What is it and where is it found?
Strawberry black spot is an economically important disease of strawberries caused by the fungus
Colletotrichum acutatum .The fungus can remain unobserved in strawberry plants until the crucial
fruiting period. Then, if conditions are favourable for the disease, it develops rapidly resulting in
substantial losses (up to 80% yield loss) both in the field and when the fruit reaches market.
Thisfungus can also infect a wide range of other plants, both within and outside the UK, such as
anemone, lupin, camellia and apple.
The disease is found in nearly all countries where strawberries are grown. It was first found in the
UK in 1983 on strawberry plants imported from California and, since then, measures have been
taken to prevent establishment and to eradicate the disease whenever it has been detected in
propagation crops. Reported outbreaks in recent years have mostly been associated with infected
runners imported from the European mainland.
Strawberry black spot
What are the symptoms?
On fruit ,sunken, brown, circular spots develop as the fruit ripens. The spots
darken with age, hence the name ?black spot?, and can expand to engulf the
whole fruit if this is left on the plant.
In
dry weather ,minute salmon coloured crusts of spores are just visible between
the seeds within the spots.
If the fruit becomes infected well before
ripening
,the development of the spots may be arrested, they then turn black and the fruits
become distorted. The fungus will inevitably cause a post harvest rot of some fruits which were
apparently healthy at picking.
On foliage , small spots can develop, while black, elongated,
depressed lesions can occur on stolons and flower stalks. However, except where conditions are
especially favourable for the disease, these symptoms are rare and inconspicuous.
How does it develop and spread?
The disease is spread when infected strawberry runners are traded. However, symptoms are rarely
seen as the fungus is usually latent on this material. Once planted, fungus in the crown of the plant
produces spores which are spread by water splash to other parts of the plant, where they cause the
symptoms described above. The fungus can survive from year to year around the crown of infected
plants or on infected crop debris left in the soil. It may also survive on a wide range of common
weeds.
The disease can be spreadwithin the crop by:
? water splash;
?insects;
?handling and picking;
and is favoured by warm, humid conditions (optimum temperature 25?C). The disease builds up
rapidly during the first year of cropping and is usually more severe in the second and subsequent
years, especially wheresuccessive waves of ripening fruit on everbearing cultivars coincide with
periods of warm, wet weather.
Early symptoms
on ripe fruits:
spots initially
brown
What is being done?
Defra Plant Health and Seeds Inspectors (PHSI) carry out regular inspections to ensure that planting
material in the Plant Health Propagation Scheme (PHPS) is free from the disease. In addition, non
PHPS strawberry propagation material is inspected for plant passporting purposes. Defra are also
prepared to sample and test any consignments of imported or suspect runners that are brought to
their attention.
What action can be taken?
There are no totally effective chemicals to control against strawberry black spot. However, the
following cultural measures can help to prevent the disease getting a hold:
Nitrogen Limit nitrogen applications to 40 kg/ha/yr on June bearers, and 80 kg/ha/yr on
ever bearers.
Mulch Apply a straw mulch between rows and on any plastic mulch to limit dispersal of
spores through water splash.
Picking Minimise the amount of ripe fruit on the crop at any one time by keeping
intervals picking intervals as short as possible.
No Paraquat Avoid Paraquat for weed and runner control as it encourages development of
the fungus.
Plant debris Wherever possible, collect plant debris from the field after harvest and either
burnor buryit deeply.
Crop Improve air circulation by crown thinning, good weed control and removal of
management rotten and over ripe berries as these will all help reduce the risk. Consider
moving off June bearers after harvest and possibly again in the spring. If possible
debris should be collected and destroyed.
Crop duration Keeping a crop for only 1 or 2 years greatly reduces the risk of development and
spread of this disease.
Fungicides General advice is given in the Horticultural Development Council (HDC) Factsheet
14/02 but qualified advice should be sought for current products. They must be
used in conjunction with appropriate cultural measures.
Keep a good look out
Strawberry black spot is an EC listed quarantine disease and should be notified on strawberry crops
whenever found. Strawberry runners must be free from the disease. When the disease is found on
propagating crops, infected runner mother plants must be destroyed immediately, hygiene measures
implemented and other measures taken as directed by PHSI. Infected propagating crops cannot be
plant passported. At the end of cropping, all affected beds are required to be destroyed and either
the soil sterilised or the field put down to grass for a period of time. When confirmed on fruiting
crops in the UK, growers are advised to implement hygiene measures and apply sprays to protect
new growth. Further information on the disease can be obtained from the HDC Factsheet 14/02.
If you suspect the presence of this disease on your premises, you should immediately inform your
local Defra Plant Health and Seeds Inspector or the PHSI HQ, York:
Tel: 01904 455174
Fax: 01904 455197
Email: planthealth.info@defra.gsi.gov.uk
Website: www.defra.gov.uk/planth/ph.htm
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