Archive for Wednesday, April 11, 2001

Interest running high in evergreen trees

April 11, 2001

Lots of calls have been coming into the extension office on evergreens turning brown. Reports from K-State at Manhattan say pine, spruce, juniper, yew and arborvitae samples are piling into Kansas State University's Plant Disease Diagnostic Lab.

"Most of their problems trace back to last summer's drought or to winter's cold temperatures. The tan to brown color usually indicates surface foliage damage. With some of the pines and spruces, however, our diagnoses are less encouraging," said Ned Tisserat, K-State Research and Extension plant pathologist.

The Extension Office forwards samples from local citizens to the campus. We also provide the lab with on-site visual reports and can help individual Kansans learn about alternatives for dealing with damaged trees.

Scots pines throughout the state still seem to be taking a beating. As usual, pinewood nematodes are causing many of the fatalities. Pine wilt is epidemic through the eastern half of Kansas and is slowly moving west.

The best way to control its spread is to cut down and then chip, burn or bury the pine trees killed by the disease last fall. Timing is critical. The removal must take place before early May, when this year's adult pine sawyer beetles start to emerge from dead trees. At that time, many of those beetles will be contaminated by pinewood nematodes the organisms that actually cause pine wilt disease. And, the sawyers' consuming interest will be finding healthy pines, where their feeding damage will look like an open door for nematodes.

Community-wide cleanup is the only hope for better control of pine wilt disease. Trees that died more than a year ago are not a high priority, however, because they no longer harbor the fly-away pine sawyers.

"But, Scots pines are also sensitive to extreme drought and high temperatures. So, I suspect some current damage is the result of dry conditions that started last summer," Tisserat said.

There are reports from northwest district forester Jim Strine of fairly widespread winter damage among the Scots pine trees there, with needle scorch on southwest-facing branches fairly typical.

"The branch tip die-back occurring on Austrian pines is often more serious, though," Tisserat said. "Last season's shoot growth tends to die when Austrian pines go through a cold winter. Apparently, new growth can't always acclimate for winter properly, so you're left with two-year-old wood.

"If this happens to the leader on top, the result can be like pruning or topping out a tree. You can get multiple tops that are structurally weaker, so may break more easily during storms."

In contrast, die-back at the top of spruces often signals more die-back to come. The trees may not survive, the plant pathologist warned. Otherwise, this kind of damage isn't always as bad as it looks.

"The cast needles may look purple. The needle drop itself may be uniform throughout the tree or concentrated on just a few south-facing branches," Tisserat said. "But what's important is whether the branches also are brittle and dry. If so, they won't produce new leaves. If not, they'll start producing new growth this spring."

Sy Nyhart is Leavenworth County extension agent.

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