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Using a Steamroom To Sterilize Pallets of Styrofoam Seedling Container Blocks
MTDC conducted several evaluations to determine the effectiveness of different treatments for reducing fungal contamination on styroblocks. Styroblocks that were tested had been used to grow several seedling crops at a large forest seedling nursery. The goal was to determine whether such treatments could kill fungi that were potential pathogens, leaving the styroblocks relatively safe to reuse.
MTDC tested several different ways of sterilizing styroblocks. One method used radiofrequency (RF) waves to treat the blocks. Other methods used dry heat (with low humidity) and wet heat (with high humidity).
Before treatment, each styroblock was sampled for fungal colonization near the bottom of cells at the drainage hole where the highest populations of contaminating fungi, including potential pathogens, tend to congregate. Two pieces of Styrofoam (about 2 by 5 millimeters) were cut from each sampled cell using sterile procedures and placed on an agar medium selective for Fusarium and closely related fungi. Plates were incubated for 7 to 10 days at about 24°C under diurnal (day and night) cycles of cool, fluorescent light. Emerging fungi were identified by genus. Selected isolates were transferred to potato dextrose agar (growth medium) and carnation leaf agar for identification of the species of Fusarium and Cylindrocarpon. Styroblock colonization was calculated as the percentage of sampled Styrofoam pieces that were colonized by a particular fungus. Specific cells were sampled in each styroblock. Two small pieces of Styrofoam were taken from each sampled cell.
After treatment, another two pieces of Styrofoam were taken from each sampled cell. The fungal colonization (the number of sampled Styrofoam pieces colonized by particular fungi) before and after treatment were analyzed statistically.
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