OSR - keep the crop competitive It is a very contrasting picture for OSR crops this autumn following wet weather which disrupted drilling schedules, but the main aim now should be to maintain the crop’s competitiveness where possible, growers are advised. Improved variety disease ratings will delay the onset of thresholds for light leaf spot (pictured) and phoma, but not eliminate them, growers are advised.
Oilseed rape crops drilled after winter barley benefitted from soil moisture and were up in a matter of days. But that wet weather hampered harvest and many crops only went in around the last week of the month or during the first week of September. It is those backward crops that concern AICC agronomists Patrick Stephenson (right) and Chris Page.
In North Yorkshire Mr Stephenson says around 30 per cent of his OSR area was drilled early. With ideal establishment conditions it is looking “pretty healthy”. “With these crops having every chance of growing away from pest and disease threats the only decision might be some autumn growth regulation,” he says. But for the remaining 70 per cent his objective is to maintain competitiveness. The warm spell around the August bank holiday saw cabbage stem flea beetle (CSFB)
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Early sown OSR crops are looking “pretty healthy” but backward crops are a concern.
numbers rocket. Growers won’t want the pain of ripping up fields for a second year and Mr Stephenson says it is important not to do anything which might thwart crop development. In addition there is ample soil moisture to trigger rapid grass weed germination, increasing the burden further on late drilled crops.
Earlier is better As well as pyrethroid sprays where necessary and an early post-emergence herbicide to deal with broad-leaved weeds, Mr Stephenson wants to maintain crop competitiveness with an early contact graminicide. “Employ it earlier than you think you need to,” he advises. “Take out what you can at the first flush - we have to remember how they are designed to work. The more established weeds are, the more they compete with the crop. Don’t wait until that happens,” he warns. When it comes to disease he fears a ‘phoma season’. With plentiful rain events in August alone an early phoma onslaught is almost inevitable but there is added risk from light leaf spot (LLS) too. “Phoma is probably a given here with so much wet weather from August onwards. Advanced crops are more resilient to the disease and the disease has further to travel from leaves to petiole and stems.” He points out phoma is easier to control and there are more options. The real question is the level of LLS activity. “Plover (difenoconazole), Refinzar (penthiopyrad + picoxystrobin) and Proline (prothioconazole) are all very good on phoma but when it comes to LLS and phoma the main active is prothioconazole. The risk then is exceeding the total dose as it is likely to be needed in the spring and at flowering for sclerotinia.”
Spray quality Chris Page says that pyrethroid sprays still offer economic CSFB control in his area but suggests nozzle type and spray quality is also an important factor. “We are wholly reliant on active contact with the pest and some coarse nozzles don’t provide the right spray quality to effectively achieve this. Even with a well-rolled seedbed they still find places to hide.” He too endorses the use of a pre-em herbicide and glyphosate ahead of drilling, but in his Midlands area many farmers have turned away from the practice due to later drilling. That extra pressure is why he urges growers to apply robust tactics to remove competitive weeds and volunteers. He wants broad-leaved weeds controlled by cotyledon stage, and cereal volunteers before they begin to compete with the crop, and doesn’t want growers to cut ‘dim and ‘fop rates. Post-emergence black-grass control begins with considering use of Centurion Max (clethodim), but he emphasises the need to allow a 14day gap either before or following up with any other herbicide or fungicide, or 10 days following insecticides only. An application of propyzamide when soil conditions allow is also advised but he points out growers shouldn’t delay fungicide applications if soil temperatures mean a single pass for both isn’t possible. To manage phoma and LLS, which he is encountering more frequently, crops will always be treated, sometimes twice. “Despite variety disease ratings improving it will delay the onset of disease thresholds, not eliminate it. As with weeds, disease control can be a bit of a moving target and growers will need to monitor crops for disease thresholds. A single combined phoma and LLS application is possible but if the weather continues to drive either disease I wouldn’t take any chances,” he says.
14 www.farmersguide.co.uk October 2017
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