Late Blight

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Late Blight
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Late blight caused the Irish potato famine
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Why the resurgence of LB as a problem in potatoes?

• New strains of the pathogen
• US-8 emerged in 1990s (1995 - caused severe
  damage to Columbia Basin potato crop)
• US-8 is more aggressive (lesions expand faster)
  than US-1, the older strain
• US-8 is here in Oregon
• Other new strains (US-6, US-7, US-11, and US-17?)
  are particularly pathogenic to tomatoes

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Late Blight Disease Cycle
Causal agent Phytophthora infestans (Oomycete,
related to algae)
http//www.apsnet.org/education/LessonsPlantPath/L
ateblit/CYCLE.HTM
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http//www.apsnet.org/education/LessonsPlantPath/L
ateblit/PATHBIO.HTM
Sporangia
Flagellated zoospore
Oospore
Sporangium germinating directly
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June 29 2005
Gigot, J. 2005
Disease progression in Ray and Tims potato field
in Mt. Vernon WA Photos by Jessica Gigot, WSU
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Gigot, J. 2005
Epicenter of late blight epidemic on organic
potato field in western Washington.
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Photos by Jessica Gigot
Gigot, J. 2005
Gigot, J. 2005
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Photos by Jessica Gigot
Gigot, J. 2005
Gigot, J. 2005
Late blight lesions
Gigot, J. 2005
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Gigot, J. 2005
Late blight stem lesions
Photos by Jessica Gigot
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Photos by Jessica Gigot
July 15 2005
June 28 2005
Gigot, J. 2005
Gigot, J. 2005
Disease progression in Ray and Tims potato field
in Mt. Vernon WA Photos by Jessica Gigot, WSU
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http//www.apsnet.org/education/LessonsPlantPath/L
ateblit/SYMPTOM.HTM
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http//www.evergreen.edu/cell/projects/tomatoresul
ts/examples/LB_topbottom.jpg
www.evergreen.edu/cell/projects/tomatoresults/exam
ples/LB_fruitA.jpg
Symptoms on tomato
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Early blight
(Alternaria solani)
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Disease Triangle
Susceptible
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Disease Triangle
X
Susceptible
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Disease Triangle
Susceptible
X
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Disease Triangle
Susceptible
X
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Conditions Favorable For Disease
High humidity (above 90) and average
temperatures in the range of 50 to 78F favor
the disease. Optimal environment for production
of sporangia is 100 relative humidity and
60-70F. In presence of free water, sporangia
germinate in 2 hrs and infect 2 hrs later.
Inside plant tissue pathogen grows best at
62-70F. Under favorable conditions, new
spores can be produced in 4-5 days to repeat the
cycle.
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Late Blight Option

• Cultural management
• Resistant cultivars
• Chemical control (coppers)

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Destroy all overwintering inoculum sources

• Destroy culls (composting, burial)
• Eradicate volunteer potatoes, solanaceous plants
  and weeds

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Plant disease-free tubers

• Certified seed can contain up to 1 LB diseased
  tubers!
• Know that your seed source is reliable.
• Inspect your seed for disease.

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Design your system to minimize leaf wetness

• adopt a wide row spacing
• dont over-apply N (delays maturity and
  increases canopy size)
• manage irrigation to minimize duration of leaf
  wetness
• Dont irrigate late afternoon or early morning
• Use drip irrigation if possible
• plant rows parallel to prevailing winds
• do not plant in areas prone to standing water or
  impeded air flow

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Photos from Jessica Gigot
Gigot, J. 2005
Diagnostics and scouting

• know how to ID potato diseases
• scout your fields regularly for early detection
  and intervention

Gigot, J. 2005
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Other cultural strategies
Destroy (flaming, flailing) diseased foliage to
prevent spread through field Maintain high
hills (good tuber cover) so spores from foliage
cannot get to tubers Destroy foliage several
weeks before harvest so all foliar tissue is
dead. The pathogen cannot live on dead tissue
so this reduces the potential for infecting the
tubers. Inspect your tubers for diseases before
storing, and discard infected tubers.
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Copper fungicides

• Copper fungicides are protectants, so they must
  be applied to the foliage before infection. The
  copper ion is absorbed by the germinating spore,
  and the copper denatures spore proteins.
• Coppers must be applied regularly throughout the
  potato production season this can be 8 or more
  sprays per season!
• Coppers are considered synthetics by the NOP and
  are permitted with restrictions.
• Champion WP (copper hydroxide) appears to be the
  material most used by organic growers and its
  efficacy against several foliar diseases in
  organic tomato production systems has been
  documented.
• In the BlightMOP project they controlled LB with
  6 sprays of 0.9 lbs/A each as oxychloride, and
  this total application rate fell within the more
  restrictive EU guidelines and did not result in
  increased soil Cu contents.

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Cultivar Resistance
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Sante was considered the most resistant main crop
cultivar that also yielded well in organic
systems. Leifert thinks that Sante has lost
resistance over the course of the 5 years of the
project.
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Foliar blight England 2001
Foliar blight ()
Julian day
September
August
October
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Promising varieties Switzerland
Foliar blight
Tuber blight

• Test variety
• Appell
• Derby
• Eden
• Innovator
• Markies
• Naturella

Yield
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Promising varieties France
Foliar blight
Tuber blight

• Test variety
• Derby
• Eden
• Emeraude
• Escort
• Estima
• Lizen
• Naturella
• Nicola

Yield
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Promising varieties England
Foliar blight -
Tuber blight

• Test variety
• Claret
• Donella
• Eve Balfour
• Lady Balfour
• Princess
• Sarpo Axona
• Sarpo Mira
• Sarpo Tominia

Yield -
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Promising varieties Norway
Foliar blight -
Tuber blight -

• Test variety
• Grom
• Peik
• N 84-422
• N 89-1756
• N 92-15138
• Santé

Yield
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Cultural Practices
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BlightMOP Conclusions

• Breeding tolerant/resistant cultivars is the best
  strategy for managing LB organically. We need
  ongoing LB breeding programs as tolerance will
  break down over time.
• Copper oxychloride (6 sprays _at_ 0.9 lbs/A) slows
  disease progress and met the EU limit for Cu
  application.
• Chitting did not control LB.
• Irrigation management reduces LB.
• Nutrient management increases yield but doesnt
  reduce foliar LB.
• Organic soil management might be helping manage
  tuber LB. Tuber resistance reduces tuber LB.
• Compost teas (etc.) have worked vs. Botrytis in
  greenhouse culture but they have not been
  effective in suppressing LB in field potatoes.
  Rhubarb extract controls LB but you have to grow
  a field of rhubarb for every field of potato.

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Variety Trials This Project
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Resistant Cultivars (available in OR now)

• On-farm trials of commercially available
  cultivars
• Island Sunshine (dark yellow flesh)
• Santé (light yellow flesh)
• Jacqueline Lee (yellow flesh)
• Defender (russet)
• What about Ozette and other unusual cultivars?
• Research station trials of numbered lines
• MSJ456-4 (round white from MI)
• AO96141-3 (russet)
• NDA5507-3Yf (yellow flesh)
• VC1009-1W/Y (yellow flesh)
• AC97521-1R/Y (red skin yellow flesh)
• Others?

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EU Cultivars of interest

• Eden
• Eve Balfour
• Lady Balfour
• Sarpo Axona
• Sarpo Mira
• Escort
• Naturella
• Torridon?
• Tollocan?
• N89-1756 (Norway)
• N92-15138 (Norway)

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Jacqueline Lee
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Island Sunshine
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Sante
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Defender
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Ozette
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Lady Balfour
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Sarpo Axona
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Late Blight Option what farmers can expect

• Early season visit (Stone and Selman - and Mosely
  if available) to discuss potato system and
  troubleshoot inoculum sources and cultural
  practices
• Diagnostics and scouting (staff and/or farmer
  depending on farm) throughout season
• On-farm variety trial of available cultivars
  (evaluate marketability, productivity, and
  resistance if disease occurs)
• Research station variety trial (inoc. with US-8)
  with farmer interaction
• On-farm trials if growers are interested (copper
  fungicides?)