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| Rhizoctonia, a fungal disease that
is an annual problem in azalea cultivars grown in containerized nursery
production in the southern and eastern United States can be eliminated by
placing plant cuttings in a hot water treatment, according to new ARS research.
ARS PHOTO |
Dec. 31, 2009 – Rhizoctonia, a fungal disease that can be found in many ornamental
plants, can be eliminated in azalea by placing plant cuttings in a hot water
treatment, an Agricultural Research Service (ARS) scientist in the U.S. and his
university collaborator have found.
Rhizoctonia
web blight is an annual problem in azalea cultivars grown in containerized
nursery production in the southern and eastern United States. The fungus lives
on all azalea plant surfaces and in the pine bark soil throughout the year, yet
only causes plant damage in July and August, when heat and humidity peak.
The
disease first affects the azalea’s internal leaves during June, with signs
often unseen by the grower. Within 24 hours, the shrub can go from appearing
healthy to having one-third of its leaves rapidly turn brown and die.
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Micrograph of Rhizoctonia mycelium
showing the classic hyphal branching. PHOTO BY MARK MAZZOLA, ARS
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Rhizoctonia
is undetectable to the human eye, which means the pathogen can be carried on
stem cuttings used to propagate new plants and circulated within nursery stock
for years. Current control efforts include treating plants with fungicide to
stop the severe plant damage. However, dipping stem cuttings in a disinfestant
or fungicide solution has not controlled spread of the fungus, so better
control methods are needed.
In a
study published in HortScience, ARS plant pathologist Warren
Copes at the agency’s Southern Horticultural Research Laboratory in
Poplarville, Miss., and Eugene Blythe, an assistant research professor at
Mississippi State University’s South Mississippi Branch Experiment Station at
Poplarville, found placing the cuttings in water at 122˚ Fahrenheit (50˚C) for
20 minutes is the most effective method to eliminate Rhizoctonia without
damaging the plant, thus eliminating the need for fungicide treatment. The
pathogen can be eliminated in less time when placed in water at higher
temperature, but the risk of damaging the cutting increases.
According
to Copes, there is still potential for the cuttings to be re-contaminated in
other areas of the production process. He is trying to identify which steps
pose the most risk for re-contamination, with the goal of maximizing control of
this fungal disease with the least amount of effort and expense for producers.
Stephanie Yao is a
communications specialist with ARS, the principal intramural scientific
research agency of the U.S. Department of Agriculture.
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