Get to grips with blight LERAPS
BEATING the offside trap is a challenge for potato growers as much as World Cup footballers.
The trick is to maintain headland blight control without breaching LERAP legislation designed to protect watercourses.
The wrong decision can have costly consequences. But growers can make life easier for themselves, says independent agronomist Martyn Cox of Ely-based Blackthorn Arable.
Rotation planning for next years crop should start soon and must consider LERAP (Local Environment Risk Assessment for Pesticides) restrictions, he says.
The alternative is expensive and agronomically challenging pesticide programmes. "LERAPs are a major complication when growing potatoes near watercourses."
Any field with a watercourse next to it is subject to a LERAP assessment. "In the fens most fall into this category making product choice very complicated. When considering fields for the coming year growers must consider this as well as rotation, variety choice, volunteers and proximity to dumps," he says.
Growers could use the 1m gap usually left between crop and field margin to use LERAP B nozzles. But that may produce an unsuitable spray pattern and compromise product efficacy, warns Mr Cox.
Where a farm has entered into an environmental scheme, uncropped or sown wildlife strips reduce LERAP problems. Headland set-aside is another option, although unlikely to appeal on rented land.
"Product switching based on proximity to the field boundary is a further option," says Mr Cox. A non-LERAP product could be used on the headland, like Curzate (cymoxanil + mancozeb), switching to LERAP restricted products such as Invader (dimethomorph + mancozeb), Shirlan (fluazinam) and Electis (mancozeb + zoxamide) for the rest of the field.
"However, it is easy to fall foul of restrictions on the maximum number of doses or application intervals when splitting applications within a field."
Growing more resistant varieties, such as Sante, on watercourse headlands is another alternative. But that can lead to PCN differences, making good record keeping vital to avoid misleading results in future.
But not all blight sprays face the same restrictions. Curzate is a good starting point followed by a 3-way systemic such as Trustan (cymoxanil + mancozeb + oxadixyl), Mr Cox observes.
Although 3-way systemics will not be available next year, four-way spray programmes based on Curzate are an effective alternative, he says.
"Once the rapid growth phase has finished, Curzate could be alternated with the new product Ranman (cyazofamid), utilising the kickback of cymoxanil and the good protectant abilities of both products. But, do not be tempted to rely on purely protectant products, as the added flexibility of cymoxanil gives added control in difficult conditions," says Mr Cox. *
• Potential headland problems.
• Nozzle changes hit efficacy.
• Product switches risky.
• Variety changes can work.
• Scope to tune spray mix.
• Plan next years cropping now.