Every year, nurseries and greenhouses around the country pump water from reservoirs and retention ponds to irrigate their plants. This helps the green industry deal with water shortages and the costs associated with using other sources of water, but it also has a major drawback: waterborne pathogens.
“We want growers to recycle water, but we don’t want them to recycle pathogens,” said Chuanxue Hong, a professor of plant pathology, physiology, and weed science in the College of Agriculture and Life Sciences and a plant pathology specialist for Virginia Cooperative Extension.
For more than a decade, Hong has been leading an irrigation pathogen and water quality project at the Hampton Roads Agricultural Research and Extension Center in Virginia Beach, Va., that has helped the horticulture and floriculture industry become more sustainable and better compete in the global market. In particular, the project is searching for biologically based control methods for pathogens, or plant-damaging molds, in the Phytophthora and Pythium genuses and developing best practices to recycle irrigation water in a way that protects water quality and improves water use efficiency.
In fall 2010, Hong and his colleagues received a five-year, $2.7 million grant from the U.S. Department of Agriculture’s National Institute of Food and Agriculture to study integrated management of these waterborne pathogens and to improve irrigation water quality.
“The goal of the project is to understand the control of these pathogens and to design or redesign an irrigation system that will protect water quality without using chemicals or unnecessary cost,” Hong said. “We hope to answer the question, ‘How can we make the production of nursery and greenhouse crops a more sustainable industry?’”
Earlier in their research, Hong and his colleagues conducted a simple experiment to show the damage caused by Phytophthora pathogens, named after the Greek for “plant destroyer.” They built two field demonstration plots: one using recycled pond water and another using well water. Within 2 1/2 months, the plants exposed to recycled irrigation water died, but the other plants were alive and well.
Today, the research team does not need further proof that genus harms ecologically and economically important plants. Instead, the team spends much of its time characterizing pathogens, developing detection technology, studying the economic threshold for implementing control methods, and creating management strategies.
Labs in other parts of the country have only identified a handful of aquatic species of those types of pathogens, but Hong and his colleagues have found 35 species in irrigation water. In total, there are more than 100 species of these harmful pathogens.
Although researchers are evaluating whether individual species are aquatic or terrestrial and what degree of damage they have on nursery and floral crops, the research team aims to develop strategies that deal with the Phytophthora genus in its entirety. And they have not left any tools out of their arsenal.
In addition to designing new or improved irrigation systems and developing biological control methods, researchers are also searching for ways to manipulate water quality in reservoirs and retention ponds to kill pathogens before they reach pump houses. “We are studying the effect of pH levels, dissolved oxygen, and electrical activity on pathogen survival,” Hong said.
The Virginia Tech-led team has already helped growers in Virginia improve irrigation practices and save money. Team members are also creating an online knowledge center to share research results and recommendations for best management practices with the green industry across the country.
According to Hong, an irrigation system that deals with pathogen problems would have lasting rewards for growers. “When farmers build a new irrigation system and modify existing systems based on the results of this project, they will benefit forever from such one-time investment,” he said.
Although the researchers have made significant strides in recent years, they have only begun to understand the impact of pathogens on nursery and greenhouse crops. They have not explored the impact of other microorganisms -- such as fungi, bacteria, viruses, and nematodes -- on irrigation water quality. For Hong and his team, the work is far from over.
According to a report by the U.S. Department of Agriculture in the most recent Census of Agriculture, the green industry generated an estimated $11.7 billion in revenue in 2009.
Every major plant-production facility in Virginia uses the chlorine protocol developed at Virginia Tech's Hampton Roads Agricultural Research and Extension Center. A malfunctioning chlorine injector cost one eastern Virginia nursery about $143,000 during a three-week period. Had it affected the entire operation, the nursery would have lost an estimated $715,000 to waterborne pathogens.
The irrigation pathogen and water quality project has several goals:
Project partners include:
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