A Guide to NTEP Turfgrass Ratings
Kevin N. Morris, Executive Director
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The National Turfgrass Evaluation Program (NTEP) is a leader in evaluation of turfgrass species. The turfgrass industry in the USA and many parts of the world rely heavily on NTEP data. The information collected and summarized by NTEP is currently requested in thirty countries.
Turfgrass breeders, researchers, and extension specialists use NTEP data to determine adaptation and use of cultivars and experimental lines. Seed companies rely on this data for advertisement and sales. Government agencies, like highway and parks departments, use NTEP data when writing specifications for bids and purchasing. Most importantly, end-users, like golf course superintendents, sports turf managers, sod growers, lawn care service operators, and grounds managers, frequently use the data before purchasing seed or sod. It is the interest of all of these users that has made NTEP data the standard for the turfgrass industry in the USA.
The quality and scientific merit of NTEP data is extremely important. However, the evaluation of turfgrass species and cultivars is a difficult and complex issue. Furthermore, turfgrass evaluation is generally a subjective process based on visual estimates of factors, like genetic color, stand density, leaf texture, uniformity and quality. These factors can not be measured in the same way as other agricultural crops. Turfgrass quality is not a measure of yield or nutritive value. Turfgrass quality is a measure of aesthetics (i.e. density, uniformity, texture, smoothness, growth habit and color), and functional use. The most common way of assessing turfgrass quality is a visual rating system that is based on the turfgrass evaluator's judgement. Subjective measures of this type are always subject to criticism and concern. However, it is a well-established fact that properly trained observers can effectively discern subtle differences between turfgrasses, using the visual rating system.
Visual ratings require consistency to ensure their merit. Therefore, NTEP evaluators are trained to notice visual differences in color, density, uniformity, disease incidence, environmental stress or other factors.
Evaluators are asked to conduct visual evaluations on cloud-covered days, when shadows and reflections are minimal. With some characteristics, like genetic color, differences are more evident prior to mowing. Mowing direction causes difference in light reflection and may influence color ratings.
Most visual ratings collected on NTEP trials are based on a 1 to 9 rating scale. One is the poorest or lowest and 9 is the best or highest rating. However, a few characteristics, such as winter kill or percent living ground cover, are rated on a percentage basis, again by using the evaluator's judgement. Most disease ratings found in NTEP reports will use the 1-9 scale, 9=no disease except where the evaluator made a judgement of the percentage of disease in each plot. Percent disease data will be found in separate tables and will normally not be included with disease data using the 1-9 scale.
How is Turfgrass Quality Evaluated?
Quality is based on 9 being outstanding or ideal turf and 1 being poorest or dead. A rating of 6 or above is generally considered acceptable. A quality rating value of 9 is reserved for a perfect or ideal grass, but it also can reflect an absolutely outstanding treatment plot. The NTEP requires quality ratings on a monthly basis.
Quality ratings will vary based on turfgrass species, intensity of management and time of year. Within species quality ratings are relative. Among species they are not. For example, an acceptable quality rating of 6 within tall fescue cultivars is not relative to the same value given among Kentucky bluegrasses. An acceptable quality rating value for a utility turf differs from the same value for a bentgrass putting green.
Quality ratings take into account the aesthetic and functional aspects of the turf. Quality ratings are not based on color alone, but on a combination of color, density, uniformity, texture, and disease or environmental stress. Turfs growing in a study may receive the same numeric quality rating, but the factors influencing that rating may differ. For example, one turf may receive a quality rating value of 5 based on overall color and density, while another may receive the same value based on disease incidence and its impact on turfgrass density.
How is Turfgrass Color Evaluated?
Genetic Color - Genetic color reflects the inherent color of the genotype. It is based on a visual rating scale with 1 being light green and 9 being dark green. Genetic color ratings are collected when the turf is actively growing and is not under stress. Chlorosis and browning from necrosis are not a part of genetic color.
Winter Color - Winter color is an assessment of color retention during the winter months. It is based on a 1 to 9 visual rating scale with 1 equaling straw brown or no color retention, and 9 equaling dark green. It assesses overall plot color and not genetic color.
Seasonal Color/Color Retention - Seasonal color and color retention ratings are a measure of overall plot color. The scale used is 1 to 9 scale with 1 being straw brown and 9 being dark green. Seasonal color can be used to successfully differentiate color differences based on damage caused by disease or insect pests, nutrient deficiency or environmental stress. Color retention is used to assess the ability of the entry to hold color as seasons change. This is especially useful in quantifying the response of warm-season grasses to temperature changes or frost occurring in fall.
How is Spring Greenup Evaluated?
Spring Greenup is a measure of the transition from winter dormancy to active spring growth. It is based on plot color not genetic color. The visual rating of spring greenup is based on a 1 to 9 rating scale with 1 being straw brown and 9 being completely green.
How is Turfgrass Leaf Texture Evaluated?
Turfgrass texture is a measure or estimate of leaf width. The visual rating of texture is based on a 1 to 9 rating scale with 1 equaling coarse and 9 equaling fine. Visual assessment of texture is difficult and less than precise. However, physical measurement is tedious, time consuming and labor intensive. Physical measurements are also variable. Care must be taken to measure leafs of similar age and stage of development. Visual ratings of texture can be used successfully to separate cultivars within species. Visual assessment of leaf texture should be done when the turfgrass is actively growing and is not under stress.
How is Turfgrass Density Evaluated?
Turfgrass density is a visual estimate of living plants or tillers per unit area. Dead patches of turf are excluded. A visual rating of 1 to 9 is used with 9 equaling maximum density. Turfgrass density can be determined quantitatively by counting shoots in a specified area. Counting is time consuming and labor intensive. Visual turfgrass density ratings are highly correlated to counts and require much less time and labor input. Shoot density varies by time of year. Density ratings are collected in spring, summer and fall to account for seasonal variation. This is particularly true for cool-season turfgrasses.
How is Living Ground Cover Evaluated?
Living ground cover is based on surface area covered by the originally planted species. It is generally used to express damage caused by disease, insects, weed encroachment, or environmental stress. Percent living ground cover is often measured in the spring, summer, and fall rated using percentage. This timing allows one to track the turfgrass response to various stresses during the growing season.
How is Seedling Vigor/Establishment Evaluated?
Seedling vigor or establishment is a visual estimate of percent ground cover, plant height, etc. that reflects the relative speed and entry develops into a mature sod. Seedling vigor is rated on a 1 to 9 scale with 9 equaling maximum vigor. Establishment is using rated on a percentage coverage basis.
How is Disease or Insect Damage Evaluated?
NTEP reports disease and insect injury based on the turfgrass resistance, using the 1 to 9 rating scale with 1 equaling no resistance or 100% injury, and 9 equaling complete resistance or no injury. Insect incidence may also be determined as counts per unit area. NTEP encourages our evaluators to identify disease and insects genus and species. This information, if available, can be found on or at the bottom of the particular table.
How is Drought Tolerance Evaluated?
Drought tolerance assessed as either wilting, leaf firing, dormancy or recovery. A 1 to 9 visual rating scale is used with 1 being complete wilting, 100% leaf firing, complete dormancy or no plant recovery; and 9 being no wilting, no leaf firing, 100% green-no dormancy, or 100% recovery.
How is Frost Tolerance or Winter Kill Evaluated?
Freezing or direct low temperature, desiccation, and frost injury can comprise winter injury symptoms. Turfgrass species and cultivars differ in their responses to each of these stresses. Direct low temperature (winter kill) and desiccation injury are generally expressed as a visual estimate of percent damaged ground cover. Frost injury is expressed on a 1 to 9 rating scale with 1 equaling 100% leaf injury and 9 equaling no injury.
How is Traffic Tolerance Evaluated?
Traffic tolerance is the combination of wear and compaction stress that occurs whenever a turf is exposed to foot or vehicular traffic. 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. It is expressed over time. The NTEP reports traffic tolerance as visual estimate of turfgrass tolerance using a 1 to 9 rating scale with 1 being no tolerance or 100% injury, and 9 being complete tolerance or no injury.
How is Thatch Accumulation Evaluated?
Thatch is generally a measured value. Thatch depth is measured by collecting 4, 5-cm plugs of turf, removing the verdure and placing a 1 kg weight on the surface of the thatch. Measurements then consist of compressed thatch depth in mm.
How are Seedheads Evaluated?
Certain turfgrass species can produce significant number of seedheads in turf. These seedheads are generally considered unsightly and reduce the quality of the turf stand. Seedheads are rated from 1 to 9; 9 equaling no seedheads.
How is Poa Annua Invasion Evaluated?
Poa annua is a weedy grass species that is a persistent problem during particular times of the year and/or in particular environments. Poa annua can either be rated as a percentage of the total coverage of each plot or on a scale of 1 to 9; 9=no poa annua.
How is Mowing Quality/Steminess Evaluated?
Some turfgrasses may exhibit poor quality after mowing. This poor quality may be due to many stems being produced by the plants during the reproductive phase of their growth cycle. This ratings reflects the uniformity and cleanness of cut exhibited by some grasses. The rating scale is 1 to 9 with 1 equal to poorest mowing quality/most steminess and 9 equal to cleanest cut /no steminess.
Other characteristics not included in this document are often evaluated and reported in NTEP reports. These data most often use the 1 to 9 scale with 9 equal to best quality, least injury, etc. Occasionally, data is collected using a percentage rating. In either case, the rating scale used will be listed in the title area of the table.