What’s Wrong With Your
Plants and Why?
Tony Glover
Regional Extension
Agent
Diagnosis Can Be Tricky
Without All The Facts
Abiotic vs. Biotic Problems
• Abiotic – non-living
agent (non-infectious).
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Extreme temperatures
Excess or deficient
water, light or nutrients
Soil compaction, soil
grade changes
Damage from cultural
practices: herbicides,
fertilizers, pruning,
mulching
Abiotic vs. Biotic Problems
• Biotic – living agent
(infectious).
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Pathogens - parasitic
microorganisms that
cause disease (fungi,
bacteria, viruses,
phytoplasma)
Pests – insects, mites,
nematodes or mammals
feeding on or damaging
plants.
Abiotic vs. Biotic Problems
Symptom Progression
• Biotic disease –
symptoms progress
and nearby plants
become infected.
• Abiotic disease –
generally a lack of
symptom progression.
Does not spread.
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Exception – nutritional
deficiency symptoms
progress slowly.
Abiotic disease – Herbicide Injury
What’s Wrong?
Biotic or Abiotic
Steps in Problem Diagnosis
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Know the Plant
Inspect the Site and Look for
Patterns
Look for Symptoms or Signs
Examine cultural practices and
weather conditions
Identify Potential Causes
Consult Resources and Reach
Diagnosis
Steps in Problem Diagnosis
Know the Plant
• Identify the species and cultivar affected
• Know what problems commonly affect
the species. For example:
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Red Maple – Phyllosticta Leaf Spot, gloomy
scale
Flowering Dogwood – Powdery Mildew, spot
anthracnose
Steps in Problem Diagnosis
Know the Plant
• What’s normal for specific plant?
Fall Needle Drop on White Pine
Steps in Problem Diagnosis
Know the Plant
• Look at the Whole Plant (foliage, stems,
branches, leaves, and roots)
• Note the color, size, and thickness of
the foliage
• Check the trunk and branches
• Examine the Roots
Check the Trunk and Branches
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Look for wounds,
cankers, exit holes
and other clues
Pitch Tubes on Bark, Southern Pine Beetle
Check the Trunk and Branches
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Sapsucker damage
to sugar maple
Don’t mistake
sapsucker damage
for borer exit holes
Check the Trunk and Branches
But…
Girdling Roots
Girdling Injury
Planted too deep
Deep Planting or Covered Later
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Check for flare at
base of trunk
Girdling Roots
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Girdling roots are a
common problem
with trees that are
planted too deep
Too Much Mulch Over The Root Ball
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Problems caused by
too much mulch
• Keeps trunk tissue wet
• Can increase rodent
damage
• Mulch can intercept
rain and irrigation
• Can keep poorly
drained soils too wet
• Can encourage surface
roots
• Can encourage
development of stem
girdling roots
Planted too deep
Old root
system has
died
Steps in Problem Diagnosis
Inspect the Site and Look For Patterns
• Determine prevalence of problem.
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Large area, all plants – generally abiotic.
Scattered, localized – generally biotic.
• Check for distribution of symptoms.
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Uniform – generally abiotic.
Random – generally biotic.
• Are the symptoms/patterns related to
geography? (soil, low spot, etc)
• Is the damage limited to one type of plant?
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Multiple plant species - often abiotic
One species – often biotic
Observation of Field Patterns
Abiotic Problem
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Gas leak from building
Symptoms
distributed in a
large area.
Damage pattern is
uniform.
Observation of Patterns
Random vs. Uniform
Leaf Spot (Fungal)
Marginal Leaf Scorch
Observation of Field Patterns
Random vs. Uniform
Boxwood Phytophthora Root Rot
Oak Nutrient Deficiency
Observation of Field Patterns
Random vs. Uniform
Random Patches
Bermuda spring dead spot
Uniform Stripes
Fertilizer application problems
Steps in Problem Diagnosis
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Know the Plant
Inspect the Site and Look for
Patterns
Look for Symptoms and/or Signs
Examine Cultural Practices and
Weather Conditions
Identify Potential Causes
Consult Resources and Reach
Diagnosis
Look for Symptoms and/or Signs
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Symptoms - plant reactions or
alterations of a plant’s appearance
due to a disease or disorder.
Signs - actual presence of the
pathogen, it’s parts or by-products
seen on a diseased host plant.
Symptoms
Signs
Steps in Problem Diagnosis
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Know the Plant
Inspect the Site and Look for
Patterns
Look for Symptoms and/or Signs
Examine Cultural Practices and
Weather Conditions
Identify Potential Causes
Consult Resources and Reach
Diagnosis
Steps in Problem Diagnosis
Examine Cultural Practices and
Weather Conditions
• Ask questions - Collect as much background
information as possible
• When was the problem noticed?
• Was the damage sudden or gradual?
• Has the problem spread?
• How old are affected plants?
• What cultural practices have been performed
recently? Herbicide Sprays?
Hail Damage
Steps in Problem Diagnosis
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Identify Potential Causes
Consult Resources and Reach
Diagnosis
Get Laboratory Assistance
• Take samples (plant, soil)
• Don’t forget pictures
Most Common Diseases of 2009
Ornamentals
Phytophthora Root and Crown Rot
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Boxwood, Juniper, Hydangea, Leyland Cypress, Pansy, Petunia,
Fungal Leaf Spots (Oak Leaf Blister, Anthracnose, and other
leaf spots)
Armillaria Root Rot
Oakleaf Hydrangea, Cotoneaster
Pythium Root Rot
Pansy and other flowers
Powdery Mildew
Dogwood, Crape Myrtle, Rose
Botryosphaeria Canker /Dieback
Leyland Cypress, Japanese Maple, Cleyera
Bacterial Leaf Spots
Basil, Begonia, Oakleaf Hydrangea, English Ivy
Azalea Leaf Gall
Sooty Mold
Various Trees and Shrubs (Hackberry Woolly Aphid)
Diseases Caused by Phytophthora
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Some of the most economically important and
damaging diseases on woody plants in the
Southeast, USA, and worldwide
The name Phytophthora derives from Greek
and literally means “plant destroyer.”
Cause problems annually
Notorious Phytophthora diseases include
rhododendron root rot, sudden oak death, and
potato late blight.
Particularly serious in or following “wet” years
Diseases often are associated with wet or
saturated soils
Phytophthora 101
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Phytophthora species resemble fungi
but are not.
They are most closely related to aquatic
organisms, such as brown algae and
diatoms.
Phytophthora organisms are often
referred to as ‘water molds’ because
they do need water to complete their
life cycle.
This group of organisms produces
swimming spores .
Disease Cycle: Phytophthora Root
Rot
Some Trees and Shrubs Attacked
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Abies – fir
Acer – maple
Arbutus – madrone
Betula – birch
Buxus – boxwood
Camellia – C. japonica
Castanea – chestnut
Cedrus – cedar
Cercis – redbud
Chamaecyparis - false
cypress
Citrus - orange, lemon,
etc.
Cornus – dogwood
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Cryptomeria -Japanese
cedar
Cupressus - cypress
Elaeagnus
Eucalyptus
Fagus – beech
Ficus - fig
Forsythia
Ilex - holly
Juglans—walnut
Juniperus –juniper
Kalmia – laurel
Malus - apple
More Trees & Shrubs
Attacked...
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Pieris – andromeda
Pinus – pine
Platanus – sycamore
Prunus - cherry, plum, etc.
Pseudotsuga - Douglas fir
Pyrus - pear
Quercus – oak
Rhododendron rhododendron, azalea
Robinia – locust
Rosa - rose
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Rubus - raspberry
Syringa - lilac
Taxus - yew
Thuja - arborvitae
Tsuga - hemlock
Vaccinium - blueberry
Viburnum -arrowwood
Ulmus – elm
Phytophthora as Pathogens of
Woody Plants
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They can attack all parts of the plant
Blight & dieback on shoots & foliage
—uncommon
Cankers on stems & trunk —e.g.,
“bleeding” cankers – occasionally
Root & crown rots — most common
Symptoms—Above Ground
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Appear after roots are diseased
Chlorosis & yellowing of the foliage
• very slight at first, then becoming obvious
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Stunted growth
Overall wilting & decline
Cankers - orange/red/brown discoloration
• on stems and trunk
• distinct margin between healthy & diseased
tissues
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Plant death
Phytophthora Foliage Blight
Trunk and Stem Cankers
“bleeding” cankers - maple
Trunk and Stem Cankers
“bleeding” cankers - Oak
outer bark
Photo: Bruce Moltzen, Missouri Department of Conservation
inner bark
Symptoms—Below Ground
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Must expose roots for examination
• this usually requires digging!
• need to know what healthy roots look like!
Reduced root volume/lack of feeder roots
Roots discolored - red, brown, dark brown
• healthy roots are white or off-white
Cortex sloughing/root rot
Cankers on root crown
• may move up stem above ground
Boxwood - Cortex sloughing/root
rot
Phytophthora Root Rot on
Boxwood
Phytophthora Root Rot on Shore
Juniper
Field Diagnosis
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Above-ground symptoms alone usually are
not diagnostic—merely indicate vascular
dysfunction
Therefore, look below ground at roots &
crown
Together, these may be diagnostic
Other pathogens also can cause root rot
• Armillaria, Fusarium, Sclerotium, Thielaviopsis,
etc.
• and sometimes Pythium spp., especially on
boxwood
Fungal Leaf Spot Diseases
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Typically have tan to gray centers
surrounded by a darker border
Fungal fruiting structures (pycnidia, spores,
etc.) can be seen within the leaf spot
Defoliation is common
Fungi survive on fallen leaves
Prolonged leaf wetness, high humidity and
poor air circulation increase disease
development
Spores are spread by wind and watersplashing, but can also be spread by
insects, on clothes, tools, and hands
Japanese Maple
Phyllosticta Leaf Spot
Defoliation due to Entomosporium
leaf spot disease - Indian Hawthorn
Less water
stays on this
protected area
Oak Leaf Blister
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Common fungal
disease on oaks,
especially red oaks
(s. red and water
oak)
Disease favored by
cool, wet springs
Symptoms appear
in late spring as
yellow, blisterlike,
circular, raised
Oak Leaf Blister
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Spots become dull
brown with age
As leaves mature,
become resistant to
infection
Affects appearance
not tree health
Fungicides not
needed, but one
application of
chlorothalonil or
mancozeb before
budbreak will control
disease
Cercospora Leaf Spot – Crape
Myrtle
Cercospora Leaf Spot
Cercospora Leaf Spot - Dogwood
Boston Ivy Leaf Spot
Armillaria Root Rot
Armillaria Root Rot – Oakleaf
Hydrangea
Armillaria Root Rot - Oakleaf
Hydrangea
Armillaria Root Rot -Oak
Armillaria Root Rot - Rose
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White fungal
growth under bark
Drainage?
Irrigation? Death
by watering hose?
No fungicides for
control
Resistant plants
best replacement
option
Bacterial Leaf Spots
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Oak Leaf Hydrangea
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Angular leaf spots running
along veins
Plant wetness, high
humidity and warmer
temperatures favor
disease development
Bacterial cells spread
by water splashing,
tools, hands, or
insects
No Fruiting structures
in spots
Many controlled with
copper fungicides
(Kocide)
Bacterial Leaf Spots
‘water soaked spots’
English Ivy
Hydrangea
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Common name for group
of black-colored fungi
that grow on honeydew
on plants and other
surfaces
Fungal growth gives
appearance of being
covered with a layer of
soot
Honeydew produced by
aphids, mealybugs, soft
scales, whiteflies
Control sooty molds by
controlling the honeydew
producing insect.
Drenches with Merit or
Safari for hackberry
aphids (early spring)
Sooty Mold
Sooty mold on crape myrtle
Asian Woolly Hackberry Aphid
Multicolored Asian lady beetle pupa
Azalea Leaf Gall
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Occurs in cool,
moist springs
Spores for next
year’s infection are
released when leaf
galls turn white
Prune infected
leaves
Camellia Leaf Gall
Spores for next year’s infection are
Camellia leaf gall early symptoms and la
released when backside of leaves
year’s infected leaves
turn
white
Leaf Gall Control
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Remove galls and destroy before they turn white
with spores
Disease most severe when foliage becomes wet
during leaf expansion in spring.
• Avoid planting in heavy shade
• Avoid wetting foliage in spring
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If the disease was severe in previous years and galls
were too numerous to pick, apply a fungicide before
new leaves and flowers emerge.
Applications can stop when leaves become full size
Bayleton. Apply first spray as new leaves and
flowers appear. Repeat 2-3 times at 10-day
intervals.
Powdery Mildew
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Common disease on dogwood
and other plants
Looks like baby powder
Use Resistant Cultivars:
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Cherokee Brave, Karen’s
Appl. Blush, Kay’s Appl. Mist,
Jean’s Appl. Snow
Start sprays at first sign of
disease (early May)
Fungicides:
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Heritage
Spectricide Immunox
Fertilome Systemic Fungicide
Fertilome Halt Systemic
Fungicide
Too late for fungicides
Spot Anthracnose
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Small reddish spots on
bracts and leaves,
trees in sun
Rake leaves in fall
Heritage, Daconil,
Mancozeb, Halt,
Immunox
Spray before
budbreak, after bract
fall, and one month
later, and September
after new flower buds
form
Dogwood Anthracnose
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Different disease than
spot anthracnose
Spots with reddish or
purple borders
Spots enlarge over
time
Leaf, twig blights,
cankers, can kill tree
Blighted leaves remain
attached through
winter
Resistant Cultivar
‘Appalachian Spring’
Hydrangea – Leaf Spot
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Several fungi cause leaf spots
on hydrangea – Cercospora,
Corynespora, Colletotrichum
Often in combination with
powdery mildew
Adequate plant spacing for
good air circulation
Avoid watering late in the day
Remove fallen leaves
Apply fungicide at first sign of
disease:
• Heritage, Daconil*, Immunox
Mancozeb*, Fertilome
Systemic Fungicide
• * Poor control of powdery
mildew, but good leaf spot
control
• Ultra-fine Spray Oil
Leyland Cypress Problems
Botryosphaeria Canker
J. Woodward - UGA
Botryosphaeria Canker
UGA
J. L. Williams-Woodward - UGA
Control of Canker Diseases
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Difficult to control once infection has occurred
Prevent canker diseases by proper
establishment and care:
• Plant in well drained soils
• adequate plant spacing
• Irrigate plants to prevent drought stress, mulch
plants
• Remove branches with cankers. Trace the dead
wood back to the base of the canker and prune at
bud or branch fork. Prune 4-6 inches below canker.
• Sterilize pruning tools frequently
• Avoid canker susceptible plants
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Fungicides are of little value
Thank You