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Talking Agronomy with Sarah Symes: Autumn is upon us


After hearing of record temperatures and low rainfall throughout September, October has well and truly pushed us all into autumn, with sporadic rainfall and cooler soil and air temperatures.

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Here in the South, mostoilseed rape crops have survived the flea beetle onslaught growers in the East have seen. A bigger problem has been turnip sawfly. Almost all our stubble turnip and oilseed rape growers have sprayed for them after either finding significant numbers of the fly or larvae, but now temperatures have started to cool down and the wet weather set in, populations have dropped off.


Noticeably, aphid numbers have also increased, some say this could be down to the lack of neonicotinoid dressing, but perhaps more likely this has been down to the warm dry September, so some of our growers have sprayed Plenum (pymetrozine) or Biscaya (thiacloprid) for control where populations have been high, due to the resistance to pyrethroids.


We have seen occasional areas that did not survive flea beetle attack despite crops being checked almost daily by growers. From now onwards we will be looking out for flea beetle larvae, which can cause damage in the stems and leaf petioles resulting in poor plant vigour. The threshold for larvae is two per plant. However, flea beetle larvae are likely to be resistant to pyrethroids and the newer insecticides aren’t systemic enough within the plant, so control will be a challenge if a problem arises.


We have been looking out for phoma, but only the odd few lesions have been found so far, so we have been holding off on any applications as thresholds have not been met. It is looking likely that one spray may be enough this autumn depending on weather conditions, which will be applied mid November onwards, that will hopefully cover us until New Year. Last year, light leaf spot was more prevalent, so we will also be looking out for leaf symptoms, and if a later spray is applied, a product with light leaf spot protectancy will be used.


A large part of our cereal area has been planted, although many of our growers still have ground to sow but have been held off with the heavy rainfall we’ve had in October. Growers with bad black-grass situations held off as long as they dared to get a chit and spray it off to start with a good clean seedbed.


With high aphid numbers around, it may be worth spraying cereals for BYDV. Deter (clothianidin) seed dressing will give six to eight weeks protection, but if the autumn stays mild, early drilled crops will require an insecticide.


Pre-emergence sprays have been applied in good time, despite the lack of moisture at application and appear to have worked well once the rain came. Crops in bad black-grass situations received Crystal (flufenacet+pendimethalin) pre-emergence and will be followed up with half to full rate Liberator (DFF+flufenacet). Crops that received Liberator pre-emergence ay receive a half rate follow up 42 days later. For larger-tillered black-grass an autumn application of Atlantis (iodosulfuron+mesosulfuron) may be required.


Some winter beans have been drilled on the lighter ground, others are still waiting for the ground to dry out enough to be able to get on.


As usual with beans, a strong pre-emergence herbicide strategy is being recommended due to the lack of options post-emergence. This will consist largely of Centium + Defy + Stomp Aqua (clomazone+prosulfocarb+pendimethalin). In black-grass situations Crawler (carbetamide) will follow up before the end of February.


Some frit fly has been seen in the South where wheat or barley has followed oats. An application of Dursban (chlorpyrifos) is being recommended in high risk situations such as a poor seedbed or late drilled crops. As usual we have seen patches of slug activity, but despite the hype in the press about exploding populations, crops are getting away well, due to good seedbeds which are firm enough to restrict movement, so only grazing on the surface has been seen.

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