Post on 13-Jul-2020
Strategies for Managing Phytophthora Blight
Chris Smart, Holly Lange, Amara Dunn, Lisa Jones
and Maryn Carlson Cornell University
Geneva, NY
Growing squash has become difficult!
Phytophthora Blight Phytophthora capsici
Wide Host Range
Symptoms • Wilting and plant
death – Crown and root rot
• Fruit rot • Stem and leaf
lesions
Symptoms on Squash
Phytophthora Blight Phytophthora capsici
Infected plant dies, pathogen remains in debris
If both mating types are present, oospores produced
A1 A2 Oospores can survive for years in soil, and will infect roots or fruit when conditions are favorable
Infected plants and fruit produce millions of spores
These asexual spores are called sporangia
One spore will produce 20-40 zoospores “swimmers” Pathogen spreads in water
splashing rain, irrigation
What do spores look like?
Oospores Sporangia Zoospores
Potential for rapid spread in a field
• 1 spaghetti squash…
…44 million sporangia
…880 million zoospores
Pcap in NY – what have we learned? 28 fields sampled 257 isolates
WNY
CNY CD
LI
Original samples 2006-2009 Many more fields sampled since 2009
What do we know?
• Both mating types are present in NY’s vegetable fields
• Regional differences in mefenoxam sensitivity –No resistant isolates found in WNY or CNY (2009), but we identified a field with resistant isolates in WNY in 2011 – In CD, 66% of isolates were resistant – In LI, 25% of isolates were either partially or
fully resistant
How Does Phytophthora Move?
• Culled fruit • Cultivation • Soil (tractor tires) • Rain
water/splashing • Irrigation water • Flood water • Does not move in
air/wind
Cull Piles
Surface Irrigation Water • 60% of NY vegetables are irrigated with
surface irrigation water
Irrigation Sources
Irrigation Ponds
Creeks
Erie Canal
Surface Irrigation Water • 60% of NY vegetables are irrigated with
surface irrigation water • Surveyed 20 sites across NY for
Phytophthora capsici once a month for 2 years – pathogen can be present in water
• Improving detection methods to identify pathogens quickly
• Comparing methods for decontamination
Irene and Lee
Pictures on left from the NY Times
P. capsici from flooded fields
• Collected from five fields with no history of Phytophthora blight
• Have data on isolates from three of the five fields
• Some diversity (not all isolates are the same)
• Most mefenoxam resistant – Working with growers, developing
management plans
What are we working on now?
• Making great use of the ‘blight farm’ • Testing potential resistant varieties with a
diversity of isolates from NY – Working with public and private breeders – Several projects with Michael Mazourek
• Testing isolates for fungicide resistance • Continue to study diversity, and changes
that may occur over time in the field • How do resistant varieties stop the pathogen
Management Strategies
• If you don’t have Phytophthora blight – KEEP IT OFF YOUR FARM!
• If you have Phytophthora blight – Promote good drainage – Choose tolerant varieties – Rotate – Rogue if possible – Use effective fungicides (ROTATE
CHEMISTRIES)
Management Strategies
• Commonly used fungicides – Ranman – Presidio (18-month plant-back restriction) – Gavel – Forum – Revus – Tanos – Phosphorous acid fungicides – Ridomil (perhaps once/season in Western NY)
Cucurbit Downy Mildew Pseudoperonospora cubensis
Attacks all cucurbits – cucumbers most susceptible
Cucurbit Downy Mildew
• Caused by Pseudoperonospora cubensis – A water mold related to Phytophthora
• Attacks all cucurbits – cucumbers most susceptible, but melon, pumpkin and other cucurbits also susceptible
• Present every year
Symptoms • First symptom is a
yellowing spot on the upper surface of the leaf
• Spots expand turning tan and papery, but are bordered by veins
• Lower leaf surface has gray spores
Young Lesion
Older Lesion
Bottom of Leaf
Downy and Powdery on Winter Squash
Mildews
Powdery Mildew
Downy Mildew
Downy Control • The pathogen blows in either from the
south, or from greenhouse production, and generally does not arrive until late July
• No commercially available squash resistant to the strains we have – but squash and pumpkin are less susceptible than cucumber or melon
• Vegetable news letters provide information on where downy has been reported
• Excellent website http://cdm.ipmpipe.org/ – Sign up for alerts
Downy Control • The downy mildew pathogen is closely
related to Phytophthora (both are water molds), many fungicides that are effective against downy are also labeled for Phytophthora blight
• Broad-spectrum protectant fungicides provide some control
• Follow outbreaks and know when the pathogen is in the area
• Smart lab members • Grower cooperators • Vegetable Extension
Educators • NYS Ag Expt Station • NYS Dept of Ag and
Mkts • USDA - NIFA
Thanks!
Questions?