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Proceedings of Past Forest Nursery Association Meetings:

Preliminary Evaluation of Fungicides for Control of Damping-Off Disease in Container Grown Red Pine Seedlings
Jill D. Pokorny and Jana K. Rykhus
1997: Bemidji, MN
Historically the fungicide benomyl has been widely used by greenhouse managers to control
damping- off diseases in container grown conifer seedlings. In 1991, product labeling for benomyl
underwent major changes and all greenhouse and ornamental uses were eliminated. Greenhouse
managers, no longer able to use benomyl, were faced with the immediate need to identify effective
alternative fungicides. This study was undertaken to investigate the effectiveness of several alternative
fungicides in controlling damping-off diseases in red pine seedlings, grown under operational
greenhouse conditions and naturally occurring disease pressure. The decision to design this study
using operational greenhouse conditions and naturally occurring disease pressure was made in
response to the immediate need to identify alternative fungicides and transfer this information quickly
to greenhouse managers, and the lack of pathological information relating to disease development.
Baseline data regarding the species of pathogenic fungi occurring on red pine, and specific disease
inoculum levels that incite disease symptoms are unknown, and the determination of such data would
have required many months of laboratory and greenhouse testing. Seedlings were grown using
cultural practices consistent with common greenhouse operations including the reuse of surface
disinfected styroblocks and the sowing of seed which received no surface washing or fungicide seed
treatment. The seedlings were grown under conditions of naturally occurring disease pressure and
were not artificially inoculated with pathogenic fungi. It was speculated that disease inoculum would
be present in cracks and crevices of reused styroblocks and in/on seeds. Damping-off and root rot
disease did develop, and disease pressure was sufficient to cause a significant reduction in seedling
quality in the untreated control treatment when compared to the fungicide treatments.
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