This month’s key messages
Thank fully by now the threat of cabbage stem flea beetle is receding in oilseed rape crops and although some (5-10% would be a best guess) have been condemned, most crops are now growing away thanks to recent rain. Growth stages vary anywhere from the 2-leaf to 8-leaf stage.
Weed control in OSR has taken quite a few different forms this season, but the launch of Belkar (halauxifen-methyl + picloram) is a welcome addition to the OSR herbicide armoury. It enables tricky broad-leaved weeds to be controlled post-emergence of the crop when establishment – under pressure from drought and pests this year – is assured.
Drilling of cereal crops into land with historically high levels of blackgrass got going in the third week of October. Sufficient rainfall arrived to stimulate a flush of black-grass pre-drilling, but thankfully, it has not been too much and did not prevent good seedbeds from being produced.
Darren’s agronomy tips for November
We are now finding uncomfortably high numbers of Myzus persicae in many OSR crops, which carry the threat of turnip yellows virus (TuYV) transmission. Given the nature of aphid resistance and the fact that many will carry Kdr resistance to pyrethroids, this job is best done with an alternative insecticide mode of action. Biscaya (thiacloprid) applied at 0.3L/ha is a good choice and can be tank mixed with a range of fungicides or herbicides, if necessary, to save a pass through the crop.
We are now starting to see phoma appearing in more forward crops and showery weather during October will have encouraged its spread. It is likely that most crops will only receive one fungicide this autumn and it is therefore important to cover both phoma and light leaf spot with this application. Work by AHDB and Rothamsted Research has indicated that light leaf spot may infect OSR crops far earlier in the autumn than previously thought, despite visual symptoms not appearing until November, December or even later. Using a product such as Proline (prothioconazole) at a rate of 0.46L/ha in early November will give effective control of both Phoma and Light Leaf Spot.
Where wheat drilling continues into November on blackgrass land, roll the seed-bed and apply a robust pre-emergence herbicide, ideally within 48 hours of drilling. Liberator (flufenacet + diflufenican) at 0.6L/ha is a good base for this application. Additional residual herbicides can then be stacked on top in the form of extra diflufenican, pendimethalin or prosulfocarb or a sequence with Avadex 15G (tri-allate). Attention to detail with application will pay big dividends. Use the correct boom height (50cm above target for 110 degree flat fans), appropriate water volume (200L/ha would be my suggestion) and a forward speed below 12kph. These will help ensure the best soil coverage and maximise residual herbicide activity.
Some growers drilled early and in dry conditions and pre-emergence herbicides have not performed well in these situations. Questions are being asked about the autumn use of Atlantis (iodosulfuron + mesosulfuron) or Hamlet (diflufenican + iodosulfuron + mesosulfuron) where black-grass has emerged with the crop.
These may be useful tools for attacking small black-grass plants at the 1-2-leaf stage while temperatures and growing conditions are still good. Atlantis at 0.4kg/ha or Hamlet at 1.5L/ha, with a residual partner, are both options to consider. Alternatively, where black-grass numbers in the crop are very high, a dose of Roundup (glyphosate) and then re-drilling may also be an option to consider (alongside why the hell they drilled so early in the first place!).