokaryote)– Reproduce by fission– Survive by dormancy
Diagnosis of bacterial disease
• Leaf lesions sometimes limited by veins (angular)
• Ooze or streaming from cut tissue• Soft rot (fruit) has foul odor• Can be culture on media – Use of selective media for identification
of pathogen.
Bacteria• Bacterial scorch
Bacteria• Galls
Bacteria• Blights
Lilacs - Pseudomonas syringae
Bacteria• Spots
Pittosporum
Tomato
Ranunculus
Bacteria• Wilts
Diagnostic
Crassula
Zucchini
Bacteria
• Soft rot
Orchid
Onion
Potato
Bacteria• Scabs and Cankers
Cherry
Peach
Watermelon Blotch
Viral diseases
• Characteristic of viruses– Sub-cellular, composed of
DNA or RNA surrounded by protein coat
– Replicate by “hijacking” plant DNA
– Require wound to enter plant cell
– Require living host– Usually transmitted by a
vector
Viral symptoms• Mosaic
Viral symptoms
Ring spot
Viral symptoms
• Other symptoms
Plant Parasitic Nematodes
• Characteristic of nematodes– Very small animals (microscopic
round worms)– Typically in the soil– Usually attack roots, sometimes
foliage– Reproduces with eggs
Plant parasitic
Stylet
Various shape and
sizes of nematodes
Plant Parasitic Nematodes• Root knot
Plant Parasitic Nematodes
• Lesion
NematodesNematodes
Lesion Nematode damage on
Rose
No nematode nematode
Plant Parasitic Nematodes
• Cyst
SoybeanCactus
Plant Parasitic Nematodes• Foliar
Lantana
African Violet
Chrysanthemum
Parasitic plants
• Characteristic of parasitic plants– Obtain all or some of their needed nutrient from other
plants.– Many has little or no chlorophyll.– Cause relatively few problems when compared to other
disease problems.
Parasitic plants
ABIOTIC PROBLEMS
• Causes of abiotic problemsPhysical agents
Temperaturemoisturelight extremes
Chemical agentssoil pH or nutrient imbalancespollutantspesticides
Diagnosis of Abiotic Problems
• Eliminate all possibilities of pathogenic attack.• Know history of the plant and its culture.• Know the range of growing conditions for the plant• Consider symptom patterns, site characteristics,