First Steps to a Clean Greenhouse

If you have had re-occurring problems with diseases such as Pythium root rot or insects such as fungus gnats, perhaps your greenhouse and potting areas need a good cleaning. Over the course of growing a crop, infectious microbes accumulate and algae flourish on moist surfaces harboring fungus gnats and shore flies.

Attention to greenhouse sanitation and disinfecting are steps that growers can take now to prepare their greenhouses for the spring growing season. Some growers wait until the week before opening a greenhouse before cleaning debris from the previous growing season. It is better to clean as early as possible to eliminate over-wintering sites for pests to reduce their populations prior to the spring growing season. Pests are much easier to prevent than to cure.

Begin by thoroughly cleaning the floor of soil, organic matter and weeds. Install physical weed mat barriers if floors are bare dirt or gravel and repair existing ones. Weed barriers not only prevent weeds, but also make it easier to manage algae. Avoid using stone on top of the weed mat that will trap soil and moisture, creating an ideal environment for weeds, diseases, insects and algae.

Benches, preferably made of wire, should be disinfected and pots, flats and trays should be new or disinfected. Bench tops and work tables should be made of a non-porous surface such as a laminate that can be easily disinfected. Avoid using bare wood for these tasks. Hose ends should always be kept off the floor and growing media kept in a clean area and covered. Avoid holding plant material and accumulating contaminated pots, media or debris in the media mixing area. Next, disinfect the growing and plant handling areas, and irrigation system.

Benefits to Disinfecting the Greenhouse

Many pathogens can be managed to some degree, by the use of disinfectants. For example, dust particles from fallen growing medium or pots can contain bacteria or fungi such as Rhizoctonia or Pythium . Disinfectants will help control these pathogens. In addition to plant pathogens, some disinfectants are also labeled for managing algae which is a breeding ground for fungus gnats and shore flies.

Although disinfecting should be done routinely, timing does not always permit this extra effort. Take the opportunity to thoroughly clean greenhouses between crop cycles when greenhouses are totally empty.

Managing Algae

Algae are a diverse grouping of plants that occur in a wide range of environments. Algae growth on walks, water pipes, equipment, greenhouse coverings, on or under benches and in pots is an ongoing problem for growers. Algae form an impermeable layer on the media surface that prevents wetting of the media and can clog irrigation and misting lines, and emitters. It is a food source for insect pests like shore flies, and causes slippery walkways that can be a liability risk for workers and customers. Recent studies have shown that algae are brought into the greenhouse through water supplies and from peat in the growing media. Once in a warm, moist environment with fertilizer, the algae flourish.

Proper water management and fertilizing can help to slow algae growth. Avoid over-watering slow-growing plants and especially crops early in the production cycle. Allow the surface of the media to dry out between watering.

Avoid excessive fertilizer runoff and puddling water on floors, benches, and greenhouse surfaces. The greenhouse floor should be level and drain properly to prevent the pooling of water prior to installing a physical weed mat barrier.

Irrigation Systems

Non-recirculating irrigation systems can be cleaned using a new product, chlorine dioxide (Selectrocide™). It is labeled for disinfecting irrigation lines and greenhouse surfaces. To thoroughly clean irrigation systems, the company recommends using two consecutive overnight treatments, and then flushing the system with clear water, making sure to discard the dislodged debris. Selectrocide™ can also be used as a continuous ultra-low dose treatment.

Copper ionization is also being used to control algae and pathogens in irrigation water. Growers in Europe have used the technology for several years and growers here are now beginning to use it. The Aqua-Hort® system consists of a control box, an electric treatment pipe and four sets of electrodes for the release of copper. The system automatically controls the output of copper ions according to the flow rate and electrical conductivity of the water. Copper ions are released within normal fertilizer standards during irrigation.

Greenhouse Benches

If possible, use benches made of wire that can be easily disinfected. Wood benches can be a source for root rot diseases and insect infestations. Algae tend to grow on the surface of the wood creating an ideal environment for fungus gnats and shore flies, and plant pathogens can grow within the wood. Plants rooting through containers into the wood will develop root rot if conditions are favorable for pathogen activity. Disinfect benches between crop cycles with one of the labeled products listed below. Keep in mind that the following disinfectants are not protectants. They may eradicate certain pathogens, but will have little residual activity.