Parts of northern Minnesota are starting to get dry so it might be a good idea to start watering your birch trees to prevent bronze birch borer infestation.
Norway pine saplings planted around campsites in Itasca Park are lightly defoliated by the introduced pine sawfly, Diprion similis. White pine is the preferred host for IPS, but they were not defoliated. IPS usually have two generations per year and sometimes three if the season is long enough. The second generation is active now, feeding on the current years' needles, so it is likely that further defoliation by a third generation can be anticipated.
The wet, cool weather in June was likely the reason for low incidences of yellowheaded spruce sawfly defoliation this year. It seems every June this creature is active somewhere, especially when young white spruce are being planted in open areas, particularly, yards and windbreaks. In Crow Wing County, larvae were done feeding two weeks ago. The insects should be in cocoons by now and overwintering in the duff.
Tar spot of maple is an example of leaf and needle blight maladies associated with the wetter that usual summer of 2000. Tar spot on red maple on yard trees was reported in Beltrami County near Bemidji. This disease occurs quite frequently in forest stands where it is generally moister during the day. Tar spot is caused by the fungus, Rytisma acerinum, which produces irregular, shiny, tar-like, circular spots on the leaf's upper surface. The dark color is due to the masses of black fungal mycelium. In yards, one can rake up and destroy the leaves that are infected and destroy them to help decrease the potential for reinfection next year. Treating with a copper fungicide at bud-break may help, if the disease persists.
Jack pines were safe from jack pine budworm again this year and will be again next year in Hubbard, Becker, Beltrami and Pine Counties, if our egg mass surveys are correct.
Rose chafer beetles
Great numbers of tan to reddish-brown beetles, with bodies densely covered with dull yellow scales and long, hairy legs were seen in central Minnesota during the first week of June. These rose chafer beetles include Macrodactylus subspinosus and other species of this genus. Rose chafers swarm, feed and mate on deciduous trees, shrubs, grapes, peonies, roses and other flowering plants, shredding leaves and blossoms and destroying fruit. Adults live about one month. Since they are often attracted to white surfaces such as white flowers and white birch trees, a cultural control to protect garden plants are white plaster pails with an inch or two of water in them. Beetles are trapped and die in the water. If insecticide control is considered, repeated application of carbaryl or other products labeled for their control may be necessary to prevent damage by incoming swarms.