Manageing Crop Diseases in High Tunnels, 2015

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


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!

http://www.extension.umn.edu/garden

http://pdc.umn.edu/


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


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


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


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


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


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


Control Weeds

• Weeds crowd the crop &

increase humidity

• Weeds harbor plant pathogens

• Control weeds within the tunnel

• Control weeds around the tunnel


Remove Diseased Plant Material

Wilt Diseases, Bacterial Diseases, Viruses, & White Mold

Remove the entire plant as soon as possible!


Remove Diseased Plant Material

• Leaf, fruit and stem infections

• Remove infected parts immediately

• End of the season, remove the plant


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


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.


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


Leaf Diseases in High Tunnels

• Fungi that need high humidity

or dew thrive in high tunnels

UMASS Extension

Leaf Mold

Powdery Mildew

Early Blight


Humidity in Tunnels

Day:

Temp

RH

Night:

Temp

Condensation


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


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.


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


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


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


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


Resistant Varieties

• Look for statements that identify a specific

pathogen or disease

High Mowing Seed


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


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


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


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?

Manageing Crop Diseases in High Tunnels, 2015

Education

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