Cherry rootstock fails to live up to promise

Colt, the cherry rootstock that replaced the old Mazzard-type stocks like F12/1 after it was introduced some 30 years ago, is itself on the way out. Although hailed as the possible saviour of the cherry industry, it has failed to live up to its perceived promise.

Leading Kent growers like Henry Bryant and Tony Redsell have been predicting Colt's demise for the past five years or more. Their chief reasons are that it induces inconsistent cropping and excessive run-off and cracking under adverse weather conditions. And, despite being semi-dwarfing compared with the Mazzard stocks, it has proved too vigorous for modern planting systems without the aid of growth-regulator Cultar.

Arguably the main reason for Colt's falling popularity was the introduction of the more precocious and reliable dwarfing rootstocks, mainly Gisela 5, in the late 1990s.

This stock has none of Colt's drawbacks and does not need Cultar to control its growth. Its main shortcoming is that it is more difficult to propagate than Colt.

Thanks to Gisela 5's advantages - and the fact that the demand for English cherries far exceeds supply - the renaissance of the cherry industry appears to be well underway. Growers are planting larger areas of Gisela 5 than the areas of Colt they have grubbed.

Farm Advisory Services Team (FAST) stone fruit specialist Don Vaughan said: "This season would have been a real disaster if the whole cherry acreage had been Colt. We had cold, dull, windy weather during stoning and all crops on exposed sites suffered, especially those on Colt. It doesn't need a lot of encouragement to shed fruit. We're seeing a lot of Gisela orchards being planted that will be coming on stream in the next two or three years."

Brian Piper, who grows 8ha of cherries on his Filmers Farm, near Maidstone, Kent, believes that this year's adverse weather will prove Colt's death knell. Ten years ago all of his cherries were on Colt but now he grows just 1ha of this variety and this season its crop was virtually nil. The rest of his hectarage is on dwarfing stocks.

He was about 10 days into picking when some 50mm of rain fell in his area within 12 hours. Until then he had a 70 per cent crop because, unusually, even varieties on dwarfing stocks, which initially were carrying good crops, ran off. Rain-induced cracking then reduced it to about 50 per cent, despite the application of anti-cracking agents like Pretect.

Last winter, Bryant grubbed the last of his Colt and now all of his 9.7ha crop is on Gisela 5. His crop suffered much less cracking than Piper's, possibly thanks to six or seven doses of Pretect that he believes did a reasonable job. "We had some run-off but not as much as when we had Colt," he said. "Colt is now fast disappearing."

Redsell, who has been exhibiting at the National Cherry & Soft Fruit Show for 50 years and is its chief steward, had some 16.2ha of cherries on Colt until about 10 years ago. Now he has only 2ha and they will be grubbed soon.

He has 10ha of cherries in the Boughton area of Kent - including 5ha of recently planted Gisela 5. He agrees that Colt is on the way out. In the 1960s he had 81ha of cherries on very vigorous rootstocks that produced very large trees requiring 50-stave ladders to pick.

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