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Potato Planting Well Underway in Scotland

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With potato planting underway in Scotland, leading agronomy firm Hutchinsons is reporting a much more favourable start to the season than last year.

Planting is at normal timing this year, whereas last year the cold weather in April delayed the start, according to Cam Murray, northern regional technical advisor.

Early disease risks
It is dry in the east of Scotland this spring, most irrigation is primarily for scab control; if the dry weather continues then it will be necessary to irrigate for overall crop establishment.   
Once potato crops are in the ground it is essential to get them up and meeting in the rows as quickly as possible, says Hutchinsons root crop technical manager, Darryl Shailes.

“In the drier south, irrigation is also often used for scab management early in the season, but it can be easy to underestimate the need for water early on, purely for canopy development. In dry years it can be a game-changer for crop establishment and maximising yield potential. So even where scab management is not so crucial, early water can be.”

“Growers in dry regions should consider irrigating as soon as the crop emerges in extreme situations, but don’t go too early as beds can be washed down.”

He adds that Rhizoctonia can be an issue in Scotland. “We are trying out in-furrow treatments with Amistar (azoxystrobin) for the first time this year for Rhizoctonia control, with a view to enhance the overall yield and to reduce the size variability across the tubers. “

Starter fertiliser boost
The use of starter fertilisers, either placed with seed or worked into the soil before planting, can help early crop establishment, notes Mr Shailes.

Mr Murray agrees with an early base fertiliser, allowing nutrients to get close to the tubers.
Trials show the benefit to canopy growth is most pronounced in dry, cool years, whereas in “normal” springs there may be less benefit, Darryl says.  

Pots planting and bed forming

“Many growers choose to do it as an insurance policy given the vagaries of the weather.”
In Scotland many growers would split their nitrogen fertiliser but Darryl Shailes says the jury is still out on the advantage from applying split doses of nitrogen fertiliser.  ”Applications are best timed so that nitrogen is available for the period of peak crop demand which occurs during the rapid canopy establishment phase.”

Focus on pre-em herbicides
Weed competition is another threat to yield and both experts agree that efforts should focus on pre-emergence control given the limited post-em options in potatoes. Mr Murray says that weed control is crucial to crop establishment and final overall yield.

There are a number of residual herbicides to consider, even after the impending withdrawal of linuron, the last use of which must be by next June, notes Mr Shailes.

Key options include products based on metobromuron, metribuzin, prosulfocarb or clomazone.

“In many respects the new metobromuron-based product is stronger than a comparable linuron-based product, when mixed with the other actives available. It also has better crop safety characteristics across a range of soil types.”  

Cam Murray concurs that the new metobromuron herbicide is crop safe on all varieties and on light land. He has been using it for a couple of years now.

While many growers will opt for a single residual herbicide application just prior to emergence, on some soil types there may be a case for using an earlier dose after planting followed by a second application, adds Mr Shailes.

Mr Murray still uses metribuzin as the base active with various combinations of partner actives, depending on weed spectrum of the field and variety tolerance to metribuzin.

Mr Murray likes to apply residual herbicides as close as possible to soil cracking usually with a contact herbicide, although slightly earlier if good moisture level is present. In the South, on heavier soils in areas prone to drying out, Darryl points out that it may be worth applying an early residual herbicide while seedbeds are still moist just after planting, before going back with a second application later. There is little value in such an approach on lighter, sandier soils, as their proneness to moving around reduces the efficacy of residual chemistry if it is applied too early, he notes.

Starting blight control
Cam Murray says that the blight programme needs to be part of the early management strategy, particularly as the new dominant strains develop in cooler weather. “We start protection at rosette stage, with a mixture of products focusing on translaminar and systemic products until we reach stable canopy and spray every 7 days, depending on blight pressure. The disease pressure and hence the spray interval will be indicated by the new Hutton criteria this year. “

PCN -  the sleeping Scottish giant
Mr Murray says that Scottish growers need to be more aware of the risk of PCN.  “I see Scotland as Lincolnshire was 15 years ago; PCN is our sleeping giant!”

pcn field damage

“Crop intervals are hugely important for a number of key potato pathogens with PCN being number one on the list. We need to use precision soil sampling to accurately map the areas of infestation within a field, and implement management strategies with the use of resistant varieties, specialist cover crops, nematicides should all be considered so this problem can be managed properly.”