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Virginia Turfgrass Journal – Ava Veith, Travis Roberson, Aaron Tucker, David McCall Ph.D. and Mike Goatley Ph.D.

The Turfgrass Pathology lab at Virginia Tech has placed a major effort on managing and better understanding spring dead spot (SDS) of hybrid bermudagrass. We have written several articles in the Virginia Turfgrass Journal about the most effective ways to manage the disease over the last few years. Why such an emphasis on this one particular disease? Aesthetics are always an important part of properly maintained turfgrasses, but the most critical factor is how spring dead spot impacts the surface dynamics of the playing surface. More specifically, do these dead patches actually change the characteristics of a turfgrass playing surface enough to affect the playability of the field and safety of the athletes using these fields? We know that SDS disrupts the surface, but we have never taken a deep dive into how that impacts field uniformity until now.

Previous studies have reported numerous factors that influence an athlete’s interaction with either the ball or playing surface such as a field’s pitch, grass species, construction (native vs. sand capped soil), soil organic matter, soil texture, soil moisture, firmness, uniformity, and/or cultural practices implemented by turfgrass managers. Each of these factors may have a positive or negative athlete interaction depending on how the athlete’s applied forces, either direct or indirect, respond to these variables. Athletes must commit to making swift decisions based on their anticipated response to the field’s surface or how a ball will roll/rebound across the field. When a sports field’s surface is inconsistent, detrimental injuries can materialize such as concussions or severe ligament injuries. To date, there have been no studies that address how turfgrass diseases compromise field playability.

Hybrid bermudagrass is one of the most widely used turfgrass species for sports field playing surfaces. Hybrid bermudagrasses grown in areas that experience winter dormancy (like Virginia) are susceptible to SDS. The pathogen causing SDS feeds on the bermudagrass’s stolons, rhizomes, and roots, weakening the plant as it approaches dormancy, leaving the grass vulnerable to winter injury. The results are SDS patches apparent at spring greenup (Figure 1). Observing these pitted areas are what stimulated the hypothesis that they could potentially compromise the field’s surface dynamics.

After some promising preliminary data collection in 2020, we initiated research to investigate SDS impacts on field conditions at the Dorey Park Recreation Center in Henrico, Virginia in May 2022. Data were collected from three SDS-infested ‘Tifway 419’ hybrid bermudagrass athletic fields grown on native soil. At each field location, 20 SDS patches were randomly selected and compared against asymptomatic areas directly adjacent. We collected data on a series of metrics with a focus here on ball rebound (BR), clegg hammer (CH), soil moisture (SM), and shear strength (SS). Additionally, we collected data using the Field Marshall (Figure 2) developed by Sports Labs (Chattanooga, TN) that measures surface firmness, vertical deformation, and energy restitution of a surface all in one tool.

Soil Moisture

We measured soil moisture in asymptomatic and diseased patches. Overall, soil moisture varied considerably by field location, with Field 8 being the wettest. Overall soil moisture may play a crucial role in player safety as it relates to field hardness and ground collision injuries. In our study, soil moisture was drier inside of spring dead spot patches in our study, regardless of field location. These effects were most evident in our wettest field. The influence of spring dead spot on soil moisture likely drives other metrics of field safety.

Ball Rebound

We tested ball rebound from 6.5ft above the surface in accordance with FIFA standards. Our data indicates that diseased areas were firmer than surrounding asymptomatic bermudagrass as vertical rebound was four inches higher within spring dead spot patches (Figure 3). However, we did not see this dynamic with our Clegg Hammer data (not shown), another metric of surface firmness. Field location also impacted ball rebound (Figure 4). Rebound was lowest on the field that was also the wettest, though more research is needed to confirm whether the two metrics are related. Our data alludes to variable ball rebound dynamics during game play in the presence of spring dead spot, with a potentially greater effect when fields are also wet. This non-uniformity in the field surface may impact athletes’ perception of ball bounce and overall performance.

Energy Restitution

Energy restitution is a measurement of energy being returned from the field surface back to the athlete. It is influenced by firmness and soil moisture, among other things. Essentially, a field with low energy restitution is similar to jumping on a trampoline with worn out springs. More energy is needed to accomplish the same task. This is an important metric to consider when discussing the implications of a surface that is either too firm or too soft. A surface too firm facilitates a higher speed of play, which encourages collisions between players as well as an increase of ground-contact injuries such as concussions or fractures. On the contrary, a surface that is too soft absorbs more energy, causing less of this energy to be returned to the player. This leads to an increased risk of ligament and other leg injuries due to the accelerated rate of player fatigue. Energy restitution was calculated by evaluating the difference between the energy of a falling mass (player) before and after collision with the ground surface using Sports Labs new device dubbed The Field Marshal.

Our results did not show a significance between field location or treatments alone, but an interaction affect. Overall, regardless of either SDS or H areas on locations did not have a significance except for SDS areas on F8 (Figure 5).

Shear Strength

The shear vane is meant to simulate a player’s rotational cleat force. It replicates the turfgrass’s ability to overcome the force generated by the athlete thus supporting their applied force as they change directions. In our study, we found that spring dead spot did not impact shear strength on two of three fields. However, shear strength was negatively impacted by spring dead spot on the wettest field tested, once again suggesting that soil moisture plays a prominent role in the extent of damage caused by spring dead spot. Our data suggests that athletes are more likely to slip in spring dead spot patches when the fields are wet. This higher likelihood of slipping could result in greater chances of sustaining ligament injuries though we have not tested this.

Conclusions

Spring dead spot will continue to be an important disease of bermudagrass on athletic fields and other recreational areas. We found several metrics to suggest that the disease has a negative impact on field uniformity. However, many of the differences we found are likely biologically insignificant in the real world. While we are just scratching the surface of how spring dead spot impacts player safety, soil moisture seems to guide the ship from what we have found to date. What we have found is that soil moisture magnifies many of the metrics associated with field uniformity in the presence of spring dead spot. We will continue to focus efforts on this in the future, as well as evaluate how other diseases with different symptomology impact player safety.