Potato yields are likely to have been hit by the extreme temperatures in June and July, and careful harvest and store management will be crucial this season to maintain quality, industry experts suggested at Potatoes in Practice 2006 in Dundee.

How much the conditions had affected yields was difficult to judge currently, Greenvale technical director Paul Coleman said.

“Crops shut down when temperatures reach 26C, and in July around half of the days were above 26C.

“We’ve definitely lost yield and production purely because of the heat, even in well-irrigated crops.”

Yield potential in non-irrigated crops could be down by as much as 50% depending on soil type, he feared, while crops that had initially been irrigated could be similarly or even more affected.

“In the fens where irrigation started, but then was quickly banned, crops will only have put down shallow roots.

Those crops might be worse than the ones not irrigated at all.”

Irrigation could have alleviated the effects of the hot temperatures somewhat, the British Potato Council’s Rob Clayton said.

“It can bring soil temperatures down a bit.”

But the impact on yields couldn’t be truly assessed until the results of yield digs became available, he added.

Branston agronomist Martin Stothard believed yields in south Lincolnshire could be 15-25% down on non-irrigated crops.

“Maris Piper on silt might be doing 16-17t/acre instead of 22t/acre.”

The cooler, wetter weather of the past 10 days would be allowing some crops to bulk up, although for others it had come too late, he added.

Quality had also suffered in the heat, Dr Clayton acknowledged.

“We’re detecting a few quality related issues, particularly secondary regrowth and splitting.”

In processing crops an early dormancy break resulting in secondary regrowth was a real challenge for fry colours, as starch was converted into sugar in the tuber, he said.

Many fresh-market crops had received maleic hydrazide applications in the past fortnight in an attempt to control secondary regrowth in the field, after a derogation for this season allowing its use had been given by retailers, Mr Coleman said.

Evidence for its in-field effectiveness had provoked debate, but the product worked by reducing cell division, so it was reasonable to suspect it could reduce sprouting in the ridge, he said.

“At worst it will reduce early sprouting in store.”

Varieties, such as Maris Piper, King Edward and Cara had been worst affected, particularly in East Anglia.

“In that region around 70% of Maris Piper, and close to 100% of King Edward have been treated.”

Minimising bruising and other quality issues was now very important as harvesting approached, Mr Stothard warned.

“Ideally, we want to take crops as green as possible for quality reasons, but the balance is growers will want to leave it as long as possible to maximise yield.”

Store management would also be critical this season, Dr Clayton said.

“This is the year where growers will see the benefits from rigorous monitoring.”

He advised growers to check with their purchaser about restrictions on grower protocols, to consider using sprout suppressants earlier, monitoring regularly for dormancy break, and to consider taking heat out of stores earlier than normal in some crops.

“That’s easier to do in packing crops, but you have to make sure you have a good skin set.”

Potatoes in Practice was organised by SCRI, SAC, CSC and BPC.

mike.abram@rbi.co.uk