5 April 2002

Big scale demands close watch

on PCN

Scale counts for a lot when

it comes to growing

potatoes profitably. But

expansion must not

jeopardise PCN control,

as one north Norfolk

enterprise explains

SHARING equipment and pooling management and marketing resources to create an 800ha (2000-acre) potato enterprise has helped three Norfolk farming families tackle diminishing returns from the crops.

But attention to crop hygiene to prevent the spread of PCN between individual operations is a major challenge.

North Norfolk Potato Growers was set up five years ago by the Harrison, Cargill and Mermagen families to supply second-early and main-crop processing potatoes to a major crisper and produce a proportion of certified seed for their own use.

The joint enterprise now grows over 800ha of potatoes across sandy clay loam soils between Fakenham and Great Yarmouth.

"Each year we co-operate more and more with the view of continuing down this route in the future," explains James Harrison who farms at Hall Farm near Cromer.

But PCN is a major concern, which is where NNPGs potato manager, Simon Alexander, plays a key role in protecting the hygiene of each farms potato ground.

"We have to be mindful of the potential complication with sharing machinery and the movement of potatoes across farm boundaries, so hygiene is of paramount importance," stresses Mr Harrison. Machines are cleaned between each field and steam cleaned when switching from ware to seed.

Nematicide use has also changed, explains Mr Alexander. "We always used to base our PCN control programme on cyst count rather than egg count. What we did not know then was that multiplication rates are much higher with low counts, and because a cyst can contain large amounts of eggs, nematode numbers simply exploded. Within five years we had a serious problem."

Accuracy vital

Application accuracy is felt to be as important as product choice, so the group has switched from applying and incorporating nematicide through a Reekie stone picker and planter to a Grimme Combistar de-stoner with Horstine Farmery applicator.

Alternative application techniques were tried, including through a bed tiller. But that required another tractor and operator, and an extra pass.

"We are in the processing market which is high volume at low cost," says Mr Harrison. "Research from Harper Adams demonstrates that the bed tiller route is the best for application accuracy, but on our soils we do not need to bed till, and it can cost up to £75/ha, which we cant justify."

Product switch

A desire to be able to check application accuracy has also prompted a switch from Temik (aldicarb) to Vydate (oxamyl), which is easier to see in the soil profile, explains Mr Alexander. Du Pont also offered the Vytest to check the distribution of the chemical at no extra cost.

"PCN control is expensive and with diminishing returns application accuracy is essential. The Vytest can be carried out in the field, and the results are immediate, which helps to confirm that distribution in the soil profile is correct. We cannot afford to get it wrong," he says. Du Pont carries out the test as requested.

Managing PCN is not just about in-crop control, he continues. A rotation of at least 1:6 and managing dumps and ground-keepers is key to reducing dependency on nematicides.

Volunteer control

Some control of volunteer potatoes in the crop is achieved with the sprout suppressant maleic hydrazide, plus pre-harvest glyphosate in cereals. After potato harvest he flat lifts rather than ploughs, and uses a disc drill to encourage chitting in the autumn to take advantage of the late frosts.

"Potatoes that have been disced stay in the top two inches of soil. If the frost does not get them, they should emerge evenly in the spring when they can be controlled with a Starane (fluroxypyr) and Ally (metsulfuron-methyl) mix. In sugar beet we use Debut (triflusulfuron-methyl)." &#42

PCNCONTROLS

&#8226 Three potato areas merged.

&#8226 Strict machinery hygiene.

&#8226 PCN numbers multiply fast, so nematicide used if any PCN found.

&#8226 Accurate application as important as product choice.

&#8226 Bed tiller application preferred, but too costly, so Grimme de-stoner used instead, plus soil profile testing.

&#8226 Groundkeeper control vital.

&#8226 Dumps managed carefully.

Planting plans

Operating as a combined enterprise potato planting costs up to £220/ha, based on ridging up, de-stoning and planting. "Planting starts in March and carries on through to mid-May," says Mr Harrison.

"We try to plant potatoes into known PCN land later in the season when the soils are slightly warmer, to give them the best chance of growing through the problem." Only 10% of the potato crop is sold directly off the field, representing about 3,500t of green top. The majority goes into store for movement between December and July.

The company grows 55ha (135 acres) of seed for its own ware production. Crisping varieties grown for storage include Lady Rosetta, Hermes and Saturna.