AGRONOMY UPDATE – EAST
Windy weather has delayed pre-emergence herbicide applications in winter wheat, resulting in a change of tactics for some growers, says Agrovista agronomist Craig Green. Black-grass is not a serious problem for most growers in my area of Norfolk. Unlike many others battling with the weed, they have been able to take advantage of the drier spell in late September and early October to push on with winter wheat drilling. Seedbeds have been very good and, on the whole, these early drillings have got away well. However, at the time of writing in the first half of October, we’d had more than our share of windy weather. Sprayers have been parked up rather than applying pre-emergence herbicides, and growers have chosen to push on with drilling to make the most of good conditions. Applying the pre-em recommendation at early post emergence will still achieve good control for broad-leaved weeds, helped by the fact that most
weeds have been slow to emerge, including black-grass due to high dormancy levels. Growers without black-grass can use PicoMax (pendimethalin + picolinafen) and some additional diflufenican (DFF) pre-or postemergence will take out most major broad-leaved weeds and annual meadow grass. They also have the option of Othello (DFF + iodosulfuron + mesosulfuron) as a very good broad-spectrum back-up.
After drilling Where black-grass has been increasing in prevalence the aim is to apply pre-ems as soon as possible after drilling. My programme is based on Trooper + Herold, to supply 240g/ ha of flufenacet, backed up with pendimethalin and DFF. This, plus Avadex (tri-allate) applied as soon as possible afterwards, will provide adequate
pre-em weed control for most fields in my area. However, if forced to go post-em, be sure to leave out the Avadex – this is a pre-em option only on the label. Do take account of crop size and check with your agronomist that it is OK to proceed with other chemistry in the recommendation. Growers with a more serious black-grass problem, as well as those growing second wheats (take-all was widespread in these crops last season), have been holding off drilling. I would urge them to continue to do so, well into November if possible. A good quality seedbed will still be key to achieve optimal results. Soils should be rolled after drilling, unless they are prone to slumping – the last thing you want is to spend money on an expensive herbicide programme, only to find that clods fall apart, enabling weed seeds to germinate and establish. The flufenacet-based programme mentioned above will provide a good start where black-grass has become more established. Adding prosulfocarb can increase black-grass kill by a few percentage points and
boost control of problem ryegrass. Following up with a further flufenacet application plus Xerton (ethofumesate) with help tidy up survivors. Or, in this area at least Atlantis (iodosulfuron + mesosulfuron) can still add some useful additional control in late autumn through to spring. Sugar beet has been performing well this season, although harvesters are returning quite a lot of tops. Letting them wilt can save a lot of bother when it comes to drilling and crop emergence. Maize has also had a cracking year, with yields averaging around 46t/ha, well above last year. Crops received moisture at regular intervals and there was enough light and heat for them to develop well. Stand-out varieties so far are Susetta and ES Cluedo, both of which performed well on light soils, surpassing expectations. Forage variety Nordic Star has produced big yields on medium soils, with large cobs and good digestibility. *Craig Green is an agronomist with Agrovista, based at Great Ellingham, Norfolk (Craig.Green@ agrovista.co.uk). ■
those that had the holding spray. However, this won’t be available next year and stocks are already short, but Recital (fluopyram + prothioconazole) at the same rate will do a good job. Fungicide should be applied as soon as possible once thresholds have been breached. This application will also provide some early light leaf spot control. With the onset of cooler winter days, this spray should last through until early spring. If light leaf spot is seen before then, be prepared to retreat with Proline (prothioconazole) or Recital from February onwards.
Kerb (propyzamide) offers a great opportunity to hit black-grass hard again (Centurion Max has already worked well this year), with a different mode of action from cereal herbicides. It will need to be applied once soil temperatures fall to 10ºC or lower at 30cm depth, probably a good month away yet. Astro-Kerb, which also contains aminopyralid, is a good choice where broad-leaved weeds are a problem. Finally, it is worth mentioning that aphids are very active in cereals this autumn. Crops not treated with Redigo Deter (prothioconazole + clothianidin) should be sprayed with a pyrethroid as soon as the crop has one leaf, to prevent transmission of barley yellow dwarf virus. Crops that did receive the seed treatment will need checking four to six weeks after emergence. It is worth remembering that although every night of frost will reduce an aphid population by half, it will take a good week of frosts before crops are clear. *Esme Shephard is an agronomist with Agrovista, based in Wiltshire (esme.shephard@ agrovista.co.uk). ■
AGRONOMY UPDATE – WEST Oilseed rape disease and pests need a careful eye to ensure the crop goes in to winter in the best of health, says Agrovista agronomist Esme Shephard. We’ve been hearing reports of early phoma infection in oilseed rape crops and in some instances these breached threshold levels well ahead of the usual mid to late October spray timing. In small crops, the threshold is 10 per cent plants infected, and for larger crops or for varieties with a phoma rating of 8 or more it’s 20 per cent. Crops that exceeded these levels have been treated with a holding spray of Difcor (difenoconazole) at 0.25-litres/ha, or Metal (metconazole) at the same rate where some PGR activity was needed. These crops probably won’t need spraying again until early to mid-November, when the same thresholds should be adhered to. Other crops should be closely monitored for phoma from now on. Close attention will be needed, especially on small plants or
varieties with a resistance score of 6 or less, as this is shaping up to be the worst season for several years. The weather has been relatively warm and there has been a regular supply of moisture in most areas, ideal for the production and spread of the airborne ascospores from infected stubbles. These land on young, susceptible leaves and develop into the classic tawny coloured leaf spots. Once established, the fungus grows into the leaf, through the petiole and into the stem. Small plants are at higher risk as the fungus has less distance to travel to reach the stems. Here, the fungus forms cankers later in the season that restrict water and nutrient transport. Serious yield loss can result, especially in severe cases where bad lodging and even stem breakages can occur. I’ll be using Frelizon (penthiopyrad + picoxystrobin) at 0.5-litres/ha on all crops, including
Virus vectors Peach potato aphids have been observed in some crops. These are vectors of turnip yellows virus so susceptible varieties will require treatment with Biscaya (thiacloprid) at 0.3-litres/ha. It is well worth adding TerraSorb to one of these applications at 1.5–2.0-litres/ha. This aminoacid based biostimulant plus trace elements helps boost root and shoot growth and is especially useful on smaller crops to help get them ready for winter.
18 www.farmersguide.co.uk November 2017
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