Survey of Turfgrass Nematodes on Golf Course Greens
Shaohui Wu, Ph.D., Horacio Lopez-Nicora, Ph.D., & Todd Hicks
Insects and fungal diseases are often blamed for turfgrass yellowing and thinning, but that is not always true. Plant-parasitic nematodes, microorganisms typically feeding on plant roots in the soil, can also cause yellowing and stunted growth of turfgrass if at high populations. Also, their feeding creates entry sites of plant pathogens, and reduced vigor and health makes the plant more vulnerable to diseases and stressful conditions such as heat and drought. However, nematode problems are often misdiagnosed as diseases or environmental stress, and improper management may lead to turf loss, creating voids for weed growth or inadequate ground coverage. Hence, in 2024 summer we conducted a statewide survey program on golf course greens in Ohio, which was aimed at assessing the nematode problem in high-input turf and finding out the major nematode types to be managed.
We distributed the survey information and supplies in June 2024 targeting sampling time around July 1-15, 2024. The program required participating golf courses to send two samples per site, and each sample was taken using a T-type soil probe or similar device to collect multiple cores (16–20 ½-inch-diameter cores for approximately 500 cc per green) at the 4-inch depth. To assist with sampling, we worked with three companies (Advanced Turf Solutions, Envu, and Syngenta) in the turf industry and created a short guide video for sampling instruction. We set six collection sites across the state to receive soil samples, which were then transported back to the turfgrass lab for processing.
In the 2024 program, we received a total of 81 samples from 40 golf courses located in 15 Ohio counties (Figure 1). The samples were processed using a semi-automated elutriator, enabling us to extract nematodes from the soil for subsequent identification and counting under a microscope (Figure 2). In addition to nematode analysis, we also sent soil samples to Brookside Labs (New Bremen, OH) for soil analysis (service code S001P). Both nematode and soil analyses were provided at no cost to all program participants, and the results were shared with each individual participant.
In the combined analysis of all samples, the predominant plant-parasitic nematode types identified based on their abundance were as follows: ring nematodes at 31% (average of 471 per 100 cm3 soil), spiral nematodes at 30% (average of 454 per 100 cm3 soil). These were followed by lance nematodes at 11% (average of 165 per 100 cm3 soil) and several other types, as illustrated in Figure 3. The nematode numbers varied significantly across different sites and locations. Based on the treatment threshold levels in bentgrass (Rutgers University version, adapted from Couch, 1995, Diseases of Turfgrass, 3rd edition), i.e., 1,500 / 100 cm3 soil for ring nematodes, 600 for spiral nematodes, 150 for lance and lesion nematodes, 14 out of 81 samples (17.3%) had populations exceeding threshold levels in these four nematode types, from Clermont, Cuyahoga, Erie, Hamilton, Medina, Richland, and Summit. A sample from Medina revealed exceptionally high levels of nematodes, with 5,088 spiral nematodes per 100 cm3 soil, which is approximately eight times higher than the threshold level of 600. Additionally, there were 384 lesion nematodes, compared to the threshold of 150. According to the golf course superintendent, these nematodes had caused obvious damages. Following the survey, a nematicide treatment was applied, which subsequently improved the health of the turfgrass.
We plan to conduct the nematode survey program again and strongly encourage participants to submit soil samples when the program is advertised. Our goal is to achieve a well-distributed geographic range of sampling sites throughout Ohio state to more accurately represent the extent of nematode issues in the state.
We thank Henry Rice from the Turfgrass Lab, Zak Ralston from the Soybean Pathology and Nematology Lab, and Dan Chrisman for labor and technical assistance in processing samples. We also thank Syngenta for sponsoring and Advanced Turf Solutions and Envu for supporting the program. Thanks to Avon Oaks Country Club, Barrington Golf Club, Blue Ash Golf Course, Montgomery County Office, Ohio Turfgrass Foundation Research Center and Portage Country Club for assisting with sample receiving, and thanks to Greater Cincinnati GCSA, Northern Ohio GCSA, Ohio GCSA and Ohio Turfgrass Foundation for helping distribute the survey.