Recently garden centers and horticulturists got panic calls from homeowners concerned about their evergreen trees because of the annual needle drop. The first time my WHITE PINE (Pinus nigra) trees dumped their old needles I was very nervous and afraid the trees were going to die. For those who don’t know, the needles on evergreen trees do not live a long time. They last anywhere from two or three years on WHITE PINE up to seven or eight years, depending upon the variety or kind of evergreen tree. If you look inside any evergreen tree the branches are bare. This is normal. This is also why you want to leave at least 12 to 15 inches of green growth on a branch when you prune or the branch will die. New needles will not grow where the old needle has died like the leaves do each year on a deciduous tree.  

Many of those who called were afraid the tree had a disease or insect problem. Some were concerned about a disease called PINE WILT. Over the past 20 years PINE WILT has killed so many Scots or SCOTCH PINE (Pinus sylvestris) trees in the Midwest that Extension Specialists and arborists in many Midwest states no longer recommend planting this once popular species as a landscape or windbreak tree. Some experts even predict that we will not have any Scots pine trees in eastern and central Nebraska within 5 to 10 years. No cure has been found so far. High value trees can be protected with a series of trunk injections of Greyhound (abamectin is the active ingredient). This is a preventative treatment and very expensive. 

          Other pine species are occasionally killed by pine wilt and display a similar pattern of symptoms. The disease appears occasionally in Austrian pine (Pinus nigra), Jack pine (Pinus banksiana), Mugo pine (Pinus mugo), and Red pine (Pinus resinosa). It is rarely found in White pine (Pinus strobus) and never found in spruce, fir, juniper, or red cedar.

          Tree age influences the risk of pine wilt.  Almost all cases of the disease has appeared in trees more than 10 years old. Therefore, pine wilt has not had a major impact on Christmas tree plantations of Scots pine or Austrian pine.

          Two years ago I wrote about PINE WILT and I am repeating the article now because so many people are still concerned and asking questions. The following is taken from a publication on pine wilt published by The University of Nebraska-Lincoln Extension Service, Iowa State University Extension, Kansas State University, and University of Missouri-Columbia Outreach and Extension Service. “Pine wilt typically kills Scots pine within a few weeks to a few months. The needles initially turn grayish green, then tan-colored to brown. The needles remain on the dead tree for a year or more.”

          “Several organisms are involved in pine wilt. The pinewood nematode (Bursaphelenchus xylophilus) is a microscopic-sized worm-like animal that feeds on the blue-stain fungi that lives in the wood of dead and dying pines, and on the living plant cells surrounding the resin canals, or water-conducting passages of pines.” This nematode in effect clogs the arteries of the tree so that it starves to death starting at the top of the tree.

          “Nematodes are unable to move very far without help from an insect vector. The life-cycle of the pine sawyer beetle (Monochamus spp.) also known as the longhorned beetle because of its very long antennae, is closely intertwined with the life cycle of the pinewood nematode. Female pine sawyer beetles lay their eggs under the bark of dead or dying pines, usually during the summer. The grubs hatch and feed under the bark, then tunnel deep into the wood. The grubs form pupae, and then adult beetles ¼ to 1 ½ inches in length emerge from the tree any time from late spring to early fall.”

          “While the sawyer beetle develops within the tree, the nematode also matures. Just after the adult sawyer beetle breaks out of its pupal shell, large numbers of pinewood nematode larvae move into the tracheae (breathing tubes) of the new adult beetle. When the sawyer beetle tunnels to the surface of the bark and flies away, it carries up to tens of thousands of hitch-hiking nematodes.”

          “Bark beetles are not directly involved in the pine wilt disease cycle, but their activities are indirectly related to nutrition of the nematodes. When the bark beetles bore into dying pines, blue-stain fungi living in the beetles also enter. The blue-stain fungi rapidly colonize the wood of the dying tree, leaving behind a characteristic cobalt-blue discoloration. Pinewood nematodes thrive on a diet of blue-stain fungi, so their numbers multiply even faster.”

          “Pine wilt is severe in parts of the Midwest, yet rare elsewhere in the United States. This is because the Midwest is prone to periods of drought that place pine trees under stress. The Scots pine is not native to the Midwest. No one knew at the time that planting a susceptible species such as Scots pine into a hot, stress-prone environment has been a recipe for trouble.”

          Next week in Part 2, I will suggest some trees that can be used to replace dead or dying pine trees, or can be planted in your yard as a specimen tree instead of Scots Pine or Austrian Pine. There are a number of trees that we can plant in eastern and central Nebraska in windbreaks and as specimen trees. Specimen trees are defined as trees that can be used in a landscape by themselves are in a small grouping.

          For more information you can reach the Nebraska Statewide Arboretum on the internet at “”. At this web site you can get information on trees including their usual height and width. They also have access to colored pictures of the trees.  

          You can also contact your County Extension Educator or go on line to On the left hand side you can type in the name of a disease or the name of a tree then click on search. A list of publications will appear. You can read those you want and/or download them to your computer or print them for your files.

          Or you can go to This is the web sight for the Nebraska Forestry Service which is a division of the University of Nebraska-Lincoln. In the upper left hand corner in the search box type in “pine wilt” or the name of the tree you want information about. A list of publications will appear. You can read those you want and/or download them to your computer or print them for your files.

Copyright 2007