Using the Weather to Control Dollar Spot

May 4, 2009

COLUMBUS, Ohio -- Phenology calendars have been found to effectively track the emergence of tree and garden pests at any given location based on the blooming of ornamental plants, and now Ohio State University plant pathologists are looking at a similar concept to control one of the turfgrass industry's most economically important fungal diseases.

Turfgrass plant pathologist Mike Boehm and his colleagues are exploring the idea of using growing-degree days to time fungicide applications to manage dollar spot --- a disease whose annual appearance can kill grass and leave behind large, irregular straw-colored patches. For those maintaining lawns, parks, sports fields and golf courses, the disease is considered an aesthetic nightmare.

"Dollar spot is a nasty disease," said Boehm, chair of Ohio State's Department of Plant Pathology and a researcher with the Ohio Agricultural Research and Development Center. "Turfgrass specialists spend a great deal of time and money managing dollar spot. It recurs every year and it's hard to control once it's established."

The symptoms of dollar spot emerge when temperatures range between 68 degrees and 86 degrees Fahrenheit and after long periods of leaf wetness due to dew, irrigation or rainfall. The pathogen that causes the disease is always present in the grass but only becomes active when conditions are right, said Boehm. The mystery remains as to what the pathogen is doing when it's not causing symptoms.

"We are trying to understand the relationship between the weather and the pathogen to determine if there are certain weather conditions that correlate with disease activity," said Boehm, who also holds an Ohio State University Extension appointment. "That's where we came up with the idea of the using the concept of the phenology calendar. Is it possible that fungi have a fungal phenology, in that under certain environmental conditions the pathogen becomes active?"

If so, researchers hope to use the information to develop more targeted fungicide applications to manage the disease. A series of replicated field studies found that fungicide applications made in either the fall or in early spring resulted in up to a 50 percent reduction in dollar spot development the following summer.

"In the nine or 10 studies we conducted, we found that 90 percent of the time the disease was reduced with a spring application. We think that the fungicide is stalling the growth of the pathogen, decreasing its inoculum potential," said Boehm. "Now we want to find out exactly when we can make those applications for the most effective control. Is it March? Is it April? The weather certainly plays a key role."

Boehm and his colleagues have been conducting dollar spot research for several years. They have developed Extension outreach materials that detail the pathogen's lifecycle and are currently conducting research on the disease's ability to resist certain fungicides.

"Turfgrass pathology is a relatively young science in that little is known about how these fungi attack the grass and how the turf defends itself. With that in mind, we focus our work on two approaches. One is how we can better use the management tools we have to take an environmental stewardship approach in using less fungicides to get the job done," said Boehm. "The other approach is learning more about the pathogen and how it's causing disease. The more we know the better we can target our management to achieve long-term economic and environmental sustainability."

Boehm and his colleagues have joined other turfgrass pathologists around the world in creating a dollar spot collaborative, whose purpose is to unify research efforts related to this important turfgrass pathogen. The group will meet this June in North Carolina to brainstorm and establish a dollar spot research agenda.

For more information on dollar spot in Ohio, refer to OSU Extension's fact sheet at http://ohioline.osu.edu/hyg-fact/3000/3075.html.

Author(s): 
Candace Pollock
Source(s): 
Mike Boehm