1. Chile Pepper vs Soilborne Pathogens: Can the plant win?
Michael Matheron
Extension Plant Pathologist & Professor
Yuma Agricultural Center

2. Known diseases of pepper
Cause
Number
Bacteria 4
Fungi and Oomycetes 14
Viruses 17
Nematodes 10
Parasitic seed plant 1
Postharvest
TOTAL 50
From Compendium of Pepper Diseases

3. Phytophthora blight
Verticillium wilt
Rhizoctonia root rot

4. Phytophthora blight Verticillium wilt Rhizoctonia root rot
All caused by soilborne pathogens
Adapted to live and survive in soil
Invisible to the naked eye

5. Questions related to disease
What is the problem ?
What is the cure ?

6. Questions related to plant diseases
What is the problem ?
What can I do to prevent or manage the problem ?

7. To effectively manage a plant
disease, we need to know what affects its development

8. Requirements for disease development
severity
Susceptible
Host
plant
Favorable
environment
Virulent pathogen

9. Phytophthora blight of pepper. Pathogen: Phytophthora capsici
Phytophthora blight of pepper Pathogen: Phytophthora capsici First described in 1922 in New Mexico Phytophthora means ‘plant destroyer’ (Greek)

10. Phytophthora blight of pepper Symptoms
Images courtesy of D. Lindsey

11. Phytophthora blight of pepper Symptoms

12. 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

15. Disease cycle for Phytophthora blight
Ristaino & Johnston. Plant Disease 83:

16. Management considerations for Phytophthora blight of pepper The host
Host resistance or tolerance to Phytophthora capsici is a desired goal

17. 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

18. Management considerations for Phytophthora blight of pepper The pathogen
Deployment of fungicides

19. Phytophthora disease management Protectant fungicides
Introduction date
Copper sulfate + lime (Bordeaux mixture)
1885
Cuprous oxide and other copper salts
1932
Dithiocarbamates (Zineb, Maneb, Mancozeb, )
Phthalimides (captan, captafol, folpet)
Triphenyl tin compounds (fentin acetate or fentin hydroxide)
1954
Chlorothalonil
1963

20. Phytophthora disease management Systemic fungicides
Introduction date
Isoxazoles (hymexazol)
1974
Cyanoacetamide Oximes (cymoxanil, Curzate)
1976
Phenylamides (metalaxyl, mefenoxam, Ridomil)
1977
Phosphonates (fosetyl-Al, Aliette; phosphorous acid salts)
Carbamates (propamocarb, Previcur)
1978
Dimethomorph (Acrobat, Forum)
1988
Dinitroanilines (fluazinam, Omega)
1992
Strobilurines (azoxystrobin, kresoxim-methyl)
Zoxamide
2004

21. 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
Ethaboxam
Fluopicolide
Presidio 43
Respiration
Strobilurines
Cabrio, Flint, Quadris 11
Famoxadone
Component of Tanos
Fenamidone
Reason
Cyazofamid
Ranman 21
Fluazinam
Omega 29
Ametoctradin
Component of Zampro 45
Cell wall biosynthesis
Dimethomorph
Forum 40
Mandipropamid
Revus

22. 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.
Oxathiapiprolin
Orondis
U 15
Multisite contact activity
Copper salts
Kocide, etc.
M 1
Mancozeb
Manzate, Dithane
M 3
Chlorothalonil
Bravo
M 5

23. 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

24. Management considerations for Phytophthora blight of pepper The environment
Predisposition of plants to disease
Drought stress
Waterlogged soil
Soil salinity

25. Verticillium wilt of pepper. Pathogens: Verticillium dahliae
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.

26. Verticillium wilt of pepper. Pathogens: Verticillium dahliae
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

27. Verticillium wilt of pepper:
Symptoms
Images courtesy of D. Lindsey

28. Disease cycle for Verticillium wilt
Courtesy of Berlanger and Powelson

29. Verticillium microsclerotia forming on dying plant tissue
Courtesy of Berlanger and Powelson

30. 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

31. 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

32. Verticillium wilt of pepper Management after harvest
Propane flaming
Destroy Verticillium microsclerotia in crop residue
Peppermint field

33. Rhizoctonia root rot of pepper. Pathogen: Rhizoctonia solani
Rhizoctonia root rot of pepper Pathogen: Rhizoctonia solani Origin of the name ‘Rhizoctonia” rhiza (Greek for ‘root’) ktonos (Greek for ‘murder’)

34. Rhizoctonia root rot of pepper:
Symptoms
Courtesy of G. Holmes Courtesy of P. Bosland

35. Rhizoctonia solani

36. Disease cycle for Rhizoctonia diseases
From Agrios, et al.

37. 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

38. 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