Control of Phytophthora Diseases on Floral Crops ARS Project Number: Control of Phytophthora and Botrytis Diseases,and Deer and Rabbit Herbivory of Floral and Nursery Crops. Dr. Mary K. Hausbeck Department of Plant Pathology Michigan State University

Project Objectives Identify the major Phytophthora spp. affecting floriculture production and determine which aspects of Phytophthora’s life history contribute significantly to control failure.Identify the major Phytophthora spp. affecting floriculture production and determine which aspects of Phytophthora’s life history contribute significantly to control failure. Develop durable production strategies for preventing and eliminating diseases caused by Phytophthora on floriculture hosts.Develop durable production strategies for preventing and eliminating diseases caused by Phytophthora on floriculture hosts. Screen novel agents for their potential as management tools for the control of Phytophthora crown and root rots.Screen novel agents for their potential as management tools for the control of Phytophthora crown and root rots.

Phytophthora Diseases

Phytopthora spp. Characterization Phytopthora spp. Characterization Phytophthora spp. were recovered from eight floricultural hosts at eleven different facilities.Phytophthora spp. were recovered from eight floricultural hosts at eleven different facilities. The isolates were identified to species using standard morphological traits and by comparing ITS regions (I & II) to the GenBank DNA database.The isolates were identified to species using standard morphological traits and by comparing ITS regions (I & II) to the GenBank DNA database. Isolates were characterized by comparing compatibility type and mefenoxam sensitivity and by analyzing AFLP fragments.Isolates were characterized by comparing compatibility type and mefenoxam sensitivity and by analyzing AFLP fragments.

Summary data for Phytopthora spp. collected from floriculture production facilities. Host Phytophthora spp. No. of isolates Compatibility Type MefenoxamSensitivity Poinsettia (2000) P. drechsleri 52A1Sensitive Poinsettia (2001) P. drechsleri 17A1Intermediate Snapdragon (2000) P. nicotianae 120A2Sensitive Snapdragon (2000) P. nicotianae 75A2Sensitive Snapdragon (2001) P. nicotianae 10A2Sensitive Fuchsia (2000) P. nicotianae 15A2Resistant Vinca (2001) P. nicotianae 10A1Sensitive Verbena (2001) P. nicotianae 12A1Sensitive Bacopa (2001) P. nicotianae 20A1Sensitive Verbena (2001) P. nicotianae 20A1Sensitive African Violet (2001) P. nicotianae 30A2Sensitive Dusty Miller (2001) P. nicotianae 30A2Sensitive Verbena (2001) P. nicotianae 2A1Sensitive

Phytophthora Characterization Results Phytophthora drechsleri was the dominant pathogen of poinsettias.Phytophthora drechsleri was the dominant pathogen of poinsettias. Phytophthora nicotianae was the most frequently isolated pathogen for other crops.Phytophthora nicotianae was the most frequently isolated pathogen for other crops. Both compatibility types were found for Phytophthora nicotianae.Both compatibility types were found for Phytophthora nicotianae.

Phytophthora Characterization Results Phytophthora nicotianae isolates were identified that were resistant to mefenoxam.Phytophthora nicotianae isolates were identified that were resistant to mefenoxam. Within a facility, Phytophthora epidemics were the result of a single clonal lineage.Within a facility, Phytophthora epidemics were the result of a single clonal lineage.

Fungicide Efficacy Trials

Rate/100 gallons 21 day interval

Untreated Untreated Uninoculated Untreated Inoculated

Acrobat 50WP 6.4 oz/100 gal Untreated Uninoculated

Subdue MAXX 21.3 EC 1.0 fl oz/100 gal Untreated Uninoculated

Truban 30WP 10.0 oz/100 gal Untreated Uninoculated

Rate/100 gallons 14 day interval

Rate/100 gallons 14 day interval

Untreated Untreated Uninoculated Untreated Inoculated

Acrobat MZ 69WP Untreated Inoculated Acrobat MZ 69WP 1.75 lb/100 gal

Subdue MAXX 21.3EC I.0 fl oz/100 gal Untreated Inoculated

Results and Potential Value An understanding of mefenoxam sensitivity has reduced growers’ costs by encouraging alternative management measures in situations where resistance has become an issue.An understanding of mefenoxam sensitivity has reduced growers’ costs by encouraging alternative management measures in situations where resistance has become an issue. Dimethomorph, mefenoxam and etridiazole have all shown promise in the control of Phytophthora diseases.Dimethomorph, mefenoxam and etridiazole have all shown promise in the control of Phytophthora diseases.

Technology Transfer Publication in trade magazines and professional journals.Publication in trade magazines and professional journals. Publication in on-line newsletters.Publication in on-line newsletters. Presentation at grower meetings.Presentation at grower meetings.

Project Team Dr. Mary Hausbeck (Michigan State University)Dr. Mary Hausbeck (Michigan State University) Dr. Steve Wraight (Cornell, USDA-ARS)Dr. Steve Wraight (Cornell, USDA-ARS) Contributors to Research Dr. Kurt LamourDr. Kurt Lamour Jeffrey WoodworthJeffrey Woodworth Blair HarlanBlair Harlan Nicole WernerNicole Werner Amanda GevensAmanda Gevens Matthew BourMatthew Bour Pavani TumbalumPavani Tumbalum

Additional Funding Sources IR-4 Ornamental Trials on Phytophthora, $2,000.IR-4 Ornamental Trials on Phytophthora, $2,000.