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Improving your seed treatment technique

1 August 2011

Seed potato growers who pay attention to their seed treatment technique could improve disease control and save themselves a small fortune in chemicals.

“A lot of seed treatment applications are not very effective, all because operators are not paying enough attention to detail,” says Dr Stuart Wale of SAC, who led a recently completed PCL-funded research project.

“Fortunately, by following some simple, basic steps things can be greatly improved.”

The key message is that surface coverage, more than residue level, is important for disease control, says Dr Glyn Harper of Sutton Bridge Crop Storage Research who collaborated in the work.

“We looked at a number seed tuber treatment methods and identified four potential ways to improve tuber coverage without compromising on residues,” says Glyn.

Using spray application equipment over a conventional roller table, Stuart and Glyn studied the results of using enhanced nozzles, use of a downward fan, improving the configuration of spray nozzles over the roller table and using an adjuvant in the spray solution to improve wetting and spreading.

Often, just 10-25% of the target dose reaches seed tubers, says Stuart. Poor tuber coverage is also common, risking unnecessary disease development.

There are five key questions to address
• Is the equipment calibrated correctly?
• Is the spray pattern correct?
• Are tubers clean?
• Is the roller table being kept full of tubers?
• Are tubers rotating at least twice under the spray mist?

Ideally, operators should calibrate equipment between each seed stock, he notes. “However, store managers are usually too busy. But they should certainly calibrate at least at the beginning of the year – it is simply a matter of measuring the throughput of seed passing over the table in a given time, the output from the spray equipment, and adjusting dilution of the chemical solution accordingly.”

A good spray pattern is vital to achieve effective tuber coverage. Nozzles can be in use for 8-10 hours a day for months, so they are likely to wear faster than field sprayers, he advises. “It’s easy to check how effective the spray pattern is, by popping some blotting paper underneath the nozzles. You want to see an even distribution of regular-sized droplets.”

Dirty seed must be avoided. “Seed treatment will only work if it reaches the tuber surface. This means tubers need to be clean of soil.” Keeping the roller table full of tubers will also ensure chemical hits the intended target, rather than being wasted on the table itself, says Stuart. “This can be a problem when seed is being graded heavily, which creates gaps. Installing a hopper to allow seed to be released uniformly will overcome this.”

Each seed potato needs to rotate at least twice while passing through the spray mist to help promote even coverage, he adds. “Uniform application is the most important thing.” Taking these few steps will go a long way to improving application techniques, Stuart maintains. “If I were spending the equivalent of £5/tonne on chemicals but only applying a fifth of that to the actual tubers, spending a little time going back to basics has to make sense.”

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