Chile Pepper vs Soilborne Pathogens: Can the plant

Chile Pepper vs Soilborne Pathogens: Can the plant

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 or leaves, about a point on an axis. A whorl. flowers 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

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