With the Scottish seed potato harvest beginning a fortnight ahead of normal, SRUC consultant Dr Stuart Wale has reminded growers of the threat from dry rot.
An early harvest is likely to reduce the risk of silver scurf, black dot, gangrene, and skin spot developing in store, but not dry rot, which Dr Wale points out can be more of a problem on susceptible varieties following an early harvest.
“Poor skin set, warm tubers, and store condensation all increase dry rot risk. In seed crops this can be minimised by treating with a fungicide into storage or at grading," he said. “Judging the need for treatment should be based on varietal susceptibility to the disease, previous experience of disease on a specific variety and presence of the disease in the seed from which the crop was grown.”
He recommends two fungicide options in this situation: Gavel (imazalil) and Storite Excel (thiabendazole) which can be used alone or in mixture.
“Bear in mind that Fusarium sulphureum – one pathogen that causes dry rot – silver scurf, and skin spot have all been found to develop resistance to thiabendazole, whereas there has been almost no resistance detected to imazalil,” he said.
Gavel is marketed by Certis and the company’s Technical Manager Laurence Power says that for the last two springs dry rot has been a contributory factor to gappy emergence of ware crops.
He urged growers to have a conversation with their seed suppliers sooner rather than later to discuss treatment.
“For maximum disease reduction in storage, Gavel should be applied as soon as possible after harvest, preferably within 48 hours.If you leave the conversation with your seed supplier until the spring there may not be any treated seed left and there are no options for treatment out of store or at planting.”