The British Beet Research Organisation (BBRO) has regained emergency authorisation for the use of Biscaya for beet leaf miner (mangold fly) control in 2016. This was confirmed by the regulatory authorities as effective on the 21st June and approval is in place for 120 days (until October 18th 2016) Application should be made via a ground boom sprayer in a minimum of 200 l/ha. No more than two sprays of Biscaya (maximum individual dose: 0.4l/ha of thiacloprid) can be made to English sugar beet crops. In recent years, there has been an increase in the incidence of late beet leaf miner and control options are very limited. Extensive damage can affect the plant’s photosynthetic ability. In large numbers, they can almost defoliate whole plants. The first generation is the most damaging, especially in late –sown crops with low leaf area. Later generations can be numerous but damage is less serious because they inhabit outer leaves and often coincide with periods of rapid growth, offsetting effects.
Current observations indicate that leaf miner populations are between first and second generations and overall, damage does not appear to be increasing. The recent wet conditions may have helped to reduce the activity of adults but new eggs will continue to be laid over the coming weeks and crops should be assessed for the need for any treatment. 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 really important to assess crops to ensure your use of Biscaya is at the optimum time.
Growers are advised to remember, the threshold for treatment is when the number of eggs and larvae exceeds the square of the number of true leaves. 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. Remember to check the underside of leaves for eggs and larvae.
More information can be found at the British Beet Research Organisations website: