Pine wilt disease will be next challenge for Aberdeen trees

Elisa Sand
Aberdeen News

South Dakota's long-needled pine trees have a new threat that can quickly starve them of water — pine wilt disease.

Austrain Pine and other long-needle pine trees are likely to be a rare sight in the coming years with the appearance of Pine Wilt Disease.

Aberdeen City Forester Aaron Kiesz said the first case of pine wilt has been found in town. Pine wilt, which causes rapid decline in trees, is the result of a fast-growing infestation of nematodes that feed on the trees and cause water-conducting pores to collapse, essentially starving their victims.

Once trees start showing signs of decline, like browning, Kiesz said, they are usually dead in about three weeks.

He discovered the first Aberdeen case in a 35-year-old Scotch pine on private property. The tree was healthy last year and is now 95% dead.

With the local discovery in northeastern South Dakota, Kiesz said, towns like Watertown can assume pine wilt is either there or will be there soon. It's going to be a statewide problem.

City Forester Aaron Kiesz shows an example of the pine cones produced by an Austrian Pine.

Nematodes are worm-like creatures that hitch a ride on sawyer beetles. While native to South Dakota, Kiesz said, nematodes appear to only affect pine trees that are not native to the state. Those trees include the long-needle pine varieties like the Austrian and Scotch and mungo, a short-needle dwarf pine.

The trees most affected are those 15 years or older, he said. Trees that decline and die should be removed quickly to prevent further spread of the disease because the sawyer beetle will go back to the diseased trees and unknowingly pick up the nematodes and take them to another tree.

There are commercial treatments but, Kiesz said, they are high-pressure injections that must be used before any symptoms appear.

While an inventory of tree varieties along city boulevards was completed in Aberdeen, Kiesz said many Scotch or Austrian pines are on private property, which means they aren't part of the survey. Pines are commonly found on private property, in city parks and in shelter belts. Of the pines in Aberdeen, Kiesz estimates 90% to 95% are non-native.

City Forester Aaron Kiesz shows an example of the pine cones produced by an Austrian Pine.

Pine wilt can be confirmed in a tree through a test conducted by the South Dakota State University Extension office. But, he said, it's easy to identify because it happens so quickly.

"Once you see it, the tree needs to be destroyed quickly," he said. The wood cannot be stored and needs to be burned or buried immediately. The stump should also be cut flush with the ground or removed completely, he said.

Pine wilt disease isn't new, according to information from SDSU Extension. it was first discovered in Missouri in 1979 and has since been connected to the loss of thousands of trees in the central part of the U.S. It's been in southern South Dakota for several decades.

Until a tree is affected, he said, there's no reason to go remove it.

"Let them stand," he said. "Enjoy them while you can. But consider what you're buying."

If residents want to plant a pine tree, they should consider a native variety. 

Austrian Pine and other long-needle pine trees are likely to be a rare sight in the coming years with the appearance of Pine Wilt Disease. This is one of a few planted on the east side of the Northern State University Barnett Center.

A reminder to diversify

Local communities are no stranger to decimating diseases. Dutch elm swept through and has resulted in the removal of thousands of elm trees in Aberdeen. Kiesz said his department continues to plant a variety of new trees in areas where elms were removed.

Ash trees are now threatened by the emerald ash borer. It hasn't yet been found in Aberdeen, but Kiesz already has plans to start removing the oldest ash trees in an effort to create a more diverse population.

Aberdeen has an estimated 5,000 ash trees along city boulevards alone. He'd like to see about 2 1/2% removed each year so when the emerald ash borer does arrive, it doesn't overwhelm city resources.

The effect from pine wilt won't be the same, he said.

"But it's a hint of what's to come," he said. "We will lose all our non-native pines."