Horticultural scientist focuses research and extension on greenhouse sustainability

Rosa Raudales
Rosa Raudales

As an assistant professor in the Department of Plant Science and Landscape Architecture (PSLA) with a 70 percent extension appointment, Rosa Raudales focuses on applied research that meets the needs of Connecticut greenhouse growers.

Raudales’s studies center on water quality for irrigation purposes and the various strategies to manage microbes and unwanted chemicals within irrigation systems.

“Water quality is an important issue for farmers, as well as for continued sustainability,” Raudales explains. “Greenhouse production is about getting the most yield with the fewest resources possible.”

Her first step was to conduct a survey to determine the needs of local growers. Most indicated that they do not test their water on a regular basis; rather, they start monitoring if they discover a problem. One pressing issue is the clogging of irrigation systems.

Raudales sampled water from several growers experiencing clogging within their irrigation systems. “We could not identify the cause of the problem based on the samples that we collected. It seems that clogging is caused by a combination of multiple factors,” she says.

This discovery prompted several research projects designed to study irrigation water. “One of my long-term goals is to identify parameters in water quality that cause clogging of irrigation systems and develop strategies to prevent this problem from happening,” Raudales says. “We found that there was a discrepancy between current published guidelines and what we found in our sampling of irrigation water. So, we’re trying to determine what factors, and at what levels, actually cause problems.”

Biofilm is one consideration. Biofilm is a collection of microorganisms such as bacteria and fungi that attach to surfaces and multiply in layers. Biofilm is very persistent in irrigation water and is thought to interfere with irrigation systems, and it may become resistant to sanitation efforts. In agriculture, one of the challenges of removing biofilm is that high concentrations of sanitizers can be phytotoxic to crops. The question becomes, how clean do the pipes need to be, and is it necessary to treat the irrigation pipes?

In one project, Juan Cabrera, Ph.D. student in Raudales’s lab, compared PVC and polyethylene irrigation pipes (the two most common piping materials) to determine which type of pipe accumulates more biofilm. The PVC pipe consistently showed more biofilm than the polyethylene.

In a second project growing poinsettias, Cabrera compared the pH of the solution passing though clean irrigation pipes with that of the solution in pipes containing biofilm. The results showed differences in pH levels in the solutions, indicating that biofilm may affect nutrient programs. But, at the same time, plants being irrigated from the biofilm pipes were somewhat protected against Pythium aphanidermatum, a devastating plant pathogen that causes Pythium root rot.

“We want to continue the research to include additional plant pathogens and younger plants, as they are more sensitive to plant pathogens,” Raudales says. “We learned from this study that it may not pay to treat water if there isn’t any issue with plant health or clogging.”

Her lab also looked at varying concentrations of total suspended solids (TSS) in irrigation water. “We tested different concentrations of TSS within greenhouse irrigation systems in an attempt to determine the concentration of TSS that leads to clogging.”

Next year, Raudales will test different iron levels and bacterial loads in the irrigation water to see how these factors affect irrigation systems. “In the long-term, we want to determine what is clogging these systems and develop practical and accurate guidelines for growers,” she says.

The driving force behind another project came directly from a local grower. Some greenhouse operations have closed irrigation systems, in which they irrigate the crops, capture the water that drains, then reuse it to irrigate crops again. This system helps conserve water and nutrients and prevents runoff into the environment. Growers typically apply a common plant growth regulator, paclobutrazol, to ornamental plants. This grower wanted to know if nutrient solution in the catchment tank could contain a residual concentration of paclobutrazol, which could adversely affect plant growth if applied to plants indiscriminately.

Raudales tested solutions from several greenhouses around the United States, collaborating with the University of Florida and the USDA in Toledo and Wooster, Ohio. Results found residual paclobutrazol in drain water. George Grant, MS student at the University of Florida, continued the project with his advisor, Paul Fisher, professor of floriculture. Grant tested various filter types to remove residual paclobutrazol from drain water.

In research focusing on hydroponics, a growing method popular with greenhouse vegetable producers, PSLA master’s student Cora McGehee studied the feasibility of using beneficial microbes to control plant pathogens and algae growth. There are fewer treatment options available for hydroponic growers, as the plant roots are exposed and more sensitive to treatment.

Lettuce was somewhat resistant to Pythium root rot, while microgreens were extremely susceptible. Biocontrols must be applied before a problem surfaces, yet excessive treatment can sometimes reduce plant growth. “What this shows us is that the fine balance of a healthy hydroponic crop may be more about environmental conditions rather than controlling the pathogens,” says Raudales.

The next step is to adjust the hydroponic solution conditions as a method to reduce microbe growth. “We will evaluate diseases when changing temperature, pH or concentration of salts, or adding silicon,” she says. This may enhance beneficial microbes, reduce disease-producing microbes or improve plant defenses.

In addition to research and extension work, Raudales serves as faculty advisor for the Horticulture Club. “I want students to be more engaged and attracted to horticulture,” she says. “One of the biggest problems in our industry is that there are not enough people to work in the field. Growers are always asking me if we have students or graduates looking for positions. I want to connect students to the industry. I also try to support students and encourage them to grow plants in the greenhouse.”

“My overall goal is to help growers become more sustainable, both financially and environmentally. In addition to preserving the environment, sustainability is important to consumers, and this could help in marketing our industry. We need to grow more with less water, in a way that is efficient, economically feasible and sustainable.”

By Kim Colavito Markesich