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Powdery
Mildew Disease in Dogwood
Margaret
T. Mmbaga and Hongyan Sheng
Cooperative
Agricultural Research Program
Seminar Series
Tennessee State University, McMinnville, TN
March 10,
1999
Introduction. Powdery mildew disease emerged as a
production problem only 4-5 years ago, but is currently the most
important disease of dogwood in Tennessee. It has become widespread
throughout the Southeast United States. It has been reported in some
northern states where there is growing concern on its effect on dogwood
in the forest undergrowth. Plants in the shade and in full sun are
equally susceptible. The disease reduces the aesthetic value of plants
by causing unsightly white powdery mass on the foliage. Studies on other
crops have shown that the disease stunts plant growth, causes leaf
distortion and browning, premature senescence and reduces the number of
flower buds; information on dogwood has not been documented.
Objectives. The plant pathology program at the
Tennessee State University Nursery Crop Research Station has launched a
project on dogwood powdery mildew with an overall objective to develop
an integrated disease management system (IDM) that incorporates
different methods of disease control with a bias on environmentally
friendly methods.
Methodology. Studies on the effect of the disease
on dogwood will be done to provide information that can guide decision
making in disease control. Studies on the ecology and epidemiology of
the disease will be done to generate information needed for the
development of an efficient disease management system. Alternatives to
traditional fungicides for powdery mildew disease control will be sought
and developed, and the different methods will be integrated into an IDM
system.
Results. Results on the economic importance of
dogwood powdery mildew have shown the disease reduces plant growth vigor
and dry matter. In 1997, plant vigor was reduced 28% and the plant
height was reduced 30%. Plant dry matter was reduced more significantly.
Roots dry weight was reduced by 72% and shoot dry weight by 82%. Similar
results were obtained in 1998. There was a negative correlation of
r=-.72 between plant growth vigor and powdery mildew disease severity.
The dramatic effect on the root system will likely have an effect on
plant health and the ability to absorb water and nutrients. The severely
weakened plants are likely to have increased vulnerability to other
pathogens. These results showed the economic importance of powdery
mildew in dogwood production.
Impact. Some growers avoid using traditional
pesticides because of economic or environmental concerns; information
from these studies will help to guide their decisions on powdery mildew
disease management in dogwood production. The project on powdery mildew
is a long term project and will develop alternatives to traditional
fungicides, products that are environmentally friendly and effective
either alone or as part of an integrated disease management system, and
reduce the reliance on traditional fungicides.
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