Being able to pick a variety based on its ability to cope with flea beetle may be high on growers’ wish lists, but creating a metric for this is not without its challenges.
AHDB has been exploring how to measure whether certain varieties are less susceptible to the pest following the suggestion some are able to tolerate larval feeding better than others.
Dr Gosling says: “Some varieties may be less susceptible to damage so larvae don’t thrive in those varieties, or it may be some varieties can compensate more and therefore suffer less yield impact.”
AHDB introduced a protocol for assessing damage in 2020 which appeared to show some statistically significant results.
Dr Gosling says: “Varieties were put on a one to nine scale based on level of damage and in 2020 we found small but statistical differences in between varieties.”
Difference However, when the 2021 and 2020 data was combined there were no statistical difference between varieties.
“We’re not sure if this doesn’t reveal the difference or that there just isn’t a meaningful difference between varieties.”
Spring assessments were done this year, but Dr Gosling says even if a protocol that works is found, cabbage stem flea beetle tolerance ratings are unlikely to be published until at least 2023/24.
AHDB is also exploring how the term ‘vigour’ – well-loved by marketeers – can be measured.
Dr Gosling says: “Everyone comes back with a different answer when you ask for the definition.
It could be size, green area index (GAI), speed of development or other factors.”
In 2020, AHDB asked trials operators to time how long it took for different varieties to reach key growth stages and then take biomass samples and plant population readings.
“However, our trials officers found it too difficult and onerous and we didn’t get good data,” he says.
The following year, the protocol was flipped and they were asked to look at the development stage of the crop at specific points in time after drilling.
Dr Gosling says: “Looking at three trials sites in Fife, Lincolnshire and Herefordshire, it does look as though we’ve got some differences in autumn vigour measure.
However, some varieties had high GAI in one location and very low in another.”
As part of the next step, AHDB will review the protocol with its trials operators and, depending on the outcome, continue the work into next autumn.
However, a vigour rating will not appear on the RL before 2024/25.