Arable News

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Blackleg and blight warning for potato growers

There are warnings of high levels of blackleg in seed potatoes this spring, as well as the disease being widespread in soils. Dominic Kilburn seeks advice on reducing the spread of blackleg, and gets some practical advice on blight

There are warnings of high levels of blackleg in seed potatoes this spring, as well as the disease being widespread in soils. Dominic Kilburn seeks advice on reducing the spread of blackleg, and gets some practical advice on blight.
Potato growers are being warned of the potentially high levels of blackleg infection in seed crops and bacteria in soils as main crop planting gets underway. In addition, following last season’s difficulties with blight, the message this season is ‘be prepared’ with robust preventative spray programmes.Norfolk-based specialist potato agronomist and consultant, Andy Alexander (pictured left) says that speaking with advisers and growers at a recent SAC conference in Perth, it’s clear that conditions for potato growers all over the country were very difficult in 2012 with Scotland, the north of England and the West Midlands struggling even more so than East Anglia, which had its own challenges with yields and quality. “Everyone’s had a bad 12 months in the industry and the important thing is to make sure that it doesn’t become two bad years,” stresses Andy.In terms of blackleg, he says that merchants are doing their best to keep seed free of blackleg and anything that growers can do now to prevent the spread of the disease will help in limiting the effects it may have on harvested and stored crops later in the season. “Last season the level of blackleg was high on account of the very wet conditions and, subsequently, through no one’s fault, seed stocks for this season are carrying high levels of the disease and there will be bacteria in the soils.”According to a Dutch bacteriologist I spoke with recently, we are getting no further forward in its control,” he adds.
Andy points out his concern that if the bacteria is carried into store at harvest then not only does this affect yield and quality, but growers suffer the double whammy of potentially having to move their crops out of store earlier and therefore unable to capitalise on the best prices.”Our saving grace will be a dry summer but growers will need to have a degree of patience when it comes to planting,” continues Andy. “Fields everywhere are wet and infected seed in wet soils will exacerbate the problem.”He reminds growers that the disease is varietal, with some varieties more prone to it than others, and, if they haven’t already done so, growers should seek advice about their seed delivery from an advisor or their seed merchant. “It’s about managing the situation and waiting for soils to dry out prior to planting. It’s better to plant a little later than planned rather than go too early into bad seedbed conditions.”You want the crop to grow away fast so don’t plant too early,” he emphasises.
Turning to blight, Andy says that, as discovered during last season, the situation regarding the onset of the disease changed very dramatically with the weather and the advice to begin a blight prevention programme with a robust strategy has never been more appropriate. “I advise over a number of large potato growing units and I won’t wait for signs of the disease in the crop before I start the programme. I’ve looked at a lot of trials work, and spoken to a lot of specialists about this, and you have to begin the programme when the crop is at the rosette stage, coupled with seven-day spray intervals.”Because of the scale of the cropping areas it’s imperative to go every seven days otherwise, when the weather changes suddenly, spray interval can suddenly become 14 days, and the blight has taken hold of the crop.”According to Andy, Smith Periods – the traditional method by which the likely risk of blight is assessed – are simply a guide as to the potential threat of the disease. “People mention risk assessments to me; well, I’ve already made mine for this season and that is to go early with a robust programme. It’s about prevention rather than cure and there must also be a robust mix of chemicals too, if the threat of resistance to products is to be reduced.”Action needed when seed is deliveredDiscussing the spread of blackleg, Sutton Bridge Crop Storage Research’s (SBCSR) plant pathologist Dr Glyn Harper highlighted the need for timely and appropriate action once seed is delivered to the farm. “Seed should not be stored in big bags; seed stored in big bags can deteriorate up to six times faster than seed stored in boxes or stores,” said Dr Harper, speaking at a recent storage event at Sutton Bridge. “At the very least, raise the bags off the ground onto pallets and allow for adequate airflow around each bag. This will help mitigate any deterioration until proper storage – or planting – can be implemented.”Professor Ian Toth from the James Hutton Institute added that storage plays a key part in keeping stocks dry and the pathogen from spreading.
Focusing on storage in general, SBCSR’s Adrian Cunnington advised growers at the event that achieving skin set, a robust ventilation regime and energy efficiency were all key to keeping stored crop healthy and marketable, particularly important after the wet 2012. Addressing store efficiency, he said that the most efficient stores use only a third of the energy used by the worst performing stores, with air leakage in some stores resulting in a terrible waste of energy.
He went on to point out that many stores built 15-20 years ago now need significant upgrades but this needn’t necessarily mean overly-costly work. “Don’t be put off making improvements; many older stores can be self-audited relatively easily, and cost-effective measures put in place to restore good efficiency results without high spend,” he stressed.Unpredictable weather adds to PCN problemsUnpredictable weather conditions make PCN control more difficult and, as the situation is set to get worse over coming seasons, will require the use of nematicide options giving longer lasting results, and put a greater focus on the level of accuracy in their application.Many of the crops that were planted into dry seedbeds, along with the incorporated nematicide last season, sat still for up to six weeks with virtually no growth, and when moisture did arrive growth was still limited by the cool soil conditions, recalled Yorkshire-based John Sarup of Spud Agronomy.”While all the time the residual efficacy of nematicide was naturally starting to breakdown, albeit at a relatively slow rate in the dry conditions, when the wet weather did arrive, it was extreme and never stopped.” As a result, when the main hatch of PCN did occur most of the activity from the more water soluble nematicides was likely to have moved down the soil profile – out of the nematode activity area in the root zone. He believed the problem was further exacerbated by the increasing numbers of the G.pallida PCN, which is naturally later hatching than the G. rostochiensis species.In these situations, Mr Sarup reported that he has seen greater control of damaging feeding losses in the growing crop and a reduction in population build-up by using the longer-lasting activity of Nemathorin (fosthiazate). “Growers really need to be looking at extended activity to limit the build-up of numbers from nematodes emerging later in the season, as well as minimising the impact of PCN damage on the growing crop,” he advised.Syngenta potato technical manager, Stephen Williams, reported trials have shown that PCN activity stopped within three days with Nemathorin, compared with an average 17 days with other nematicides,” he said. “As the season progresses that makes it especially effective in controlling late hatching nematodes.”

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