…but growers response mixed
USER reaction is mixed. Jimmy Stockdale, who grows about 364ha (900 acres) of potatoes around Seamer, Scarborough had one of the first Downs machines. He already had eight years experience of cold-cutting, mostly shy-setting Shepody, for McCains. "The attraction of the hot knife was that it should keep the blades clean."
Blade distortion meant he used heat only on 17t of SE1 Pentland Dell 50-55mm top end seed for a ware crop. "They were perfectly OK although they had a bit of a ragged cut." Planted beside whole 35-45mm Dell there was no evidence that either approach was better, he says. "They are still in the ground but they are both going to do over 20t/acre.
"Clearly you must put high-grade good-quality seed through. The key thing is that we only cut the large ones graded out beforehand which wouldnt have been usable. We effectively made new seed. I think the potential is marvellous.
"We get a lot of enquiries to cut because we have cold and warm stores to help. Its very important to warm tubers before cutting to avoid bruising and to cure them at 12C for five to seven days. Its then equally important to cool them," says Mr Stockdale.
John Chinn from Ross-on-Wye hot-sliced about 1000t for himself and neighbours and is convinced the technique has a good future. About two-thirds of his 243ha (600 acres) of mainly salad and baby-new crop came from hot-cut seed. There was no detectable difference in yield or disease in a split field of hot-cut and uncut Maris Peer, he says.
Mr Chinn admits the need to maximise tuber numbers for his particular markets influences his opinion. Planting mixed seed cut into heel and rose ends is bound to lead to more variable-sized ware, he adds.
"The real benefit is that you can cut your best seed to plant more acres so you dont have to use the poor. I think the Scots are scared of the quality of their seed. A lot of it has very high blackleg."
Clearly choice of variety and blackleg susceptibility is important, and in theory testing beforehand should help identify potential risks, he says. "The problem is that blackleg testing is not really reliable because of what can happen with later handling and storage.
"We cut some German Serafina and the crop was horrendous with 27% blackleg, though a Sutton Bridge test showed only 50% had low levels in the seed. And I certainly wouldnt cut the crispers Erntestoltz and Hermes. But we also cut Estima, which is quite susceptible and had no problems at all."
Faced with over-bold seed samples and a possible shortfall, former farmers weekly barometer grower Steven Mackintosh produced 22ha (54 acres) of Fambo and Maris Piper at Ross-on-Wye, Hereford-shire, for early green top lifting from seed hot-cut by Mr Chinn.
"We planted about 15% closer to allow for some not growing and to compensate for unevenness in sprou-ting between rose and heel ends. There was very slightly more blackleg from cutting. But there was no noticeable difference in yield at all. I was very pleased with the results and would certainly do it again."
But Sandy Murray who has 182ha (450 acres) of potatoes at Black Den Farm, Brechin, Angus, about half for seed, is far from enthusiastic. He bought a Hot-Knife after having some Hermes hot-sliced by Mr Smith in 1998. "The results were reasonable, though we had a bit of blackleg which we put down to the wet spring."
This year Mr Murray used his own machine to slice 500t for himself and others. "With hindsight I wish I had never bought it. The biggest problem was getting the heat correct. There was no way of telling the temperature of the blades which should be 800C."
The combination of reduced pressure to avoid blade distortion and what he now suspects were quite high initial levels of erwinia leaves him fearful for his own crops. "The early lifted ones were OK. But there is definitely more blackleg where we cut, and yields will definitely be down."
CSC trials found 8%, 13% and 40% blackleg in crops from uncut, hot- and cold-sliced seed respectively, he says. *