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ISSUE 17   September 28, 2001



A recent survey conducted by the North Dakota Forest Service and the USDA Forest Service shows that more than 1,000 acres of trees were defoliated by forest tent caterpillars (FTCs) in the Turtle Mountains of north-central North Dakota this year. The greatest amount of defoliation was seen in aspen, but defoliation occurred in most hardwoods. The caterpillars were apparently avoiding boxelder in the Turtle Mountains this year. A survey of the Turtle Mountains in 1977 showed that almost 200,000 acres (nearly all of the Turtle Mountains) were defoliated by FTCs that year. We are hoping not to see that level of damage repeated twenty-five years later in 2002. For additional information about this insect see the May 10, 2001 issue of the NDSU Crop and Pest Report or go to:




Distribution of the yellowheaded spruce sawfly (YHSS) appears to be spreading southward in central North Dakota. Although no insects were found (not to be expected at the time of observations), damage consistent with that caused by the YHSS was found at two locations approximately ten miles north of Bismarck. Pictures and additional information about YHSS can be found at:




The fungus Sphaeropsis sapinea (also called Diplodia pinea) will often cause shoot blights, but can cause cankers and death of larger branches when trees are injured. Sphaeropsis sapinea caused substantial injury to pines in Bismarck following hail storms last summer. Sphaeropsis sapinea should be considered as a possible cause of injury to pines in other areas where hail storms occurred in 2001. Additional information about Sphaeropsis shoot blight can be found at:




Several silver maple and linden trees in Fargo and West Fargo were heavily infested with cottony maple scale this year. The population of this insect seemed to explode in Grand Forks in 1998. Heavy spray activities during the summers of 1996 and 1997 were suspected of reducing the populations of natural enemies of the cottony maple scale in Grand Forks. This insect is rarely a serious problem for more than two years. Additional information about the cottony maple scale can be found at:


Marcus Jackson
Extension Forester

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