Plant Pathology 101 Master Gardener Training Carrie Harmon, Phil Harmon Plant Pathology Dept., UF Gainesville and the Southern Plant Diagnostic Network UNIVERSITY OF FLORIDA IFAS EXTENSION

Environment Disease Pyramid Disease Time Pathogen Host

Diseases and disorders Disease occurs when Pathogen Host Environment Disorders lack pathogens Plant Put it in human terms… radiation, salmonella

Diagnosis is critical Incorrect changes to cultural management can make problems worse. Fungicides only work on fungal diseases. The applicator needs to know if plant damage is disease, if the disease is caused by a fungus, and which fungus is involved.

Disease diagnosis Diagnosis: changes in time/space Questions to ask: What pathogen structures (signs) occur when and where? What symptoms develop over time? What is the pattern of dispersal?  field signature or distribution abiotic vs. biotic (images helpful!) What are the known diseases associated with this host?

Disease diagnosis Injury and disorders often: occur “suddenly” may affect all or many plant species may have regular, uniform pattern follow equipment patterns, boundaries look at pattern of problem in relation to other items in the area – driveways, construction activities, etc.

Symptoms and Signs Symptoms: Changes in growth or appearance of a plant in response to a damaging factor. Sign: Evidence of the damaging factor.

Main types of pathogens Fungi Bacteria Viruses Others Fungi are the most common cause of plant disease. The image on the left is a petri plate with a fungus growing in it (this fungus causes gray leaf spot of St. Augustinegrass. The center image shows fungal growth on a diseased plant. This is the pathogen. Parts of the pathogen on a diseased plant are called a “sign” of disease, mushrooms are another sign.

Armillaria produces white fungal growth under the bark of diseased plants This sign is diagnostic. Removing the bark allows you to see the fungus. Armillaria produces white fungal growth under the bark of diseased plants This sign is diagnostic. Removing the bark allows you to see the fungus.

Sclerotinia sclerotiorum produces two distinct signs Sclerotinia sclerotiorum produces two distinct signs: large black survival structures in hollow stems of diseased plants are sclerotia; and white fluffy cottony growth is also produced by this fungus.

The black bumps in the blighted area of this holly stem contain small black fruiting bodies of the pathogen, Sphaeropsis tumefaciens. The black bumps in the blighted area of this holly stem contain small black fruiting bodies of the pathogen, Sphaeropsis tumefaciens.

Spores are usually too small to see Spores are usually too small to see. In this case many spores are released from the “puffball” mushroom together and they look like smoke rising from the fruiting body of this fairy ring causing fungus. Spores are usually too small to see. In this case many spores are released from the “puffball” mushroom together and they look like smoke rising from the fruiting body of this fairy ring causing fungus.

In this case, many spores of Colletoctrichum form on this rotting blueberry and appear orange in color. In this case, many spores of Colletoctrichum form on this rotting blueberry and appear orange in color.

Daylily rust spores are also orange and can rub off the leaves onto your hands and clothes but are harmless to humans.

Powdery mildews generally produce white flat growth on diseases plants Powdery mildews generally produce white flat growth on diseases plants. The white growth is another sign that consists of hyphae and spores.

Main types of pathogens Fungi Bacteria Viruses Others Bacteria are not often seen. Occasionally bacterial ooze can be seen leaking from bradford pear shoots wilted from fire blight. Oozing plant sap can be caused by a number of other things including insect feeding. Bacterial diseases produce symptoms, but usually no signs. Photo by Mark Longstroth Photo by Hank Dankers

Main types of pathogens Fungi Bacteria Viruses Others Viruses are too small to see with anything except the best microscopes. Viral diseases produce symptoms but no signs of the pathogen that are visible to the naked eye. Micrograph by Carl Wetter http://mmtsb.scripps.edu/viper/1f15.html

Main types of pathogens Fungi Bacteria Viruses Others Mycoplasma-Like-Organism (MLO) Ex. Coconut Palm Lethal Yellowing MLO MLO’s are also too small to see and do not produce visible signs. ? http://www.inbar.int/publication/txt/tr10/little.htm

Types of disease symptoms What does the disease do to the plant? Underdevelopment of tissues or organs. Examples include such symptoms as stunting of plants, shortened internodes, inadequate development of roots, malformation of leaves, inadequate production of chlorophyll and other pigments, and failure of fruits and flowers to develop. Overdevelopment of tissues or organs. Examples include: galls on roots, stems, or leaves, witches' brooms, and profuse flowering. Necrosis or death of plant parts. These may be some of the most noticeable symptoms, especially when they affect the entire plant, such as wilts or diebacks. Other examples include shoot or leaf blights, leaf spots, and fruit rots. Alteration of normal appearance. Examples include mosaic patterns of light and dark green on leaves, and altered coloration in leaves and flowers. From: Riley, M.B., M.R. Williamson, and O. Maloy. 2002. Plant disease diagnosis. The Plant Health Instructor. DOI: 10.1094/PHI-I-2002-1021-01

Incidence VS. Severity Incidence: Percent of the crop affected Severity: a measure of impact on a plant or the crop

Common disease symptoms Courtesy R.L. Forester Courtesy J.W. Pscheidt Peach leaf curl, caused by Taphrina deformans. Crown gall of uonymous by Agrobacterium tumefaciens. Overgrowth of leaf tissue causes thickening and distortion. Galls form on all plant parts, caused by many pathogens.

Common disease symptoms Wilting Biotic factors Root, crown or stem rots Vascular wilts Root crown or stem damage from insects or animals Mainly fungal and bacterial causes Used by permission of M.Williamson Stem wilt of Exacum from INSV infection

Common disease symptoms Leaf spots Cankers Foliar blights Root rots Black spot of rose on right; sycamore anthracnose on left; These are symptoms of the disease. You cannot see the pathogen in these photos.(no signs)

Cercospora leaf spot of crinum lily (symptoms no signs)

Common disease symptoms Leaf spots Cankers and diebacks Foliar blights Root rots Citrus canker on left; Nectria canker on apple center; sycamore anthracnose canker symptom right Photo by A. L. Jones Photo by Dean Gabriel

Severe dieback resulting from stem and bole cankers caused by Botryosphaeria dothidea

Stem canker caused by Botryosphaeria dothidea

Needle blight on Leyland cypress

Entomosporium leaf spot on Dwarf Indian Hawthorne There are resistant cultivars

Image credit: Celeste White Sphaeropsis tumefaciens symptoms include galling and shoot proliferation on holly and Ixora (left and center) and cankers also on holly noticeable by cracked bark and discoloration of vasculature underneath. Image credit: Celeste White Sphaeropsis tumefaciens

Main types of diseases Leaf spots Cankers Foliar blights Root rots Foliar blights affect leaves and stems. Ramorum blight left and white mold (Sclerotinia sclerotiorum) right

Main types of diseases Leaf spots Cankers Vascular wilts Root rots Soil borne organisms, usually fungi cuase root rot. Abiotic factors also cause root rot—water logged soil. Soil borne organisms, usually fungi cuase root rot. Abiotic factors also cause root rot—water logged soil.

Main types of diseases Leaf spots Cankers Vascular wilts Root rots Photo by R.O. Hampton Leaf spots Cankers Vascular wilts Root rots Viral diseases Photo by W. Witcher

Unknown ringspot virus symptoms on phalenopsis orchids

Rose mosaic symptoms

How do we approach a plant problem? A Five Step Process… 1. Determine that a ‘REAL’ problem exists. 2. Look for PATTERNS, in the community, on an individual plant and on an individual plant part. 3. Determine the TIME development of the damage pattern. 4. Ask QUESTIONS. 5. SYNTHESIZE the information.

1. Determine that a ‘REAL’ problem exists… Identify the plant. Learn about it’s normal characteristics. Determine normal vs abnormal characteristics. Look for symptoms and signs. Symptoms: Changes in growth or appearance of a plant in response to a damaging factor. Sign: Evidence of the damaging factor.

2. Look for Patterns… Look for patterns in the plant community. Is the damage on more than one plant? Is the damage on more than one plant species? Look for patterns on an individual plant. Is the damage on the entire plant or certain parts? Is the damage on certain age of growth? Look for patterns on an individual plant part.

Patterns of damage… Non-uniform, expanding damage patterns are usually caused by living factors, because of movement of feeding sites, life cycles, and population increases and decreases. Uniform, non-expanding damage patterns are usually caused by non-living factors such as chemical injuries, temperature changes, and mechanical damage.

Damage patterns in the plant community… Used by permission of R. Billings Loblolly pine killed by southern pine beetle

Used by permission of M. Williamson Cotton field with chemical damage

Rhododendron with a Phytophthora sp. infection.

Woody container plants with Chemical injury .

Turfgrass displaying Fairy Ring symptom.

Damage patterns on an individual plant… Used by permission of W. Sinclair American Elm displaying symptoms of Dutch Elm Disease.

Rhododendron displaying symptoms of Nitrogen Deficiency.

Damage patterns on an individual plant part… Douglas Fir with Rhabdocline Needlecast.

Fir with Freeze Injury.

Used by permission of M. Williamson Downy mildew of Buddleia caused by Peronospora harotii.

Kalmia with a viral infection.

3. Determine the TIME development of the damage pattern… Progressive spread with time to other areas is characteristic of living factors. Intensification of symptoms where damage first occurred but no spread to new sites is characteristic of non-living factors.

4. Ask QUESTIONS… Get a history of the problem. Get a history of all pesticides and fertilizers that have been applied. Find out the history of the site. Could environmental conditions explain the problem? Look for obvious symptoms and signs… Don’t ignore the roots… Beware of secondary insects and pathogens… Be patient and avoid jumping to conclusions…

5. SYNTHESIZE the information… Refer to literature…

Send a sample to the Plant Disease Clinic UF Plant Disease Clinic Building 78 Mowry Road University of Florida Gainesville, FL 32611 352-392-1795

Samples must contain the right material: an entire plant or several plants if practical. Diseases may show up on any part of the plant. Foliage diseases Keep most roots and soil intact if possible Check for injuries, disease on the main stem/trunk

Dead Plants Tell no Tales Avoid dead plants Choose plants which show a range of symptoms: moderate to severe

Sample Quality: Packaging & Shipping Keep soil on roots No extra water Wrap in dry paper then double bag in plastic Disinfest exterior of bags Strong crush-proof box, tape all seams

Packaging & Shipping Good Intentions

Actual Results

Packaging and Shipping blunders Soil on foliage during shipping creates “diseases” that were not there when the sample was collected.

Packaging and shipping blunders Sample Soup Don’t add water or wrap in wet paper towels

Good Packaging Plastic bag to keep soil on roots Dry paper towels to protect leaves from contact with plastic bag

Disease management Watch for problems Rule out abiotic factors Look for symptoms and signs Consider the recent weather Consult references, agent Send a sample to the disease clinic Follow progress Keep records