Five Facts about Late-Season Dollar Spot

There are several environmental factors that are likely contributing to the late-season dollar spot epidemic. In this Talking Turf we will cover many of these “facts” and how they each may be playing an important role in dollar spot development.

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Seasonal dollar spot epidemics are common throughout many regions of Canada. Golf course superintendents typically begin preventive programs in June and continue through the remainder of summer. Historically though dollar spot epidemics have continued to linger into September and early fall in many areas. We call this late-season dollar spot.

There are several environmental factors that are likely contributing to the late-season dollar spot epidemic. In this talking turf we will cover many of these “facts” and how they each may be playing an important role in dollar spot development.

Fact 1: Longer nights

As summer turns to fall, the duration of sunlight is rapidly declining. By the middle of September, the length of daytime more closely resembles the shortest day of the year (Dec. 21st) than the longest day of the year (Jun. 21st). In late summer and early fall, we experience approximately 3 hours less sunlight than earlier in the summer.

What does this mean? It is at night that many of our turfgrass pathogens take advantage of favourable environments. At night, relative humidity rises and the winds begin to calm. We now have 3 more hours of these conditions than earlier in the year.

At the host level, the reduction of light is likely limiting the plant’s growth potential. A reduction in growth potential limits the plants ability to grow out of infection. This may explain why we tend to see greater dollar spot “pitting” in the fall compared to summer. The environment is more conducive for the pathogen than it is the host.

Fact 2: Lower sun angle

Sun angles can dramatically influence shade patterns on golf courses. With each passing day, trees and other structures will be casting longer and wider shade patterns. This effect is more pronounced during the morning and evening hours.

Shade can cause a cascade of problems in the turf environment. On the pathogen level, turf shielded by shade will have longer leaf wetness periods. Many disease-causing organisms need leaf wetness or high humidity for infection and the dollar spot pathogen is no different.

In late September and October, it is not uncommon to have canopy dew linger throughout the day. What we may lose in favourable temperatures for dollar spot development, we gain in leaf wetness duration.

Another consequence of lower sun angles is lower transmission of Ultraviolet light. As the sun angle begins to drop, less UV-A and UV-B is able to transmit through the atmosphere and penetrate the ground. Why can this influence late season dollar spot? Dr. Brandon Horvath’s team at the University of Tennessee has demonstrated that high energy wavelengths (such as UV-B) can regulate the development of dollar spot. These findings were apart of multi-year studies in the lab and field.

Fact 3: The Great Lakes can moderate surrounding air temperatures

Large bodies of water such as the Great Lakes can influence temperatures during the spring and fall. During spring, these large bodies of water can cool nearby surrounding air temperatures. During fall, however, the Great Lakes can act as heat sinks, which can moderate air temperatures in the surrounding areas.

This can greatly influence dollar spot development during the fall months. While other areas may just be a few degrees too cool for dollar spot development, golf courses in close proximity to one of the Great Lakes may still see continued dollar spot activity much later in the season.

Fact 4: Less traffic

In late summer and early fall, many golf courses will see much less traffic on playing surfaces. There are less employees. Less mowing requirements. In addition, there is usually a significant drop in cart traffic and daily golf rounds played.

Reducing this traffic may be influencing dollar spot development. It is widely established that mowing frequency can influence dollar spot severity. The same with rolling programs. A shift in the frequency of these practices may be influencing dollar spot development.

Fact 5: Exteris Stressgard is a great solution for late-season dollar spot.

Exteris Stressgard represents a breakthrough in fungicide innovation. This solution includes two modes of action and is formulated with Stressgard Technology. In addition, this product is equipped with specialty adjuvants to promote and improve coverage on the leaf surface all while mitigating morning dew in the days after application.