Plant Diseasesplanthealthcare-mortonarb.org/uploads/2/0/7/0/20707530/... · 2019-10-26 · Fungal...
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Plant Diseases
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The Disease Triangle
Susceptible host plant
Pathogen
Favorable climate
Time
Host Plant
Time
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Diseases and Pathogens
Can be spread or transmitted to other plants
Caused by biotic or living organisms called pathogens - fungi - bacteria - viruses - nematodes - phytoplasmas - parasitic plants
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Vector Means by which a pathogen is spread
Vector can also be wind, rain splash, insects,
humans, soil, and pruning tools
Example: elm bark beetles spread the fungus that
causes Dutch elm disease, so the beetles are the
vector of the disease
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Types of Disease Symptoms
Blight
Leaf spot
Mosaic
Stunting
Marginal necrosis
Distortion
Wilt
Canker
Gall
Rot
Witches Brooming
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Blight Large dead areas on leaves, shoots or flowers
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Leaf Spots Small, discolored areas on foliage
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Mosaic Patches of yellow and green tissue on a leaf
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Stunting
Abnormally small
size of plant or
plant part
http://www.mntca.org/resources/treeid/tree_dec_opp_ash_green.html
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Marginal necrosis Brown, dead tissue around the edges of leaves
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Distortion Twisting or abnormally shaped leaves and shoots
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Wilt Flaccid, limp condition of leaves or shoots resulting
from water deficiency
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Canker Localized, often sunken, dead area on a twig,
branch, or stem
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Gall Abnormal swelling of a portion of a branch, leaf,
root or bud, a tumor
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Rot Tissue breakdown or decay
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Witches brooming Twig growth resulting from a lack of apical
dominance causing side shoots to elongate equally,
forming a dense cluster or broom-like mass of twigs
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Fungal pathogens
Fungi (sing. fungus) Cause the majority of plant diseases
Rots, cankers, leaf spots, blights, blotches, and wilt diseases
Spread by insects, wind, rain, pruning tools, infested plant tissue, soil
Need water for disease development
Most fruiting bodies are tiny and look like black pepper to the
naked eye
Spores emerge from the fruiting bodies
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Fungal Diseases
Apple scab
Powdery mildew
Black spot on rose
Leaf curl and leaf blister
Cedar rusts (apple, hawthorn, quince)
Anthracnose (sycamore, ash, oak)
Guignardia leaf blotch
Cankers (Thyronectria, Nectria, Botryosphaeria)
Black knot
Volutella
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Apple scab Most common crabapple disease
Begins as olive-green leaf spots with fuzzy edges
Leaves eventually turn yellow and fall off
Also infects fruit
Very common in wet springs
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Powdery mildew
Affects many woody and herbaceous plants, including vegetables
Common during periods of warm days and cool, wet nights
More severe when air circulation is poor
Look for white to gray powdery appearance on leaves
May affect winter hardiness
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Black spot of rose
Affects rose species
Symptoms - black spots with fringed margins on
usually the upper leaf surface
Infected leaves turn yellow and drop from the plant
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Leaf Curl or Leaf Blister (Taphrina)
Fungus that causes blister-like distortion of leaves
Hosts include:
Peach (Peach leaf curl)
Oaks (Oak leaf blister)
Plums (Plum pockets)
All caused by Taphrina fungus respective to their host
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Peach leaf curl
Oak leaf blister
Plum pockets
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Oak leaf blister
Leaves form blisters that are at first yellow to gray, become red or brown, leaves may drop prematurely
Not usually a significant problem
May lose leaves in serious infection
Fungus overwinters in bud scales
Spores germinate in spring as buds break
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Three kinds of cedar rusts
Cedar apple rust
Junipers and crabapple or apple leaves
Cedar hawthorn rust
Junipers and hawthorn leaves
Cedar quince rust
Junipers and fruits and twigs of rose family plants, especially hawthorns
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Cedar apple rust
Forms large galls on junipers which
grow orange tendrils in spring rains
Spores are released as tendrils dry
Infection causes spots on apple leaves
Spores are released from spots
Spores landing on juniper twigs can cause galls
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Cedar Hawthorn Rust
Forms smaller galls on junipers which grow orange tendrils in spring rains
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Cedar Quince Rust Does not form galls on junipers, but lives
in trunk and twigs
Forms gelatinous masses in spring rains which release spores
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Anthracnose
A term used to designate diseases caused by
morphologically similar fungi
Some anthracnose diseases are only leaf diseases
and some also attack twigs
Common hosts are sycamores, maples, oaks, and ash
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Sycamore Anthracnose
American sycamore is host
Common fungal disease in cool, wet weather
Kills leaves, buds, shoots and one year old twigs, causes
witches brooming
Trees leaf out a second time, but pay a price in energy
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Ash Anthracnose
Symptoms: large irregular tan to
brown lesions that form on
expanding leaflets
Leaves become distorted
Damage is aesthetic
Disease overwinters in fallen leaves
In spring, spores are blown onto
newly emerging leaves
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Oak Anthracnose
Can show three different patterns depending on when leaves were infected
When infected early, young leaves brown and shrivel
When infected later, large irregular dead areas on distorted leaves
When infected late, small necrotic spots on leaves
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Guignardia leaf blotch
Common on horse chestnuts and buckeyes
Brown leaf blotches with a yellow border
Can see black pepper-like fruiting bodies
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Canker Diseases
Causes dieback and wilting
Cankers form on infected bark and sapwood beneath
canker becomes discolored brown
Disease is more severe on stressed plants
Usually a chronic problem
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Thyronectria canker
Most common canker disease on honey locusts
Cankers girdle branches and cause branches to die
Fruiting bodies form at the junction of living tissue and dead twigs
More common on trees suffering from drought stress
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Nectria canker Perennial canker disease of
many hardwoods
Destroys cambium
No chemical control
Avoid wounding trees
Keep trees healthy
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Botryosphaeria canker Common fungal canker disease on many trees and shrubs
Common hosts: apple, ash, crabapple, dogwood, elm, holly,
honeylocust, linden, maple, mountain ash, oak, pine,
redbud, rhododendron, and sycamore
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Volutella on Boxwood
Fungal canker disease which causes stem dieback
Damage looks similar to winter injury
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Black knot
Serious fungal disease of plums and cherries
Can stunt or kill tree
Causes dark fungal galls, which eventually girdle
branch, killing it
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Vascular diseases (wilt diseases)
Verticillium wilt
Dutch elm disease
Oak wilt
Pine wilt
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Verticillium wilt
Soilborne disease that affects over 300 plants
Acute or chronic problem
Fungus produces toxins that causes tyloses to plug up xylem
Streaking seen under bark
Usually not seen until middle of summer
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Dutch elm disease
Begin seeing new infection symptoms starting in June
Initially flags are seen caused by production of tyloses
Flags enlarge and spread throughout the tree
Streaking under bark
Trees eventually die
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Oak wilt
Fungal disease
Similar action to Dutch elm disease
Tree wards off fungus by forming tyloses which plugs xylem
Branches wilt
Streaking under the bark
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Red oak group
Red oaks more susceptible than white oaks
Symptoms usually appear in late spring, early summer
Leaves turn bronze and fall off tree in summer
Kills red oaks within 4–6 weeks
Spread by beetles, root grafts
Leaves become straw
colored from the leaf tip,
but remain attached to
branches
Infection occurs in crown
Branch die back occurs
Usually takes several years
to tree to die
White oak group may
temporarily “wall-off” the
fungus
White oak group
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Bacteria (sing. Bacterium)
Microscopic organisms
Require a vector and natural opening or
wound to penetrate plant tissue
Spread by wind, rain, insects, pruning tools
Cause leaf spots, rots, bacterial galls, wilts
and cankers
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Bacterial Diseases
Bacterial blight of lilac
Crown gall
Wetwood and slime flux
Fireblight
Bacterial leaf scorch
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Bacterial blight of lilac
Leaves develop brown
spots or blotches, often
with yellow haloes, which
coalesce and may
eventually turn the entire
leaf brown
Shoots and flowers may
turn brown and limp, flower
buds turn black
Prevalent in rainy seasons
or with frequent overhead
irrigation when tissues are
succulent
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Crown gall
Bacterial disease that causes tumor-like growths on lower stem near the soil line
Gall can girdle stem and kill all growth above it
Many hosts, especially common on ground cover Euonymus
Bacteria survive in soil
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Wetwood or slime flux
Common bacterial disease on many trees, especially elms and poplars
Liquid seeps out of the tree, frequently at tree crotches
There is no satisfactory control for wetwood
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Fire blight
Bacterial disease of plants in the Rose family
Serious disease that can kill trees
Spread by pollinators, wind, rain, pruning tools
Leaves remain on the tree, look like they were scorched by fire
Sometimes see characteristic shepherd’s crook
Can see bacterial oozing in wet weather
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Bacterial Leaf Scorch
Marginal necrosis, usually with yellow edge
Most hardwoods are effected
Has not been detected at TMA
Also looks like environmental scorch
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Viruses (sing. Virus)
Sub-microscopic particles that cannot be seen with
standard microscopes
Must be in a host cell to reproduce
Cause stunting, curling, and twisting or odd coloring
Spread by insects, plant propagation, and seeds
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Viruses Wide range of host plants, especially on roses and ash trees
Yellow mottling and yellow or white ringspots and line patterns are typical symptoms. Sometimes also see poor vigor, stunting or reduced leaf size.
Need serological testing to confirm viruses
Transmitted via aphids and leafhoppers
No cure
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Nematodes
Microscopic roundworms
Found in soil and plant tissue
May be vectored by insects
Pinewood nematode is the
cause of pine wilt disease
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Pine wilt Most common in Scots pine, but found in all pines
(extremely rare in white pines)
Caused by pine wilt nematode, which is vectored by the pine sawyer beetle
First symptom is gray green needles which progress rapidly to yellow, then brown
Trees die in less than one season
Occurs midsummer to late fall or late winter to spring
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Foliar nematodes
Angular leaf spots
Columbine, begonia, Cyclamen, Gerbera, Hibiscus,
geranium, Brunnera, Hellebore
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Phytoplasmas
Microscopic pathogens
Cause growth distortion,
stunting, witches brooming,
and yellowing
Cause “yellows” diseases
(Ash and elm)
Found only in phloem
Vectored by phloem feeding
insects such as leafhoppers
Electron microscopy of cross-section of gladiolus phloem tissue infected with
phytoplasma. Numerous phytoplasma bodies are apparent in the upper sieve
elements. The sieve element in the lower left-hand corner is apparently free of
phytoplasma bodies. x6000. Courtesy of Assunta Bertaccini.
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Yellows Symptoms
Ash Elm
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Common Conifer Diseases
Needle diseases more serious than leaf spots because evergreens cannot refoliate
Dothistroma needle blight
Rhizosphaera needle blight
Diplodia (i.e. Sphaeropsis) tip blight
Phomopsis
Cytospora Canker
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Dothistroma needle blight
Affects Austrian and ponderosa pines
Red and Scots are resistant
Begins with brown spots and bands on needles, eventually needle turns brown with base remaining green
Fungal spores are released during wet weather any time during the growing season from May to October
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Rhizosphaera Needle Cast
Common on stressed blue spruce
Likes warm, wet weather
Infects new growth, but they do not show symptoms until fall or early spring
One year old needles fall off, can see fruiting bodies in rows on needle
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Stigmina
Identified in 2006
Similar symptoms as Rhizosphaera
Photos by Jim Walla Photos by Justin Knott
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Diplodia tip blight (i.e. Sphaeropsis)
Common fungal disease of stressed pines
Common on Austrian, Scots, mugo, and red pines
Disfiguring disease that kills new shoots
New needles are stunted, twisted, and killed
Sometimes see resin exudation
Starts on lower branches
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Phomopsis
Fungal disease of junipers
Causes tip blight of branches, only new
growth is effected
Initially starts as yellow spots, progresses
into shoots
Tips become light green and then reddish
brown, eventually gray
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Cytospora canker
Common fungal disease of spruces, especially Colorado and Norway
Affects older trees (at least 15 years old and 20 feet tall)
In spring, needles turn purple, brown and fall off
Kills older branches and progresses upwards
More common on stressed trees
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Root Rot Infections
Symptoms
Uniform canopy dieback, leaf drooping, almost like
drought stress, brown or black roots, sloughing roots
Fungal pathogens
Phytophthora, Pythium, Armillaria, and Rhizoctonia
Bacterial soft rot
Due to excess moisture
Soil will smell acrid and sour
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Above-ground Root Rot Symptoms
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Below-ground Root Rot Symptoms
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Fungal decay
Mushrooms at the base of
the tree
Conks on the stem
Mycelial mats found
under sloughing bark
Sometimes sunken or
darkened areas on the
stem
conk : a shelf-like, typically hardened basidiocarp of a
wood decaying fungus, usually a polypore
(Ganoderma applanatum). www.APSnet.org
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Bacterial Soft Rot
Found in areas with excessive moisture
Soil will smell acrid, pungent, and swampy
Bark of dying roots will easily slough off and dying
roots will be discolored tan-brown
Fine roots will be black (dead)
Canopy will have symptoms of water stress,
dieback, and wilt
Plants recover when water is removed
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Armillaria root rot
Common landscape disease on
700 plant species
Kills roots and lower trunk
Above ground symptoms are
similar to other diseases – early
fall color leaf drop, stunted or
yellow leaves, dieback
Can infest fast or slow
Look for white, fan-shaped
mycelia under the bark on major
roots and at base of trunk
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Information for Diagnosis
Need a good history of the problem
Host plant (name, accession number)
Weather conditions (day, week, or month)
Type of care given (herbicide use, mulching, pruning)
Condition of surrounding plants (turf, wet areas,
competing plants, surrounding symptomatic plants)
Soil moisture
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Identify the plant
• Family, genus, species, and cultivar, if possible • What are the environmental
requirements for the plant?
• Are these needs being met?
• Each plant has its growing conditions that it thrives in • Water, nutrients, soil pH, sunlight
• Determine the age of
the tree
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Identify the plant
• Each plant has its own set of common diseases, insect problems and cultural needs • Biotic: fungi, bacteria, viruses,
phytoplasmas, insects
• Abiotic: pollution, mechanical damage, poor planting space, environmental
• Establish what a healthy plant
would look like
• Seasonal variation, weather
Tilia platyphyllos 'Laciniata'
Herbicide damage
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What is normal for the plant?
What is perfectly healthy for one species may be a symptom of a
serious problem for a different species
Resin on bristlecone pine Pine needle scale
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What’s the plant’s history
• When was the plant put in the ground?
• Was it planted correctly?
• Has anything changed around the plant?
• What sort of care has it received in the past?
• Consider fertilization, mulching, pesticide spray program
• Check the depth and location of the mulch
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Abnormal symptoms
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Look for Patterns
• Are other plants in the vicinity affected?
• Non-uniform damage patterns
• Uniform damage patterns
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Non-uniform patterns
• Random branches on a plant
• Usually caused by living factors
• Insects or pathogens
• Specific symptoms and signs
• Limited to a one or a few hosts
• Plants within a family or genera
• Initially do not see wide-spread damage
• Takes time to multiply and spread
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Uniform damage patterns
• All leaves of a certain age affected
• Are there symptoms of dieback and re-sprouting?
• Damage seen over a wide area
• Neighborhood, city, street, yard
• Usually caused by nonliving factors
• Frost, drought, flooding, chemicals, construction
• Multiple plant species may be involved
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What is the environmental history?
• Winter temperatures
• Late frost
• Hail storms
• Water
– Drowning and drought have
similar symptoms
• Sources of water
• Exposure to sun Cold damage on thin-leaved hostas
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Environmental observations
• Includes soil characteristics – Construction fill, soil type, clay content, soil moisture, pH
• Construction history, grade changes
• Identify surrounding plants – Competition or allelopathies
• Growth restrictions – May have originated at planting
• Sources of abiotic stress – Salt, exhaust, mechanical damage, stem-girdling roots
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Define the abnormality
• Try to determine the primary problem and plant part
where the initial damage occurred
• Sometimes there is more than one problem
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Time Development of Damage Pattern
• Observe the development of the pattern
• Direction of dieback
• Damage caused by living organisms are progressive and
spread with time
• Damage caused by nonliving organisms are not
progressive and do not spread with time and usually
effect several species in the area
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