Flea beetle season began slowly; I actually thought early in August that perhaps this year we would have it easy, as the early-drilled oilseed rape went in and started to emerge and little damage was found.
When the main OSR area went in around the middle of August, I was confidently telling my growers I had seen little damage and that I was cautiously optimistic that this year we might get away with it; the forecast was warm, and wet; it looked like the period of drought was at an end and I had high hopes this weather would see OSR leaping out of the ground, leaving the flea beetle at a standing start. And then the rain (of which we had little anyway) disappeared from the forecast, temperatures soared, and the phone calls on the last weekend in August started to get me concerned.
Flea beetle had come out in force, rapidly consuming our rape crops in a frenzy that lasted not days, but weeks. Walking rape has been a disheartening job ever since, with cotyledon rape disappearing from one week to the next, plants being taken off as they emerge and even bigger plants struggling to grow away from the damage. The application of pyrethroids to try to knock down populations has not saved crops. With resistance to this chemistry, widespread hopes were not high that it would be the solution to our problems; however with no other defence available, and crops disappearing under seas of shiny black beetles, applications were made to try to save struggling crops, often to no avail.
While the flea beetle has indeed made the most of the situation, they cannot be blamed completely for the failure of crops. The unprecedented lack of rain has seen establishment struggle. Seedbeds that were worked before drilling lost moisture which has never been replaced and seed has sat in dust awaiting rain.
There is a stark difference this year between direct drilled and conventionally established rape – with the OSR that has been direct drilled faring much better, probably due to holding on to more moisture.
Due to the dry conditions many pre-ems that were planned go on the OSR were pulled, and in places where cranesbill can be problematic, Belkar (halauxifen+picloram) has been put on farm to be applied post-em. However, no crops yet have received this chemistry as we wait for better establishment to deem the crop viable. But the time for redrilling has passed and, with still no rain, seedbed conditions are as dry as ever. Unfortunately, this has meant crops have been written off and attention is now turning to what we can grow instead.
Winter beans could have been a good option but, with the dry summer and high heat resulting in germination tests being worryingly low, growers are struggling to source seed.
Another option could be to put in a spring crop such as spring oats. This crop has low inputs, provides a good break crop from take-all and, while little can be applied in terms of herbicides, the spring sowing means we can utilise stale seedbeds until late in the season.
This year has been the perfect storm – or rather, the imperfect storm – for our rape crops. The hot, dry weather favoured the high populations of flea beetle and high activity, while the dry conditions prevented the rape from moving quickly and outgrowing the feeding frenzy. Can any more changes be made, or approaches differ, to protect us from these early threats, or are we at a point where we question the viability of OSR on-farm? These are questions we will try to address before the start of the next OSR growing season.