The first cases of QoI-resistant cercospora beticola, the fungal disease that causes cercospora leaf spot in sugar beet, have been identified in the UK.
Samples were taken from infected beet plants at sites in Suffolk, Lincolnshire and Cornwall as part of routine resistance monitoring by Bayer in 2016. All three were found to be resistant to the company’s QoI fungicide trifloxystrobin. The FRAC code list 2017 states that cross-resistance is shown between all members of the QoI group, commonly known as strobilurins.
Trifolxystrobin is co-formulated with cyproconazole in Bayer’s product Escolta. Bayer campaign manager for root crops, Edward Hagues, says that one of the main purposes of co-formulation is resistance management.
“Triazole fungicides are unaffected by this resistance and will continue to provide protection against the disease. The best fungicide programme for beet continues to be two Escolta sprays at 0.35l/ha, giving excellent control of the major sugar beet diseases – powdery mildew and rust – and a proven yield-boosting effect.”
BBRO lead scientist Dr Mark Stevens acknowledges that the finding is concerning, but says it needs to be kept in context.
“These were three samples, taken in one year and collected as part of a large-scale European monitoring programme, and does not mean there has been an escalation in the threat level posed. Further analysis is required to determine the extent and significance of this finding.
“Cercospora usually occurs infrequently and at low levels in the UK because our cooler weather is not conducive to its development. When it is seen, it is usually later in the season, when it has less impact on yields. Good crop hygiene is important to minimise the risk of future disease carryover.”