Improving turf quality (Research)

TifSport, a high turf quality and fine-textured interspecific triploid (2n=3x=27 chromosomes) Bermudagrass hybrid, was released in 1995 (Hanna, Carrow and Powell, 1997). It’s genetic purity, improved cold resistance, superior sod strength, pest resistance, turf density and improved traffic tolerance have made it a popular choice to plant on golf courses, athletic fields, lawns and landscape areas.

L. Cella and other researchers (2005) found that golf ball lie varied among Kentucky bluegrass cultivars and the number of plant tillers showed the highest correlation to ball lie. It was brought to our attention that, although TifSport performed well on golf courses, high handicap golfers wanted to see the ball with a higher lie. Therefore, we initiated this study to see if nitrogen levels combined with growth regulators would increase the lie at four different mowing heights or schedules. We used a modification of an instrument (see top-left photo on page 96) described by Cella and others (2004) to measure ball lie.

Experimental procedures

TifSport Bermudagrass (plot established in 2004) and two experimental vegetatively propagated Bermudagrasses – Tifton 11 and Tift No. 4 (ST-5) – were established in 2005. Tifton 11 and Tift No. 4 also were selected for testing because both of these experimental cultivars show potential for golf course use. The design was a strip plot test with four replications. Treatments included three nitrogen levels combined with Primo (trinexepac-ethyl) and Cutless (flurprimidol) and four mowing heights. A treatment with one pound of nitrogen per 1,000 square feet per month plus Primo was considered a general practice used by golf course superintendents.

The nitrogen/Primo/Cutlass treatments were:

• 0.5 pound of nitrogen per month per 1,000 square feet
• 1 pound of nitrogen per month per 1,000 square feet
• 1.5 pounds of nitrogen per month per 1,000 square feet
• 1 pound of nitrogen per month per 1,000 square feet plus Primo
• 1.5 pounds of nitrogen per month per 1,000 square feet plus Primo
• 1 pound of nitrogen per month per 1,000 square feet plus Primo plus Cutless
• 1.5 pounds of nitrogen per month per 1,000 square feet plus Primo plus Cutless

Primo was applied at nine ounces per acre in Primo-only treatments and at four ounces per acre in Primo/Cutless treatments. Cutless was applied at four ounces per acre. Treatments were applied once a month during the growing season, May through October.

The mowing heights were:

• 0.5 inch (12.5 mm), twice a week
• 1 inch (25 mm), twice a week
• 1.5 inches (37.5 mm), twice a week
• 1.5 inches (37.5 mm), once a week

Mowing heights were selected to approximate practices used in various areas of the golf course. Quality and color ratings usually were taken at the end of the month before the new treatments were applied.

Ball lie

Ball lie measurements were taken by dropping two golf balls into each plot from a height of six feet and then measuring the distance the ball sank into the turf (see top-right photo on page 96). Data on turf quality were collected in 2005 and 2006. Data on ball lie were collected in 2005 (three dates) and 2006 (three dates) for TifSport but only in 2006 (one date) for Tifton 11 and Tift No. 4 (ST-5). Rating used ranged from one to nine with nine being the best turf quality. A rating of at least seven is needed for acceptable turf quality.

A golf ball is 1.65 inches in diameter. The values listed in tables for ball height indicate the number of milimeters the ball sank into the surface of the grass. Therefore, the smaller the number, the higher the ball lie. All ratings and ball-lie measurements were rounded to the whole number because decimal values have little practical value. An analysis of variance was used to determine the effects of various treatments on turf quality and ball lie. Fisher’s LSD test was used to determine differences between treatments (SAS Institute, Cary, N.C.).

Turf quality

There were only small differences in overall turf quality except for the 0.5-pound-of-nitrogen-per-1,000-square-feet treatment in which turf quality was reduced for TifSport and for Tifton 11 in 2005. We also observed lighter green color (data not shown) for the 0.5 nitrogen treatment for TifSport and Tifton 11, but not for Tift. No. 4. We observed a little discoloration in the Cutless treatments for a few days after treatment. Cutless appeared to discolor Tift 97-4 more than the other genotypes, probably because this cultivar is the most naturally dense grass of the three tested. We observed the least discoloration in Tifton 11, and it’s the most coarse grass of the three tested.
One pound of nitrogen per 1,000 square feet per month appeared adequate for maintaining desirable turf quality in all three grasses (see comparison photo, bottom right, on page 96). However, 0.5 pound of nitrogen per 1,000 square feet per month might be adequate for Tift No. 4, a dense, naturally dark green, shade-resistant genotype. Neither Primo nor Cutless improved overall turf quality in this test. However, clipping removal (not measured in this test) probably would have been reduced by the growth regulators.

Turf quality tended to improve for TifSport from 2005 to 2006 as the turf ‘matured’. Treatments with Cutless (at the rate used) caused browning and swirling of the turf at 0.98 inch and 1.46 inches mowing heights for about a week after treatment in TifSport and Tift 97-4, which was especially pronounced at the October treatment. There were only small differences in turf quality because of mowing heights (see table 2 at right).

Ball height

The nitrogen level had little effect on keeping the golf ball from sinking into the grass (see table 3 on page 97). All combinations of nitrogen, Primo and Cutless were effective in improving ball lie in TifSport. As TifSport (planted in 2004) matured from 2005 to 2006, the ball lie improved. Treatments had almost no effect on ball lie in Tifton 11 and Tift No. 4. Tifton 11 is quite vigorous – producing dense turf – so it apparently can mature turf soon after planting. Tift No. 4 is a naturally dense turf. The highest ball lie was achieved with 1.5 pounds of nitrogen combined with Primo and Cutless.

It appears from these results that one pound of nitrogen plus Primo can produce a good ball lie. Users would need to decide for themselves whether the slight improvements in ball lie are worth the extra cost of another half pound of nitrogen and/or Cutless per month. A lower level of Cutlass also might prevent some of the discoloration observed in this study.

Mowing at one-half inch twice a week produced the best ball lie in all three Bermudagrasses (see table 4 at right). The lowest mowing height produced the most dense turf. As mowing height increased and mowing frequency decreased, the ball sank further into the grass for TifSport and Tifton 11, and for Tift No. 4 going from the one-half inch to one inch mowing height. There were no differences in ball lie at the 1.5 inch mowing heights for Tifton 11 and Tift No. 4. The ball lie in TifSport improved from 2005 to 2006, probably because of the production of a more mature turf.

Another consideration in this mowing height is how far the bottom of the ball is from the ground for the various mowing heights (numbers in parenthesis in table 4). Although the ball sinks less into the grass at the half-inch mowing height, the ball is further from the ground at the one inch and 1.5 inches mowing heights.

Treatments with Primo or Primo plus Cutless were the most effective for preventing the golf ball from sinking into TifSport. The nitrogen level by itself appeared to have little effect on ball lie. Tifton 11 was exceptional at all treatment levels and mowing heights for keeping the ball from sinking into the turf. GCI

Wayne W. Hanna, Ph.D., is a professor in the department of crop and soil sciences at University of Georgia, Tifton Campus. He can be reached at 229-386-3184.

The author wishes to thank the USGA for financial support to conduct the research and to Raymond Cooper for requesting Cutless. Appreciation is expressed to Patrick O’Brien, director of the southeast region USGA Green Section and to Jimmy Allen from Pike Creek Turf for discussions regarding need for the research, and to Larry Baldree and Amanda Webb for technical assistance.Literature cited

– Hanna, W.W., R.N. Carrow, and A.J. Powell. 1997. Registration of ‘Tift 94’ Bermudagrass. Crop Sci. 37:1012.
– Cella, L., T. B. Voigt, and T.W. Fermanian. 2004. Measuring ball lie on golf course fairways. Crop Sci. 444:214-217.
– Cella, L., T. B. Voigt, T.W. Fermanian, and B.E. Branham. 2005. Do growth characteristics affect ball position on Kentucky bluegrass fairways? Internat.Turfgrass Res. J. 10:661-665.