Growers on wireworm alert after wet weather

Growers are being warned that wet soils could increase the risk of wireworm damage in British potato crops this season.

Recent research has identified high soil-moisture as a precursor for pest activity, crop science firm Syngenta has revealed.

Syngenta’s assessment comes as UK potato planting continues apace in a bid to make up for delays caused by unseasonably wet winter and spring weather.

Syngenta technical manager Andy Cunningham warned of a “double whammy” of potential problems in potato crops planted this spring.

Recent wet weather, combined with lower potato production in autumn last year and the fact that overwinter cover crops can harbour wireworm populations, could exacerbate the pest threat, he said.

“Wireworm is an increasing issue in cereal rotations, particularly where there’s grass weeds in stubble or left as cover - be that with stewardship scheme compliance or limited chance for cultivations in the autumn that disrupt the pest,” Cunningham said. “Weather conditions have severely curtailed growers’ opportunities for Integrated Pest Management (IPM) cultural controls of wireworm.”

Syngenta trials in Lincolnshire last year showed that Syngenta pesticide, Nemathorin, applied at the time of planting reduced the proportion of wireworm damaged tubers to just 2 per cent of the harvest, compared to 9 per cent in untreated areas, according to Cunningham.

Severity of damage was also reduced, with no tubers in the Nemathorin treated areas showing more than five holes, and significantly fewer with one to five holes, he said. Over 2.5 per cent of the untreated crop had an unacceptable three or more wireworm holes.

Cunningham also reported that trials had shown using Nemathorin at a higher rate of 30 kg/ha in a high-pressure field situation had halved the number of tubers seriously affected by wireworm.

The application of Nemathorin at 30 kg/ha is permitted where PCN or free-living nematodes are being targeted, he said.

“PCN remains the most serious soil pest of potatoes – hitting yields in the current crop and, if left unchecked to multiply, the future viability of fields for potato growing in the rotation,” Cunningham said.

“In an average of eight recent trials where PCN was present, Nemathorin delivered an average yield increase of more than 17 t/ha over untreated. In the same trials, Velum Prime achieved just 4.5 t/ha extra yield.”

In terms of financial reward, Cunningham calculated on a 40 t/ha crop the Nemathorin returned over £2050 per ha margin over input cost, compared to less than £500 with Velum Prime.

“Furthermore, when the soils in all the trials were analysed, the Nemathorin treatment held the multiplication rate down to 2.5, compared to 9 in the untreated. In the Velum Prime treatments, the PCN continued to multiply at a rate of 7.5 times,” he said.

“IPM measures for all soil pests, including variety selection, rotation interval, adapting harvesting dates and target markets can all help growers and agronomists mitigate against damage,” said Cunningham. “But where there is a risk of losses, the use of Nemathorin could provide additional protection to yield and assure the sustainable long-term viability of potato production.”