Sugar beet growers are being urged to protect their crops from sub-zero temperatures to avoid any losses through frost damage.

Freezing temperatures followed by sudden thaws could cause plants to rot, rendering them unable to be processed, British Sugar warns.

Temperatures have plunged as low as -12C in some beet-growing areas, but they are forecast to rise to several degrees above freezing this weekend, heightening the risk.

While beet factories can accept and process frozen beet, problems may occur when roots begin to thaw, says Paul Bee, British Sugar’s agricultural communications manager.

Freezing temperatures of -3C or below can rupture cell tissue in the roots and when the roots thaw, the sugary juice from these cells converts to dextran, a gum-like substance which blocks sugar filtration in the factory process.

To ensure beet will be accepted for processing, growers should inspect their crops for frost damage, or if they are unsure what to do, they should contact their British Sugar area manager, Mr Bee says.

Lifting should be carried out according to delivery plans and adjustments can be made to the beet harvester to remove frosted crowns, if present, he adds.

“When they are inspecting fields, growers should look at the crown of the beet to see if it is frozen. “Get some roots and chop them and if there is frost in the roots, there is discoloration. If they have discoloration, at lifting the topping mechanism of the beet harvester can be lowered so that it takes out more of the frozen beet.”

Exposed sugar beet clamps – especially freshly harvested beet – will sustain frost damage at temperatures below -2C. Any frozen beet should be removed from the outer surface of clamps and delivered while it is still sound, Mr Bee advises.

“Clamps which are covered and protected should be fine, but any clamps which have the face uncovered may be frozen,” he says.

“Frozen faces will need skimming off. You take the face off and deliver that to the factory and the rest is left in the clamp.”

Clamped beet should be delivered to the factory before harvesting additional roots and growers should lift according to delivery requirements.

“The aim is to keep the beet in the ground where possible, but to leave enough harvested to meet delivery requirements,” says Mr Bee.

So far, the freezing temperatures have not interrupted the lifting progress, he adds. “Harvesting has continued as normal and factories are fully supplied. There has been no effect on quality or sugar content and processing has been going well.”

AICC agronomist Pat Turnbull has not yet heard any reports of frost damage in north-west Norfolk, but there have been some reports of damage in the fens. “The first deep frost may not get past the tops, but if the next frost penetrates the crowns it could become more serious,” she says.

But Dr Turnbull says it is too early to assess how bad the damage to the remaining beet crop is because the thaw has only just begun, She warns that “Maus” type clamps – long, narrow clamps which have a larger surface area than traditional clamps – may be most susceptible to frost damage.

Case study

Cambridge grower Edd Banks says he stopped lifting beet at the start of the latest cold spell. “The temperature dropped as low as -6C here, but I’m less worried about the beet that is still in the ground because it has a good level of foliage,” he says.

The frost has been quite severe, he adds, but the snow may have covered the crop and acted as a buffer. He plans to leave the remainder of his beet in the ground and lift it after Christmas, assuming the snow has melted and temperatures have risen sufficiently.

“I’m just going to leave it in and let it [the frost] grow out,” he says. “I’d be worried if it had been lifted and left in clamps.”

But he adds: “I don’t think there’ll be a beet grower in the country who hasn’t had frost damage in one way or another.”