Maintaining Turf Mixes and Blended Stands

Turf grass mixes and blends will have specific characteristics (color, texture, wear and disease resistance, etc.) based on the grasses you select. Once you develop and establish a mix or blend, can you expect these characteristics to remain forever? Do cultural practices such as mowing, fertility and irrigation change the makeup of the stand? Are some species more aggressive than others? These are a few of the questions we have tried to answer at the University of Missouri Turfgrass Research Center (Columbia, Mo.).

Over the past 20 years, a proliferation of Tall-Fescue varieties has led to the availability of many fine-textured and aggressive cultivars that are relatively more compatible with Kentucky Bluegrass and Perennial Ryegrass. The newer turf-type Tall Fescues produce more tillers than the old Kentucky 31, which results in a finer turf texture. This allows these Fescues to compete with the more aggressive Kentucky Bluegrasses, resulting in a more compatible mix. Finer leaf texture also gives the turf-type Tall Fescues a more pleasing appearance because their leaf widths are similar to many of the Bluegrasses. Additionally, the turf-type Tall Fescues do not look as clumpy as older varieties. However, in a thinned stand, they still can develop a clumpy appearance.

Dr K L Hunt (of the University of Missouri, Columbia) has performed research to examine the establishment and maintenance of singe-species blends and mixes of Tall Fescue, Kentucky Bluegrass and Perennial ryegrass under several specific conditions: two mowing heights (1.6 and 2.2 cm); three nitrogen levels and application timings (680g in autumn, 1360g divided between spring and autumn [all rates are grams of nitrogen per 100m2], and no irrigation.

This work resulted in several conclusions. Tall fescue (initially 60 percent of the mix) remained competitive with Kentucky bluegrass and still composed almost half of the mix after 5 years. However, with Perennial Ryegrass, the Tall Fescue decreased by 40 percent and was not competitive over the 5-year period. This could have been due to the face that Perennial Ryegrass germinates much faster than Tall Fescue for a stronger start. In the three-species mix of Tall Fescue, Kentucky Bluegrass and Perennial Ryegrass, Tall Fescue decreased to only 9 percent of the mix after 5 years. The competitiveness of Kentucky Bluegrass and the faster start of Perennial Ryegrass apparently won out. Nitrogen levels and mowing height had little effect on the balance of species in any of the mixes. Hunt found better quality in the blends that contained tall fescue during a drought in 1987. This adds credibility to recommendations to sew Tall Fescue in non-irrigated situations. Hunt also concluded that turf stressed by low mowing height (1.6cm) was more prone to disease. This may have played a role in the final composition of species in the mixes in this study.

This study dealt with mowing heights similar to golf-course fairways. What would happen if the mowing height were increased to an athletic-field height? What about supplemental irrigation? How would traffic affect the composition and recovery of these mixes? These questions arose as a result of Hunt’s early work.

More Research on Mixes and Blends

To answer questions such as these, other researchers (headed by Dr J H Dunn, also at the University of Missouri) designed a study to determine the influence of additional management factors on Tall Fescue, Kentucky Bluegrass and Perennial Ryegrass mixes and blends. With various combinations of these species, we set up study plots in the autumn of 1989) see box, ‘Missouri researchers…,’ page 9).

While the addition of irrigation to this study improved the quality of some plots, it also created a moist environment that promoted diseases in warm temperatures. Kentucky Bluegrass and Perennial Ryegrass maintained better quality under irrigation than Tall Fescue, which was more susceptible to disease. Conversely, Bluegrass and Ryegrass were more likely to ‘shut down’ and go dormant under dry conditions. Therefore, their quality fell below that of Tall Fescue at the non-irrigated site. Again, this shows the higher drought tolerance of Tall Fescue over Bluegrass and Ryegrass.

Under irrigation, diseases increased, including a higher rate of brown patch in all mixes and blends containing Tall Fescue. However, the Tall-Fescue blend did have less brown patch than the dwarf-type Tall-Fescue blend. The dwarf types tend to grow more slowly, reducing their ability to recover as rapidly. However, mixing dwarf-type Tall Fescues with other species made brown-patch infection less noticeable and similar to the standard Tall Fescues. Kentucky-Bluegrass and Perennial-Ryegrass mixes and blends were both susceptible to dollar-spot infection, but Perennial Ryegrass was far more susceptible over the life of the study. However, mixing Perennial Ryegrass with Tall Fescue decreased dollar spot in the stand by 30 to 40 percent compared with Perennial Ryegrass alone. We saw a similar response in the mixes of Tall Fescue and Kentucky Bluegrass. In 1993, brown patch was 33 percent less in a mix compared with the Tall-Fescue blend.

This demonstrates how mixes can be beneficial when one species in highly susceptible to a particular disease.

The balance of species within the mixes varied somewhat over time from the original seeding. After 5 years, we found that the Tall- Fescue/Kentucky-Bluegrass mix consisted of 62 percent Tall Fescue and 35 percent Kentucky Bluegrass. In the dwarf-type Tall-Fescue mix with Kentucky Blue-grass, the average balance was more equal-48 and 44 percent, respectively. (In both cases, the remaining few percent consisted of weeds.) This shows that Tall Fescue can remain competitive with Kentucky Bluegrass. However, Kentucky Bluegrass was more competitive in the irrigated site.

All mixes that included Perennial Ryegrass were dominated by that species over the 5-year study period regardless of mowing height and irrigation. This is consistent with the work completed by Hunt in 1989.

We were surprised to find that mowing heights and simulated traffic had little effect on the balance of species within the mixes. However, the study did not use constant traffic. Perhaps the balance of species would have been different if the mixes were exposed to more intense traffic. Nevertheless, in the early 1990′s, we applied heavy traffic to the Tall-Fescue, Kentucky-Bluegrass and Perennial Ryegrass NTEP trials at the University of Missouri and found only minor differences among species in the rate of wear and recovery. All species eventually recovered.