Download Can the Plant Win? - Chile Pepper Institute

Chile Pepper vs Soilborne Pathogens:
Can the plant win?
Michael Matheron
Extension Plant Pathologist & Professor
Yuma Agricultural Center
[email protected]
Known diseases of pepper
Cause
Number
Bacteria
4
Fungi and Oomycetes
14
Viruses
17
Nematodes
10
Parasitic seed plant
1
Postharvest
4
TOTAL
50
From Compendium of Pepper Diseases
• Phytophthora blight
• Verticillium wilt
• Rhizoctonia root rot
Phytophthora blight
Verticillium wilt
Rhizoctonia root rot
All caused by soilborne pathogens
– Adapted to live and survive in soil
– Invisible to the naked eye
Questions related to disease
•
What is the problem ?
•
What is the cure ?
Questions related to plant diseases
•
What is the problem ?
•
What can I do to prevent or manage
the problem ?
To effectively manage a plant
disease, we need to know
what affects its development
Requirements for disease development
Susceptible
Host
plant
Disease
severity
Favorable
environment
Virulent pathogen
Phytophthora blight of pepper
Pathogen: Phytophthora capsici
First described in 1922 in New Mexico
Phytophthora means ‘plant destroyer’
(Greek)
Phytophthora blight of pepper
Symptoms
Images courtesy of D. Lindsey
Phytophthora blight of pepper
Symptoms
Oomycetes initially described as fungi,
but over time, significant differences
compared to true fungi became apparent
Characteristic
Oomycetes
True fungi
Primary cell wall component Cellulose
Chitin
Vegetative nuclear state
Diploid
Haploid
Asexual spores with flagella
Yes
No
Several biochemical differences as well, such as
Reaction to specific fungicides
Disease cycle for Phytophthora blight
Ristaino & Johnston. Plant Disease 83:1080-1089
Management considerations for
Phytophthora blight of pepper
The host
Host resistance or tolerance to Phytophthora
capsici is a desired goal
Management considerations for
Phytophthora blight of pepper
The pathogen
Inoculum avoidance
– Use plants and transplants free of the pathogen
Inoculum survival
– Crop rotation to nonhost plants
– Solarization of soil
– Some organic amendments can affect survival of
Phytophthora in soil
Management considerations for
Phytophthora blight of pepper
The pathogen
Deployment of fungicides
Phytophthora disease management
Protectant fungicides
Protectant Fungicide
Introduction
date
Copper sulfate + lime (Bordeaux mixture)
1885
Cuprous oxide and other copper salts
1932
Dithiocarbamates (Zineb, Maneb, Mancozeb, 1951-1962)
1931-1962
Phthalimides (captan, captafol, folpet)
1949-1965
Triphenyl tin compounds (fentin acetate or fentin
hydroxide)
1954
Chlorothalonil
1963
Phytophthora disease management
Systemic fungicides
Systemic Fungicide
Introduction
date
Isoxazoles (hymexazol)
1974
Cyanoacetamide Oximes (cymoxanil, Curzate)
1976
Phenylamides (metalaxyl, mefenoxam, Ridomil)
1977
Phosphonates (fosetyl-Al, Aliette; phosphorous acid salts)
1977
Carbamates (propamocarb, Previcur)
1978
Dimethomorph (Acrobat, Forum)
1988
Dinitroanilines (fluazinam, Omega)
1992
Strobilurines (azoxystrobin, kresoxim-methyl)
1992
Zoxamide
2004
Fungicides active against Phytophthora
Target site
Common name
Trade name
FRAC
Code
Nucleic acid
synthesis
Mefenoxam
Ridomil Gold
4
Mitosis & cell
division
Zoxamide
Gavel
22
Respiration
Cell wall
biosynthesis
Ethaboxam
22
Fluopicolide
Presidio
43
Strobilurines
Cabrio, Flint, Quadris
11
Famoxadone
Component of Tanos
11
Fenamidone
Reason
11
Cyazofamid
Ranman
21
Fluazinam
Omega
29
Ametoctradin
Component of Zampro
45
Dimethomorph
Forum
40
Mandipropamid
Revus
40
Fungicides active against Phytophthora
Target site
Common name
Trade name
FRAC
Code
Lipid synthesis and
membrane integrity
Propamocarb
Previcur
28
Unknown mode of
action
Cymoxanil
Curzate
27
Fosetyl-Al
Aliette
33
Phosphorus acid
& salts
Phostrol, etc.
33
Oxathiapiprolin
Orondis
U 15
Copper salts
Kocide, etc.
M1
Mancozeb
Manzate,
Dithane
M3
Chlorothalonil
Bravo
M5
Multisite contact
activity
Management considerations for
Phytophthora blight of pepper
The environment
Soil and atmospheric water
– Since Phytophthora is a “water mold”, water
management is critical
– Proper placement and duration of irrigation
– Enhance movement of water through soil
– Provide adequate field drainage in areas
subject to high levels of rainfall
Management considerations for
Phytophthora blight of pepper
The environment
Predisposition of plants to disease
– Drought stress
Waterlogged soil
– Soil salinity
Verticillium wilt of pepper
Pathogens: Verticillium dahliae
Verticillium albo-atrum
Verticil: A circular arrangement, as of
flowers or leaves, about a point on
an axis. A whorl.
Verticillium wilt of pepper
Pathogens: Verticillium dahliae
Verticillium albo-atrum
Verticil: A circular arrangement, as of
flowers or leaves, about a point on
an axis. A whorl.
Courtesy of Berlanger and Powelson
Verticillium wilt of pepper:
Symptoms
Images courtesy of D. Lindsey
Disease cycle for Verticillium wilt
Courtesy of Berlanger and Powelson
Verticillium microsclerotia
forming on dying plant tissue
Courtesy of Berlanger and Powelson
Verticillium wilt of pepper
Preplant management options
Plant resistant or tolerant varieties if available
Crop rotation to nonhost plants
– Verticillium has large host range (> 200 plant
species)
– Microsclerotia can persist in soil for several years
– Certain crops (broccoli) can significantly reduce
microsclerotia population in soil
Chemical soil fumigation
– Effective but expensive
– Application restrictions, loss of some products
Soil solarization
Verticillium wilt of pepper
Management options in growing season
Apply optimal rates of nitrogen & phosphorus
– Effective on some plant species
Avoid overwatering
– On young plants of some species, overwatering
increases infection and subsequent disease
severity
Verticillium wilt of pepper
Management after harvest
Propane flaming
– Destroy Verticillium microsclerotia in crop residue
Peppermint field
Rhizoctonia root rot of pepper
Pathogen: Rhizoctonia solani
Origin of the name ‘Rhizoctonia”
rhiza (Greek for ‘root’)
ktonos (Greek for ‘murder’)
Rhizoctonia root rot of pepper:
Symptoms
Courtesy of G. Holmes
Courtesy of P. Bosland
Rhizoctonia solani
Disease cycle for Rhizoctonia diseases
From Agrios, et al.
Rhizoctonia root rot of pepper
Management options
Plant resistant or tolerant varieties if available
Use fungicide treated seed
– Rhizoctonia solani has a very large host range
Avoid saturated soil
Avoid planting in soil having large amounts of
undecomposed plant residue
– Could enhance growth and survival of Rhizoctonia
solani in soils
Chile Pepper vs Soilborne Pathogens:
Can the plant win?
There is no silver bullet
Develop and deploy an Integrated Disease
Management Plan
– incorporating all tools that will contribute to
reducing disease development to the maximum
possible extent