Beet Research Organisation regains emergency authorisation for use of Biscaya

Leaf miner in beet
Leaf miner in beet

British Beet Research Organisation (BBRO) has regained emergency authorisation for the use of Biscaya for leaf miner (mangold fly) control this year.

This was confirmed by the authorities as effective on the 21st June and approval is in place for 120 days (until October 18th 2016).

Biscaya is a systemic insecticide that provides control of pollen beetles in oilseed rape and mustard, aphids in broccoli/calabrese, brussels sprouts, cabbage, cauliflower, carrots, parsnips, peas, oilseed rape and potatoes and a reduction of damage by orange wheat blossom midge in wheat.

No more than two sprays of Biscaya (maximum individual dose: 0.4l/ha of thiacloprid) can be made to English sugar beet crops.

BBRO's 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.

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.

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.

Aphid numbers increase

The relatively warm autumn and winter temperatures and the presence of alternative host crops such as oilseed rape is considered to be contributing to these large populations.

As crops lose the protection of seed treatments these high populations increase the risk of virus infection.

Although there is currently no approved foliar products available for this pest, please continue to monitor late/backwards crops.

However, once plants reach 12 leaf stage mature plant resistance will have an impact and the risk of virus spread declines.