Favourable weather conditions have led to reports of foliar disease in sugar beet crops. So far, only bacterial leaf spot and downy mildew have been confirmed, but with unsettled weather forecast to continue, growers are being advised to inspect crops for signs of other foliar diseases and be prepared to apply fungicides as soon as disease is detected.
The principal disease threats to note are rust and powdery mildew, though the extent to which they manifest is largely determined by conditions during the season.
Fortunately, the effects of disease in recent years has fallen with the diligent use of fungicides by growers and selection of varieties with improved disease resistances. These measures have ensured crops are no longer as badly affected as they once were.
“Of the main foliar diseases powdery mildew and rust remain the principal threat to yields,” says Jack Hill, Bayer commercial technical manager for Norfolk.
“Powdery mildew has the potential to be more damaging. It manifests as a grey mould on the upper side of the leaf which can quickly cause the outer leaves to be lost. It is a disease which exploits stressed crops as was the case in 2018 when the early summer drought led to a high incidence of disease,” he says.
With the exception of some areas in 2018 however, rust has been the main concern of recent years and although the dry summer last year ensured it was slow to take hold, it quickly became established once conditions changed towards the end of the summer.
“The onset of rust varies with the weather during the season, but it typically occurs towards the end of July,” says Mr Hill.
“There have been cases where it has emerged far earlier however, most notably in 2017 when it was reported in early June. With conditions potentially favourable, growers should be inspecting crops regularly in readiness to make the first application of Escolta (cyproconazole + trifloxystrobin).”
Rust typically manifests as orange/brown pustules on the upper side of the leaf surface and, left untreated, can often lead to yield losses of up to 14%, which is roughly equivalent to 12t/ha based on an 85t/ha crop.
More than 10 years of trials demonstrate that protecting yield potential comes down to the timely application of Escolta, the fungicide that has given the greatest protection in trials.
“In trials spanning more than 10 years the average yield response from two applications of Escolta has been an extra 9.6t/ha over the untreated. For those with sugar beet on a contract price of £22.50/t, this means an extra £216/ha in enterprise output. It is an extremely high level of return.” says Mr Hill.
Getting the best from Escolta
“It is important to note that fungicide timing is a function of disease onset, not calendar date. Once disease is detected or reports confirm it is circulating, Escolta should be applied at the full rate. It is important to maintain water rates to ensure the spray penetrates the whole canopy,” he says.
“The first spray of Escolta should be followed up with a second application, also at the full rate, four weeks later. This will keep canopies clean into September and October. In addition to protecting yield potential, a clean canopy will continue to support sugar accumulation and root growth into the autumn,” he adds.