Peppers are in the Solanaceae family, the same family as tomatoes, eggplants and potatoes. Of all the peppers, bell peppers are the most popular worldwide because of their flavor and nutritional value. When we think of bell peppers, we often think of color: green, red, yellow, orange, and now available in lavender, white, brown and deep purples. The brighter the color, the higher the sugar content and sweeter the flavor. Bell peppers are a good source of vitamin C and fiber.
Greenhouse peppers are usually grown vertically, with two separate stems trained similarly to vine tomatoes. Year-round production is occurring at higher elevations in Mexico. Among other current research findings is the conclusion that higher plant densities provide higher profits. To better utilize limited space and meet the demand for large-scale greenhouse production, dwarf varieties are also being developed, including cascading and compact narrow-growing types.
Yield can vary depending on the variety grown, as well as the height of the greenhouse, type of irrigation system, growing medium, pruning patterns, plant density, light intensity, light availability, water quality and many other factors.
Challenges of greenhouse production
Among the challenges of growing peppers is premature fruiting, which can be due to small pot size, irregular temperatures and improper fertilization. Pepper plants must also be managed carefully so that they set and hold the first fruit. Promoting the plant to go from vegetative growth into reproductive mode involves establishing an average daytime temperature of about 69°F (21°C) and 60.8-62.6°F (16-17°C) at night.
Growers must also make sure there is an adequate fruit load established before the first fruit are picked, or the first harvest will cause the plant to revert to vegetative mode.
There are several soil substrate/waterborne pathogens to watch for with peppers, including damping-off (Pythium species) This pathogen can cause low germination, seedling death, shriveled stems and stem lesions. Pythium can be spread in both infected soil and irrigation water, rapidly contaminating irrigation ponds and creeks.
Because greenhouse root diseases are hard to control, especially in the warmer temperatures resulting from global warming trends, prevention is critical. To prevent Pythium, Plants should not be overwatered or overfertilized with nitrogen and temperatures should remain in adequate ranges as warm temperatures can create an environment for pathogen growth.
Growers should use the right production strategies (well-drained media, avoiding high salts and excess nitrogen). Both rockwool and coconut coir are used to grow bell peppers, rockwool being categorized as ‘contained’ and coir being ‘loose’ media. There are growers who have found that coir substrate can improve quality, yield and extend fruit shelf life, but the selection of media should be based on level of grower experience, general environmental conditions and other factors.
Growers should also practice outstanding ongoing operational cleanliness, including effective biofilm prevention and water disinfection. Biofilm is pervasive on most surfaces that are in frequent contact with water and can harbor pathogens such as Pythium.
Prevention of Pythium and other pathogens in pepper production
There are many treatment options to keep pathogens under control in irrigation water and some of them also work to disinfect the surface of irrigation tubes.
Physical water treatment methods have varying degrees of disinfection effectiveness and cost, both cost of equipment, equipment upkeep and required electricity costs. They include reverse osmosis, rapid media filtration, heat pasteurization and UV radiation. None of these methods are useful for reducing biofilms.
Disinfection through oxidation kills pathogens outright and prevents the accumulation of biofilm to varying degrees. During oxidation, electrons are transferred between atoms and molecules, disrupting pathogen cell structures. Efficacy of oxidation depends on a method’s oxidizing ‘power’ and the period over which oxidation occurs.
Oxidation can be achieved through:
- Repeated application of chemicals such as chlorine, chlorine dioxide and sodium hypochlorite. However, the efficacy of chemicals is pH-dependent and beneficial microbes are killed along with pathogens. Use of chemicals also poses risks for greenhouse workers and can be a food safety concern if absorbed into plant cells.
- Constant copper oxidation is costly as it involves the application of a direct current to generate copper ions.
- Continually passing ozone (O3) gas through the irrigation water provides oxidation but is pH-dependent, technically intensive and expensive.
- Regularly adding hydrogen peroxide or peroxyacetic acid is another method of oxidation but requires higher concentrations and longer exposure times than ozone. It also causes manganese and iron to precipitate. Long-term use can degrade plastics.
- Enhanced oxidation by nanobubbles is a chemical-free method to prevent root disease and biofilm accumulation while also significantly raising dissolved oxygen levels (DO) in the root zone.
How nanobubbles disinfect
Nanobubbles measure between 70 and 120 nanometers in diameter, roughly 2500 times smaller than a grain of salt. At a typical concentration of hundreds of millions of nanobubbles per ml and with neutral buoyancy, they hover uniformly within a liquid, constantly enhancing natural oxidation of water.
Nanobubbles move randomly and continuously through all parts of a water system via Brownian motion, helping enhance oxidation processes. This natural oxidation helps reduce waterborne pathogens and biofilm that can harbor these pathogens.
Nanobubbles also remove biofilm through their constant movement and oxidizing action, penetrating and physically abrading biofilm that has built up within water basins and irrigation pipes.
They also prevent the formation of biofilm in two ways. Their constant, random movement and extremely high densities oxidize (lyses) free-floating microbes before they can adhere to irrigation pipe surfaces and begin to form biofilm.
Secondly, nanobubbles are negatively charged and are attracted to the positive surfaces of irrigation pipes. This attraction causes them to completely cover pipe surfaces, preventing any existing free-floating microbes from attaching and forming biofilm.
Case Studies
Moleaer’s nanobubble generators were installed at Nova Crop Control in The Netherlands in 2020 and resulted in a 75% reduction in pathogens including Pythium.
Moleaer’s nanobubble generator was installed at Green Circle Farm in August 2019. Dissolved oxygen levels were increased to 22 ppm, which resulted in healthier root development and increased pepper and cucumber yields. The presence of the nanobubbles also caused a reduction in disease occurrence, allowing the growers to use 40% fewer chemical root treatments and enabling them to remove their ozone treatment system.
Similar results have been achieved at many other greenhouse operations.
