Colin Palmer of pest and disease consultancy Rural Services said the disease is a minor problem compared with others in the past that wiped out whole plantations.
"This has affected a few trees in some plantations," he said at the British Christmas Tree Growers Association Christmas tree competition. "Only two or three growers have had major plantation losses. Most have about five-to-10 per cent of their trees with some symptoms, and these are not always enough to stop trees being sold. I'm not convinced it's going to develop into a major problem. The jury's out on that."
He added: "It doesn't necessarily go on from year to year. Trees that have it this year won't necessarily have it next year. The whole thing is very complex. It has come from nowhere and it would be foolish to ignore it, but it is not something large like ash dieback."
Palmer said a great deal remains unknown about the disease. "We don't know why a pathogen that we've known about since the war has suddenly developed into a problem. There must have been a stress factor to change it from benign to aggressive, but what is that stress factor? There is more we don't know than we do."
He is currently conducting a trial of fungicides in the West Midlands that should give results next July. "The trial will give us some leads but I will be surprised if it gives us any answers," he said. "It is a very detailed trial and each of the 1,000 trees is identified individually. We should get a lot of information out of it."