In the mid-1960s there was research of native tar spots on red maple and mountain maple, cause by R. Is there any research on tar spot in Ontario? There are studies that indicate tar spot is sensitive to air pollutants such as sulfur dioxide (Bevan & Greenhalgh 1976 Vick & Bevan 1976), although another study contradicted this finding (Leith & Fowler 1988, New Phytol. Some people speculate that higher levels of tar spot in the last 15 years are a result of increased pollution emission controls. There are also some anecdotal reports that native tar spot is increasing on red and silver maples. In some of these reports, the tar spot epidemics on Norway maple were said to have caused premature defoliation, while other reports found tar spot was merely an aesthetic nuisance, without seeming to cause any serious effects. In November 2007, maple tar spot was even on national TV news. 20, 2004, page A1), Orillia Packet & Times (Sept. 7, 2003, page A4), Barrie Examiner (Sept. In southern Ontario, there are frequent newspaper reports on maple tar spot, such as in the St. Is tar spot of maple becoming more severe? The fungus may have been in Ontario prior to 1990, but noticeable outbreaks on Norway maple did not seem to occur until after the mid-1990s. A documented report of the first appearance of tar spot on Norway maple comes from a research study on an island in Lake Huron, where the disease was first noticed in 1998 (Webster et al. At the University of Guelph, we noticed that Norway maple trees on campus were showing very high levels of tar spot in the late 1990s. platanoides near Kingsville, Ontario” (Can. As for tar spot on Norway maple, a report from 1957 states that “tar spot was moderate in a small plantation of A. There is some anecdotal evidence that the disease is becoming more severe. These native tar spots show fluctuations in severity from year to year, depending on rainfall at the time of spore dispersal and infection. The tar spot of native maples has probably been here since maples reclaimed their territory after the last ice age. An extension report ( /niagara/hort-news-fall-98.html) from Cornell University speculates that the fungus was introduced into North America in the late 1930s. (1998) found that this disease on Norway maple had been first reported in Ohio in the 1940s. In searching through American records, Hudler et al. Extension specialists were first alerted to the presence of large black spots on Norway maple in 1983 in upstate New York (Hudler et al. For such a noticeable disease, there has been amazingly little scientific research done on tar spot in North America. In the last 20 years, tar spot of maples seems to have increased in frequency across the eastern Great Lakes Region and most of the American Northeast. After those reports, there was very little research activity on tar spot in Europe until the 1970s, when air pollution effects on tar spot were reported in Britain (Bevan & Greenhalgh 1976, Env. There have been several scientific studies on maple tar spot in Europe starting in the late 1800s (Müller 1893, Wissenschaft. These are the two most common maple species. In Europe, tar spot is found on a variety of maples, including Norway maple and sycamore maple ( A. Norway maple is considered the most common street tree in these areas, partly because it was extensively planted after countless shade trees were lost to Dutch elm disease in the mid-1900s (Nowak and Rowntree 1990, J. Researchers also stated that tar spot of Norway maple was most commonly found in the American Northeast, and southern Ontario (Hudler et al. americanum, occurs on the native red and silver maples ( A. Both the plant host and the fungal pathogen were imported from Europe. 1998, Mycotaxon 68:405) it was revealed that the fungus Rhystisma acerinum is the cause of tar spot on Norway maple ( Acer platanoides). In 1998 studies at Cornell University (Hudler et al. The size of the circular or elliptical spots can range up to several cm across, depending on host and pathogen species. It has a thickened black layer on the upper side of the leaf blades. The disease looks similar on these plants. A large variety of plants have their own tar spot diseases such as maple, willow, holly, tulip tree, oak, and even goldenrod. The black blotches belong to a disease known as tar spot. Instead they are greeted with big black splotches on yellowing leaves of Norway maple. Many visitors come to this region in the fall expecting to see the golden red hues of our national emblem. What are those polka-dot trees? Questions like this one is becoming more common with recent outbreaks of tar spot on maples in southern Ontario and neighbouring areas. Tom Hsiang, Lynn Xiuling Tian and Coralie Sopherĭepartment of Environmental Biology, University of Guelph, Guelph, Ontario
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