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Late autumn control of weeds, pests and disease is key

Good farm agronomy will be vital over the next few weeks to build on the promising start that most autumn-sown crops have made

Agronomy update – Late autumn control of weeds, pests and disease is key.Good farm agronomy will be vital over the next few weeks to build on the promising start that most autumn-sown crops have made and ensure they enter the winter in optimum condition.Black-grass is the main target for many wheat growers. “Temperatures have been coming down quite markedly recently but soils will still be warm enough for Atlantis (mesosulfuron + iodosulfuron) to work,” says Norfolk-based Agrovista agronomist Craig Green (left).”It is better to tackle black-grass now than leave it to overwinter – Atlantis works best on small, actively growing weeds with 2-3 true leaves.”Fortunately most growers managed to apply pre- or early post-emergence treatments based on flufenacet plus diflufenican/pendimethalin, which worked very well and will help take the pressure off Atlantis. Where Avadex (tri-allate) was applied in sequence fields are spotless, says Craig.
“A few growers preferred to press on with drilling and might have struggled to catch up with spraying due to the ensuing windy weather. They will need to keep an eye on black-grass growth stage – by the time we get to November these plants will be tillering.”
Growers looking to boost control of black-grass in oilseed rape should be ready to spray propyzamide as Kerb if using this active alone, or as Cohort if following an earlier Crawler (carbetamide) spray to take out higher populations of hard-to-kill black-grass, he advises. Cranesbill is another problem weed in many crops and Craig recommends an application of Fox (bifenox) any time now to reduce the problem. Aphid watch
The Indian summer encouraged plenty of aphids into cereal crops, increasing the risk of barley yellow dwarf virus respectively. Crops that did not receive an insecticide seed treatment should have been monitored from the off, but treated crops should also be checked as the chemistry will be starting to run out of steam, says Craig.He advises spraying an approved pyrethroid on cereals if aphids are spotted, adding that growers should check pyrethroid labels for buffer zone recommendations. “If warm weather returns further vigilance will be needed – these are contact sprays so aphids could reappear. However, one or two sprays are usually sufficient – we’d hope to get enough cold weather later in the season to drive aphids back into hedgerows.” Similarly, he recommends Plenum (pymetrozine) on OSR if peach potato aphids are found.Phoma was reported in OSR in parts of the south east at the beginning of October and is likely to have begun spreading into East Anglia, says Craig.  “We usually see it a couple of weeks after Kent. Look for pale lesions and treat with flusilazole if you still have some in the store, otherwise prothioconazole. Thresholds are when 20 per cent of plants are infected, or 10 per cent if plants are small.”
Where PGR activity is also needed on more forward crops (four leaves plus) to suppress top growth and promote better roots, Monkey (prochloraz + tebuconazole) is a good choice. “Tebuconazole has a useful growth regulatory effect and prochloraz is good on phoma,” comments Craig. Where growth regulation is the priority metconazole (eg Sunorg Pro) should be used provided crops are actively growing). If active phoma or light leaf spot are present it will need mixing with flusilazole or prothioconazole. Micronutrients such as boron, magnesium and manganese can be applied as required at the same time as these fungicides, he adds.It is better to tackle black-grass now than leave it to overwinter, growers are advised.Ferric phosphate
Slugs still need watching especially in smaller, later-drilled crops. “They are particularly prevalent after oilseed rape, where the canopy kept soils damper, and there are some heavy, cloddy soils which are also high risk.” Widespread rolling of seedbeds will have helped, but where slug pellets are required ferric phosphate should be the first choice, particularly in high risk areas (check WIMBY on the EA website) or where metaldehyde limits have been reached.”In terms of controlling levels in surface water it is essential that growers start using this active instead of metaldehyde, especially when the risk of run-off is high,” says Craig. “All my recommendations include ferric phosphate – it is better to spend a bit more money now so we can keep metaldehyde as an alternative, rather than lose it altogether.”Root crop lifting continues apace, so far in good conditions. Once the harvesters have left he advises growers to check fields for compaction. “Few growers will have had a chance to put right any damage caused by the wet 2012 harvest and, with soils remaining relatively dry at depth, now is a good opportunity to check suspect areas with a spade to see what action is needed.”Beet growers should also check any yellowed areas for beet cyst nematode. “You can see cysts on the root hairs. If they are present, make a note and draw a sketch map of the farm showing the patches. When you come to crop the same fields again in five years or so, you’ll have a record of where to target BCN-tolerant varieties.”A close check will be needed as many yellow patches this year have been caused by magnesium deficiency, a common side-effect of dry soils as well as compaction, he advises. “It is also good time to do general soil sampling, and the best time for PCN tests – you can then order Vydate (oxamyl) in plenty of time and avoid the problems seen last year due to the quantity of material needed at short notice.”Energy maize
The energy maize harvest is drawing to a close, with yields around average due to the earlier dry weather and ensuing weed control problems, he reports. “We have also seen instances of eyespot, especially in second and third crops. Any maize still in the field in November should be checked carefully for dry matter and harvested as soon as possible, as the disease can defoliate a crop very quickly in cold weather.”As the rush to get fieldwork completed subsides, now is a good time to check the paperwork is in order. Cross compliance requirements should be near the top of the list, says Craig. Nutrient management plans and the soil protection review need to be kept up to date, stock checks should be undertaken and the sprayer given its annual MOT. “Also ensure your waste disposal tickets are to hand. Cross compliance inspections are common at this time of year – two of my growers have had visits already and there will be plenty more to come.”Finally, grandfather rights for spray operators, which allow people born before 31st December 1964 to spray without a certificate, will be withdrawn after 26th November 2015. These operators will need a new qualification, although this will take significantly less time, and cost less, than the existing Level 2 qualifications for pesticide users.”The proposed release date for the qualification is 26th November 2013,” says Craig. “I would urge operators to register through local City and Guilds NPTC assessment centres as soon as possible to allow plenty of time to undergo the new assessment test, rather than leaving it to the last minute and risking failure.”*Craig Green is an agronomist with Agrovista and is based at the company’s Great Ellingham depot, Norfolk ([email protected]).

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