THE USE OF COMPOST OR COMPOSTING PROCESS TO SUPPRESS PYTHIUM APHANIDERMATUM IN USED ROCKWOOL

In the greenhouse industry, many growers (over 50% of greenhouse vegetable production area world wide) use rockwool as a growing substrate. At the end of its useful service (about 1-3 years), rockwool is disposed of as waste. Rockwool has been proven as an excellent growing substrate for plants because it can provide balanced aeration and water holding capacity, and is chemically inert. The objective of this study was to investigate methods to eliminate or suppress possible plant pathogens existing in rockwool after it has been used for hydroponic vegetable production. The treated rockwool may then be reused for continued crop production. Pythium aphanidermatum was inoculated on roots and in the growing substrate rockwool of greenhouse grown Momordica charantia plants. The infected rockwool, containing infected roots, was shredded and mixed with compost at 1:1 or 1:3 ratios. Cucumber seeds were then sown in these mixtures to investigate the efficacy of compost to suppress P. aphanidermatum. Also, the same infected rockwool was mixed with yard and leaf waste at 1:1 and 1:3 ratios and composted for 6 weeks. P. aphanidermatum was analyzed at the beginning and at the end of the composting to determine the efficacy of composting in killing P. aphanidermatum. Results showed that by mixing used rockwool with compost, P. aphanidermatum was suppressed but not completely eliminated. Composting used rockwool with yard and leaf waste at 1:1 or 1:3 ratios completely eliminated P. aphanidermatum zoospores’ infection capability; however management of the composting process is required to ensure all the materials in the composting pile are exposed to high temperature (>57°C) for at least 7 days.