Algae is not desirable in hydroponics and creates significant problems, such as reduced crop yield and decreased dissolved oxygen. It also affects plant physiology and, thus, needs to be controlled. An experiment conducted at the Department of Horticulture and Landscape Architecture Research Greenhouses in Stillwater sought to find a solution to the algae problem by determining the optimum applications and timing of two hydrogen peroxide products (Zeretol and PERpose Plus). Pepper' Early Jalapeno 'and 'Lunchbox Red' and tomato 'Geronimo' and 'Little Sicily' were used in the experiments.

All hydroponic systems, regardless of the type, must deliver water, nutrients, and oxygen to achieve success for plant production. Algae needs water, nutrients, and light to grow - the very resources provided by a hydroponic system. Algae growth is often seen in hydroponic systems, particularly those with recirculating nutrient solution systems. Under uncontrolled conditions, algae will cause organic loading and clogging of pipes. Algae also poses a threat to hydroponic crops by competing for nutrients and releasing harmful toxins that might inhibit or stop crop growth. 

Manual cleaning of hydroponic systems has long been a common practice, but it is a labor-intensive and time-consuming job. Chemical algicides are also used but can be harmful to the environment. Recently, more environmentally friendly chemical methods have risen to the forefront. Hydrogen peroxide is preferred because it breaks down into harmless products of water and oxygen, but higher concentrations of hydrogen peroxide have been recognized as a toxic molecule that can cause damage to plant cells. 

Researchers planted both the pepper and tomato seeds in Horticubes and transplanted them to an ebb and flow table with 40-gallon-capacity tanks. They then applied four different rate and timing combinations of Zerotol and PERpose: 35 mL weekly and biweekly, 70 mL weekly and biweekly, and a control without hydrogen peroxide application. Each plant was scanned using a chlorophyll meter to determine the chlorophyll concentration. Data on photosynthesis rate was also taken from each plant. The dissolved oxygen level of the solution was measured every day. After harvesting the plants, 300 mL of solution was collected from the five tables in the experiment and sent to a lab for quantitative algae analysis. 

Researchers found that the dry weight of algae, chlorophyll a, and algal cell counts were significantly affected by the rate and application timing of the two hydrogen peroxide products. As the hydrogen peroxide increased, dry weight, algal cells, and chlorophyll a were found to decrease. However, weekly and biweekly applications of 70 mL of either product were not significantly different from each other in controlling algae growth, so weekly applications would be recommended. Biweekly or weekly applications of both products resulted in better growth in both tomato and pepper plants, although 70 mL biweekly application of either product caused phytotoxicity and resulted in decreased growth. 

Results from both plants as well as algae analysis suggests that weekly application of 70 mL of either product-controlled algae and improving the growth of pepper and tomato plants. According to Dr. Bruce Dunn, Professor, Horticulture & Landscape Architecture, Oklahoma State University, "This research gives growers a quick and easy way of controlling algae without affecting plant growth, which will reduce labor needs and production turnaround. In the future, continuous cropping could be possible, leading to sustained production." 

The full article is available on the ASHS HortScience electronic journal website: https://doi.org/10.21273/HORTSCI16193-21