Beet growers could potentially have a new foliar disease to contend with
Beet growers could potentially have a new foliar disease to contend with in their crops with the recent arrival of stemphylium. Dominic Kilburn reports.
Stemphylium symptoms start with small, irregular yellow spots (left) which then begin to die from the centre forming brown spots 1-3mm across (right).
The first case of a new disease to affect sugar beet in the UK has been found in a Norfolk crop and it is one which, according to Dutch research, could have financial crop loss implications of up to 50 per cent if left untreated.Discovered in a crop close to the Norfolk coast, stemphylium is a foliar disease similar to mildew and rust in that it typically appears from early July onwards, and comes with symptoms starting with small, irregular yellow spots (in July/August) which can be confused with nutrient deficiency, says the BBRO.The spots begin to die from the centre forming brown spots 1-3mm across and, while heavily infested leaves die, more yellow spots appear on new leaves. Progressive leaf loss follows in August-September with subsequent yield loss.According to BBRO lead scientist, Dr Mark Stevens (left), stemphylium is a disease the Norwich-based organisation has kept an eye on since it first appeared in the Netherlands in 2007, where it has since spread rapidly across much of the country. “Dutch researchers were talking about it back then and, bearing in mind that the UK crop has inherited a number of diseases from the near continent, it is something we have been very aware of,” he says.”The Norfolk sample was sent to our plant clinic where we identified the stemphylium spores and Dutch researchers have also confirmed it,” he adds.The exact species of stemphylium that is affecting crops in the Netherlands has yet to be determined, emphasises the BBRO, but this will be important in identifying other host crops or weeds which will have implications for its control, and likely spread, should it become established in the UK.On-going field trials by the Netherlands’ own beet research organisation, IRS, have been established to study the control of stemphylium using a range of fungicides, including products not currently registered for use in sugar beet. Losses, expressed in financial terms in trials carried out from 2008-2013 have ranged from 9-51 per cent between the untreated and the best fungicide-treated plots, reports the BBRO.Mainstay broad-spectrum fungicides currently used in UK crops such as Escolta (cyproconazole + trifloxystrobin) and Spyrale (difenoconazole + fenpropidin) have shown little activity against stemphylium in IRS trials, says Dr Stevens, however greater efficacy was seen with Opera (epoxiconazole + pyraclostrobin).”Opera is probably going to be the best option of any currently-available fungicides to prevent the spread of stemphylium – it’s already used for the control of powdery mildew, rust and cercospora in sugar beet.”Like other foliar diseases, it will all be about stopping stemphylium early in the season to limit its impact,” he adds.Dr Stevens concludes: “We are keeping a watching brief on this and it’s important that growers are aware of the new disease and to keep an eye out for it in their crops.”If anyone has seen symptoms in the current crop and wants to get them checked out, then they should send a sample into the BBRO’s plant clinic.”