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  1. Earlier and more intensive soil sampling to accurately determine Potato Cyst Nematode (PCN) risk ahead of planting is vital if growers are to beat this increasing problem, says leading agronomy group Hutchinsons.

    Although many growers are routinely testing soils for PCN, John Keer of Richard Austin Agriculture says there is still considerable scope to improve procedures.

    Soil sampling as early as possible can potentially make the biggest difference to managing the problem as this allows greater flexibility to alter crop rotation and grow something other than potatoes on fields where high populations are detected, says Dr Keer.

    “Many people will typically be sampling from now through the winter, but quite often this means it is too late to change the rotation next spring.

    “We are increasingly conducting more sampling in the preceding spring, up until the end of March or mid-April, with a view to altering cropping for the following year if the PCN population warrants it.”

    Even where land is believed to be PCN-free it is still worth testing fields well ahead of planting to confirm there are no hidden issues, he adds. “This is often a problem on rented areas thought to be virgin potato land, but may have had crops or potato waste on them in the past.”

    Build a long-term picture

    Sampling should be more intensive to build a better picture of the overall situation and reduce the risk of missing PCN hotspots within a field. That means ensuring samples do not represent any more than 1ha, Dr Keer continues.

    He also advises growers to GPS map the locations of soil samples, so that repeat future tests can be carried out on the same area to better gauge the success of changes to management practices in reducing PCN counts.

    “PCN management is not about managing it over just one crop. It has got to be a rotational plan based on an accurate measure of the problem in the first place and integrates a range of control options that include nematicides, resistant varieties, cover crops and longer rotations. By using an integrated management plan it should be possible to keep levels below 5 eggs per gram.”

    A similar view is shared by Hutchinsons agronomist Andrew Goodinson, who advises across 1,000ha of potatoes in Herefordshire.

    “Although we’re not seeing the really high egg counts that some other regions experience – early-20s per gram is typical - PCN is an increasing problem in this area that is being spread on machinery, such as harvesters, cultivation equipment and sprayers.

    andrew goodinson hutchinsons optim
    “Once hotspots develop they can spread very quickly, so we have to be much more proactive in soil testing fields we suspect could be at risk. Tests are more intensive than in the past, with one sample per hectare or even one per half-hectare where we think there’s a problem.”

    Mr Goodinson says even very low egg counts will warrant treatment with an integrated programme as this can prevent a more significant problem spreading. “If you have a high population, you’re better off avoiding growing potatoes on that land altogether.”

    He also believes in the benefit of early soil testing for PCN, but acknowledges that in some cases – especially where land is rented - growers may not know exactly which land potatoes will be grown on until relatively late in February or early March.

    PCN control key points

    •    Take soil samples early to allow cropping changes
    •    Aim for one sample per 0.5-1ha max
    •    Map sample locations
    •    Avoid spreading PCN by cleaning machinery if possible, removing volunteer potatoes, disposing of potato waste carefully
    •    Use integrated control measures, including:

    o    Resistant varieties
    o    Longer rotations
    o    Nematicides
    o    Cover crops (e.g. mustard)

    Alternaria has been more prolific than usual this season, especially in crops that have been under moisture stress, according to Mr Goodinson.

    “There’s been hardly any blight, but lots of Alternaria. We know from previous experience that varieties such as Markies, Vivaldi, Kind Edward and Melody are susceptible, but this year we have seen it across more varieties.

    “It seems to be areas of fields affected rather than whole fields and is season-related. Affected crops tend to senesce early, which means they’re losing potential yield, but it’s too early to tell the scale of any impact.”

    While Mr Goodinson has achieved good results from fungicide programmes targeted at Alternaria, based on actives such as difenoconazole, mandipropamid, mancozeb and fluazinam, he is aware of others who have found the disease harder to control.

    He suspects this difference may be down to variances between the two species of Alternaria; the predominant A. solani and A. alternate, although suggests more industry research is needed to better understand these differences and their impact in the field.

    “We’ve sent leaf samples for analysis to try and help determine exactly what is there and plan how to control it in the future.”

  2. impact of residual stacking on black grass controlTo date, relatively wet weather across much of the UK during July, August and September has resulted in moist soil conditions, ideal for weed germination says Dr David Ellerton, Hutchinsons technical development director.

    “Growers should ensure that they create seedbed conditions that maintain this moisture, promote weed germination and enable them to utilise glyphosate to reduce overall weed levels, not just black grass, before drilling. On the worst black grass fields, delaying drilling will optimise this opportunity.”

    He adds that to achieve successful weed control a suitable herbicide programme is crucial.

    “In most cases, programmes should begin with a pre emergence application using a combination of active ingredients. The mix should include flufenacet as the base ingredient, plus additional pendimethalin, diflufenican, picolinafen, flurtamone, prosulfocarb, tri-allate, flumioxazine or flupyrsulfuron, depending upon the field’s grass weed population.”
    “Pre emergence grass weed control is particularly important in winter barley, where there are few options available for post emergence application. Even fewer options are available for pre and post emergence weed control in winter oats and growers are likely to have to take advantage of EAMUs (formerly SOLAs), albeit at the grower’s risk.”

    Dr Ellerton believes that the choice of herbicide combinations should take in to account field-by-field knowledge of previous performance of products on grass weeds or, ideally, on the results of resistance tests.

    “Broad leaved weed spectrum should also be carefully considered in matching products to individual fields. Strategies for control of black grass, ryegrass and bromes are broadly similar and all of the above active ingredients offer good control of annual meadow grass, albeit at reduced dose rates.”

    “On a positive note for annual meadow grass, chlorotoluron has returned to the market – at a significantly reduced dose - in combination with diflufenican and pendimethalin. Varietal restrictions still apply, so it is essential to check tolerance before making any application. Until recently this product was only cleared post emergence of the crop from the 1 to 3 leaf stage up until the end of October. However the product has now received clearance in winter cereals (not oats) for use pre emergence up to before GS 30.”

     He reminds growers that whichever combination of active ingredients are chosen, it is vital that the first application is made pre emergence rather than delaying to post emergence of the crop. Trials have shown reductions in grass weed control of over 20% in some cases from a delay of only a few days.

    “When pre emergence applications are planned, growers should remember the importance of sowing at the correct depth to avoid crop damage. Drill-depth restrictions will vary between products but seed which is covered by 33mm of settled soil should be suitably protected for most products.”

    As a general principle, the more serious the grass weed infestation the higher the herbicide dose required and the greater the number of active ingredients that should be applied - a technique known as ‘stacking‘ he says.

    “This is particularly important when there is known resistance to post-emergence ALS inhibiting active ingredients, such as iodosulfuron, mesosulfuron or pyroxsulam. Where post emergence applications of ALS products with grass weed activity are necessary, they should be made once the majority of grass weeds are at 1 to 3 leaves and weather conditions are suitable for active growth.
     It is also important to include a residual component to extend the length of control.”

    “Applications made in the autumn are usually more consistent than those made in the spring, when target weeds are also larger and enhanced metabolism resistance is more of an issue. In addition, delaying until the spring usually results in lower yields, due to an extended period of weed competition prior to application.”

    “Nevertheless, timing trials with contact herbicides show very clearly that seedbed moisture, as well as temperature and weed size, is critical to achieve optimum control, so applications should only be made where conditions are appropriate.”

    Accurate spray application

    Delivering the product to the target via the sprayer is as important as choosing the right products to use advises Dr Ellerton.

    He adds that when the target is the soil, then spray quality is less critical and provided good and even coverage is achieved, a satisfactory result should follow. When the target is an emerged weed (grass or broadleaved), then in addition to ensuring active weed growth and dry leaves at application, attention should also be paid to suitable forward speed for good boom stability, spray quality which should be fine-medium and that the boom height is suitable to the type of nozzle being used e.g. 110°FF should run at 50cm above the target.

    “All of the above details can play a major part in determining optimum efficacy of autumn contact herbicides.”