Growers urged to beat rust threat

• Be alert for higher disease risk

• Keep close eye on beet crops

• Two-spray programme is best

Cool wet weather has seen sugar beet crops come under intense disease pressure, with rust infection the greatest concern for growers and agronomists.

Protecting green leaf area in the coming weeks is a priority to enable plants to build yield – particularly after this season’s challenge of late establishment was followed by the effects of heat stress in June.

Cooler and wetter conditions in many areas over recent weeks have been especially favourable to rust development – and growers should keep a close eye on their beet crops, says Syngenta technical manager Andy Cunningham.

In similar high-pressure situations last year, trials in Lincolnshire found that a two-spray Priori Gold programme in August reduced the infected leaf area from over 85% of the crop in untreated plots to just 19.8%.

Higher yields

Beet treated with Priori Gold – a co-formulation of azoxystrobin and difenoconazole – yielded an average 87t/ha, compared to under 75t/ha in untreated crops and 83t/ha in crops treated with either mefentrifluconazole + fluxapyroxad; or fluopyram + prothioconazole.

With a higher sugar content in Priori Gold treated roots, the two-spray programme returned an extra margin worth £680/ha hectare over untreated crops, with other fungicide options generating a £312/ha or £260/ha return respectively.

“Priori Gold was clearly the best product for controlling rust in the trial. But other trials have repeatedly demonstrated its outstanding broad-spectrum effects on other beet diseases – including ramularia, powdery mildew and cercospora too.”

Low cercospora risk

Relatively cool conditions this season have been far less conducive to cercospora, which is favoured by hot and humid weather – with temperatures in excess of 24⁰C and 10-15 hours daily at 90% plus humidity.

As a result, a low cercospora risk to crops this summer across most of the beet area is currently predicted by the disease model used by the British Beet Research Organisation, says Mr Cunningham.

“If the BBRO cercospora forecast does indicate the risk to be rising over the coming weeks, growers’ experience highlighted excellent results with Priori Gold control of Cercospora during last year’s extreme heat.”

To further alleviate any heat stress effects, many growers also combined Priori Gold applications with Quantis biostimulant treatments.

Two actives target disease

The azoxystrobin element of Priori Gold – also marketed in the UK as Angle – will be favoured this season for its physiological greening effect. This will enable plants to go on adding root weight and sugar content later in the season.

The overall efficacy is further bolstered by difenoconazole that is proven to protect against a broad disease spectrum.

“Together the two actives are incredibly powerful for beet disease control,” says Mr Cunningham. “Furthermore, it is a highly cost-effective option that can deliver higher margins for growers.”

Growers can make two applications of Priori Gold per crop at a rate of 1 litre/ha, with the latest time of application when roots have reached harvestable size (GS49) and not less than 35 days before harvest.