Suppression of Rhizoctonia and Pythium damping-off of radish and cucumber seedlings by addition of fish emulsion to peat mix or soil

The efficacy of fish emulsion in enhancing plant growth and suppressing seedling damping-off diseases caused by Rhizoctonia solani and Pythium aphanidermatum was investigated on peat mix and soil. Fish emulsion (1%-4%; m/m peat mix) or equivalent inorganic fertilizer (N-P-K) was incorporated into pathogen-infested peat mix and incubated in plastic bags for 1, 7, 14, and 28 days prior to planting radish or cucumber seeds. Plants were rated 14 days later for incidence and severity of damping-off. Negligible protection of seedlings from damping-off occurred in peat mix incubated for 1 day with fish emulsion. After 7 days incubation, however, 70%-80% of the seedlings remained disease-free in peat mix amended with 4% fish emulsion. After 28 days, equivalent levels of disease protection were found with all concentrations of fish emulsion. As the inorganic N-P-K treatment was adjusted to reflect N-P-K levels in the fish emulsion, no disease control was obtained, indicating that disease protection was not due to increased plant nutrition. Incorporation of 0.5% (m/m soil) fish emulsion into soil 5 days before planting radish provided effective control of damping-off disease. Fish emulsion (2% and 4%; m/m muck soil) also effectively and consistently suppressed damping-off of cucumber seedlings in muck soil naturally infested with damping-off pathogens. Pasteurization of the peat mix followed by re-infestation with R. solani resulted in a much higher level of disease than that obtained in unpasteurized infested peat mix. Addition of fish emulsion resulted in restoration of disease suppression within 7 days. These results suggest that fish emulsion may not be toxic to the pathogens but may create a biological climate in peat substrate or soil that is suppressive to the disease. Fresh and dry mass measurements of plants produced in 4% fish emulsion were 2 to 3 times greater than in nonfertilized peat but were comparable with those receiving equivalent N-P-K. The results suggest that fish emulsion has both nutritive value for plant growth as well as disease suppressive properties. Thus, it may be an ideal product for use in organic or conventional transplant production.