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Greenhouse sanitation practices and procedures will determine your crop performance

There is some history behind this topic of greenhouse sanitation and it’s importance. When I started working as a greenhouse crops specialist in Alberta in 1980, most of the vegetable crops were grown in soil. Two crops of cucumbers were grown and the season ended around the end of October or early November. The primary focus was fumigating the soil with chemicals and washing the greenhouse surfaces with a bleach solution. Root knot nematodes and fusarium and verticillium wilt causing fungi were affecting crops so much that production was down to less than 50 cucumbers per square-metre and industry sustainability was threatened. Growers switched to steam pasteurization of soils, however a few weeks after cucumbers were planted, nematodes attacked the plants near the greenhouse poles. So, steam was not effective in completely eliminating these nematodes. They moved to areas where steaming was difficult that is where the poles were. 

The incidence of wilt causing fungi also increased sometimes after steaming and when investigated further it was found that spores from the air colonized the soil. They multiplied faster in the absence of any natural antagonists. Thus, soilless cultivation systems were developed and by the end of 1984, most of the vegetable growers switched to soilless culture. 

Many crop management practices which have been developed, used, and changed include a switch from two-crop system to three crops per year which resulted in major insect, fungal and viral diseases because there was no break in between crops and no time to sanitize greenhouses. The three-cucumber crop system was designed to supply the market with fresh produce with minimum break in supply. This also necessitated to switch seedling supply from other sources, not grow them in a section of the greenhouse.

With this shift to soilless cultivation, greenhouse sanitation practices also changed. For example, white plastics being used to cover the soil surface, there is a better array of sanitizing products along with plant health improvements.  

A vacuum cleaner is being used by a grower to pick up the debris. It cleans between the heat pipe rails as well so that one does not have to displace them for cleaning.

Example of a well cleaned and sanitized greenhouse planted with cucumbers. Note the yellow sticky traps. I have also seen yellow sticky rolls as well to mass trap insects especially thrips.

Example of a cannabis facility where growers must maintain good sanitation at all the times.

Here are few logical steps which most growers follow:

• Prepare a plan based on the current crop conditions. For example, a grower had a bad infestation of thrip in cucumber crop. He examined all the facts and wrote a plan as to what and how should it be done. After last harvest, the cucumber plants were treated with a pesticide and then crop was removed by putting the plants in plastic bags right there rather than dragging them to a central area for collection and disposal. The old yellow sticky tapes were removed after the crop was taken out. 
• Then the debris was removed, floor plastic was replaced, greenhouse was sprayed with proper, registered products, yellow stick tapes were installed and seedlings planted for a fall crop. 
• Prepare a list of chemicals which are registered and don’t leave a residue for next crop. Know about the active ingredients and their rates to be used for spray and for surface cleaning. Also, what precautions need to be taken for their use and also re-entry times. Many growers use Ozone for disinfection of air when there is no crop. Plan to use these chemicals based on your assessment of problems. If virus is an issue, then focus on the use of Virucidal products. 
• During summer when growers are switching to second crops then some growers “solarize” the greenhouse by shutting the greenhouse and let the temperature rise to 40 C and above. All sensors for temperature, irrigation and others should be removed or protected during such treatments. 
• Cull piles are likely to be a major source of new infections. Ideally, they should be located downwind from the greenhouse or removed completely off site. I recall a situation where there was heavy contamination of Fusarium stem rot on cucumbers and the grower dumped the dead plants near the greenhouse. Later on, we were able to trace the source of infection in the intake air coming from that cull pile area. 
• Don’t forget to clean and disinfect carts, wires, temperature sensors, machinery, totes, sprayers, tools, door handles, hose ends, wheels etc.
• Cleaning and disinfecting drippers and stakes is also important.
• Biofilms in irrigation lines should also be looked after. Lines could be flushed with hydrogen peroxide-based products or with other agents available.

The pictures accompanying this article highlight some points I have made about the sanitation. 

Paying attention to greenhouse sanitation during the crop production cycle and at end of the season is vital to manage a healthy crop. This will also reduce pesticide use.