1. Diseases

Mostly caused by fungi and viruses.

Infection may come from:
1. Soil (soil borne)
2. Seed (seed borne)
3. Residue of previous crop.
4. Green bridge (volunteer plants or alternative
hosts).
5. Transfer from another crop.
Cultural
1.
◦
Rotations.
◦
Cultivations to destroy crop residues.
◦
Use of good quality seed.
2.
Resistant varieties
3.
Fungicides
◦
Seed dressings
◦
Foliar sprays
• Essential to detect disease outbreaks early.
• Inspect crops during the growing season
every 7 -14 days.

Pay particular attention to:
◦ Susceptible varieties
◦ Late sown spring crops
◦ Lush crops
◦ Crops adjacent to the same
species.
◦ Disease outbreak warnings.
◦ Eg-Blightnet, Crop Monitor &
Aphid Monitor
Seed borne – Seedling Blight
Root and Stem – Eyespot, Take All
Foliar Disease – Septoria, Rhynchosporium
Ear Diseases – Fusarium, Ergot
Seed borne disease

Seedling blight –
Microdochium nivale
Controlled by

Good seed treatment
– important if using
farm saved seed
Root & Stem Disease
Take all
Controlled by

Rotation

Take all Decline
Eyespot
Controlled by

Fungicide Spray (T1)
Risk to crop depends on

Sowing date

Infection rates

Rainfall

Tillage

Soil type

Previous crop
Foliar Disease
Septoria
Controlled by

Fungicide Sprays (T1, T2)

Resistant varieties
Rusts
Control

Fungicide spray

Resistant variety

Control volunteers

Good frost
Mildew
Controlled by

Fungicide
(T0, T1, later for
ear)


Resistant variety
Avoid excessive
nitrogen
Rhynchosporium
Controlled by

Fungicide spray

Minimise trash

Resistant
variety
BYDV
High risk in crops after grass
Direct & Indirect transfer
Controlled by

Long cultivation window – 3 weeks

Bury grass + trash

Seed treatment to control virus vectors

Monitor aphid migration + Spray aphicide




Sooty Moulds
Septoria nodorum
Mildew
Fusarium – pink grains (mycotoxins)
Can effect yield
Bigger significance when marketing grain
(shrivelled grain, low specific weights,
mycotoxins, ergot)
Ergot
Fusarium
Main timings
 T1 timing – Leaf 3 emerged (usually coincides with GS32, but
 can be as early as GS31 or as late as GS33).
 T2 timing – Flag leaf emerged (GS39).
Additional timings


T0 timing – 2-4 weeks earlier than T1 but not fixed.
Used when:
– Early planted winter crops with lush growth in early spring
– Where mildew, yellow or brown rusts are active
– When eyespot requires earlier treatment
T3 timing – Ear spray
- May be used to control ear diseases and 'top up' foliar disease
control on the flag leaf on susceptible varieties under high disease
pressure.
- Should be timed at mid flowering
Severity of disease depends on
Disease pressure
- amount of inoculum present
- weather conditions - Spread through rain splash
- Dry & humid important for rusts
- Moist & humid important for
Septoria & Rhynchosporium
Resistance of plant to disease pressure
- choose resistant varieties, lower input costs
Estimating Disease Risk
Up to 80% of wheat yield is from top 3 leaves
VITAL to protect them.
Ear – 22%
Flag leaf – 43%
Leaf 2 – 23%
Leaf 3 – 9%
Leaf 4 – 3%

Phoma Leaf Spot / Stem Canker

Light Leaf Spot

Sclerotinia Stem Rot

Clubroot

Verticillium Wilt
‣ Can affect crops from
emergence onwards
‣ The fungus grows down the
petiole and invades the stem to
produce stem cankers that cause
premature ripening and lodging
‣ Plants with large leaves are less
vulnerable than small plants
‣ Managed at the leaf spot stage
in autumn/winter using resistant
varieties and fungicide sprays
‣Risk can be predicted from
disease levels on the pods of
the previous year and
summer temperatures
‣Managed using resistant
varieties and fungicide sprays
‣Control may be affected by
fungicide resistance but spray
timing is more important
‣Often causes little damage
but can halve yields when
severe and poses a threat
to other broad-leaved crops
in the rotation
‣Risk is dependent on the
amount of spore production
during flowering and the
occurrence of suitable
weather for petals to stick
to the leaves
‣Fungicides give very
effective control but must
be applied before infection
takes place
‣ Widespread in the UK
‣ Yield losses in affected crops
can exceed 50%
‣ Lengthening rotations
remains the most sustainable
long-term strategy on-farm
‣ Use lime to maintain soil pH
near 7
‣ An emerging soil-borne
problem that is now
common
‣ Yet to have much impact
on yield

Bacterial – Blackleg, Dickeya, Soft Rots.

Viral – Leaf Roll, Potato Mop Top Virus.

Fungal – Late Blight, Common Scab,
Silver Scurf

Seed Borne – Silver Scurf, Blackleg

Soil Borne – Common Scab

Volunteers – Blight

Dumps - Blight

In Store – Blight, Silver Scurf, Bacterial Rot,
Dry Rot
Powdery scab
Identifying powdery scab
(Spongospora subterranea)
Powdery scab is a particularly difficult disease to control due to presence of
soil and seed borne infection. Spores can survive for at least 6 years in the
soil, and possibly far longer
Sources of infection
Planting infected seed into ‘clean’ soil will
threaten the current and future crops. high
proportion of seed can have trace levels
infected.
Continuing to multiply seed in
infected soils will compound the problems for
seed growers and transfer the problems more
rapidly to the ware grower
Managing the risk of powdery scab
Risk factor
Variety
Low risk
High risk
Less susceptible varieties
E.g. Sante, King Edward, Desiree,
Culta
Highly susceptible varieties
E.g. Premiere, Cara, Maris Piper
Estima
Site
Long crop rotation (greater than
10 years)
Previous history of powdery scab
Seed Health
Seed tubers with no powdery scab
Powdery scab present
Growing conditions
Dry soils at tuber initiation
Deep planting
Wet soils at tuber initiation
Fungicides
Only available to seed growers – Shirlan soil drench at planting as SOLA
Superficial blister-like pimples on the
skin of developing tubers
These erupt to liberate powdery spores
Leaving a jagged edged scab
Produces cankers when scab infects an
eye
Key points
•Know
market
powdery scab
tolerance
for
•Check varietal susceptibility
•Field history – infected tubers
•Only
plant
less
susceptible
varieties in fields with a history of
powdery scab
•Source seed of an appropriate
health status to meet customer
quality standards
•Do no plant seed tubers infected
with powdery scab if you want to
control this disease in the longterm
Common scab
(Streptomyces scabies)
Identifying common scab
Common scab is a disfiguring skin blemishing disease, it does not impact on
crop yield but can significantly effect crop value.
Sources of infection
Streptomyces is present in every soil, but
incidence
is
determined
by
variety
susceptibility. Infection occurs in potatoes only
when soil is dry at tuber initiation.
Severe infection results in corky
lesions that can be pitted, raised
lumps on the skin or areas with a
raised brown reticulated ‘netted’
pattern. Symptoms can also be more
superficial brown flecks on the
surface of the tuber
Key points
Managing the risk of common scab
Risk factor
•Know market
common scab
Low risk
High risk
Variety
Less susceptible varieties
E.g. King Edward, Desiree,
Highly susceptible varieties
E.g. Maris Piper, Markies, Up-todate, Kerrs Pink
Site
High organic matter, cultivated to
a fine tilth
Light soils on a slope and clay
soils poorly cultivated
Seed Health
Planting seed infected by common scab increases risk but only to a
small extent
Growing conditions
Crops irrigated to 4-6 weeks after
tuber initiation
Chemical control
No means of chemical control. Applying a sulphur product can reduce
scab incidence but only sometimes
Cloddy soils
tolerance
for
•Check varietal susceptibility
•Avoid
planting
susceptible
varieties in fields with a history of
common scab
•Cultivate to produce a clod-free
fine tilth
•Irrigation at tuber initiation is the
only reliable control measure
Black scurf
(Rhizoctonia solani)
Identifying black scurf
Black scurf can impact on tuber yield and quality. The disease can
kill eyes during storage, effect stems before emergence (stem
canker) and form black scurf on progeny tubers after senescence
Sources of infection
In Northern Ireland black scurf on
seed planted is the main source of
infection. Sometimes infection can
come from residues of the previous
crop in that ground
Managing the risk of black scurf
Risk factor
Low risk
High risk
Variety
All varieties are equally
susceptible
All varieties are equally
susceptible
Site
Long crop rotation
Potato crops grown in succession
Seed Health
Seed without black scurf planted
in ley ground
Seed with black scurf
Potatoes rotated with vegetables
Growing conditions
Fungicides
Dry years increase risk
RhiNo, Monceren, Rizolex, Rovral, (Amistar, as a soil drench)
Infected sprouts become blackened
and may not emerge in severe cases
Clusters of black fungal structures
on the potato skin which form 7-10
days after haulm death. Can be
picked off by the thumb nail
Key points
•Kills eyes, delays emergence,
increases tuber defects (cracks,
misshapen, netted skin)
•Pre-planting
effective
fungicides
very
•To assess seed risk;
Wash 50 tubers and count number
with black scurf
If more than 5 tubers have black
scurf treat seed with fungicide
pre-planting
Silver scurf
Identifying silver scurf
(Helminthosporium solani)
Blemishes on the tuber surface are present in almost all potato stocks and
lesions develop during storage resulting in weight loss and blemishing
reducing the value of tubers for the seed and mare markets
Sources of infection
Disease is primarily seed borne, but
most spread occurs during storage.
Spores from silver scurf patches are
carried in air, dust and machinery
Silver lesions on the surface of the
tuber which often coalesce to form
large silver patches. These can
cause the skin to shrivel and flake
off
Symptoms are not always present at
harvest, wash tubers and check for
development during storage
Key points
Managing the risk of silver scurf
Risk factor
Low risk
High risk
•Use fungicide treated seed to
reduce infection on progeny
•Harvest early
Variety
All varieties equally susceptible
More obvious on red skinned tubers
Site
No clear effect
No clear effect
•Rapid
drying
using
ventilation after harvest
Seed Health
Completely clean seed
Silver scurf on seed planted
increases risk
•Silver scurf needs a warm humid
environment to spread quickly
Growing conditions
Early harvest (before midSeptember)
Late harvest
Storage conditions
Clean stores, rapid drying, cold
stored
Unventilated ambient storage
•Cold dry storage controls silver
scurf better than the use of post
harvest fungicides
Fungicides
Fungazil 100Sl, Storite, Extratect
•Store hygiene important
forced
Dry rot
F. coeruleum, F. avenaceum, F. sulphureum
The main cause of blanking in potato crops, reducing yield and tuber
uniformity
Sources of infection
Soil borne fungus which infects the tuber
through wounds caused at harvest and grading.
Dirt in stores, machinery and boxes can harbour
disease. Planting infected seed can increase the
risk.
Disease can be carried over in soil
residues from previous crops
Identifying dry rot
Light brown rot which develops
concentric rings with white or light
blue pustules on the surface
Key points
Managing the risk of dry rot
Risk factor
Low risk
High risk
Variety
Lady Rosetta, Sante
Navan, Desiree Estima, Maris Piper
Site
Ley ground, long rotation
Short rotations including cereals
Seed Health
Stocks free of dry rot
Tubers with rots from farms with a
history of dry rot
Growing conditions
Cold wet summers
Warm summers
Harvesting
conditions
Ensure skins are set and minimize
damage
Late harvesting and rough handling
Storage conditions
Quick drying and cool dry storage
Clean equipment and stores
Dirty equipment
Grading sprouted tubers
Fungicides
Fungazil 100 SL, Extratect at harvest
•Wash and disinfect stores, boxes
and equipment every year
•Tuber susceptibility to infection is
low in Autumn but greatly
increases from December. Aim to
grade seed potatoes before
December.
•Be gentle at planting.
Rots
starting then increase the risk of
dry rot in the progeny crop.
Skin spot
Polyscytalum pustulans
Identifying skin spot
Skin blemishing disease. Also kills eyes, delays emergence and
reduces yield.
Raised brown/black pimples on the
skin of tubers. Often surrounded
by a small halo of black tissue.
Sources of infection
Planting diseased tubers increases
skin spot on progeny. Fields in colder,
wet areas can carry infection
Key points
Managing the risk of skin spot
Risk factor
Low risk
High risk
Variety
Most varieties
Kerr’s Pink, King Edward
Site
Ley ground, long rotation
Short rotations
Seed Health
Stocks free of skin spot
Stocks with skin spot on tubers
Growing conditions
Dry summers
Cold wet summers
Harvesting
conditions
Early harvests
Late harvesting from wet soils
Storage conditions
Quick drying and dry storage
Clean equipment and stores
Damp, cold, unventilated storage
Fungicides
Fungazil 100 SL, Extratect, pre-planting or at harvest
•Wash seed to look for symptoms
•Apply a fungicide before planting
if skin spot is present
•Harvest early
•Keep tubers dry during storage
Notifiable •Brown Rot
Diseases •Ring Rot
Notifiable •Colorado Beetle
•Potato Cyst Nematode
Pests
Blight
How does blight spread and
survive?
 Sporangia: air-borne or spread in
rain (short-lived: days not months)
 Infected plant material e.g. potato tubers
(can survive months, best method for longdistance spread)
 Oospores: long-term survival in soil
(several years)
Implications for blight control
 Infected tubers remain the key source of primary
inoculum for late blight
 Use healthy seed
 Prevent/destroy potatoes sprouting in dumps or
growing as volunteers in other crops
Implications for blight control
 Start spraying when there's a risk of blight or the
crop meets within the drills (whichever is earlier)
 How do you know when there’s a risk of blight?
 Blight forecasts/warnings issued by CAFRE & AFBI
 We look at temperature trends and outbreaks when
issuing these
Blightnet
Recommendations for blight control
 Start with healthy seed, eliminate dumps
 Start spraying when there's a risk of blight or the crop
meets within the drills (whichever is earlier)
 Start with a product containing a systemic or translaminar
 Continue with either a translaminar or a protectant ensuring
that spray intervals are not over-extended
 Complete the programme with at least 3 sprays of a
product with tuber blight activity, reducing the interval if
there’s severe risk
 Ensure protection is maintained by regular spraying until
the haulm is dead