Cultivars and disease resistance

From SportsTurf’s Feb issue, Pamela Sherratt’s “Q&A” column:

Q: While attending a conference session on gray leaf spot disease recently, I heard a speaker advise the audience to use a blend of turfgrass cultivars that displayed good genetic resistance to the disease. Using more resistant cultivars was just one tactic in a broader, more holistic approach that he felt was necessary to combat this pervasive disease. At the end of the presentation, an audience member asked where he might go to find more information about turfgrass cultivar selection and how to access the names of the best performing cultivars. I will attempt to address that question here.

A: The quick answer to the question about turfgrass cultivar performance is to recommend the National Turfgrass Evaluation Program ( website. NTEP is a non-profit organization that has (together with USDA) developed uniform evaluation trials of turfgrass species in the US and Canada. Trials are conducted at various locations and data is collected and disseminated on an annual basis. Trials include data on turfgrass quality, spring green-up, resistance to diseases and insects, tolerance to heat, cold, drought and traffic tolerance, etc.

This information is available through annual progress reports posted on the website. In addition to the NTEP data posted online, many schools, particularly land-grant universities, conduct turfgrass cultivar performance trials and publish their findings in annual research proceedings. Examples of schools that conduct trials and publish reports include Rutgers University, North Carolina State, University of Minnesota, University of Georgia, Oklahoma State, and Virginia Tech.

The Turf Breeders Association is a good place to look if you are searching for a turf breeder or seed-producer in your location. Turf breeders may be based at a university or with a seed company and they have extensive knowledge about the cultivars they sell and the availability of seed that year. Many of these turf breeders speak at STMA and regional conferences and have successful outreach programs. Dr. Bill Meyer and Dr. Leah Brilman are two that spring to mind. It’s also a good idea to have a rapport with a local seed supplier, as they will know what’s new and what is performing best in cultivar trials. Keep in mind that some of the cultivars listed in trials may not be commercially available yet, or may not produce consistent seed yields to make them commercially viable. This is sometimes the case with Kentucky bluegrass cultivars.

Evaluating the data from cultivar performance trials also deserves a mention. The cultivars are ranked 1-9, with 1 representing worst and 9 representing best. A quality rating of 6 or lower is considered unacceptable. The best rating of 9 is given to healthy turf with a fine leaf texture, high density and dark green color. The ratings are typically made monthly and are subjective in nature, though there are NTEP guidelines that each grader follows. Other data includes percent ground cover and depth of thatch. Cultivar differences are based on use of Least Significant Difference (LSD) statistics for mean separation. Per the NTEP website: “The LSD value(s) is located at the bottom of each table. To determine whether a cultivar’s performance is truly different from another, subtract one entry’s mean from another entry’s mean. If this value is larger than the LSD value, the observed difference in cultivar performance is significant and did not happen by chance. For example, two cultivars, ‘X’ and ‘Y’, have mean turfgrass quality values of 7.0 and 5.0, respectively, with the LSD value being 1.0. Since the difference between ‘X’ and ‘Y’ (2.0) is larger than the LSD value (1.0), cultivar ‘X’ performed significantly better than cultivar ‘Y’ for mean turfgrass quality. Please remember that results can vary from year to year and from location to location. Therefore, always reference the LSD value when interpreting test results.”

One of the most important considerations when selecting athletic field cultivars is its ability to withstand wear injury and compaction stress. As defined in the NTEP rating guidelines, wear injury occurs immediately upon trafficking a turf. Wear injury symptoms are often expressed within hours and definitely within days. Compaction stress injury is more chronic and is expressed over time. Traffic tolerance ratings are conducted at several sites and simulated traffic is applied using different types of equipment, so there may be some variation among results, but the data does give a good indication of a particular cultivar’s tolerance level. Since not all states have a traffic trial it’s important to use data from the closest regional trial.

Since so much perennial ryegrass is used on sports fields, another important consideration when selecting athletic field cultivars is disease resistance, particularly the level of tolerance to destructive diseases like gray leaf spot, Pythium and brown patch. It’s important to note that some cultivars are more resistant to disease than others, but none are immune. Other criteria that are particularly desirable for turf on athletic fields include spring green-up (important for spring sports like lacrosse and baseball), seedling vigor and overall turf quality, which is a combination of color, texture and density.

In summary, the NTEP website is an invaluable tool for selecting the best cultivars for athletic fields in a given location, but establish a good rapport with your local seed supplier to see which of your preferred cultivars are available.