T O Plant Disease

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TO Plant Disease
Master Gardener Talk April 2009

• Phil Harmon
• Assistant Prof. and Extension Specialist
• Plant Pathology Dept., UF Gainesville

UNIVERSITY OF FLORIDA
IFAS EXTENSION
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DiseasePyramid
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Diseases and disorders

• Disease occurs when
• Pathogen
• Host
• Environment
• Disorders lack pathogens
• Plant
• Environment

Put it in human terms radiation, salmonella
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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.

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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?

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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.

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Symptoms and Signs

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

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Main types of pathogens

• Fungi
• Bacteria
• Viruses
• Others

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Sclerotinia sclerotiorum produces two distinct
signs
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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.
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In this case, many spores of Colletoctrichum form
on this rotting blueberry and appear orange in
color.
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Main types of pathogens

• Fungi
• Bacteria
• Viruses
• Others

Photo by Mark Longstroth
Photo by Hank Dankers
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Main types of pathogens

• Fungi
• Bacteria
• Viruses
• Others

Micrograph by Carl Wetter
http//mmtsb.scripps.edu/viper/1f15.html
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Types of disease symptomsWhat 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
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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.

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Common disease symptoms

• Wilting
• Biotic factors
• Root, crown or stem rots
• Vascular wilts
• Root crown or stem damage from insects or animals

Used by permission of M.Williamson
Stem wilt of Exacum from INSV infection
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Common disease symptoms

• Leaf spots
• Cankers
• Foliar blights
• Root rots

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Cercospora leaf spot of crinum lily (symptoms no
signs)
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Common disease symptoms

• Leaf spots
• Cankers and diebacks
• Foliar blights
• Root rots

Photo by A. L. Jones
Photo by Dean Gabriel
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Main types of diseases

• Leaf spots
• Cankers
• Foliar blights
• Root rots

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Foliar Phytophthora on Vinca
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Main types of diseases

• Leaf spots
• Cankers
• Vascular wilts
• Root rots

Soil borne organisms, usually fungi cuase root
rot. Abiotic factors also cause root rotwater
logged soil.
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healthy
inoculated
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Plants on the left were not inoculated. Plants
on the right were inoculated (note the lack of
roots and the black coloration).
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Main types of diseases
Photo by R.O. Hampton

• Leaf spots
• Cankers
• Vascular wilts
• Root rots
• Viral diseases

Photo by W. Witcher
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Unknown ringspot virus symptoms on phalenopsis
orchids
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A Five Step Process
How do we approach a plant problem?

• 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.
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1. Determine that a REAL problem exists

• Identify the plant.

• Learn about its 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.

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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.

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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.

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Woody container plants with Chemical injury .
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Damage patterns on an individual plant part
Douglas Fir with Rhabdocline Needlecast.
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Fir with Freeze Injury.
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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.

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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

• Dont ignore the roots

• Beware of secondary insects and pathogens

• Be patient and avoid jumping to conclusions

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5. SYNTHESIZE the information

• Refer to literature

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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

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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
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Dead Plants Tell no Tales

• Avoid dead plants
• Choose plants which show a range of symptoms
  moderate to severe

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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

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Packaging Shipping
Good Intentions
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Actual Results
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Packaging and Shipping blunders
Soil on foliage during shipping creates
diseases that were not there when the sample
was collected.
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Packaging and shipping blunders
Sample Soup

• Dont add water or wrap in wet paper towels

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Good Packaging

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

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Diagnostic results

• Fungicide recommendations given
• Compare active ingredients to the list of
  available products for homeowners
• Homeowners guide to fungicide on
  EDISavailability varies from location to
  location and store to store

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Primary turf pathogens

• Fungi
• Bacteria- very few examples, none in FL
• Viruses- SAD virus not detected in FL
• One other viral disease also St. Aug (L. Datnoff)
• Others- Labyrinthula sp. Affects Poa triv...
• Marine slime mold relative

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Large Patch

• Systemic
• Insignia
• Heritage
• Banner
• Bayleton
• Premix
• Armada
• Headway

Problematic Spring and fall north FL and fall
winter and spring south FL Avoid excess Nitrogen
fertility in fall Fungicides with activity should
be used preventatively where the disease occurs
year after year
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large patch on St. Augustinegrass
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Gray Leaf Spot

• Cultural inputs
• Avoid excess water soluble nitrogen
• Avoid herbicides that contain atrazine during
  summer

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Take-all root rot

• Systemic
• azoxystrobin
• thiophanate-methyl
• pyraclostrobin
• myclobutanil
• triadimefon
• propiconazole

Problematic On St. Augustinegrass sod and
bermudagrass golf greens in summer Disease worst
where other stresses exist Often occurs in a
complex with damaging nematode pops., Pythium
root rot Fungicides with activity should be
rotated in a preventative summer fungicide program
can have negative effect on turf, use
preventative rates only once per season, do not
use propiconazole on putting greens summer
water products in with 0.25 of water
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Stem Blight, Dieback, Cankers

• Symptoms cankers on woody stems, dieback,
  vascular discoloration
• Signs some dieback fungi produce fruiting
  structures

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Strandberg and Brennan
Swollen branches and proliferation of shoots on
dahoon holly (Ilex cassine L.) infected with
Sphaeropsis tumefaciens.
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Image credit Celeste White
Sphaeropsis tumefaciens
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Stem Blight, Dieback, Cankers

• Management keep plants healthy by following good
  management practices

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Leaf Spots, Rusts, Mildews

• Symptoms spots, chlorosis, defoliation
• Signs spores, fruiting structures

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Frangipani rust disease
Credit Doug Caldwell
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Guava Rust
So many pustules are produced that spores powder
the hand Credit Stephen Brown
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Pustules on leaf of Eugenia Credit Stephen Brown
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Rusts

• Management pruning, site selection, reduce
  humidity, resistant cultivars
• Chemical strobilurins (Heritage, Insignia),
  DMIs (Eagle, Banner, Bayleton). benzimidazoles
  (Clearys 3336)

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Credit Doug Caldwell
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Powdery on Phlox
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Powdery Mildew

• Management pruning, site selection, reduce
  humidity, resistant cultivars
• Chemical strobilurins (Heritage, Insignia),
  DMIs (Eagle, Banner, Bayleton). benzimidazoles
  (Clearys 3336), bicarbonates

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• Fungal leaf spots

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Not disease with ixora, nutritional potassium
phosphorous deficiency , especially during cool,
dry winters.
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Botrytis on Pansy
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Downy Mildew

• Symptoms leaf spots, sometimes angular,
  chlorotic, etc.
• Signs gray to black fuzzy growth on underside of
  leaf

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Downy mildew- Awabuki viburnum
Plasmopara viburni
Credit Doug Caldwell
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Root Rots

• Symptoms brown mushy roots, stunting, wilting,
  yellowing
• Signs not many

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• Root rots

Soil borne organisms, usually fungi cause root
rot. Abiotic factors also cause root rotwater
logged soil.
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healthy
inoculated
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Plants on the left were not inoculated. Plants
on the right were inoculated (note the lack of
roots and the black coloration).
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Thanks.Questions?

• Phil Harmon
• pfharmon_at_ufl.edu

Phil Harmon Department of Plant Pathology,
UF 1453 Fifield Hall Gainesville, FL
32611 Phone [phone]x340 Email
pfharmon_at_ufl.edu