Disease Management
Terry Kirkpatrick, Plant Pathology
M. Elena Garcia, Horticulture
University of Arkansas
Plant Disease
A malfunction of one or more plant
systems due to continuous irritation
that results in some symptom
– Horsfall &Cowling, 1977
At least 90% of plant disease control is
accomplished through proper cultural methods
and sanitation.
Unfortunately, modern agriculture sometimes ignores
the fundamental concepts for convenience.
Types of Diseases
Biotic: result of infection of plant by a
pathogen; able to spread to healthy plants
Types of pathogens: fungi, bacteria, viruses,
nematodes, parasitic plants
Abiotic: result of environmental or cultural
problem; cannot be transmitted
Types: light, temperature, hail, lightning, fire,
wire girdling, pot-bound roots, air pollution,
chemical injury, herbicide injury, nutrient
deficiencies, chemical toxicity
Biotic Diseases
Fungi ------ ~80%
Bacteria ----- ~15%
Nematodes ----- <5%
Viruses ------ <5%
The Disease Triangle
Disease development
depends on:
1. Presence of pathogen
Amount of disease
HOST
Total of conditions favoring
susceptibility
(source of inoculum)
2. Host- Plant
susceptibility
3. Environmental
conditions must be
favorable (light,
moisture,
temperature, soil
fertility)
HOST
Immune-no association other than coincidental
causal entity (pathogen) has no effect.
Susceptible – unable to suppress a pathogen;
adverse response of plant to causal organism
Resistant-ability to suppress the activity of
a pathogen; may or may not have
adverse effect on plant.
Susceptible
Resistant
Pathogen – an organism that is
capable of causing disease
Virulence – relative ability of the pathogen
to cause disease
Avirulence – inability of a pathogen to cause
disease
Virulent
Avirulent
In order for disease to occur, both a susceptible host and a
virulent pathogen must be present
You can’t control the weather……
But you can control the
plant’s environment, at
least to some degree
Environment
Pathogen
Environmental Manipulation
Host
Environmental management for disease
control
• Irrigation: availability; quality; type
• Site selection
• Pruning; thinning; trellising; plant spacing; row
spacing
• Beds vs. flat planting
• Annual vs. perennial (strawberry)
• Mulching
• Fertility; pH; overall plant nutrition balanced
• Timely harvest
How do diseases Spread?
Soil-borne diseases
Wind-borne diseases
Seed-borne diseases
Vector-transmitted diseases
Soil-Borne Diseases
Introduced into soil
Inoculation
Wind
Infected seeds
Infected transplants
Other infected plants
Contaminated tools
Water
Crop residues provide an environment for
pathogen
Can affect roots or any part of the plant
Smut, bacterial wilt, fusarium wilt, dampening-off
Wind-Borne Diseases
Spore transportation
May be great distances
Transport directly to aerial potions of
plants
Inoculate soil
Rusts, powdery mildew, late and early
blight of tomato, apple scab
Seed-Borne Diseases
Recommended to purchase certified
disease-free seeds
Seed sterilization
Bacterial blights and anthracnose of
peas
Potato ‘seeds’
Viral diseases may spread by seeds
Vector-Transmitted Diseases
Insects
Carried from plant to plant on the
mouth parts of insects
People
Pruning
Nematodes
Fungi
Epidemiology
1. Single cyclic disease – most soilborne
pathogens.
70
60
50
40
Disease
30
20
10
0
Time
Epidemiology
1. Multicyclic disease – Foliar pathogens
100
90
80
70
60
50
40
30
20
10
0
stationary
exponential
Disease
lag
Time
Moisture on foliage is a primary factor.
Symptoms caused by fungi:
May be local or general
Necrotic symptoms
Leaf spots
Blight
Canker
Dieback
Root rot
Damping-off
Basal stem rot
Soft or dry rot
Anthracnose
Scab
Decline
Excessive growth
symptoms
Clubroot
Galls
Warts
Witches’ brooms
Leaf curls
Additional symptoms
Wilt
Rust
Smut
Mildew
Fungal Symptoms
Anthracnose- Pumpkin
Anthracnose- Strawberry
Sherrie Smith, University of Arkansas, Cooperative
Extension
Sherrie Smith, University of Arkansas, Cooperative
Symptoms caused by bacteria:
Galls: crown, twig, or
cane
Hairy root
Soft rots
Cankers
Wilt
Scab
Blight
Leaf spots
Root nodules of
legumes
Fire blight
Sherrie Smith, University of Arkansas Cooperative Extension
Bacterial Symptoms
Cabbage Black Rot
Watermelon Bacterial
Fruit Blotch
Sherrie Smith, University of Arkansas, Cooperative
Extension
Symptoms caused by viruses:
May occur on any part
of plant
Stunting
Premature death
Mosaics
Mottling
Streak
Ring or line pattern
Vein clearing
Vein banding
Chlorotic spots
Ring spots
APLPV - American Plum Line
Pattern Virus - Plums
Sherrie Smith - University of Arkansas, Cooperative Extension
Pictures of Viral Symptoms
Bean- Yellow Mosaic Virus
Sherrie Smith, University of Arkansas, Cooperative
Extension
Tomato-Tobacco Mosaic
http://www.avrdc.org/LC/tomato/tomv/html
Some Symptoms caused abiotic
diseases:
Low temperature
Late frost tip or bloom
necrosis
Bark split
Internal branch necrosis
Winter drying of
evergreens
Cold water rings
Leaf margin necrosis
Frost injury to fruits
High temperature
Sunscald on fruit
Water core
Blossom end rot (citrus)
Light
Etiolation (low light)
Scald (high light)
Low moisture
Leaf scorch
Wilting
High moisture
Flood damage
Oedema
Rot
Low oxygen
Black heart of tubers
Some Symptoms caused abiotic
diseases:
Herbicide injury
Leaf or fruit
deformities
Chlorosis
Necrosis
Stunting
Death
Grazon Damage
Sherrie Smith, University of Arkansas,
Cooperative Extension
Air pollution
Chlorosis
Bleached leaves
Stunting
Leaf margin necrosis
Premature
defoliation
Ozone-damaged plant (left) and normal plant (right)
Photo courtesy NARA, photographer Gene Daniels/U.S. EPA
Managing Plant Diseases
Manage cropping system in a way that prevents
disease from occurring
Identify disease
Biotic or abiotic
Fungi, bacteria, virus, or nematode
Foliar or soil-borne
Take disease triangle into consideration:
Improve quality and ability of host to withstand disease
Reduce or eliminate populations of pathogens
Encourage environmental conditions favorable for
hosts and unfavorable for pathogens
Why is Disease ID Important?
Altering irrigation system to reduce leaf
wetness will help against foliar disease,
but not soil-borne disease
Crop rotations affect soil-borne disease,
but not wind- or insect-dispersed
diseases
Fungicides control fungal disease, but
not viruses
Sanitation: A Key Strategy to
Disease Prevention
Plant in sites free of
disease
Clean equipment to
prevent spread of disease
through fields
Clean pruning tools in
10% bleach solution
between cuts
Remove crop residue to
reduce inoculum buildup
Remove weeds that may
serve as pathogen host
Prune diseased portion
from plants
Remove severely infected
plants from field
Prevent further spread of
viruses
Properly dispose of infected
debris
Place infected debris in
center of hot compost heap
Burn debris
Place in sealed container in
trash
Cultural Practices to Improve
Host Health
Choose resistant cultivars
Avoid excess or deficient
crop nutrition
Use transplants rather
than seeds to avoid
exposure to soil-borne
seedling diseases
Plant seeds shallowly to
limit pathogen exposure
Correctly prune woody
plants to improve air
circulation and light
infiltration
Scab resistant apple cultivar
‘Liberty’ (left) with susceptible
cultivar ‘McIntosh’ (right)
Cultural Practices that may
reduce pathogen presence
Adjust soil pH
Liming negatively
affects some fungal
pathogens (e.g. club
root )
Increasing pH inhibits
survival of some
bacteria (e.g. scab,
cotton root rot)
Prune out diseased
portion of plants to
avoid further spread
Crop rotations break
cycle of certain
pathogens
Spatially: move
location of species
within field
Temporally: grow
different species from
year to year
Keep in mind many
pathogens attack
numerous species
within a plant family
Cultural Practices that affect
environmental conditions
Use appropriate types of
irrigation
Overhead irrigation
encourages spread of
foliar disease
Avoid overwatering
Improve soil drainage
Improve air circulation
through wider row
spacing, decreased
planting density, and
pruning
Time tasks appropriately
Cool soils slow
germination of many
seeds (e.g. corn, beans),
increasing susceptibility to
soil-borne disease
Late-season pruning or
fertilization discourages
hardening-off, increasing
occurrence of abiotic
disease (e.g frost injury)
Post-harvest cold storage
to delay growth of soft rots
Physical Control
Soil solarization
Increased
temperatures due to
solar heat kill many
soil-borne pathogens
near soil surface
Cover soil with clear
plastic
Soil temperatures
may reach 52°C
Biological Control
Limited options for disease
control
Increase diversity of soil
microbes through proper
soil management and
addition of organic matter
Cross-protection
Inoculation of plant with mild
strain of disease to provide
protection against more
virulent strains
Example: Galltrol-A®;
nonpathogenic strain of
Agrobacterium; protects
against crown gall
Coniothyrium minitans
Fungal pathogen of
Sclerotinia sclerotiorum and
S. minor (cause of white
mold on cole crops, carrots,
and beans
OMRI-Listed product:
Contans® WG
Other control
Chemical Control
Potassium-, Sodium-, or AluminumBicarbonates
Formulations differ in efficacy against certain
diseases (e.g. Potassium bicarbonate more
effective in control of powdery mildew)
Studies have found a variety of
concentrations most effective, ranging from
0.5-2%
Some benefit seen from addition of surfactants
Foliar burning resulted when concentration too
high
OMRI-Listed products: Kaligreen® and
MilStop® broad spectrum foliar fungicide
Chemical Control
Sulfur : prevents fungal spores from
germinating; phytotoxic
Also has some insecticidal and acaricidal
properties
Toxic to beneficial insects, fish, mammals
Should not be used if oil has been sprayed
in the previous month
Chemical Control
Lime-sulfur: kills recently germinated fungal spores
phytotoxic
Spraying during high temperatures (>85F) increases
phytotoxicity
Toxic to mammals
Copper: inhibit growth and germination of spores
phytotoxic
Labeled for use on over 100 crops to control fungal and bacterial
diseases
Should be used with care due to toxicity to several non-target
species
OMRI-Listed products: Champion WP ®, Crop Clean COCS ®,
Britz Copper Sulfur 15-25 Dust ®, Nordox 75WG ®, Concern®
Copper soap Fungicide, Cueva Fungicide Concentrate ®, Cueva
Fungicide Ready to Use ®, Lilly Miller Ready to Use Cueva
Copper Soap Fungicide®
Resources
http://www.nysaes.corne
ll.edu/pp/resourceguide/
http://www.longislandhort.corn
ell.edu/vegpath/photos/index.
htm
http://ipmnet.org/plantdisease/glossary.cfm
http://plantpathology.uark.edu/
2539.htm
http://plantclinic.cornell.edu/
http://www.ag.auburn.edu/hort
/landscape/exam_pics.html#di
seases
Acknowledgements
This presentation address general organic production practices. It is to be
to use in planning and conducting organic horticulture trainings. The
presentation is part of project funded by a Southern SARE PDP titled
“Building Organic Agriculture Extension Training Capacity in the
Southeast”
Project Collaborators
•
Elena Garcia, University of Arkansas CES
Heather Friedrich, University of Arkansas
Obadiah Njue, University of Arkansas at Pine Bluff
Jeanine Davis, North Carolina State University
Geoff Zehnder, Clemson University
Charles Mitchell, Auburn University
Rufina Ward, Alabama A&M University
Ken Ward, Alabama A&M University
Karen Wynne, Alabama Sustainable Agriculture Network