Turf MD: The history of preventive fungicide programs

Preventive fungicide applications are defined as done before disease development, or extremely early in disease development. Conversely, curative applications are made after disease development has occurred.

Examples include snow molds, occurring in the northern U.S. where conditions are favorable, which can be devastating. Preventive fungicide applications are the primary method of control for major snow molds. Superintendents apply these fungicides made before snowfall.

Often, if no application is made because of snowfall before treatment or any other reason, the turf damage in late winter or early spring is vast.

Another example is dollar spot, which causes turf damage through large portions of the country from May into early October. Preventive treatments for dollar spot often require multiple applications over a growing season.

When a superintendent is developing a preventive fungicide program, they must put considerable thought into what fungicides they use and their rotation or mixture sequence to minimize the resistance risk. They must also consider expected control length in addition to the overall cost and success of preventive programs.

Much of the success of preventive fungicide programs in enhancing golf course turf is due to the safety, quality and characteristics of new fungicides developed. Fungicides used in a preventive way have resulted in a drop in the stress level for superintendents from their predecessors.

History lesson

Looking back, no disease drove home the need for preventive fungicide programs like Pythium blight. Nowadays, we have fungicides and preventive strategies to control Pythium blight. However, when I was growing up there were no Pythium fungicides a superintendent could use in a preventive program.

I remember leaving work at our local course, only to return early Sunday morning to see two or three greens lost to Pythium blight. The devastation was quick and complete.

Before the early 1970s, only contact fungicides existed. For Pythium blight, there were only a couple fungicides available. These fungicides like ethazole (Koban) and chloroneb (Terraneb SP) were labeled for 3-5 days but often during peak conditions would provide control for 1-2 days.

Prior to that, the only labeled product was fenaminosulf (Dexon) and it broke down in sunlight causing control to be measured in hours. It wasn’t until 1977 — with the release of metalaxyl (Subdue) — and later propamocarb (Banol) in the early 1980s — that a preventive strategy emerged for controlling Pythium blight.

Why we’re here

I want to finish with a quote from the first edition of the book Management of Turfgrass Diseases (1981) by the late Joseph Vargas, Jr., about the importance of a preventive fungicide program. The quote is probably politically incorrect now, but it speaks to those who remember Dr. Vargas and his communication style.

“In spite of the fact that Pythium blight is a severe disease that spreads rapidly, many superintendents in prime Pythium blight areas such as the bermudagrass- Kentucky bluegrass transition zone, still refuse to institute preventive fungicide programs, even during hot humid weather. It must be the gambling spirit in them, because they know Pythium blight will come when the weather gets hot. Betting against Pythium is like playing Russian roulette with five chambers loaded and one empty.”

Pythium blight will be remembered as the catalyst for the acceptance of preventive fungicide programs.

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