National study shows clear progress in CSFB battle

Oilseed rape cropping success has markedly improved this season in all parts of the country, reveals the 2021 National Cabbage Stem Flea Beetle Management Study.

Growers across the UK sowing more than 15,000ha of OSR last autumn reported an average re-drilling rate of just 5 per cent in the benchmarking study run by Bayer with ADAS and NIAB in late March/early April. This compares with 14 per cent identi ed in the almost identical 2020 study.

What’s more, 91 per cent of this season’s crops survived to the spring and 89 per cent are being taken through to harvest, against 67 and 60 per cent respectively in 2020.

“This much improved position results from a combination of noticeably lower autumn CSFB pressure and much better soil moisture conditions at drilling,” observes Bayer study co-ordinator, Lizzie Carr-Archer (right). “Less than 20 per cent of crops were reported to have su ered an intense or substantial challenge from CSFB last autumn, with over 80 per cent seeing a moderate or low challenge. This is in contrast to 2019 when over half of the crops faced a particular challenge from the pest.

“At the same time, only around 15 per cent of this season’s crops had to deal with fairly or very low soil moisture conditions at establishment compared to nearly 40 per cent last season.”

Drilling date

Also clear from the two years of Bayer studies is the fact that early August drilling is fast becoming the norm across the country. Nearly half of the 250+ crops involved were drilled before August 20th compared to less than a third in 2019, with far fewer in the traditional mid-late August slot.

What’s more, the results underline that this move is more than justi ed, even under the lower CSFB pressure and better establishment moisture conditions recorded last autumn.

For the second year running, overall cropping success in 2020/21 showed a clear decline with delay in drilling, although the less challenging establishment season meant the di erences in crop survival to harvest were less marked than 2019/20. However, the trend was remarkably similar, with performance from September sowing, in particular, su ering under a period of relatively higher pest pressure and lower moisture levels (Figure 1).

“The relatively poor performance of September drillings was mirrored in the establishment scores given by growers for their various crops,” notes Ms CarrArcher. “An average score of 6.8 (on a 0 to 10 scale from crops lost to perfect establishment) contrasted with scores of 8.0 or more for all earlier sowings.

“Once again, though, our study recorded higher levels of CSFB larvae from earlier drilling wherever there was a particular autumn challenge from the pest. This is something those moving drilling forward need to be especially aware of in their management.” pressure and much better soil a clear decline with delay in drilling, although the less challenging establishment season meant the di erences in crop survival to performance from September sowing, in particular, su ering

Figure 1: Overall OSR crop survival by sowing date

2020/21 2019/20

On or before August 7 August 8–20 August 20–31 September 1–15

Variety value

For the second year in a row too, growers across the country have found hybrid oilseed rape better at dealing with the cabbage stem ea beetle challenge than conventionally-bred varieties, with noticeably lower levels of larvae and better larval recovery.

Like the previous year, there was not much to choose between hybrids and conventional varieties in immediate establishment terms. And, as one might expect, all three indicators of success – establishment, larval level and larval recovery – showed a clear improvement on autumn 2019. Once again, hybrids proved better able to deal with CSFB larvae.

“Successful OSR establishment is much more about having su cient moisture at drilling and preserving it through the most vulnerable cotyledon stage until rooting is well enough developed than it is about breeding or, indeed, seed size,” Ms Carr-Archer points out.

“Our trials and eld experience suggest the main cabbage stem ea beetle management value of hybrids lies in their superior ability to grow away from the pest. But we also know that hybrids vary quite widely in their ability to do this, depending on their particular growth habit.

“Those with a relatively fast speed of autumn development are better able to make-up for any early leaf damage ahead of winter.”

Establishment regime

Unlike 2019/20, when the intensity of the CSFB and moisture challenges almost certainly masked any di erences between establishment regimes, the current season highlighted subsoiler seeding systems as noticeably less successful than other approaches. While these regimes had a slightly higher average re-drilling rate than other low disturbance regimes, the main reason for their relatively poor performance lay in crop survival to spring (just 75 per cent against around 90 per cent for direct drilling and minimum tillage). “This may relate to the less consistent sowing depths achieved by many such regimes, but perhaps we shouldn’t read too much into these di erences, given the sheer diversity of establishment regimes growers may de ne as either subsoiler seeding or minimum tillage,” suggests Ms Carr-Archer.

Management techniques

Of the 17 main techniques growers are employing to manage the cabbage stem ea beetle threat at establishment, four stood out as the most successful in the latest study. Sowing earlier than normal, employing seedbed fertilisers, using vigorous fast-developing hybrids and spreading organic manures were all rated at 6.3 or more on a 0–10 scale of e ectiveness.

Also rated above 6.0 were minimising tillage and double rolling, while leaving OSR volunteers from previous crops and spraying with insecticides scored lowest (Figure 2).

Interestingly, with an average score of 5.9, encouraging natural enemies by avoiding insecticides was considered more e ective than using insecticides.

“While 42 per cent continued to apply insecticides last autumn, this was far lower than the 67 per cent doing so in 2019, with far more growers than the previous season employing only one or two sprays rather than three or more,” Ms Carr-Archer notes. “That this change may owe more to the lower observed CSFB pressure last autumn than anything else, however, is suggested by the fact that they were still being used by almost two thirds of growers with the best-performing crops under signi cant autumn CSFB pressure.” FG

Figure 2: E ectiveness of techniques to manage adult CSFB

Employing seedbed fertilisers Minimising tillage Sowing earlier than normal Using vigorous, fast-developing hybrids Spraying with insecticides Spreading organic manures Leaving OSR volunteers from previous crops Leaving long cereal stubbles Employing higher seed rates Double rolling Companion cropping Using farm-saved seed Leaving a covering of chopped straw Encouraging natural enemies by avoiding insecticides Sowing later than normal* Applying deterrent sprays or colourants* Treating seed with Lumiposa*

4.2 5.0 6.9

6.1

6.4 7.2

6.3

5.2

6.0 6.1

5.1

5.8 5.4 5.9 6.1

5.0 5.3