ACCURATE APPLICATION of nematicide before planting potatoes is important – apply too little and its effectiveness in controlling potato cyst nematode (PCN) can be limited, too much and the grower is outside of label recommendations.

It could be argued that both errors have the potential to cause severe financial losses – it’s essential to make sure applicators are working correctly before potato planting starts.

For Channel Island farmers growing the famous Jersey Royal potatoes, planting is already finished. Du Pont – manufacturer of the nematicide Vydate – and the States of Jersey Environmental Department have organised a series of calibration workshops to help growers in setting up their machines.

Although the crop spends only 12 weeks in the ground, the need to control PCN is a key part in the production of early potatoes which generate over £20m/year – half of Jersey’s income from agricultural products.

“Applicators may look to be simple pieces of kit but there is plenty that can go wrong if they are not well maintained,” says Du Pont’s Phil Carpenter.

“In time, the applicator’s fluted metering rollers will wear and become unreliable. This means that while a machine can be set to apply the required rate overall – normally 40kg/ha of Vydate – it may not be applying it evenly across its width.”

Typically the 2.5m wide cultivators used in Jersey to incorporate the nematicide are fitted with three hoppers, each feeding to two fish-tail distributors. Mainland UK potato growers will, of course, have wider machines with more hoppers but the principal still holds true.

Following a calibration sequence which sees the drive shaft being turned a set number of times to represent a known area, Mr Carpenter tests the output from each metering system by weighing the amount of Vydate delivered at the outlets.

Not only should the amount be the same in each tube, it should also be of a correct weight for the area covered – a laptop computer program cuts out the mental arithmetic required.

“I like to aim for a +/- 2% accuracy to allow for actual field conditions,” says Mr Carpenter. “If there are discrepancies the test will identify the problem and moves can be made to correct it.”

Those with worn out or damaged metering rolls might consider fitting a new cassette metering system being introduced this year by Horstine Farmery. The cassettes simply slide into the base of the hopper – prices start at about £97.

The calibration check also takes a look at the overall state of the applicator – particularly the land-wheel drive belt, which should be properly tensioned to prevent inaccuracies caused by slippage.

fwmachinery@rbi.co.uk