Knock-on effects of the summer heatwave continue to concern UK potato growers, with secondary tuber growth expected to cause storage problems.

Stop/start growth in the hot weather has caused apical buds to break dormancy and form premature sprouts, resulting in either “chained tubers” or “dolls”, says Scottish Agronomy’s Eric Anderson.

“Where chain tuberisation occurs before haulm death or destruction, substantial transfer of starch and nutrients from the older to the younger tuber can continue after haulm destruction.

“In extreme instances this can result in a collapse of tissue in the primary tuber known as ‘heel-end’ or ‘jelly end’ rot or ‘glassy tuber’ if it applies to the whole tuber.

“For processing varieties, fries made from affected tubers will turn dark when cooked, with Russet Burbank potatoes particularly susceptible to this physiological disorder.”

Any crop with secondary growth should not be considered for long-term storage, warns Mr Anderson.

The geographical extent of the problem is largely unknown and depends on whether adequate moisture has been available, says Adrian Cunnington from the BPC’s Sutton Bridge experimental unit.

He advises growers to monitor field crops often and closely assess whether they will continue to meet market specification rather than waiting until lifting.

Some crops not yet exhibiting secondary growth may have already experienced the premature dormancy break that can cause sprouting in store.

In this case, growers can apply a sprout suppressant earlier than normal, says Mr Cunnington. But they must be aware that early use of CIPC may exacerbate the risk of skin spot and affect curing.

“When actual secondary tubers have been formed, the risk of rotting is high,” he says.

“It may be possible to grade out these potatoes, but if primary tubers are experiencing glassiness, the internal quality is already affected.”