Disease threatens walnut trees

March 10, 2012 at 12:56 PM

LaSALLE, Ill. (AP) — Black walnut trees are known for their lumber, a sturdy, attractive wood that is used to make furniture and for veneers. Because of their height, a well-maintained tree can fetch a pretty penny: Before Jim Kuch of rural Mendota started planting walnut trees, he was told a mature, 20-year-old tree could be worth $10,000.

“In an acre, you can plant 500 black walnut trees. That’s spacing them 10 feet apart. When you get to 15 and 20 years, the value could be $10,000 a tree,” he said. “There is no better retirement program.”

Without careful pruning, Kuch knows many of his trees will never be worth that much. Since putting in his first 300 trees, he hasn’t planted them with the precision he recommends, letting seedlings grow where they may.

The black walnut has another fan, a fungus that can grow in the tree’s phloem — a layer of tissue that, like an artery, transports nutrients inside the tree. The fungus is spread by walnut twig beetles, which burrow beneath a tree’s bark. It produces cankers that disrupt the flow of nutrients, resulting in dieback, decline and, eventually, death of the tree, according to Illinois Department of Agriculture. And that disease could destroy the state’s native walnut population, the department warns.

The disease, called thousand cankers disease, has not yet been spotted in Illinois, and state officials hope to keep it that way. To prevent Illinois’ black walnut trees from being attacked by that fungus, Gov. Pat Quinn recently approved regulatory measures to restrict the movement of potentially-infested products into Illinois.

There are no management strategies for TCD, according to state agriculture officials. Illinois Department of Natural Resources forester Randy Timmons said information and prevention are the best tools available.

“The more that people become aware of them (the beetles and fungus), the greater chance we have of slowing or stopping their spread,” Timmons said.

He serves as district forester for District 4, which includes La Salle, Marshall and Putnam counties, and as the acting regional forester for Region 1, which includes northwestern Illinois from the Iowa and Wisconsin borders east through La Salle County and south to Peoria and Tazewell counties.

Black walnut trees are native to Illinois. Timmons described the tree as a sturdy variety without many natural predators.

“Walnut likes to be in that place where moisture runs. It also does very well on the soil types we have here,” Timmons said.

“In the heart of the Midwest is some of the best walnut-producing area in the United States,” Timmons said. “Some of the nicest walnuts grow in deep ravines along the Illinois River system. Those deep ravines can cause these trees to grow very straight.”

Illinois is not known for growing varieties that produce commercial volumes of edible nuts, but rather for the kind of trees that are well-loved in the furniture industry.

“Black walnut has kind of a dark bark. The older trees have a somewhat deeper furrow to them,” Timmons said. “When you scrape the surface of the bark — just lightly — it’s a very chocolate brown just under that bark. That’s the same color as the heartwood.

“Black walnut has a very desirable heartwood… It works well, it glues well, it takes a finish very nicely. As far as value, it’s the king of our area,” he said.

It’s a common tree in the state’s natural areas, though not as well-known as oaks and hickory trees, and on many small family farms.

“They’re the focal point on farms or the landscape even, and they’ve been there for 100 or 120 years, and we’ll lose them,” if the disease spreads to this area, Timmons said.

“It’s a very devastating disease when it gets started,” Timmons said. “Our main emphasis is to keep it from being spread to Illinois.”

The state previously rolled out a “Don’t Move Firewood” campaign when emerald ash borer beetles were found in Illinois, and the campaign to prevent TCD is similar.

Now, individuals and businesses that want to take “regulated materials” from a TCD infested area and move them into or through Illinois must have a phytosanitary certificate from the state of origin to verify that they are in compliance with state agriculture regulations.

According to a press release from the department, “regulated materials” are defined as all parts and products of the tree passing through an infested state, regardless of origin; all life stages of the walnut twig beetle; all life stages of the Geosmithia fungus; and any article, product or means of conveyance determined by the department to present a risk of spread.

Exceptions are nuts, nutmeat and hulls, processed lumber if it is bark-free and kiln-dried with squared edges, and finished word products without bark, including walnut furniture, musical instruments and gun stocks.


Copyright 2012 The Associated Press.