SEAISLE PASPALUM introduction

Seashore paspalum (Paspalum vaginatum) has generated quite some interest in the turf world in the last few years - some of the interest is positive, while some is negative. Paspalum can now be found on a select number of golf courses and has recently become available for home

lawn use as well. Plugs of 'Sea Isle 1' became available at select turf growers across Australia last summer as evaluations of the grass for home lawn use were in initial stages. Homeowners looking for an alternative to St. Augustine grass began asking about the grass and many took the plunge and replanted their lawns to this species. At that time, there were several unanswered questions regarding management of the grass under home lawn conditions.

These included:
- How much and how often to fertilise
- Mowing height and frequency
- Herbicide tolerance
- Insect, disease, and nematode problems
- Establishment
- Irrigation needs under watering restrictions

Fertilisation
Paspalum responds best to frequent, light fertiliser applications - exactly what you don't find happening in most home lawn fertility programs. It grows very rapidly in response to nitrogen - again, not what you necessarily want in a home lawn. Two studies in Gainesville in the spring of 2000 looked at effects of common home lawn fertilisers and specific sources of nitrogen on Seashore Paspalum. Over a two-year period, there were no differences in quality, shoot and root growth, or multispectral reflectance (a measurement of the plant's ability to assimilate and use light for photosynthesis) in these studies. Dr. Unruh found similar results in a large-scale experiment looking at different sources of fertilisers. Fertiliser source is not important in maintaining a Seashore Paspalum lawn.

Additional Paspalum research was begun in 2001 - 2002 to look at effects of nitrogen and potassium rates. Nitrogen was applied in 4 applications for a total annual rate of 0.5kg, 2kg, or 4kg of N per 100m2 (1, 4, or 8 pounds of N 1000 ft-2). Potassium was applied at the same time at annual rates of 0.5kg, 2kg, or 4kg of K per 100m2 (1, 2, 4, or 8 pounds of K 1000 ft-2). As might be expected, there were differences in quality, growth, and multispectral reflectance in response to the varying nitrogen rates (table 1). The same quality scores were achieved with either 2kg or 4kg of N per 100m2 (4 or 8 pounds of N 1000 ft-2). In reality, these rates are probably excessive for Paspalum, with a second year of data indicating that less N may be better.

Mowing Height and Frequency
Seaisle paspalum generally requires lower mowing than most home lawn species. When mowed at higher heights, it tends to shade itself out and develop excessive thatch. However, Paspalum does not like to be scalped and will decline in response to losing too much leaf tissue at one mowing. This can be a tricky component of the management regime when combined with the rapid growth response to nitrogen and homeowner-based mowing schedules. A study was initiated last year with weekly mowing heights of either 25mm, 50mm, or 75mm (1, 2, or 3 inches). Throughout the growing season, highest average quality scores were obtained with the higher mowing heights, in contrast to what is thought to be best for the grass (table 2). Why did this happen? The mowing height was lowered too quickly when the study began and scalped the 25mm (1") treatments. The grass never fully recovered all year and parts of it always remained scalped.

Establishment
Seaisle paspalum has to be established vegetatively - by sod, plugs, or sprigs. While some homeowners may choose to sod, many people are purchasing plugs and letting the lawn fill in. A study was initated to evaluate best nitrogen rates for grow-in. Plugs were established in mid-July 2001 at 30cm (12 inches) on center. Two nitrogen sources and three nitrogen rates were evaluated for rate of grow-in and overall quality.

Fertiliser was applied in three separate applications at one week after planting, 4 weeks after planting, and 6 weeks after planting. Nitrogen was supplied as either ammonium sulfate or sodium nitrate. Rates were 125g of N per 100m2 (0.25 lbs of N 1000 ft-2), 250g of N per 100m2 (0.50 lbs of N 1000 ft-2), or 500g of N per 100m2 (1.0 lbs of N 1000 ft-2) at each application. There was also a control that received no nitrogen.

At 4 weeks after planting (one fertiliser application) and 5 weeks after planting (two applications), there were no differences in cover between the 500g (1 lb.) rate of either nitrogen source and the 250g (0.50 lb.) rate of ammonium sulfate. During early grow-in periods with plugs, when parts of the ground are bare, the possibility of nitrogen leaching is greater. Use of 250g of N per 100m2 (0.50 lb. of nitrogen 1000 ft-2) will provide establishment as quickly as use of 500g (1 lb.) and will be less likely to cause leaching.

Irrigation Needs
Seaisle paspalum needs supplemental irrigation to remain green during times of drought like any other turfgrass. Because it grows a deep root system that can forage for water deep in the soil, it has good drought avoidance mechanisms when managed properly. This does not mean that it will stay green under drought conditions.

In a study conducted in the rhizotron cells of the UF Turfgrass Envirotron Research Facility, Sea Isle 1 and 'Floratam' St. Augustine grass were both subjected to weekly irrigation schemes of 25mm, 12mm, 6mm or 0mm (1, 0.5, 0.25, or 0 inches) of irrigation weekly. There were no differences in quality between the two grasses averaged over the course of the study. There were however differences in quality between irrigation treatments averaged over the course of the study. If you consider a quality score of 5.5 to be acceptable, then applying 12mm (0.5 inches) of irrigation weekly would produce an acceptable level of turf quality. If a score of 6 is considered acceptable, then 25mm (1 inch) of water would need to be applied weekly. This indicates that the water requirements of seashore paspalum are very similar to Floratam. Further work is needed on irrigation requirements and drought tolerance of seashore paspalum.

The Bottom Line
So, will seashore paspalum be viable as an alternative turfgrass for home lawn use? Homeowners enjoy the look and feel of the grass and many are eager to try it. However, if it is to be used in home lawns, we clearly need homeowners and lawn maintenance people who have an understanding of how to manage it properly. Many people involved in home lawn care attended our state-wide seminars held last autumn, where everyone involved learned about seashore paspalum.

Table 1.
Average scores of Sea Isle 1 over the growing season in response to nitrogen.






Table 2.
Average quality scores of Sea Isle 1 over the growing season in response to weekly mowing height.






Table 3.
Quality scores averaged over two grass species subjected to deficit irrigation regimes.

Seaisle Paspalum - A New Option for Australia

Seaisle paspalum growing on a golf course in Hawaii. This species is very well suited to the environmental and climatic conditions of tropical or sub-tropical areas.

The grass species Paspalum vaginatum, or 'Seaisle paspalum' has been in existence for thousands of years, but interest in use of this grass for landscapes, athletic fields, or golf courses has occurred only in the last few years. This is a warm-season grass that is native to tropical and sub-tropical regions world-wide. Seashore paspalum grows naturally in coastal environments, often found in brackish marsh water or in close proximity to ocean waters. It also grows in areas that receive extended periods of heavy rains and low light intensity. Its best growth occurs in response to warm temperatures and long daylengths.

Advantages

Seaisle paspalum produces a high quality turfgrass with minimal fertility requirements. While it will exhibit best growth and quality under optimal environmental conditions, it can exist under less than optimal conditions for extended periods of time. Some of the stresses for which it exhibits a wide range of tolerance include:

Seaisle paspalum can grow directly on ocean beaches or nearby in a salt affected marsh

- Seaisle paspalum can grow directly on ocean beaches or nearby in a salt
  affected marsh
- excellent tolerance to saline or recycled water (to ocean salt water levels)
- good drought tolerance under proper management
- produces a high quality turfgrass with reduced nitrogen requirements
- tolerates a wide range of soil pHs (from 4-9)
- minimal pesticide requirements
- excellent wear tolerance
- tolerates extended periods of low light intensity, such as from prolonged
  cloudy or rainy periods
- good insect and disease resistance
- tolerance to flooding or extended wet periods

Characteristics of paspalum that make it favorable for lawn/landscape use:
- minimal seedhead production
- prostrate growth habit reduces mowing needs and provides for dense, fast-
  growing cover
- minimal weed problems under proper management
- exhibits fine leaf texture similar to hybrid bermudagrass
- produces a dense root system in sand or clay soil
- goes off-color and into winter dormancy later than other warm-season
  grasses

Disadvantages
- produces moderate amounts of thatch during periods of active growth
- emerges from winter dormancy and greens-up slightly later than other warm-
  season grasses
- does not perform well under tree shade


Establishment
Seaisle paspalum must be established vegetatively by sod or sprigs. Sprigging rates should range from 7-15 kb per 100m2 (5 - 10 bushels per 1000 square feet). The best time for establishment is during periods of most active growth, when temperatures exceed 22°C (70° F).


Fertility
Proper fertilisation of any lawngrass is an important component of the best management practices of your home lawn. Fertilisation and other cultural practices influence the overall health of your lawn, and can reduce or increase its vulnerability to numerous stresses, including weeds, insects, and disease.
Seaisle paspalum responds well to low fertility rates. As with any lawn, the fertility regime will determine not only the rate of growth and curb appeal of your lawn, it will also determine the amount of maintenance required to keep it in optimal condition.

During establishment of a Seaisle paspalum lawn, small amounts of fertiliser should be applied on a regular basis to hasten growth and ground cover. "Spoon-feeding" 250g of N per 100m2 (1/2 lb. of N per 1000 square feet) in two applications during a 3-4 week period will stimulate growth. To encourage root development, phosphorous should be applied during establishment at rates equal to or greater than the nitrogen. Potassium needs of Seashore paspalum are also greater during establishment, particularly when irrigated with saline water. Until the grass provides a uniform ground cover, a 1:2:3 fertiliser ratio of N:P:K in biweekly applications will provide the needed nutrients. If sodding Seashore paspalum, ground cover will be immediate, but at least two weeks will be needed to insure that the root system is functional and capable of supporting the shoot system. If sprigging, coverage will take longer and establishment fertility requirements will need to be in place until both root and shoot systems have grown in.

Following this establishment period, the fertility regime should be reduced. In north Queensland, 1 - 1.5kg of N per 100m2 (2-3 lbs. of N per 1000 square feet) per year will produce a good quality Seaisle paspalum lawn. It is best to apply fertiliser in small increments (at least 2-3 applications) from late March or early April through August. In south Queensland, an additional 0.25 - 0.5kg of N (1/2 to 1 lb. of N) can be applied yearly. Never apply more than 250g of water soluble N per 100m2 (0.5 lb. of water-soluble N per 1000 square feet) at any one time. Up to 500g of N per 100m2 (1 lb. of N per 1000 square feet) may be applied as long as at least 50% of the nitrogen is in slow-release form. Phosphorous application should be made depending upon results of soil tests. As some Queensland soils contain ample amounts of phosphorous, little or none may be required. Generally, if phosphorous is needed, apply no more than 250g - 500g (1/4 to 1/2 lb.) of phosphorous for every 500g (1 lb.) of nitrogen applied. Potassium requirements of Seashore paspalum are generally low, with rates of 250g - 500g (1/4 to 1/2 lb.) of potassium per 500g (1 lb.) of nitrogen being adequate. Potassium requirements will be higher during rainy seasons, however, when potassium can be leached through the soil. Additional potassium may also be needed if salt water intrusion or storm surge problems occur.


Mowing
Proper mowing practices are essential to maintenance of a healthy lawn. As with fertility, height and frequency of cut can determine the level of lawn maintenance. Seashore paspalum used in home lawns should be mowed at 19 - 38mm (3/4 to 1.5 inches) in height. Higher mowing heights will reduce turfgrass density and increase weed problems. Mower blades should be kept sharp to avoid tearing leaf tissue. When mowing, never remove more than 1/3 of the leaf blade at any one time. If the grass takes on a scalped appearance, too much leaf material is being removed at one time. If the lawn is under stress from drought, shade, nutrient deficiencies, insects, or diseases, it is best to maintain a higher cutting height until the stress pressure is relieved. Do not mow when the grass is wet or the soil is soggy.
Grass clippings can be left on the lawn. These do not contribute to thatch build up, but are readily decomposed by microbial action. Clippings also serve as a nutrient source, and can actually reduce the fertiliser requirements when returned to the lawn.


Irrigation
Due to the tolerance of Seashore paspalum to periods of drought, irrigation is recommended on an as-needed basis. Signs of water deficit include rolling of leaf blades, wilting, and foot imprints that remain on the lawn after walking on it. At these signs of water deficit, apply 12 - 18mm (1/2-3/4 inch) of irrigation to the entire lawn. Do not apply smaller volumes of water more frequently, as this will not encourage root growth. To avoid overwatering when rainfall is adequate, reduce the frequency of irrigation. Overwatering lawn grasses not only wastes water, but results in weakened root systems, nutrient leaching through the soil, and poor stress tolerance.
Because Seashore paspalum is very tolerant of poor water quality, it can be irrigated with recycled water or water subjected to salt-water intrusion. It is important to realise, however, that even this grass can develop salt toxicity problems with repeated use of saline water over extended periods, particularly in areas receiving little rainfall. Where rainfall is ample, this will flush out accumulated salts in the soil and minimise salt toxicities.


PEST PROBLEMS

Weeds
Current herbicides available to homeowners are generally not labeled for Seashore paspalum. Irrigation with saltwater has been one method used to effectively control both grassy and broadleaved weeds in Seashore paspalum. Herbicides that do not injure paspalum include pendimethalin, halosulfuron, and mixtures of 2,4-D, dicamba, and MCPP. Consult your County Extension Service office for proper identification of weeds and a prescription for environmentally friendly control of the problem.

Insects
In general, Seashore paspalum has few problems with insects and chemical requirements for their control are minor. It is subject to occasional problems from mole crickets, sod webworms, spittlebugs, white grubs, billbugs, cutworms, and fall army worms. It generally has no problems with chinch bugs.

Disease
Seashore paspalum has relatively few disease problems when maintained under recommended fertility levels and cultural practices. Organisms which may cause problems include fusarium blight , which may be found under hot, humid conditions, or when the grass is under drought stress. When infected, the entire turfgrass plant will change color from green to reddish brown to dark brown. Helminthosporium disease may also occur under conditions of high humidity or soil compaction. This disease is seen as small purple leaf spots with brown centers and light tan halos.