Blackleg is a challenging disease to control but recent research has provided some clues as to where scientists should focus their efforts. Jo Learmonth reports
Genetic resistance, timing from haulm destruction to planting and transportation methods all have a role to play in blackleg control in what has been a difficult year for the disease.
Speaking at Potatoes in Practice, independent potato consultant, Dr Stuart Wale, said: “Blackleg has been difficult this year. There is a very nice relationship with the colder and wetter the June is, the more blackleg there is around and this year June was not great. To help the industry we are going to need a good autumn.”
While weather has a significant effect on blackleg incidence, Prof Ian Toth, researcher at the James Hutton Institute, said work funded by a Scottish Government and AHDB potato grant working on blackleg had led to new discoveries concerning the disease.
Evidence is suggesting the increase in blackleg over several years is not due to new strains appearing. Pectobacterium atrosepticum remains the standard strain in Scotland and strains look the same as they have done over the last 40-50 years, said Prof Toth. “We need to look elsewhere for an answer to why blackleg is still causing all these problems.”
Another new finding will cause researchers to look again at control methods, said Prof Toth. “We found that you can put a completely clean tuber in the soil, it becomes contaminated and blackleg disease can develop within the same year.”
The researchers also found bacteria move more freely through the plant in some varieties and therefore are more likely to cause disease. Prof Toth said: “Knowing this, we may be able to develop a more accurate model for resistance.”
Out in the plots, there was more discussion from experts on blackleg. Prof Gerry Saddler, deputy head of science and advice for Scottish Agriculture (SASA), told growers that the period of time from haulm destruction to planting is critical. Even when tubers are in store and well dried, the period of time from when they come out of store, to when they are planted, can undo good work.
Prof Saddler said: “If you get a film of condensation building on the tubers or if the tubers are damaged in any way through handling, bacteria may get into the tubers then blackleg can result.
“Nowadays, potatoes are transported in large polypropylene sacks. If tubers are in these sacks for any great length of time the temperature is going to be fluctuating and the tubers on the bottom have a huge weight above them which is not ideal. I realise they have to be moved around but keep this time period as short as possible.
“Maybe the old way of transportation, in wooden boxes, is the better way; there is the possibility of air movement through them and the weight from the top to the bottom isn’t going to be that great. I appreciate from a haulage point of view it is perhaps not the most efficient way to do it but in the drive for greater efficiency we may have lost something.”