Maintaining the ultradwarfs

The “ultradwarfs,” those bermudagrasses that can be routinely mowed at 0.125 inch or less, have received substantial publicity during the past five years. Some of the factors contributing to this interest are:

  • The ultradwarfs are capable of producing a high-quality putting surface meeting the highest golfing standards when properly managed.

  • Most have improved genetic purity to produce more uniform greens.

  • They are new and most people like to try new turfgrasses.

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Each ultradwarf cultivar has slightly different management requirements, each golf course will be different and each green on a golf course may require a little different management depending on the site's specific macro- and microenvironment. So, to best maintain greens, you should evaluate your greens each week and implement only the practices needed to produce the putting surface needed for your membership. Learn from your neighbors, but use their practices only if they will improve your greens.

I believe that all of the ultradwarfs are capable of producing an outstanding putting surface. The differences among the ultradwarfs are in what it takes to produce the putting surface. In many ways, management of the ultradwarfs is not much different than for Tifdwarf. However, the ultradwarfs are less forgiving if you neglect optimum management practices. Let's look at some of the general maintenance principles that apply to most of the ultradwarfs.

SUNLIGHT

It is important to remember that the ultradwarfs are bermudagrasses, and bermudagrasses need ample sunlight. Observations indicate that the ultradwarfs do well with 8 to 10 hours of full sun each day during the growing season. Studies on other bermudagrass cultivars have shown that morning sun is more important than evening sun. If sunlight on a green is inadequate, adjust your management for specific greens to increase light, ensuring you take into account the time of year (due to angle of sun, clouds, etc.). Raising the height of cut can improve shade tolerance because more leaf area is available to intercept the light.

THATCH PREVENTION

Thatch prevention is one of the most important considerations with the ultradwarfs because of the dense growth of these bermudagrasses. When should you start controlling thatch? My general response is that you should start developing a plan and strategy for controlling thatch the day that you plant the grass. A key concept is that you should practice thatch prevention rather than thatch control.

Thatch is the layer of dead organic matter mixed with stems and roots between the soil surface and the green vegetation. The specific management protocol for managing this thatch will depend on the month, weather, fertility and growth patterns of the grass. These practices are vital to prevent excessive thatch formation and provide optimum putting speeds with true ball rolls.

If thatch becomes excessive (exhibiting signs such as hydrophobicity, scalping, sponginess, etc), you'll need to implement elimination procedures. Do so gradually, however, because severe verticutting or aerifying will result in damage to greens that is visible for several weeks. Verticutting during active growth periods will reduce down time because the grass is growing faster for quicker recovery.

FERTILITY REQUIREMENTS

Because of their increased density, the nitrogen needs of the ultradwarfs are less than Tifdwarf. Too much nitrogen can increase thatch problems, so you should apply only enough to maintain a quality putting surface and density (do not fertilize on the basis of turf color). Usually this amounts to about 0.5 to 1.5 pounds of nitrogen per month — about 0.5 pound for every two weeks of active plant growth.

The ultradwarfs need more N during the most active growing periods of the year. In addition, nitrogen rates can be increased after vertical mowing or aerification to help turf heal and recover.

You need to watch potassium levels on soil test reports and ensure adequate levels (on an annual basis, apply at least 1 pound of K per pound of N).

Fertility levels will vary depending on whether you have an 8- or 12-month (or somewhere in between) growing season. The longer growing season will require more fertility than a shorter growing season. Some superintendents feel there are benefits to rotating (changing) the N source.

The ultradwarfs respond to micronutrients. Indications are that Manganese helps with disease resistance, especially when the soil is slightly acidic (pH about 6.0 to 6.5). Granular fertilizer products should be size SGN 100 or less, or a highly soluble granular material to reduce pick up by mowers. Use of liquid products may improve consistency of color and putting surface performance.

IRRIGATION

You must irrigate to prevent stress. Heavy, infrequent irrigation is preferable to frequent, light irrigation after turf is established, to encourage deep rooting (a shallow root system will require more frequent irrigation). Root zones of the ultradwarfs can become hydrophobic because of the turf's density. Therefore, periodic application of a good wetting agent, frequent aerification or use of high-pressure water injection can lessen hydrophobic conditions and encourage deeper rooting.

AERIFICATION

A good goal for aerification in the northern parts of the ultradwarf growing area is to impact 10 to 15 percent of the surface area at one time. In tropical climates, try to impact 15 to 25 percent of the surface with aerification. Ultradwarfs need to be aerified two to five times a year using 0.5 inch tines (0.625 inch in mid-summer) on 2-inch centers. Remove aerification cores and debris and use sufficient topdressing material to fill aerification holes. You can use solid tines, star tines or a high pressure injection, as needed, to enhance infiltration. This will also improve root growth, reduce surface firmness and reduce dry spots. The USGA website (www.usga.org) can be consulted for details on how tine size and spacing impacts surface area.

Research shows that inadequate maintenance of ultradwarfs will result in thatchy and spongy putting surfaces. Therefore, I encourage each superintendent considering using an ultradwarf to carefully review the needed management practices to determine if personnel and budget will support the required inputs. However, the extra effort is rewarded by the high quality putting surface these new grasses provide, and the satisfaction and enjoyment of the golfers playing on them.

Dr. Wayne W. Hanna is a research geneticist with the U.S. Department of Agriculture's Agricultural Research Service. Hanna is based at the University of Georgia Coastal Plain Experiment Station (Tifton, Ga.).

SUGGESTIONS FOR PREVENTING THATCH

A. Frequent light topdressing or dusting with sand is critical for growing a layer of healthy biomass instead of a layer of thatch. You need to start early in the spring when the grass begins growing. You may want to dust every two or three weeks in the spring and fall when the grass is growing slower but once every week in the summer when the grass is rapidly growing. Use fine, dry, bagged sand if possible (coarse sand can be picked up by mowers). Use a spinner-type machine. Light and more frequent applications are much better than too much at one time — the ultradwarfs do not like heavy topdressing.

Topdressing maintains pore space in the stolon/rhizome layer to improve water movement and aeration. Without sand, the stolons and rhizomes become compacted with decaying leaf material, creating low oxygen conditions, which reduces root health and growth. Ultimately, the stolons and rhizomes die and become part of the problem rather than providing carbohydrate reserves for the plant.

B. Brushing daily (with the brush behind the front roller or somewhere in front of the mower's bedknife) and turf grooming two or three times a week are excellent ways to help prevent thatch. The type of brush is probably not that important. The purpose of the brush is to raise the stolon tips so the mower can cut them cleanly. Grooming should be more aggressive when the grass is rapidly growing and less aggressive in the spring and fall when growth has slowed down. Some superintendents have eliminated the need for light verticutting by using brushing, grooming and light topdressing.

C. Light verticutting alternating with topdressing is an excellent tool for promoting a smoother ball roll. The typical times for verticutting are June, July and early August — in more tropical climates, spring and fall are also good times.

The success of verticutting depends to a large degree on location, weather and fertility rates. Some greens may benefit from vertical mowing in two directions, whereas this may not be necessary for others.

Most ultradwarfs generally do not tolerate deep verticutting, though some superintendents in south Florida have had good experience verticutting 1.25 inches deep in May (not after June) to remove thatch and then topdress. Some verticutting can be eliminated if greens are regularly brushed and groomed.

Vertical mowing, especially if deep and aggressive, may create an environment conducive for decline, slow recovery and a poor playing surface during periods of high stress (high temperatures, cloudy weather, rain, etc.). Preventative fungicide application may be necessary prior to verticutting. It's worth repeating: Thatch prevention via the methods I mentioned above is preferred over thatch remediation.

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