Virus yellows risk lower than 2005

Recent cold weather means most sugar beet crops are at relatively low risk from virus yellows this season, according the latest forecast from the British Beet Research Organisation (BBRO).

Mean temperatures during January and February were around 1-1.5C below last year, which combined with severe frosts, has killed off and slowed the population growth of many virus-transmitting aphids, explained the BBRO’s Alan Dewar.

“These lower temperatures delay the time when aphids go into the crop, so they infect it at a later growth stage, which reduces the spread and effects of the virus.”

The lowest risk is in eastern areas, where 5.7% infection is predicted for untreated crops sown after 30 March, followed by 7.3% in the west and 14.6% in the north. This compares to 26.9%, 12.3% and 42.1% respectively this time last year.

Where Gaucho (imidacloprid) or Poncho Beta (beta-cyfluthrin + clothianidin) treatments have been used, infection risk is reduced significantly in all regions to around 0.5-1.5%, the forecast shows.

While some growers who have opted for a seed treatment may feel it was not necessary given the low risk this season, there may be extra benefit from protection against soil pests, Dr Dewar added.

“One consequence of the cold weather is the slow growth of young seedlings, which makes them much more vulnerable to soil pests like springtails, millipedes, pigmy beetles and symphylids. Growers using treatments may see a benefit.”

Further technical advice can be found at www.uksugarbeet.co.uk