26 September 1997

Bad year for blight and next year may be worse

Potato prices may be in the doldrums, but that did not deter a healthy attendance at last weeks Potato Harvest 97 event in Suffolk. Charles Abel was there and reports some of the technical highlights below. Turn to p70 for the latest on harvesting and handling machinery

ARE YOU worried about controlling blight next year? You should be, according to experts at Potato Harvest 97.

After the worst blight pressure in living memory growers need to guard against a repeat next season. Removing likely sources of infection and being aware of the greater likelihood of fungicide resistant blight are key considerations, said Mike Storey, British Potato Council director of R&D.

"In particular, growers need to appreciate the wider implications of using very tight spraying programmes this year," he noted.

ADAS blight specialist Nick Bradshaw agreed. "Its been a horrendous year for blight, with the disease going through generations in just five to seven days. That has increased selection pressure for resistant strains considerably."

Low levels of blight which is resistant to phenylamide fungicides like metalaxyl (in Fubol), oxadixyl (in Recoil, Ripost, Pepite and Trustan), benalaxyl (in Galben M) and ofurace (in Patafol) have been observed for some time, he noted. Those may now be more prevalent next season. Furthermore, other fungicides could also come under pressure, following intense selection pressure this season, he acknowledged.

Whether there will be more fungicide resistant blight about next year will only be known when test results are released early in the New Year, he said.

However, work at Bangor University has confirmed blight was predominantly the more aggressive A1 and A2 types this season, he added. This so-called new blight produces more spores and grows faster, accelerating disease development in the crop. But, new fungicides have been tested against these strains and no fall in their efficacy has been noted, Mr Bradshaw said.

The presence of both A1 and A2 types also raises the risk of the two combining to produce hardy resting spores. Those could survive the winter and initiate an earlier blight epidemic next season. However, with very few blight populations containing both A1 and A2 types that is a risk not a certainty, stressed Dr Storey.

Growers need to observe good crop hygiene, destroying out-grades, haulm and other residues and considering all potential sources of infection next season, including volunteers, he added.

&#8226 At Potato Harvest 97 the BPC launched a new booklet produced in association with the Fungicide Resistance Action Group to help growers avoid fungicide-resistant blight. It examines the performance, mode of action and the risk of resistance developing to each fungicide on the market.

"The key to preventing resistance is to avoid over-reliance on one fungicide group and to design spray programmes which maximise the key features of each group," said David Slawson, editor of the leaflet. A second leaflet deals with fungicide resistance in storage diseases.

Be aware of the risk posed by fungicide-resistant blight, warned BPCs Dr Mike Storey. Satellite mapping and in-field monitors could help in future.

Satellite monitoring

Initial results from a trial to see whether blight infections can be spotted from space have proved promising. "We could clearly identify fields with 5-95% infection," said Mike Storey, British Potato Council director of R&D. That could aid risk forecasting to adjacent crops and market intelligence. However, detecting pre-symptomatic blight is proving more tricky. The BPC-funded study with satellite specialists Logica will be extended next year. The technology – which is used to check planting returns – could also help forecast crop yields, added Dr Storey.

Blight monitors

MAFF-funded work to evaluate blight forecasting devices suggests different machines suit different conditions. "That probably reflects differences in the models they use for forecasting infection," noted Nick Bradshaw, ADAS blight specialist. Assumptions about when blight spores arrive in a crop and how aggressive that blight is may be needed to ensure the models give more consistent advice, he said.