Karen Hills, Univ of VT - Dept. of Plt. & Soil, "137 Hills Ag. Bldg, 105 Carrigan Dr", Burlington, VT 05405, United States of America
Soilborne diseases such as root rot and damping-off affect a wide variety of ornamental and crop plants and cause significant economic losses for commercial growers. Though it has been documented that organic amendments can suppress soilborne disease, the effect of initial soil health on the development of suppression is not well understood. In addition, using organic amendments does not always result in disease suppression. This study investigated the ability of raw dairy manure, composted dairy manure and oats to suppress damping-off in two Vermont soils with differing levels of initial microbial activity and soil organic matter. Cucumber seedling bioassays were conducted to assess the development of suppression over time and to compare efficacy of the organic amendments to the commercial biocontrol product, Root Shield. Significant suppression was not observed on all sampling dates after the addition of the amendments. There were differences observed on days 20, 40, 80 and 160. Correlations between microbial activity (FDA hydrolysis) and disease rating were observed on days 40, 80 and 160. Root shield was not effective in suppressing disease on any of the sampling dates.
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