Saturday, October 25, 2008

Greenhouse and Nursery - Cleaning and Reusing Pots and Flats

With the cost of production increasing dramatically over the past 3 years, greenhouse and nursery producers may be considering reusing pots and flats. It is very important that you disinfest pots before you reuse them. The following is a good article on the subject.

Cleaning and re-using pots, trays and flats may be an economical move for some growers, but it is important to do it right. Plant pathogens like Pythium, Rhizoctonia and Thielaviopsis can persist in root debris or soil particles on greenhouse surfaces. If you know the previous crop had a disease problem, it is a safe move to avoid re-using those containers. It is also a good idea to avoid planting crops that are prone to Thielaviopsis problems, like pansies, in containers that have been previously used.

Even if there was no evidence of disease in the crop, all containers should be washed thoroughly to remove all soil particles and plant debris before being treated with a greenhouse disinfectant – organic matter can protect pathogen spores from coming in contact with the disinfectant solution. There are several products available for disinfecting greenhouse surfaces: quaternary ammonium products (Greenshield®, Physan 20™, Triathlon®), and hydrogen dioxide (ZeroTol®, OxiDate®). Follow label directions for these products - labels indicate that pots must be soaked for at least 10 minutes in these products to be fully effective. A 10 percent solution of household chlorine bleach (one part bleach to 9 parts of water) may be used for pots and flats, but the solution has a shorter activity period than other disinfectants, losing half its strength in 2 hours. Sanitation with chlorine bleach also requires a longer soaking time. Chlorine bleach is also phytotoxic to some plants, and must be used in a well-ventilated area to protect workers.

Tina Smith from the University of Massachusetts has an excellent fact sheet called “Cleaning and Disinfecting the Greenhouse” that describes the greenhouse disinfectants and their proper use in great detail, including links to labels of disinfecting products. The fact sheet can be found at:

Reprinted from the October 24, 2008 edition of the Greenhouse TPM/IPM Weekly Report from the University of Maryland Cooperative Extension, Central Maryland Research and Education Center.

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