9/28/2022 - By Marlon Carrera

Greenhouse operators have been challenged over the years with how to keep their production free of pests and diseases. This is applicable to products like vegetables, ornamentals, fruits and many others. In most operations, the approach is to “attack” the problem by using conventional control or bio controllers. However, some of the most successful operations are going beyond that by working at the root cause of pests and diseases.

This proactive approach includes taking appropriate steps ahead of time to ensure a production with minimal risks of severe pest pressure or disease dissemination.

10 Tips for a Start Clean, Stay Clean Operation:

1.       Greenhouse Operations - Cleaning out: At the end of their production cycle, or the season, operations remove all the remaining products in their space and clean out all the debris or green waste that might still be in the greenhouse. All this is properly disposed of far away from the greenhouses.

Outcome: No alternative hosts for bacteria, fungus spores or pests.

2.       Greenhouse Operations - Facility Disinfections: After the mechanical cleaning of the greenhouse, it is important to incorporate a chemical disinfectant to eradicate any possible bacteria, viruses and spores in all the surfaces, including the floor, walls, tables, recycled pots or trays, tools and equipment.

Outcome: Sterilized facilities and equipment free of pests and diseases.

3.       Greenhouse Operations - Weed Prevention: A good practice to avoid weeds inside the greenhouse is the application of a pre-emergent herbicide, mostly on the edges of the greenhouse bays, or wherever is needed. Some pre-emergent herbicides' effectiveness can last up to 6 months and maintain a house and production environment free of weeds.

Outcome: No weed presence hosting pests or diseases.

4.       Greenhouse Operations – Clean Soil or Growing Media: A clean soil or growing media is one of the easiest ways to promote a Start Clean, Stay Clean. program. There are several options for soil media in the market and it is important to ensure your operation is using the cleanest possible media. If recycling is happening, it is encouraged to have the media disinfected via pasteurization or from a steam system.

Outcome: Prevention of possible pathogens in the soil and consequently, reduction of possible root or plant diseases.

5.       Greenhouse Operations - Clearing out the Pipelines: Cleaning of the irrigation pipelines that support the usage of irrigation booms, sprinklers, irrigation drips or fog/mist systems is highly encouraged. This action requires the use of a safe disinfectant that can kill all the bacteria, spores or algae that may be inside the pipeline. Some products require a line shock and clean water flush after, to secure the eradication of pathogens in the pipelines.

Some of the most common products that have been used for this purpose are Hydrogen Peroxide or Quaternary Ammonium based products. Chlorine is not recommended for this protocol since Chlorine loses effectiveness during contact with organic material as well as the volume of water sitting in the pipes.

Outcome: Avoid inoculation of bacteria or fungus, as well as algae dissemination.

6.       Greenhouse Operations - Water Treatment: Greenhouse operations might use well water, recycled water, river water or public water and for that reason, it is vital to get a water test to ensure your water source is free of pathogens. However, the injection of a safe disinfectant can provide a piece of mind [SB3] to any greenhouse operator. There are several different injector[SB4]  systems that can be adapted to support this practice. Here (California, Bay Area) it is common to see operations using Chlorine as well as Hydrogen Peroxide or Quaternary ammonium-based products.

Outcome: Prevention of bacteria or disease outbreak, as well as algae control.

7.       Greenhouse Operations - Green Goods Source: Greenhouse operations use different input sources, these can be tissue culture (TC), unrooted cuttings (URC), liners (RC), seed and divisions. The safest but more expensive options are [SB5] the TC inputs since they are coming from a sterilized lab environment. Every greenhouse operation manages different inputs, and it is important to ensure that whatever they are using is coming preferably from a certified supplier.

However, a regular practice is also self-propagation where the greenhouse operation has its own mother plants and takes URCs from them on a regular basis. Clean and reliable inputs are 99% of the success in a greenhouse operation.

Outcome: Inputs free of pests and diseases.

8.       Greenhouse Operations - Water Management: In greenhouse operations, we use the terms " wet grower" and "dry grower." When water is used in excess, the production might be classified as a wet grower and possibly cause more problems of fungus, algae and weeds, due to the wet environment. Therefore, it is important to have the mindset of a dry grower and ensure that products are getting just what they need and not an overabundance of liquid.

Outcome: Suppression of diseases, algae and weeds.

9.       Greenhouse Operations - Scouting program: A solid scouting program can support the “Start Clean, Stay Clean.” program by establishing rigorous thresholds, validating the effectiveness of all the previous steps, as well as any preventive, conventional or biological applications used along the way. Most operations are using yellow or blue sticking cards for this purpose, but a visual scouting on plants is also recommended.

 Outcome: Awareness about pest or disease presence in the operation and factual control decisions.

10.   Greenhouse Operations - IPM: Closing the cycle of actions with a comprehensive pest and disease management program would support your efforts to maintain facilities with the lowest possible risk of common pests. These greenhouse pests include thrips, whiteflies, mites, aphids, mealybugs and fungus gnats. But also, for diseases like botrytis, rhizoctonia, fusarium, Pythium, Colletotrichum and virus. Preventive applications are by far more of an economical solution than control applications.

Outcome: Facilities free of pests and diseases.

For more information on any of the tips mentioned, reach out to your local Harrell's representative.

Check the links below for additional references of the Start Clean, Stay Clean program.

How Greenhouse Sanitation Helps You Start Clean and Stay Clean - Greenhouse Grower

Start clean, stay clean! - Greenhouse Management (greenhousemag.com)

Start Clean. Stay Clean. (growertalks.com)