Sooty mold

In Region 1, sooty mold growth on a wide variety of host trees, particularly, bur oaks, white and jack pines and white spruces was noted this summer. Sooty molds are characterized by a black or brownish growth that covers the foliage and branches of the host tree. This covering can be of varying thickness. Most sooty mold grow on the honeydew secreted by aphids and other sucking insects. The hot, dry, early spring and summer created an environment favorable for sucking insects. Occasionally, sooty molds physically cover the foliage with very heavy growth and this reduces transpiration and photosynthesis which, in turn, reduces vigor in young trees affecting growth and possibly survival. The scattered, infrequent occurrence of sooty mold usually makes the disease a problem only for ornamental and Christmas tree plantations. The fungus declines once the insect infestation associated with it stops. The best way to control sooty mold is to reduce the amount of honeydew present on the leaves and branches by controlling the aphids or scale insects that produce the honeydew.


During the first week in July, greenstriped mapleworms had caused heavy defoliation of red maples in Crow Wing County on the southeast side of North Long Lake. The insect pest was first observed in l997 on July 29th at this location. Little branch dieback is expected due to the effects of defoliation. Its adult stage, the rosy maple moth, was seen in great numbers around night lights, in several counties of central Minnesota, into late May of this year. Scattered and spotty, heavy defoliation of red, sugar, and silver maples is predicted next July, especially in cities and towns where lights have attracted the moths.