Nutrient Management

Proper fertilization and Maintenance of Zoysia Grass is very important for sustaining a healthy lawn. Fertilization and other cultural practices influence the overall health and quality of the lawn and reduce its vulnerability to numerous stresses, including weeds, insects, and disease. It is very important that anyone fertilizing their lawn be familiar with and follow the Florida Friendly Landscaping Best Management Practices (BMPs).

These practices are designed to maintain healthy lawns and reduce any potential nonpoint source pollution of water resources that might result from lawn and landscape fertilization and other cultural practices. There are now state and local regulations that cover lawn fertilization, so be aware of city and county guidelines and always follow the directions on the fertilizer bag. For more information on BMPs, please refer to ENH979, and contact GES Lawn and Pest for information.

A soil test should be done to determine soil pH and what nutrients are available to the lawn. The local Extension office has instructions and supplies for taking soil samples and submitting them to the Extension Soil Testing Laboratory for analysis. In particular, phosphorus levels are best determined by soil testing. Since many Florida soils are high in phosphorus, it is often not necessary to add phosphorus to a lawn once it is established.

Florida Rule (5E-1.003) mandates that the fertilizer application rates cannot exceed 1 lb of nitrogen per 1000 square feet for any application. Based on the percentage of nitrogen that is in a slowly available or slow-release form in a fertilizer, UF/IFAS recommendations call for applying a ½ pound (water-soluble nitrogen source) to 1 lb (slow-release nitrogen source) of nitrogen per 1000 square feet of turfgrass. For information on determining how much fertilizer this equals.

As a general rule, the first fertilizer application of the year should be early April in Central Florida and mid-April in North Florida. In South Florida, fertilizer applications may be made throughout the year since growth is year-round. UF/IFAS guidelines for lawn grass fertilization offer a range of fertilizer rates over which a particular species may be successfully maintained in the various regions of the state. These ranges account for individual homeowner preferences for low-, medium-, or higher-input grass. Additionally, localized microclimatic effects can have a tremendous impact on turf grass growth. A range of rates allows for these environmental variations. An example of this would be a typical home lawn that is partially shaded and partially sunny. The grass growing in the shade needs less fertilizer than that growing in full sun. Fertilization is also affected by soil type, organic matter in soils, and practices such as clipping management. Recycled clippings provide some nutrients back to the turf grass and may reduce the need for fertilizer inputs. Additionally, a newly sodded lawn on a sand soil with no organic matter requires more fertilizer than a lawn that has been fertilized for years. In Florida, new homes and new developments may be next to much older developed landscapes, and a one-size-fits-all approach to fertilization is not reasonable. Thus, the guidelines provide a base range from which the end user can begin a fertilization program. The homeowner is encouraged to initiate a program based on these guidelines and to adjust it over time based on how the turf grass responds.

Zoysia grass responds better to a "spoon-feeding" fertilizer regimen (smaller quantities applied more frequently) rather than supplying larger quantities infrequently. Current UF/IFAS recommendations state that zoysiagrass should receive 3 (North Florida) to 6 (South Florida) applications per year in most situations (Table 3). Research suggests that new cultivars of zoysiagrass can persist on less nitrogen, and the UF/IFAS recommendations for zoysiagrass are under review. Avoid applying nitrogen fertilizer simply to promote green color. Instead, monitor growth and apply only when the growth rate has dramatically declined. Potassium nutrition also is important and should be applied at rates equal to nitrogen. During excessively rainy periods, potassium may need to be applied more frequently due to its leaching ability.

Since zoysia grass is very slow to green-up in the spring, avoid applying fertilizer until after the turf has become fully green to avoid premature green-up, which is prone to frost injury. This is especially important in North Florida, where late spring frosts may damage the grass. Delaying spring fertilization until the turf is actively growing and can use the fertilizer also reduces the potential for nitrogen leaching from fertilizer. Likewise, don't fertilize too late in the year, as this can slow regrowth the following spring. An application of iron can enhance spring green-up. Applying nitrogen on zoysia grass in early spring and late fall significantly increases the risk of large (brown) patch disease.

On high-pH (> 7.0) soils or where high-pH water is applied, yellow leaf blades may be an indication of iron or manganese deficiency. Application of soluble or chelated sources of these micro-nutrients can provide a green-up due to elevated pH.

For iron deficiency, spray ferrous sulfate (2 ounces in 3–5 gallons of water per 1000 square feet) or a chelated iron source (refer to the label for rates) to temporarily enhance color. Iron applications every 6 weeks help maintain green color and, unlike nitrogen, do not promote excessive top growth.

Note that iron is not a substitute for nitrogen, which provides the building blocks for turf grass growth and is required for turf health. While both iron and nitrogen deficiencies result in yellowing of turf grass, they are distinctly different deficiencies in plants. Applying iron does not cure yellowing due to nitrogen deficiency, and iron fertilizer is not a substitute for nitrogen fertilizer. Foliar iron fertilizers, such as iron sulfate or chelated iron solutions, help cure iron deficiencies, and nitrogen fertilizers applied according to BMPs cure nitrogen deficiencies.

Mowing

If fertilized as recommended, zoysia grasses require frequent mowing during the summer to look their best. Medium- to coarse-textured zoysiagrasses should be mowed weekly, or when they reach a height of 3–4 inches. They should be mowed at a height of 2–2.5 inches with a rotary mower. Fine-textured zoysia grasses maintained at heights below 1 inch require more frequent mowing. Because zoysiagrass leaves are very coarse, they can be quite difficult to mow. Clippings should be left on the ground after mowing. They do not contribute to thatch buildup, as is often assumed, but are actually readily degraded by microorganisms. A sharp, well-adjusted rotary or reel mower should be used.

Watering

Zoysia grass responds to drought by turning brown and going dormant in a short period of time (within a week under typical drought conditions). In the absence of rain or irrigation, zoysia grass stays dormant for extended periods of time. Once irrigation or rainfall resumes, zoysia grass will regain its green color.

Irrigating on an "as-needed" basis is the best way to water any established, mature grass as long as the proper amount of water is applied when needed. Irrigation is needed when leaf blades begin to fold up, wilt, or turn a blue-gray color, or when footprints remain visible after walking on the grass. Apply ½–¾ inch of water per application. This applies water to roughly the top 8 inches of soil, where the majority of the roots are. Be sure to follow any local watering restrictions. contact GES Lawn and Pest for additional information on proper watering techniques.

To determine application rates of a sprinkler system, place several straight-sided cans (e.g., tuna fish or cat food) throughout each irrigation zone. Run each zone to determine how long it takes to fill the cans to the ¾- or 1-inch level, then record the time. Each zone will likely take different amounts of time to give the same quantity of water. The recorded run times for each zone should then be programmed into the irrigation clock for automated systems. If the variation in the catch cans is great, a more thorough audit of the irrigation system is needed. Refer to ENH61, How to Calibrate Your Sprinkler System contact GES Lawn and Pest for help. Irrigation frequency should change seasonally, with less water needed in the fall and winter. Do not adjust the amount applied, just the frequency.

Thatch Management

Zoysia grasses typically develop a thick thatch layer in the years after establishment—especially when over fertilized with nitrogen. This thatch must be controlled or removed mechanically to maintain a uniform grass appearance. This is most often done using a vertical mower or core aerator every year or two. Some have noted that scalping, during or shortly after spring green-up, helps reduce thatch buildup. One of the most important methods of reducing thatch buildup is to keep nitrogen fertility at the recommended levels. Proper mowing heights also help prevent thatch buildup.

Pest Management

Like other lawn grasses grown in Florida, zoysia grass lawns encounter pest problems. Periodic control of one or more of these problems is necessary to grow a healthy turf. The local county Extension office can help identify pest problems and provide current control recommendations

Weeds – One of the best attributes of zoysia grass is its ability to resist weed invasion due to its thick, dense growth habit. Insect and disease problems can damage zoysia grass, creating voids in this dense mat where weeds can invade. Fortunately, unlike St. Augustine grass and centipede grass, zoysia grass is very tolerant to many effective pre- and post emergence herbicides, giving a wide range of options to the turf manager. Refer to ENH884, Weed Management in Home Lawns, for more information contact GES Lawn and Pest .

Insects – The most serious insect on zoysia grass is the Hunting bil lbug. Bill bugs feed on roots, causing the turf to die in irregular-shaped patches. The damage most often occurs in the fall and spring when populations are high and when damage may be misdiagnosed as dormancy. Stems and rhizomes break easily, have irregular feeding marks, and the turf will not hold together if cut. Most damage occurs on infertile or dry soil. If 10–12 bill bugs are seen per square foot, control may be necessary.

Mole crickets and white grubs can also negatively impact zoysiagrass. Mole crickets feed on grass roots and leaf blades, and their tunneling activity dislodges plants from the soil, causing them to dry out. White grubs, like bill bugs, feed on roots, causing the turf to turn yellow, wilt, and eventually die. Both of these insect pests often attract raccoons, skunks, armadillos, and birds, which may actually cause more damage than the insect itself.

Sod web worms can cause periodic cosmetic injury but are not believed to severely damage the turf. These insects mine the green tissue from the leaf tips, but they do not "notch" the leaf blades.

Nematodes – Many turf managers state that nematodes are serious pests on zoysiagrasses; however, this is not well documented in scientific literature. UF/IFAS researchers and turf grass breeders are aggressively working to identify the extent of zoysia grass susceptibility, and they are identifying superior cultivars that can withstand nematodes. The UF/IFAS Extension Service Florida Nematode Assay Laboratory in Gainesville can diagnose whether nematodes are a problem by looking at a soil sample taken from the margin of the affected area. Proper cultural factors to encourage zoysiagrass root growth lessen nematode stress. These include applying less nitrogen, providing less frequent (but deep) watering, and ensuring adequate soil potassium and phosphorus.

Diseases – Without a doubt, the most troubling disease for zoysia grass is large (brown) patch. This disease becomes active when soil temperatures (4-inch depth) are between 65°F and 75°F each fall and can be a problem through the following spring. Although zoysia grass is probably not more susceptible to this disease than St. Augustine grass, recovery can be slow due to zoysia grass's prolonged dormant to semi-dormant condition. Zoysia grass is the first turf species to go off-color in the fall and the last to green-up in the spring. Therefore, if a large (brown) patch disease outbreak occurs, damage will be visible well into the next summer. With this in mind, it is important to treat preemptively to ward off any likelihood of this disease.