SUGAR BEET growers need to be vigilant for signs of Cercospora Leaf Spot on crops, British Beet Research Organisation has advised.

Now is the time of year for the disease, which appears on leaves as small round spots with reddish borders that eventually coalesce and cause defoliation, it said.

While the disease is rare in the UK, it is an increasing problem in central and southern Europe and is moving north – possibly due to warmer summers, said Mike Asher from Broom’s Barn Research.

“We know that Cercospora has always been present on wild sea beet around our coasts. It just needs some warm summers with intermittent rainfall.”

High humidity, water on the leaf from dew or rain and daytime temperatures of 25-30C are optimum conditions for its development, the BBRO said.

If left uncontrolled, yield losses can exceed 60%, but this is rare, as effective fungicides are available – but at a cost, he added.

“Two applications are normal in France (about £40/ha total), Germany and Holland. In the USA, Italy, Greece and Spain four or five may be necessary.

“This compares with the current single fungicide application (for mildew; about £17 per ha).”

Suspected infections should be reported to mike.asher@bbsrc.ac.uk