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Crop Duration and Soil Inoculum as Predictors of Black Dot Risk after Storage

Publication Date: 
13 August 2009
Author/Contact :
G Harper (SBEU) & J Peters (FERA)


This report summarises the work carried out during the second and final year of this
trial to determine how knowledge of crop duration and soil inoculum enables
prediction of risk of black dot during storage. The results are discussed in relation to
the findings of the previous trials carried out since 2004.
The conclusions from the second and final year of this trial:
1. For all tested varieties, the level of black dot soil inoculum is a highly significant
factor in the development of the blemish in store.
2. For all tested varieties, crop duration is a highly significant factor in the
development of the blemish in store.
3. There is little overall difference between the different tested maturity groups in
the relationship between crop duration and black dot disease incidence or
4. There are differences between potato varieties in the susceptibility to black dot.
Practical overall recommendations
Soil inoculum: planning the crop
Quantitative PCR can be used to accurately determine black dot inoculum levels in
soil. This provides valuable information for planning of field layouts and potato
variety choices.
Crop variety
There is a range of susceptibilities to black dot within currently available potato
varieties. Knowledge of the potential risk of black dot, based on soil inoculum levels
or previous agronomic experience, should be used to select appropriate varieties as
part of the disease control strategy.
Crop duration
Crop duration should be carefully managed particularly when susceptible crops are
grown in black dot infected sites. For varieties that are susceptible to black dot, such
as Maris Piper, there is a higher risk of economic loss due to black dot when crops are
grown for more that 115 days duration (from 50% emergence to harvest).
Potential risk analysis based on soil inoculum, crop variety and crop duration made
prior to planting should be used to inform future crop storage management.

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