DALLAS “Have you ever driven down the road and seen someone mowing the lawn wearing a mask? This is an example of the relationship between allergies and mold spores in lawns.” Dr. Phil Colbaugh, research plant pathologist at the Texas Agricultural Experiment Station in Dallas, cites a common image seen in Texas throughout the warm weather months.
Colbaugh is studying the relationship between landscaping choices and practices, seasonal weather and potential exposure to allergenic mold spores. While his research will eventually include flowering plants, woody ornamentals, trees and herbs, Colbaugh is currently focusing on turfgrasses. His research results are being prepared for peer review, but have not yet been published.
The research began with a goal of determining whether different turfgrasses support different levels of allergenic mold spores. Emily Williams, research associate in plant pathology, said the initial study involved clippings from residential lawns in Richardson and Plano.
High school students participating in Colbaugh’s annual Summer Environmental Research Internship program spent eight weeks collecting turfgrass clippings from St. Augustine and Bermudagrass lawns in these two North Texas communities. Then they counted allergenic mold spores washed from the plant materials.
Sunny Bermudagrass locations had the highest total mold spore counts, Williams said, and both sunny and shady Bermudagrass samples contained more spores than did the St. Augustine samples.
The results also showed a large difference in lawns with full sun versus lawns with full shade. Both the sunny Bermudagrass lawns and the sunny St. Augustine lawns had three times more allergenic mold spores than shady lawns.
“Texas is a really bad area for asthma and allergy sufferers,” Colbaugh said. “The potential for exposure to allergens is high, and the exposure to mold spores is just one component in a complicated picture.”
The Asthma and Allergy Foundation of America annually ranks allergy capitals. In 2004, Dallas / Fort Worth, Austin, Tulsa and Oklahoma City all ranked within the Top 10 of 100 American allergy capitals.
Allergy is a genetic susceptibility to the IgE anti-body, which is present within the body of an allergy sufferer. When IgE comes into contact with inhaled allergens such as pollen and fungal spores, histamine and other compounds that produce an allergic reaction are released.
According to the National Institute of Allergy and Infectious Diseases, more than 50 million Americans, or one in six, have allergies. That makes allergies the sixth-leading cause of chronic disease in the United States, costing $18 billion dollars annually.
Asthma, a constriction of the muscles lining the lungs, is often triggered by rapid allergic reactions and can become life threatening if not treated quickly and properly. Fungal spores, in particular, pose a threat for people with asthma.
According to AsthmaNow.com, 9 million children and 14 million adults have been diagnosed with asthma. The condition also leads to more than 10 million missed school days each year and causes more than 14.5 million missed work days, valued at $2 billion to $3 billion annually.
Sensitization, a heightened reaction to allergens, can be caused by repeated exposure to fungal spores during routine activities, such as mowing the lawn or playing on the grass. Therefore the type of turfgrass may be a key factor in the allergic asthmatic reaction.
The most aggravating types of mold spores for asthma sufferers come from the fungal genus Alternaria, a member of the family Dematiaceae, which are recognized by their dark coloration, Williams said. Fungi reproduce by means of spores, microscopic structures that contain the main allergenic irritant. Dematiaceae and other types of fungal spores dwell on dead vegetation, such as decomposing turfgrass clippings, and in the soil.
Fungi play a vital role in the environment as decomposers. Dr. Harriet Burge of Environmental Microbiology Laboratories Inc., said a fungal-free environment is not possible or desirable. Fungi constitute an integral part of the environment, whether urban or rural.
“What was important to us was that we saw big differences in lawn types and spore counts,” Colbaugh said. “Bermudagrass lawns were found to support twice as many spores as St. Augustine grass. It means the type of grass you choose to put down for your lawn or your athletic field may make a difference to those who suffer from allergies and asthma. St. Augustine supports fewer of the fungal spores that trigger allergic or asthmatic reactions.”
Should grass clippings be left on a lawn or removed after mowing? Colbaugh and Williams advise leaving them.
“They are a great source of nutrients, including nitrogen, potassium and phosphorus, reducing the need for additional chemical fertilization,” Williams said. “They contribute organic matter to the soil over time. Bagging these materials for curbside garbage collection is costly, and it takes up limited landfill space. And there are ways to reduce the potential for spore numbers on established lawns.”
In recent related research, Colbaugh and Williams have shown that when a lawnmower with a mulching blade was used, spore numbers were much lower than when a standard blade was used.
Colbaugh and Williams emphasize they are not providing medical advice. Their goal is to provide science-based research in an area that lacks information. Ultimately, they hope this research will help everyone make informed choices about lawns and sports turfs.
This summer the researchers are measuring the differences among a number of turfgrass types under test plot conditions. They are tracking maintenance items such as fertility, mowing height, mowing frequency and irrigation, all of which affect the number of fungal spores within the turfgrass. They are also monitoring daily weather patterns to understand the influences of rain, dry weather, high winds, or high and low humidity.
“Preliminary results are confirming what we learned last year about Bermudagrass,” Williams said. “Bermuda supports much higher numbers of allergenic mold spores than do the other types of grasses tested.” Those grasses include St. Augustine, Zoysia and Reveille Hybrid Bluegrass, which was developed at the Dallas center by Dr. James Read.
The next step in their research is to conduct air sampling during and immediately after mowing, to determine exposure risk to the mower, Williams said. They would also like to determine whether the number of spores within the turfgrass clippings affects the number of spores in the air within the home landscape. No date has been set for that research effort, due to the high cost of the sampling equipment needed to conduct the test.
Until they can perform these aerobiological tests, Colbaugh and Williams plan to study other landscape materials, such as compost piles and mulching materials.
This summer, interns have explored the abilities of inorganic and organic mulching materials to support the growth of Alternaria.
“Preliminary experiments have shown some organic mulching materials do support fungal growth while others do not,” Williams said. “These are preliminary experiments and we look forward to furthering this research in an effort to provide even more information for clinicians and homeowners.”