News from the ornamental workshop

Well, I'm back from my meeting. The big news was that "Thousand canker" disease has just been found in Tennessee. Thousand canker is a disease of black walnut that was first identified in Colorado, where black walnut is not native, and therefore, nobody was too concerned. The disease is caused by a fungus (native to the Southwest) carried by a beetle (native to the Southwest) that causes a minor twig die-back on native walnuts of the southwest. The black walnut is not adapted to the fungus or insect, and so it is very susceptible. It had no sooner occurred to people that walnut wood travels around the country via the wood-carving trade, and perhaps something should be done to protect walnuts in their native range from exposure to this disease, when it turned out that it was too late: the disease was in the native range, and now there's nothing that can be done: walnut trees are doomed. The question is how long it will take for the disease to spread, and whether any trees will be resistant. I'll beg everyone on this forum to please not move firewood across state lines- it moves a multitude of pests. Please do not move walnut logs around: a square inch of bark can harbor thousands of these beetles. Do not move any walnut wood that has attached bark.

The other big news affects us more directly: nurseries are suffering from the recession, and nursery owners are responding by cutting costs. They are not spraying for diseases and a number of extension agents reported that nurseries are fertilizing at half-rate, leading to sickly plants. I suppose your response should be to buy carefully, but to BUY. We don't want nurseries to go out of business.

Thanks, Nina . . . didn't you tell me that the walnut canker was quite slow moving once it infected a tree?

When you say "No hope" does that mean that cure/treatment is unlikely? I know how hard it is to treat trees "in the wild."

Yes and no- it takes 10-15 years for the tree to be killed, but when you first see the symptoms, the tree only has a year or two left to live. So by the time you see it, it's too late.

Bark beetles are almost impossible to treat: protectants can never be sprayed on well enough to give perfect coverage- think of all the crevices!- and you can't spray every week for 20 years. Systemics generally work poorly in the bark region. So not only are forest walnuts doomed, yard walnuts are, too. Spread depends on a lot of things: is it a fast beetle? [the asian longhorn beetle is a slow beetle, and we've been able to keep one step ahead of it so far. The emerald ash borer is a fast beetle, and we've been able to do nothing] Is the fungus tightly associated to the beetle? [don't know yet].

Hello Nina. Is this disease likely to lead to the kind of devastation that the Elm bark Beetle has caused in the UK, albeit on a slower rate of spread and death?

Interestingly (?) when we were in Lexington, KY for the World Equestrian Games last week, part of the course went through an area crowded with walnut trees -- huge ones. At least 1/3 of them were dead. Another 1/3 didn't look healthy and the living trees all had had a bumper crop of nuts this year.