Cabbage stem flea beetle – Risk mitigation strategies – Part 1
14 Aug 2018
In our State of the Nation survey, we found that over 70% have suffered from cabbage stem flea beetle (csfb) damage in the past three years, and in this blog ADAS experts, Dr Pete Berry, head of crop physiology and entomologist Dr Steve Ellis, discuss some of the ways to mitigate csfb damage when establishing the crop.
Getting the crop off to a good start
Steve said, “When we say get the crop away well that doesn’t necessarily mean bang it in as early as possible, at really high seed rates. It’s taking account of soil moisture and judging the conditions to get the most vigorous plant development, which could be anytime within quite a big window.”
Pete said, “The winter oilseed rape sowing window is really mid-August until mid-September, but timing it so that the seedbed has enough moisture in it is crucial. If it is dry all August, I wouldn’t hesitate to wait to drill until conditions are right in September, to get that vigorous growth.
We need to recognise there is a downside to drilling and establishing a crop really early. It produces an over large canopy that is then difficult to manage throughout the season. There is that potential trade off from drilling early.
It’s all about seed to soil contact, so a fine seedbed and the smaller the aggregate size the better. A sowing depth of 20mm is generally sufficient.
If it’s dry, minimise the time between the primary cultivation, if you are having one, and drilling, so there isn’t any chance of the soil drying out between jobs.
Rolling is absolutely essential and consider rolling twice to really consolidate.
By and large the hybrid varieties are more vigorous, but it is not a hard and fast rule. The vigour difference is more apparent when the conditions are challenging, like dry or cold.
In the absence of csfb, a low plant population ideally, 20-25 plants/m2 achieves the highest yields. With csfb there has to be some insurance in terms of a slightly greater seed rate, but don’t overdo it because a very high plant population has an over large canopy that is more susceptible to lodging, and the yield loss this causes.
Again, as with the sowing date, there is a trade-off to be had. The message would be a modest increase in seed rate but not overdoing it.
Avoid small seeds, if the 1000 grain weight is less than 3g and you are trying to establish those in marginal conditions then that does reduce the establishment of the crop.”
Companion cropping and spraying insecticide at night
Steve said, “To date we have not done any work on companion cropping so it is difficult to comment on how effective it might be. As for spraying at night, some reports I’ve heard say it is better than during the day, whereas others have suggested no difference’.”