British Beet Research Organisation (BBRO) has regained emergency authorisation for use of Biscaya (thiacloprid) for leaf miner (mangold fly) control in 2016.
This was confirmed by the authorities as effective on June 21 and approval is in place for 120 days until October 18.
BBRO said application should be made via a ground boom sprayer in a minimum of 200l/ha. No more than two sprays of Biscaya (maximum individual dose: 0.4l/ha of thiacloprid) can be made to English sugar beet crops.
Current observations by BBRO indicate that leaf miner populations are between first and second generations and overall, damage does not appear to be increasing.
Recent wet conditions may have helped to reduce adult activity but new eggs will continue to be laid over the coming weeks and crops should be assessed to determine whether they need treating, said BBRO.
BBRO trials have shown that the most effective stage for treatment is at egg hatch/larval emergence. For many crops, this may be over the next few weeks but it is important to assess crops to ensure chemical use is at the optimum time, said the organisation.
The threshold for treatment is when number of eggs and larvae exceeds the square of the number of true leaves, said BBRO.
For example, a plant with six true leaves would need a population of 36 or more eggs and larvae to warrant treatment and a crop with 10 true leaves would need a population of 100 or more eggs and larvae.
Growers should also check the underside of leaves for eggs and larvae, said BBRO.