By KEVIN WALKER
Michigan Correspondent

LANSING, Mich. — The Michigan Dept. of Agriculture (MDA) last week announced quarantines on the importation of black walnut timber and chestnut tree nursery stock.

The two pests in question are thousand cankers disease (TCD) for the walnut and chestnut gall wasp for the chestnut. The situation for each tree is a little different. For black walnut, TCD is a threat that would likely come from the following western states: Arizona, California, Colorado, Idaho, Nevada, New Mexico, Oregon and Utah.
Black walnut material cannot be brought in from those states, with certain exceptions. Nuts, for example, are excluded from the quarantine.

“It’s known to have killed thousands of black walnut trees in Colorado; it’s all in the western states right now,” said Mike Bryan, nursery program manager for the MDA’s plant section. “The net effect of an infestation is we could lose all of the black walnut trees in the state.

“Black walnuts are a valuable tree. We have a couple of companies that export black walnut timber. We have buyers from other countries that come to buy the logs.”

Black walnut timber is highly prized for its veneer, for making musical instruments and furniture. Michigan has an estimated 8.5 million black walnut trees. Regulatory agencies in other states contacted the MDA about the problem. Missouri and Iowa have also put quarantines on the importation of black walnut material into their states.

“All of the states in the Midwest have discussed putting a quarantine on this,” he said.

TCD, which is a fungus, spreads via the black walnut twig beetle, which can fly.

“They tunnel into the tree and carry the fungus with them,” Bryan said.

“Reinfection occurs as the population builds up. This one kills the tree because the canker builds up and disrupts the flow of fluids and nutrients. Trees that are dying have thousands of cankers on the bark.”

On the same day, May 27, 2010, MDA Director Don Koivisto imposed a quarantine on chestnut tree nursery stock coming into the state.

“Michigan’s growing chestnut industry is at risk,” Koivisto said in a news release. “We rank number one in the country for number of chestnut farms: 54 farms encompassing 813 acres. Not to mention, chestnuts are among the many different specialty crops grown in Michigan. We want to prevent the introduction of chestnut gall wasp into our state to ensure the continued health and viability of chestnut groves across Michigan.”

The chestnut trees being raised now are European and Asian varieties rather than the American chestnuts that were largely killed off by disease in the last century.

“It’s an infant industry that’s growing in popularity,” Bryan said.
According to Bryan, the chestnut gall wasp lays its eggs in plant tissue and the plant develops a gall, or growth.

“It kind of swells up,” he said. “There’s a whole family of insects that do this. The floral structure is completely taken over by the gall, so no fruit is produced. That weakens the tree and a lot of times they die.”

The pest has some natural enemies, but none is 100 percent effective against it. The quarantine imposes special, rigorous inspection requirements on chestnut tree nursery stock, from the following states: Alabama, Georgia, Kentucky, Maryland, North Carolina, Ohio, Pennsylvania, Tennessee and Virginia.

More details on the quarantines are available at the MDA’s website, at www.michigan.gov/mda