Powdery scab situation
Powdery scab is a serious disease in Scotland. Although there have been no systematic surveys
of the disease it is considered by most seed and table growers to be the most serious challenge to
the industry. In general, it appears to be more of a problem with seed growers
who are
concentrated in the north and northeast of Scotland than table potato growers. Some seed
growers have stopped growing potatoes because their land was so heavily contaminated and
they could not produce disease free tubers. It is feared much more than late blight
because there
are no effective control measures. Growers could grow more resistant varieties but those
demanded by the market are mostly susceptible. Experience suggest that
many soils are contaminated.
But the Scottish Agricultural College developed a soil test for Spongospora as described by Brierley et al. (2008), and launched in 2009/10. The test uses a single soil sample per field, made up of hundred 10 g core samples from a representative 4 ha block in the assessed field.
The test results categorise risk of powdery scab as ‘low’ (Ss undetected), ‘medium’ (trace to 9.9 sporosori g-1 soil), or ‘high’ (>10 sporosori g-1). There have been more fields in the low risk category and fewer fields with high risk than was expected. Many growers submit samples annually.
Powdery scab has declined as a problem in potato production in Scotland since the test was introduced, which could be due to climate change (consistent warm and dry spring conditions), and use of potato cultivars with reduced powdery scab susceptibity.However, the soil test has provided increased
confidence to grow susceptible varieties in low risk fields, and decision support for necessity for fluazinam soil incorporation
Big seed producing company buy regularly virgin land (with no potato history) to crop their potatoes free of Spongospora diseases.
The weather conditions are highly favourable for the disease. In addition the pathogen
has some importance as the vector of potato mop-top furovirus.
Research
A PhD student did investigations on the influence of root
exudates on the release of
primary zoospores by the resting spores, using monoclonals (Norvene
Fornier). An Post-doc worked on the biology, detection and control of the pathogen (Pieter van de Graaf).
Lesley Torrance and her research group are mainly working on the virus (identification, genetics). Recently at SASA a PhD student started
a project entitled 'The importance of potato mop top virus in Scottish seed potatoes' (Triona Davey)
Contact addresses
:
Powdery scab
Stuart Wale
Orchard Cottage
Ardlethen
Ellon
Aberdeenshire AB41 8PF
Scotland
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Last update: January, 2025