Two-spray strategy sweetens yields for beet growers

A two-spray fungicide strategy can keep key sugar beet diseases – powdery mildew and rust – at bay and so boost root yields and profit margins for growers.

Disease control has pushed beet yields up by around 13-14t/ha in a three-year trial, and has given a clear financial benefit for sugar beet farmers.

Mark Stevens, lead scientist at the British Beet Research Organisation (BBRO), believes a robust fungicide approach is needed to protect the leaf canopy and hence boost yields.

“For early lifted beet in late September/early October, a one-spray strategy looks good; for anything after that we would recommend a two-spray approach,” he says.

With the British Sugar price for beet at £27.53/t and a single fungicide spray costing around £18-25/ha then disease control clearly makes financial sense, he adds.

Just under half of UK beet farmers are estimated to use a twin-spray fungicide approach, and so many could be losing out on the potential yield benefits.

Dr Stevens is now looking at an early warning system to see if control is worthwhile when the disease spores arrive in the field some two to three weeks ahead of when symptoms are first seen.

“We will look to monitor the spores coming into crops to see if a fungicide application earlier than normal could lead to better control,” he says.

First fungicide applications usually takes place in the last two weeks of July to the first week of August when diseases are first detected in sugar beet crops.

Diseases are usually seen first in the southern UK beet areas of Suffolk and then develop slightly later in the more northerly growing areas into Lincolnshire and Nottinghamshire.

Recent weather patterns leading to cooler and wetter summers have tended to favour rust diseases over mildew, and 2012 was a rust year with little mildew seen.

Using the beet variety Bobcat, Dr Stevens showed yield gains of around 13-14t/ha using a two-spray regime across the last three years of 2010, 2011 and 2012.

His work used two fungicides, Bayer’s Escolta (cyproconazole+trifloxystrobin) and Sygenta’s Spyrale (difenoconazole+fenpropidin).

The use of broad-spectrum fungicides has only been widely used in sugar beet over the last decade and before that sulphur was used largely for disease control.

While untreated plots yielded 89t/ha, a two-spray Escolta programme gave a root yield of 103t/ha and Spyrale 98t/ha when lifted for harvest in December.

Dr Stevens says canopy retention is key, as keeping the leaf free of foliar diseases will boost photosynthesis and hence yield.

This two-spray policy also helped push the all-important sugar content of the beet up by almost 0.5% to around 16.6%, he adds.

In 2012, rust covered nearly 6% of the untreated crop leaf area by late October compared with less than 2%, with areas given the two-spray programme leading to a subsequent lift in yield.

Dr Stevens said the two-spray programme was the most cost-effective strategy to boost yield, although he is also looking at a three-spray approach.

This three-spray programme with applications in July, August and September gave a benefit in 2011 when the beet was lifted late after Christmas.

However in 2012, the three-spray programme did not get a yield benefit over the two-spray approach and Dr Stevens plans more work this year.

“We need to understand more about fungicide applications and whether it is best to try and control the disease before it is seen in the crop,” he says.

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