Managing Late Blight in
Potatoes and Tomatoes
Gardenscape 2011
Late Blight
• Fast moving fungal disease attacks
members of the Solanaceae family
• Sensitivity
– Tomato + potato > eggplant and pepper
• Damages leaves + stems = reduced yields
• Infects tubers and fruit = storage decay
Late Blight in History
Late Blight on the Prairies
• Relatively rare problem .. Primarily
because “typical” Prairie summer
conditions (hot and dry) are not
conducive to the development and spread
of Late Blight
2010
• Late Blight widespread across N. America
• Widespread across SK by July
• Hits commercial potato growers as well as
backyard gardens
• Many backyard gardens wiped out.
• Commercial growers – mixed bag … even
with advance warning and $$$ spray
programs
Why so much Late Blight in 2010?
Why so much Late Blight in 2010?
2009
- blight widespread across eastern N.
America
- blight blows into SK late in the season
- causes minor crop loss due to late
arrival
- but did it get into the seed potatoes?
Why so much Late Blight in 2010?
2010
- planted seed contaminated with blight ??
+
- ideal weather for development and
spread of blight (cool, windy and wet)
So, what about 2011?
So, what about Blight in 2011 ?
Pathogen
- Only way late blight can overwinter in SK
is infected potato tubers
- Disease carries into next year if ....
a) diseased tubers discarded as culls
manage to sprout
b) diseased tubers used as seed
Managing Blight in Potatoes in 2011 ?
Pathogen
Diseased seed
- heavily infected tubers ...
- easy to detect and discard
- will likely rot after planting = no spread
- may spread spores to otherwise
healthy seed at cutting time
Managing Blight in Potatoes in 2011
Pathogen
Diseased seed
- Lightly infected tubers ...
- infected late in fall or at cutting time
- no visible signs of rot
- will likely sprout and develop into
diseased plant = starting point of field
infection
Al-Mughrabi - 2010
Managing Blight in Potatoes in 2011
Managing the Pathogen
- Plant certified seed ... but even the
commercial seed growers struggled to
keep blight under control in their crops in
2010.
- Ask your supplier about Blight pressure
and their blight management program in
2010
- Check the seed carefully yourself
Managing Blight in Potatoes in 2011
Host
- Cultivar sensitivity
Sensitive – all reds, Shepody
Moderate – Norkotah, Burbank, Yukon Gold
Tough – Alpine, Classic, Milva, Yukon Gem
Shepody
Y. Gold
Burbank
Milva
Research Supported by ADF
Managing Blight in Potatoes in 2011
Managing the Pathogen
Warming seed prior to planting = ideal
conditions for spore formation of Blight
Hold seed cold until planting
Disinfect cutting equipment/surfaces
regularly
Cut “problem” seed lots last
So, what about Blight in 2011 ?
Managing the Pathogen
Scout field ... starting at emergence
“When in doubt ... Pull it out”
Managing Blight in Potatoes in 2011
Managing the Environment
- Avoid high risk fields in 2011
- low spots
- spots with poor air movement
- proximity to problems ???
- What’s going on next door ?
Managing Blight in Potatoes in 2011
Managing the Potato Crop
Wider spacing = more air flow = dry canopy
Avoid excess N fertility and water … as
bushy plants = wet canopy
Water early in the day so canopy dries
before nightfall
Water hills … not the foliage
Managing Blight in Potatoes in 2011
Managing the Potato Crop
Good soil coverage minimizes infection of
the tubers
- gradually build a deeper than normal
hill
- re-hill following heavy rain
- tubers set high in the hill = high risk
Managing Blight in Potatoes in 2011
Sprays to Manage Late Blight ?
Limited options available to gardeners
Copper spray (Bordeaux)
Need to be applied preventatively =
BEFORE the BLIGHT ARRIVES
Need complete coverage of foliage
Need to cover both leaf surfaces
Need to re-apply as crop grows and after
every rain/irrigation event
Managing Blight in Potatoes in 2011
Managing the Potato Crop
Harvest after vines are dead/dried/removed
Grade out suspect tubers going into storage
** If more than 5% of tubers rotten …
Forget About Storage
Store cool (4-6C) and dry
Inspect frequently (visual + sniff test) and
re-grade
Managing Blight in Tomatoes in 2011
** Late Blight cannot be transmitted or
carried over on tomato seed
** Late Blight can be introduced on
transplants
Some cultivars more Blight resistant
- Juliet (Ve) and Santa (grape types)
- Legend (T+M) (standard type)
- Defiant (J) (standard type)
Managing Blight in Tomatoes in 2011
Many of the same management
recommendations as for potatoes …
Site selection
Fertility and water management
Row spacing + ….
- prune and stake to further improve air
flow
Protective spraying
Managing Blight in Tomatoes in 2011
Protected cultivation
- Late Blight not a problem in greenhouses
as do not have continuous wet foliage
Managing Blight in Tomatoes in 2011
At harvest time …
- Blight risk increases in fall due to higher
RH and cooler temps + big canopy
- consider benefit vs cost of harvesting
mature green
- keep harvested tomatoes separate
during ripening + regrade frequently
- grow to love green tomato pickles
Future ...
2011 will be a challenging year as ...
- commercial seed system is not free of late
blight
- many backyard potato growers save seed for
replanting = 10,000 starting points across SK?
- backyard gardeners still unfamiliar with blight
and blight management
Future ...
If ...
- 2011 is hot and dry
- we educate ourselves on blight management
It is possible that Late Blight may “recede”
through 2011 ... and by 2012 or 2013 we will
be back to “normal”
If not .....
If it keeps raining ...