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Managing Crop Diseases
in High Tunnels
Michelle Grabowski
© 2012 Regents of the University of Minnesota. All rights reserved.
Diseases of Vegetables
are caused by…
Bacteria
Nematode
Phytoplasma
Virus
Fungi
© 2012 Regents of the University of Minnesota. All rights reserved.
Identify the Problem
• What’s wrong with my plant? online diagnostic
tool www.extension.umn.edu/garden
• Send a sample to the UMN Plant Disease Clinic
http://pdc.umn.edu
• Knowing the pathogen allows you to
– Prevent movement of the pathogen
into and within the tunnel
– Reduce pathogen survival
– Target management strategies
Wikipedia.com
Know Your
Enemy!
© 2012 Regents of the University of Minnesota. All rights reserved.
Scout Plants Regularly
• Every 1-2 weeks, closely examine
5-10 random plants
• Examine
– Inner lower leaves
– Both sides of the leaf
– Fruit & Stems
• Find diseases before the
damage is severe
Disease Management in a
High Tunnel
© 2012 Regents of the University of Minnesota. All rights reserved.
Where Do Pathogens Come From?
• Seed – some fungi, several bacteria
• Plants, compost, potting soil etc.
• Contaminated tools, equipment, shoes
• Insects – viruses especially
• Wind and weeds
Precious Ground
© 2012 Regents of the University of Minnesota. All rights reserved.
Clean Seed
• Look for certified disease free seed
• Do not save seed from diseased plants
• Sterilize seed in hot water (118-122F, 15-30mins)
• Sterilize with bleach (25oz Chlorox: 100oz Water)
OSU Extension
OSU Extension
© 2012 Regents of the University of Minnesota. All rights reserved.
Clean Transplants
• Purchase from a reputable, local grower
• Grow your own transplants
• Start with clean pots, sterile
potting media, clean seed
www.hightunnel.org
Scout transplants for disease
Remove & destroy diseased plants
Treat neighboring plants
© 2012 Regents of the University of Minnesota. All rights reserved.
Clean Equipment & Amendments
• Use only ‘clean’ soil amendments
• Clean equipment & tools prior to use in tunnel– 10% bleach or commercial sanitizer
• Keep tools specific for high tunnel work
PA dept of Ag.
Compost should heat to 160F
© 2012 Regents of the University of Minnesota. All rights reserved.
Clean Workers
• Do not allow use of tobacco products in the
high tunnel.
• Workers should wash hands with soap and
water after use of tobacco products.
• Do not move back and forth between field
and high tunnel
• If disease occurs in one tunnel,
work in that tunnel last
SAMUEL ARANDA/AFP/Getty Images
© 2012 Regents of the University of Minnesota. All rights reserved.
Control Weeds
• Weeds crowd the crop &
increase humidity
• Weeds harbor plant pathogens
• Control weeds within the tunnel
• Control weeds around the tunnel
© 2012 Regents of the University of Minnesota. All rights reserved.
Remove Diseased Plant Material
Wilt Diseases, Bacterial Diseases, Viruses, & White Mold
Remove the entire plant as soon as possible!
© 2012 Regents of the University of Minnesota. All rights reserved.
Remove Diseased Plant Material
• Leaf, fruit and stem infections
• Remove infected parts immediately
• End of the season, remove the plant
© 2012 Regents of the University of Minnesota. All rights reserved.
Fungicides in High Tunnels
• Fungicides do not ‘cure’ disease – Must be
applied preventatively.
• Legally a ‘Greenhouse’ for pesticide application
• Cannot use pesticides in a high tunnel if – Label prohibits use in a greenhouse.
• Ok to use pesticides in a high tunnel if– Label allows greenhouse use
– Label says nothing about greenhouse use
• Read and follow all label instructions
© 2012 Regents of the University of Minnesota. All rights reserved.
Environment and Disease
• Fungi and bacteria need moisture or high humidity
to infect, reproduce, spread.
• Keeping leaves and fruit dry will significantly
reduce disease.
• Viruses, phytoplasmas and nematodes not as
directly affected by moisture.
© 2012 Regents of the University of Minnesota. All rights reserved.
Managing High Tunnel Environment
• Many fungi and bacteria spread on splashing water
• Use drip irrigation
• No splashing water from rain or irrigation
Septoria Leaf Spot
© 2012 Regents of the University of Minnesota. All rights reserved.
Leaf Diseases in High Tunnels
• Fungi that need high humidity
or dew thrive in high tunnels
UMASS Extension
Leaf Mold
Powdery Mildew
Early Blight
© 2012 Regents of the University of Minnesota. All rights reserved.
Humidity in Tunnels
Day:
Temp
RH
Night:
Temp
Condensation
© 2012 Regents of the University of Minnesota. All rights reserved.
Managing humidity & dew
• Use a wetting agent on polyethylene
(sprayed on or part of the formulation)
• Space plants for air circulation
• Stake and prune plants
• Remove all weeds
© 2012 Regents of the University of Minnesota. All rights reserved.
Managing Humidity and Dew
• Open side vents, doors or end walls
to increase air flow through plants
• Consider adding end wall vent above
doors if end wall does not open
• Ridge vents are available
• Open vents to release
humid air in the evening.
• Keep air warm at night.
© 2012 Regents of the University of Minnesota. All rights reserved.
Managing Humidity and Dew
• Monitor relative humidity (%RH) and dew point
– Sling Psychrometer – accurate, hand powered,
affordable
– Data Logger –accurate, automatic, computer based
www.abqindustrial.net
© 2012 Regents of the University of Minnesota. All rights reserved.
Manage Soil Moisture
• Choose a well drained site
• Improve drainage prior to construction
• Irrigate just enough to water the plants
• Promptly repair leaks
• Continuously wet soils– Check irrigation
– Redirect water
– Use raised beds
© 2012 Regents of the University of Minnesota. All rights reserved.
Rotate Crops
• Many pathogens infect all crops in the same family
• Some pathogens infect crops from several families
• Rotate between families at least every 2-3 years
Tomato
Family
Squash
Family
Onion
Family
Bean
Family
© 2012 Regents of the University of Minnesota. All rights reserved.
Plant Resistant Varieties
• Resistant – A plant that can defend itself from
a pathogen. May be complete or ‘partially’ or
‘moderately’ resistant.
• Tolerant – A host plant that will become
diseased but will not be seriously affected.
Fusarium Wilt
© 2012 Regents of the University of Minnesota. All rights reserved.
Resistant Varieties
• Look for statements that identify a specific
pathogen or disease
High Mowing Seed
© 2012 Regents of the University of Minnesota. All rights reserved.
Grafting for Disease Control
• Effective against soil borne pathogens
– Verticillium wilt
– Fusarium wilt
– Corky Root
– Nematodes
• Can be costly
• Look for resistant varieties first
Wikipedia.com
www.growing produce.com
© 2012 Regents of the University of Minnesota. All rights reserved.
Disease Control in High Tunnel
PATHOGEN
• Clean seed & transplants
• Clean inputs, tools & workers
• Control weeds
• Remove infected plant parts
• Use fungicides to protect healthy plants
• Identify every disease problem
• Choose targeted control strategies
SAMUEL ARANDA/AFP/Getty Images
© 2012 Regents of the University of Minnesota. All rights reserved.
Disease Control in High Tunnels
ENVIRONMENT
• Manage the ventilation and plant
spacing to reduce humidity and
condensation
• Use drip irrigation to reduce
moisture on foliage and fruit
• Choose well drained soils or
improve the drainage of the area
V. Grubinger Extension.org
© 2012 Regents of the University of Minnesota. All rights reserved.
Disease Control in High Tunnel
CROP
• Rotate Crops
• Use resistant varieties
when available
• Use grafting for soil borne
diseases and wilts
• Control weeds inside and
outside of tunnel
Thanks
Questions?