Applying two fungicide sprays to late-lifted or disease-susceptible sugar beet crops could be a worthwhile investment this summer, experts suggest. “We’ve seen rust is rife in almost every other crop this year,” says Syngenta’s Beth Hall. “And, with the likelihood we’ll see another open (mild) autumn, I expect there will be a long period when disease can still be active and crops put on yield.”

Trials at Broom’s Barn last year (high powdery mildew pressure) found that two sprays of Spyrale (fenpropidin + difenoconazole) – 1 litre/ha in late July, followed by another 1 litre/ha in late August – gave a 9t/ha adjusted yield benefit over a single July spray (1 litre/ha), she says. “We’re only adding an extra £15-20/ha cost, so it’s clearly paying for itself.”

Broom’s Barn’s Mike May says two-spray programmes have shown promising results in trials, but it is too early to accurately predict what the incidence of rust and powdery mildew will be this season.

“Rust normally comes in fairly late, so it will depend what the weather does. We are expecting a fair bit of powdery mildew in the south (Arable, 22 June), but if it stays wet, it may not be a bad year. If it turns very hot, we might see cercospora.”

Sugar beet spraying - 2

Two fungicide sprays will help protect sugar beet crops against mildew or rust later into the season, says Syngenta’s Beth Hall

Mildew normally comes in later in July and if growers have susceptible varieties, but only want to spray once, they should wait until symptoms are seen, he adds. A split dose of one fungicide in mid-July, followed by another three weeks later could be appropriate where crops are lifted late and growers want to spread spraying workloads around harvest. “There is quite a range of growth stages out there, so don’t go too early on backward crops.”

It is also important to watch for long harvest intervals on some products (eg seven weeks for Punch C (carbendazim + flusilazole)), where crops are to be lifted earlier, says British Sugar’s Colin Walters.

“Number one, all crops should have a triazole or strobilurin-based fungicide. Some growers are still using sulphur, but it is outclassed and while it may save you £5, it won’t give the yield boost.”

He suggests a two-spray approach will not be worthwhile on crops lifted in the first six weeks of the campaign, but may be on rust-susceptible varieties – particularly if weather is wet into August.

paul.spackman@rbi.co.uk