sdu faculty of forestry journal special edition 2009 - Orman Fakültesi

SDU Faculty of Forestry Journal
Serial: A, Number: Special Issue, Year: 2009, ISSN: 1302-7085, Page: 189-193
NON-NATIVE HOSTS AND CONTROL OF Rhytisma acerinum
CAUSING TAR SPOT OF MAPLE.
Tom HSIANG 1* , L.X. TIAN 1 , C. SOPHER 1
Dept. Environmental Biology, Univ. Guelph, Guelph, Ontario, Canada.
* thsiang@uoguelph.ca
ABSTRACT
Tar spot of maple is an increasingly common disease in eastern North America.
Rhytisma acerinum, causing large tar spot, was apparently introduced from Europe, and
causes the most extensive problems on introduced maple species such as Acer platanoides
(Norway maple). However, this pathogen was recently confirmed via molecular methods on
native North American species of maple, A. saccharum and A. negundo. This raises the
possibility of pathogenic adaptation to native species that will result in more widespread
epidemics. Ascospore production on Norway maple was observed to occur over a relatively
short period annually (May 25 - June 22, 2006; May 25 - July 3, 2007; and May 21 - June
13, 2008). The duration of spore dispersal was dependent on the frequency of rainfall from
the start of dispersal. Field studies on fungicidal control of tar spot on Norway maple were
conducted in summer 2008, using nine chemicals and a water control. All nine chemicals
were found to be effective if applied between late May and early June. A single application
was sufficient to control disease in summer 2008.
Keywords: disease, fungi, Acer, fungicides
1. INTRODUCTION
Tar spot of maple is caused by species of the ascomycete genus Rhytisma, and
has a worldwide distribution wherever maples are found. Tar spot has been
increasing in abundance across Eastern North America in the last 15 years, with
leaves of Norway maple (Acer platanoides) bearing multiple black spots. There has
been relatively little research done on tar spot in North America. The only
scientific reports have come from Connecticut (Waterman, 1941) and New York
(Hudler et al., 1987; 1998). The most recent peer-reviewed research report is one
from New York (Hudler et al., 1998), which found that the fungus Rhytisma
acerinum is the cause of tar spot on Norway maple, both of which (host and
pathogen) are immigrant species, while a native fungal species, R. americanum,
occurs on the native red and silver maples (A. rubrum and A. saccharinum). This is
probably the reason that a Norway maple may be heavily infected with tar spot
while an adjacent red maple (A. rubrum) or silver maple (A. saccharinum) may
have no spots. The work report here continues from the earlier report (Hsiang and
Tian, 2008) which examined the spore dispersal and identity of the fungus on
various maples in North America. The purpose of this work was to continue to
examine the epidemiology of this disease, by gathering overwintered maple leaves
from southern Ontario weekly from March through August 2007 and 2008, and
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