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Archive for Thursday, October 18, 2007

Fatal wilt, other problems pounding Kansas pines

October 18, 2007

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— Pine wilt infections among Kansas' pine trees are beginning to have visible effects. Cases could continue to emerge into December, according to a Kansas State University scientist.

But, identifying victims of the always-fatal disease may be tricky.

An array of troubles have been battering Kansas pines this year, and the effects of other problems can look a lot like pine wilt, said Megan Kennelly, horticultural disease specialist for K-State Research and Extension.

Wilt can attack Scots, Austrian, mugo and occasionally white pines.

Since its first appearance in 1979, the disease has become widespread in the eastern one-third of the state. It's currently spreading west at about 10 miles per year and becoming common in central Kansas, Kennelly said.

"I've been getting numerous calls from homeowners this fall. Pine wilt is now a serious problem for the thousands of pines in this district," said Chip Miller, the K-State Research and Extension horticulturist based in Salina.

Scots are the least drought-tolerant and most wilt-susceptible of the pines that Miller sees.

"I'm concerned some homeowners may ignore their dead trees, assuming drought was the cause of death," he said. "Any stress, including drought, can also make a pine more susceptible to pine wilt. And, if a tree has the disease when it dies, it then becomes a kind of Typhoid Mary."

For trees, drought stress usually shows up as a condition called leaf scorch, Kennelly said. It's most likely when Kansas summers bring hot, dry, windy weather.

Yet, anything that limits their water supply can scorch leaves - to the point of killing them. This year, for example, another cause in some areas was last spring's abrupt change from an atypically warm March to freezing weather in April. The growing season's periods of excessive rain also interfered with some tree roots' ability to do their job. Other causes included compacted soils and bulldozed roots.

"Besides that, due to last spring's wet weather, we're also seeing an unusually high incidence of shoot death caused by a tip blight disease," Kennelly said. "Plus, some pines entered a natural needle-dropping period this fall, so look worrisome to people who've never seen that kind of process before."

She outlined two major reasons for tree owners to try to pin down their pine's problems:

¢ In the months ahead, the pines with scorch or tip blight or needle drop will simply require watering, when needed - even through the winter. Early next spring, those with tip blight - which can infect Ponderosa, Scots, Austrian and Mugo pines - will also need two correctly timed applications of an appropriate fungicide to protect their new and elongating buds.

¢ Pine wilt requires a specific, drastic response. To keep the disease and its insect vectors from spreading, owners must remove dead pines by late winter and immediately burn or bury the wood or reduce it to chips. Even a few inches of exposed tree stump can help harbor and spread pine wilt.

Kennelly suspects that tree owners usually judge whether a tree has pine wilt on the basis of the disease's well-earned reputation for killing quickly. Visibly infected pines rarely survive for more than a year. In most cases, they wilt and die within a few months, even weeks.

Any county or district K-State Research and Extension Office can help concerned tree owners in identifying pine problems, she said. For a small fee, Extension offices also can forward samples to K-State's Plant Pathology Diagnostic Lab for testing.

"Or, you can just destroy your dead pine - regardless of how it died and skip the inconvenience and cost of testing. Just be sure the whole tree is totally gone before next April," Miller said.

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