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?