Transcript Top Plant Diseases in the Home Landscape

Sustainable Management of
Common Plant Diseases in the
Landscape
Dr. Elizabeth Little
Department of Plant Pathology
University of Georgia
Plant Disease Triangle
Host
Pathogen
Stressed or
injured plant
Disease
Capable of causing
disease (many are
host specific)
Environment
WATER!
(wet foliage or soils, high humidity, poor air circulation)
Types of Plant Diseases
• Root and crown problems
– Root rots, crown rots, nematodes, galls,
drought, overwatering, poor planting, poor
soil, inappropriate site
• Foliage and stem diseases
– Leaf spots, cankers, herbicide damage
• Systemic diseases
– Viruses, bacterial scorch, aster yellows
Soil and Fertility Management
• Healthy plants resist disease
• Proper site preparation will avoid
many problems.
• Right plant/right place
• Promote healthy plants and healthy
soils with:
– Compost amendments
– Mulching
– Nutrient additions
• Most plant health
problems in the
landscape are due to a
problem with the roots
or soil, but diagnosis of
root problems can be
confusing
• The above ground
symptoms of any root
stress will look the
same, even though root
stress can have
different causes: poor
nutrition, drought, soil
compaction, or root
disease
Root Disease
Symptoms
• Wilting
• Stunting
• Leaf yellowing and
drop
• Softening and
discoloration of
roots and stems,
• Branch dieback
• Plant death
Pythium root rot
Armillaria
• Most plants you
buy already have
some root rot
• Prevent root rot:
– Plant high
– Improve soil
drainage
– Redirect water
– Do not over-water
– Do not overfertilize
– Right plant/right
place
• Root rot diseases in the landscape are often
associated with improper planting, irrigation,
or site preparation
Juniper Dieback
Junipers like dry, sunny conditions, and do not like poorly
drained sites
Most fungal leaf spots are mostly an
aesthetic problem
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Oak leaf blister
• Phyllosticta leaf spot
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Spot anthracnose
• Discula leaf spot (birch)
Cercospora leaf spot on Hydrangea
Black spot
of rose
Leaf Symptoms
Management of Black Spot
• Sanitation (destroying leaves, cutting
back diseased canes)
• Mulching each year
• Resistant cultivars!!
• Increase air flow, plant in full sun
• Keep leaves dry when irrigating
• Fungicide Sprays (protectants every 7
to 12 days or systemics)
Seiridium canker on Leyland Cyprus
• Very common
• Drought-stressed and wounded trees
• Irrigate trees during periods of drought
Mycosphaerella
leaf spot on iris
Entomosporium leaf spot
on red-tip (Photinia)
Prolonged leaf wetness, high humidity and poor
air circulation increases foliar diseases
Defoliation on Photinia due to Entomosporium leaf
spot disease, overcrowding, and poor air circulation
Entomosporium on Indian Hawthorne
Resistant Cultivars Available
Powdery Mildew
• Reduces yield and weakens plants
• Surface mycelium – easy to diagnose
• Some survive as spores in debris, others blow
in each year (cucurbit powdery mildew)
• Management:
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Damage is minimal in most plants
Some cultivars with resistance
Increase air circulation
Sulfur - oldest fungicide, not very efficacious
Sodium and Potassium Bicarbonate
Ultrafine oils interfere with infection
Biologicals
Powdery mildew
Rust diseases
• Very complex lifecycles
– Autoecious: one host (geranium rust)
– Heteroecious: two hosts (daylily rust,
cedar-apple rust, fusiform rust)
• Spores are spread by wind and
water-splashing
• Fungicides usually not needed for
landscape plantings.
• Resistant cultivars are better
options in crop plants.
Daylily rust
• Yellow spots on
upper side of leaf
• Orange spores
directly beneath on
leaf underside
• Destroy infected
leaves
• Resistant cultivars
• Fungicides
Cedar-apple
rust
• Orange telial horns
disperse spores to
apples, crabapples in
spring
• Leaf spots and fruit
distortion occur on
apple/crabapple
• Spores then spread
back to cedar in
summer
Cedar apple
rust on
crabapple
Cedar Quince Rust
Fire blight of apple, pear, crabapple,
pyracantha, cotoneaster, photinia
• Occurs in warmer, wet springs
• Secondary summer infections can occur
during wet years
• Prune affected branches to reduce spread
What’s wrong
with my tree?
• “We” cause the majority
of tree decline problems
• Construction damage,
mechanical injury,
improper planting,
girdling roots, and
compacted soils all
stress trees
• Natural events also
contribute, i.e. drought,
lightning, fire, etc.
• Disease and insects
Red Maple
with Gradual
Dieback
Can you spot
the cause of
this decline?
Bacterial Scorch of
Sycamore – many
tree species are
susceptible, no cure
Phytoplasma Disease – Aster Yellows
• Cause stunting and color
deformities
• Systemic bacteria in phloem
• Interfere with growth and
development
Viruses – no cure,
inspect planting material
Ring spot symptom – always a
virus disease
Herbicide Damage
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Root-knot nematodes are common
Plants are stunted, roots galled
Healthy plants can resist infections
Some plant species more resistant
When a disease problem is suspected,
obtain background information:
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Pattern in landscape
Number of plants affected
Part of plant affected
Irrigation time/frequency/areas
Recent weather conditions
Chemicals used on or near the site, rates
Fertilizer applied (rate, form of application)
Insects present