Independent potato blight fungicide trials have produced mixed results, according to reports given at the BPC Blight Forum held in Peterborough at the end of last month.

The three-year long British Potato Council-funded trials conducted by ADAS and SAC revealed two clear winners in the fight against tuber blight - Ranman TP (cyazofamid) and Shirlan (fluazinam).

The trials evaluating the performance of mid to end-season sprays also found a clear benefit from using early season blight fungicides, especially systemic products.

But the relationship between levels of foliar and tuber blight was not so clear from the findings.

The results of the 2003-05 trials had been drawn together to highlight how the newer fungicides performed against tuber blight compared to the Fentin products now disfavoured.

SAC’s Ruairidh Bain said: “The loss of tin isn’t much of a loss. But high incidences of tuber blight can occur where there is little obvious foliar blight. We also found the effectiveness of some fungicides was lost due to weathering.”

He said more work was needed to develop a tuber blight assessment procedure.

“We also need to obtain more accurate information on the relative importance of different primary sources of inoculum, such as seed-borne blight and oospores, and develop the appropriate fungicide strategies,” he claimed.

Meanwhile Dutch research also revealed at the forum has found sprayer boom swing can have a significant effect on late season blight control.

The trials found treated areas of a potato crop had a 20 per cent reduction in blight infection.

Jan van de Zande from Plant Research International in the Netherlands said measurements of spray on the leaves of the crop showed some areas received just 40 per cent of the full dose, while others were oversprayed by 60 per cent.

“Relatively small movements of the sprayer boom can mean areas of a field are less protected against blight due to under-spraying. Over and under-dosing occurs in the same places in the field during a season, which means there is a cumulative effect.” he claimed.

Zande said the differences in spray deposition tend to increase as the season progresses and incidences of blight ranged from nothing to 80 per cent of an untreated crop.

In addition, he revealed that some of the most dramatic variations in boom movement were found in wet patches in fields.

“We are planning further research to establish the effect of these in-field variations, and will also be looking at the differences tyre and track-width have on spray deposition variances,” he claimed.

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