Evergreen Trees or Conifers have had problems over the past few years. The first time I remember noticing a problem is when the conifers at Pioneers Park in Lincoln started to die off and had to be removed because of disease. Then for the past 20 years a disease called PINE WILT has killed many Scots  or Scotch Pine (Pinus sylvestris) trees in the Midwest . So many that Extension Specialists in several states no longer recommend planting this once popular species as a landscape or windbreak tree. Some experts have even predicted that we will not have any Scots pine trees in eastern and central Nebraska within 5 to 10 years unless an inexpensive treatment is found. No cure or long term preventative treatment has been found so far. There is an annual preventative injection for Pine Wilt that must be injected prior to infestation and is expensive.

          Other pine species are occasionally killed by Pine Wilt and display a similar pattern of symptoms. Austrian pine (Pinus nigra) in particular seems to be somewhat susceptible. The disease appears occasionally in Jack pine (Pinus banksiana), Mugo pine (Pinus mugo), and Red pine (Pinus resinosa). It is rarely found in White pine (Pinus strobus).

          Tree age influences the risk of Pine Wilt.  Almost all cases of the disease have 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.(4)

          Many Pine trees have turned brown and died here in Lincoln and Pine Wilt is still a problem since I wrote a three part series about this disease in 2006. But two other diseases are hitting the Austrian Pine trees, the Blue Spruce trees, and some other conifers. Many think it is the Pine Wilt that is killing the conifers but the Sphaeropsis tip blight (also known as Diplodia tip blight), a fungal disease, is killing many Austrian Pine, and the Blue Spruce trees are being damaged by Rhizosphaera Needle Cast.

          “One of the most common fungal diseases of pines in Nebraska is Dothistroma needle blight. This infection kills major branches and may even kill the entire tree under high disease pressure. It is one of the most common fungal diseases of pines in Nebraska . This disease is responsible for much of the premature needle drop that occurs in windbreaks and ornamental pine plantings. Twenty pine species are affected by this disease, but in the central and eastern United States the fungus is found most commonly and causes the greatest amount of damage on Austrian and Ponderosa pine. Scots pine is usually not severely damaged.” (3)

          “Removing infected branches and tips through pruning will improve the aesthetic quality of trees, but will do little to reduce Sphaeropsis tip blight spread since the major source of inoculum is infected seed cones that may remain on the tree. Avoid pruning or shearing in Christmas tree or other pine plantings when conditions favor infection due to the danger of infection through wounds.” (1)

          “It has been shown that infection of new shoots can be reduced significantly with fungicidal treatment applied twice during the period when current year shoots are most susceptible. This period begins with the opening of shoot buds and extends for about two weeks. In Nebraska , the first application is typically made during the third week in April and repeated the first week in May. Fungicides applied after mid-May are usually ineffective. Depending on the product being used, recommended fungicide timing may differ from above. Read and follow all label directions carefully before making any applications.”(1) Contact your full service garden center, a certified Arborist, or you local County Extension Educator for a list of recommended fungicides and when to apply in your County.

          “Blue Spruce and Colorado Blue Spruce are usually healthy, pest resistant landscape evergreens for eastern Nebraska . Unfortunately, even this seemingly healthy plant can be affected by disease and Rhizosphaera Needle Cast is one of the most commonly seen problems. This fungal disease affects the lower parts of the tree first, then spreads upward. Infected needles turn a purplish-brown color and are prematurely cast. Infection of the tree's needles takes place in the spring, but the tree does not begin to show disease symptoms until the following spring- a year later. At that time, very small black specks begin to appear on the upper surface of the needles. These specks, which can be seen with a hand lens, are fungal spores growing out of the natural openings in the needles called stomata. These fungal spores will go on to infect more needles on the tree.” (2)

          “Infected needles usually turn a purplish-brown color, then fall off in late summer of their second growing season, although some needles adhere to the tree branches over winter and produce spores the following spring. Needles on the lowest branches are usually infected first and the disease gradually progresses up the tree. On severely infected branches only current-year needles will be present as the second-year needles drop off in early summer. Although severely infected trees can be killed by this disease, usually they just become less attractive as the center of the tree thins out and some lower branches die, especially after premature defoliation has occurred for 3-4 years in a row.” (2)

          “The most important control measure with this disease is to plant only healthy trees. Inspect the tree's needles before buying it to ensure that it has not already been infected by Rhizosphaera. Infections on established trees can be controlled by spraying the tree in early June and again in early July with Bordeaux mix (Copper) or chlorothalonil fungicide. Two years of fungicide application will usually restore moderately infected trees to full foliage quality. Heavily infected trees may require additional sprays. Early treatment will usually control Rhizosphaera needle cast after only one year's spraying.” (2)

          In part 2 of this series, I will discuss some of the reasons we are having these problems now, preventative and control measures, and recommended replacement trees.

References and for more information:

1.     Sphaeropsis Tip Blight of Pine by Amy D. Ziems , Extension Educator—Plant Pathology, NEBGUIDE number G1845, © May 2008.

2.     Rhizosphaera Needle Cast of Spruce, © 2009 University of Nebraska-Lincoln Extension| Lincoln , NE 68588

  1. Seasonal Landscape Problems-Dothistroma Needle Blight, © 2009 University of Nebraska-Lincoln Extension| Lincoln , NE 68588
  2. Pine Wilt in Nebraska by Amy D. Ziems , Extension Educator-Plant Pathology and Mark O. Harrell , Forest Health Specialist, NEBGUIDE number G1899, © May 2008 University of Nebraska-Lincoln Extension| Lincoln , NE 68588

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