Joseph W. Rimelspach
Many can remember first seeing red thread (Laetisaria fuciformis) and the novelty of being able to see the strands of pink or reddish fungus at the ends of leaf blades. Twenty years ago this was a relatively "new" disease to be found in lawns and high-cut turf areas, and it was relatively unimportant in terms of causing serious damage to turf. This was not a new disease, since it was first observed in 1854 as a disease on ryegrass pastures in Australia. Reports in the United States were first made in the 1930s.
But today, especially over the past several years, there have been wide-spread reports of occurrence of this disease in Ohio and throughout much of the Midwest and northeastern United States. In the past five years, the disease has been observed to be active during every month of the year and on all the common cool season turfgrasses - perennial ryegrass, Kentucky bluegrass, fine fescue, creeping bentgrass, and tall fescue. The disease is most active when temperatures are cool and moderate, when the turfgrass foliage is wet, and when the grass is growing slowly.
Many are asking, is there so much more red thread these days? Some comments relative to this question are presented in this report.
Lawns have shifted from predominately Kentucky bluegrass lawns to lawns that include more perennial ryegrass. Kentucky bluegrasses can be susceptible to red thread, but in general most cultivars have some degree of resistance. There have been great advances in the quality of perennial ryegrass cultivars available to the industry. The speed of germination and establishment are key factors in making perennial ryegrass very popular these days, especially in our instant-gratification society. The droughts of 1977, 1988, and 1991 and other minor drought years were periods when extensive lawn renovation and repair were done. In many of these situations, a bluegrass and ryegrass mixture of seed was used, and in many of these situations the ryegrass predominated.
Due to a number of factors, many lawns are receiving less or reduced fertility than in the past. The shift has been from heavy spring fertilization to fall and late-fall fertilization programs. There has also been strong environmental pressure to reduce nitrogen use in urban landscapes, and there are economic incentives and factors that may impact the rate of fertilization. At the same time urban "soils" in new developments continue to be low quality. These soils offer meager nutrients and consist of poor physical characteristics for grass growth and root development.
The last several springs have been cool and wet in many areas. These weather patterns have been ideal for the growth and development of the red thread fungus. The pathogen has been active over long periods, and turf quality has been reduced during these times. Always remember the importance of weather patterns and the role they play in turfgrass disease development. Are the weather patterns more favorable for growth of the fungal pathogen, or more favorable for the growth of healthy turfgrass?
During recent years there have been considerable shifts in mowing habits, moving from the common practice of, in many communities, removing clippings to the use of mulching or recycling lawn mowers. Some individuals in the lawn-care industry have noticed trends toward more persistent red thread in lawns where clippings are mulched compared to lawns where the clippings are removed. This is an interesting observation and one that needs additional research to determine the impact on disease development and severity. Other factors may also be involved that have not been identified.
Some key strategies in managing healthy turfgrass and minimizing the severity of red thread are presented here. The goal is not to eradicate the disease but to manage the situation and maintain quality turfgrass.