Setaria for coastal pastures

WARNING

Users of agricultural (or veterinary) chemical products must always read the label and any Permit before using the product, and strictly comply with the directions on the label and the conditions of any Permit. Users are not absolved from compliance with the directions on the label or the conditions of any Permit by reason of any statement made or omitted to be made in this publication.

Pasture improvement may be associated with an increase in the incidence of certain livestock health disorders. Livestock and production losses from some disorders are possible. Management may need to be modified to minimise risk. Consult your veterinarian or adviser when planning pasture improvement.

Introduction

Setaria (Setaria sphacelata var. sericea) is a summer-growing perennial grass suited to the moist subtropics of the Northern Rivers, Mid Coast and Manning districts of New South Wales. It performs best on coastal lowlands receiving more than 1000 mm average annual rainfall.

Setaria is widely grown for grazing by dairy and beef cattle, but high oxalate levels make it undesirable for horses and donkeys.

Narok and Solander setaria are the varieties approved for NSW. Splenda setaria is suited to the wet tropics of North Queensland and as a 'cut and carry' forage for Asia and the Pacific.

Information on Setaria incrassata can be found in Purple pigeon grass.

Origin

The Setaria sphacelata complex is confined in origin to the African continent. It occurs throughout Africa but is rarely dominant over large areas. It is widely adapted, growing in highland grasslands through to low-lying areas subject to seasonal flooding.

The major value of the introduced cultivars of setaria lies in their adaptability over a wide latitudinal range and their marked response to fertile soil conditions.

General description

Setaria is a tall (90–180 cm) tufted perennial, without elongated rhizomes, and has widely varying vegetative characteristics. The base of young shoots is strongly compressed into a fan shape. Leaves are generally broad and predominantly hairless. The inflorescence structure is a cylindrical spike-like panicle 8–25 cm long and 7–8 mm wide, varying in colour from brown to purplish brown.

The '1000 seed' weight varies between 0.60 and 0.98 grams.

Cultivars

There are four commercial cultivars:

  • Nandi
  • Kazungula
  • Narok
  • Solander.

Nandi and Kazungula became available in the early 1960s. Narok was released in 1969 and Solander in 1984. Nandi (Kenyan highland ecotype) and Kazungula (Zambian ecotype) are direct introductions of older African varieties with the same names. Both cultivars are inferior pasture types and demand for them has declined following the release of Narok.

Narok was bred for its frost tolerance and better winter growth. It produces higher quality, leafier pastures than Kazungula or Nandi. The market for Narok seed has remained strong, particularly for dairy pastures.

Solander is comparable with Narok for frost tolerance and winter growth. Solander has twice the number of tillers producing inflorescences, resulting in a doubling of seed production. Solander produces high-quality leafy forage and has enormous potential for beef pastures in the higher-rainfall subtropics.

Dairy farmers who have tried both Solander and Narok regard Narok as the best quality cultivar, although experimental data indicates no significant differences in quality. Narok and Solander are the most desirable cultivars because of their growth at low temperatures.

Kazungula is the most drought-tolerant and flood-tolerant cultivar but has the highest oxalate levels, followed by Narok and Solander. Nandi has the lowest oxalate levels.

Seasonal growth patterns

Growth rate is markedly affected by temperature, rainfall and soil fertility. The seasonal growth pattern is similar to kikuyu under grazing conditions; however, setaria can accumulate dry matter faster when locked up for hay.

Good growth follows storms in spring and continues until late April. Under warm frost-free conditions, light pick is produced during winter. On the coastal lowlands very little production occurs during winter; however, green leaf carries well into winter.

Narok and Solander are the most frost-tolerant cultivars. With Narok, negligible leaf damage occurs at temperatures of –2.8°C to –3.3°C, but heavier frosting results in leaf kill. Surprisingly, research has shown that Paspalum dilatatum has equivalent frost-tolerant characteristics to those of Narok setaria.

The graph below shows growth rates on the North Coast for setaria, kikuyu and paspalum. These apply generally to ideal sites for each species.

Source: Ashwood, Griffiths & Moore, Milkonomics, Feed Plan, NSW Agriculture, 1992.

Where to sow

Setaria is sown on all soil types of the North Coast, although it does best on deep soils with good moisture-holding ability. On dry, shallow, hill soils, rhodes grass is preferred.

Narok and Solander setaria should not be established in areas prone to frequent flooding.

Although persisting under low soil fertility, setaria requires medium to high fertility for productive growth.

Companion legumes

Legumes are necessary to provide nitrogen to the grazing system as well as providing forage which is higher in nutritive value and free of oxalate.

The subtropical legumes shaw creeping vigna and forage arachis are highly recommended. Aztec atro and greenleaf desmodium are suitable for warm frost-free situations. Maku lotus is suitable only if sown with light seeding rates of setaria. Do not oversow Maku lotus into established setaria stands.

With regular renovations and strategic close grazing, white clover and kenya clover can be maintained within setaria pastures.

Establishment

Surface sow onto a well-prepared, firm, moist seedbed, then roll. Under dry spring conditions, a light covering of soil no more than 1.5 cm can be advantageous.

In the Northern Rivers districts, February is the best month to establish setaria.

When aerial seeding setaria and cool-season legumes into soybeans at the early leaf-fall stage, increase the conventional setaria seeding rate by 25% (i.e. sow at 0.75 kg 'pure live seed' per hectare). If using this establishment technique, the overall success rate is often better when setaria is sown with kikuyu, rhodes, or other suitable tropical grasses. Aerial seeding setaria into glyphosate-treated pasture is rarely successful.

The seeding rate depends on seed quality. The recommendation of 0.6 kg 'pure live seed' per hectare is a good guide; 1.5–2.5 kg/ha of commercial seed of good quality is the usual range. A low seeding rate is used to favour low-growing, shade-intolerant legumes such as white clover.

Fertiliser

Phosphorus is an important plant nutrient for rapid root development. Nitrogen requirements can be met by maintaining legumes in the grazing system, although setaria can respond to much more nitrogen than is usually supplied by legumes.

Setaria has an exceptionally high potassium requirement, and regular applications of potassium are required on marginal soils; otherwise, legume persistence and productivity will decline.

On the North Coast up to 500 kg of superphosphate, 100 kg of muriate of potash and 50 kg of nitrogen per hectare will be required at sowing. Annual maintenance dressings of up to 200 kg of superphosphate and 50 kg muriate of potash per hectare will be required for high production levels.

On acid soils, the trace element molybdenum is often required by the companion legume.

Dairy farmers using up to 300 kg nitrogen/ha/annum in three split applications must also apply maintenance requirements of lime as well as phosphorus and potassium.

Weed control

Setaria generally competes aggressively with weeds. A strong stand of setaria will reduce the frequency of fireweed (Senecio madagascariensis, S. lautus) to scarce levels. On the floodplain soil of the Richmond River, setaria prevents re-establishment of tussock sedge (Carex appressa) and greatly slows the re-invasion of rushes (Juncus spp.).

Setaria is not an ideal competitor for giant parramatta grass (Sporobolus fertilis), although leachate from chopped setaria straw inhibits the germination of parramatta grass seed.

Established setaria is tolerant of the broadleaf weed control herbicides 2,4-D, dicamba and MCPA — check registration status and label instructions before use.

Renovation

With setaria, the majority of leafy tillers develop in the outer sections of the tussock. As the tussocks enlarge in diameter and a sod-bound condition develops, production may decline. A mechanical renovation will arrest a productivity decline and restore gaps between tussocks for white clover to grow. It also allows oversowing with legumes.

A chisel ploughing with a wide point spacing (35–45 cm) is preferred to disc harrows.

Follow-up rain is required to minimise longer-term damage.

Grazing management

  • In early establishment, avoid grazing plants until they are well anchored by strong secondary roots and resist being pulled out. This is especially important when the soil is moist.
  • A light grazing to take out the top of the plant allows more light to reach the young legume plants.
  • Once established, management should be based on maintaining the persistence and productivity of the companion legume.
  • Either continuous hard grazing or lax grazing is detrimental to setaria pastures.
  • Rank growth of setaria is most undesirable for milking dairy cows because of its low digestibility, low protein and low voluntary intake.
  • Young leafy regrowth (3 weeks) can have digestible dry matter levels of 70%. After 6–8 weeks, digestibilities drop to 50–55%. Old regrowth has low digestibility and protein levels.

A CSIRO grazing experiment conducted in south-east Queensland over 6 years, where beef steers grazed nitrogen-fertilised setaria, showed no overall significant animal performance differences between a rotational grazing system and a continuous grazing system. In fact, in 1 year, Narok gave higher gains with continuous grazing than with rotational grazing.

Mineral content

Because Narok setaria has a relatively low sodium content, cattle continuously grazing such pastures may require salt supplementation, especially if the stock water is low in sodium.

Phosphorus content is often moderate to low by National Research Council standards for high-producing dairy cows, and supplements may be needed.

Weaned dairy calves on setaria pastures benefit from short-term supplementation with common salt and an approved animal supplement of dicalcium phosphate.

Oxalate problems

All cultivars of setaria contain oxalate:

  • Kazungula has the highest levels;
  • Narok and Solander have intermediate levels;
  • Nandi has the lowest levels.

Horses and donkeys grazing grasses high in oxalate may suffer from ill-thrift, lameness and swelling of the head bones ('big head'). The disease can develop within 2 months of grazing setaria; however, it usually takes 6–8 months. Mares and foals are the most susceptible. It is therefore obviously undesirable to graze horses and donkeys on setaria, but if this is unavoidable, do not allow horses and donkeys to graze setaria for periods longer than 1 month in any one summer. Direct your enquiries on 'big head' to your veterinary practitioner or Local Land Services District Veterinarian (www.lls.nsw.gov.au).

Encourage legume components in setaria pastures to help offset the effects of oxalate and to improve pasture quality.

Oxalate is less of a problem with cattle. If given the opportunity, cattle can adjust to the high oxalate content of setaria by building up rumen micro-organisms which destroy oxalate.

Dairy cows that have not grazed setaria for a few weeks should be gradually accustomed to lush, potentially hazardous, setaria pastures. Toxic levels of oxalate cause a sudden drop in blood calcium (acute hypocalcaemia), which can result in coma and death.

Sometimes the unaccustomed cattle are placed on setaria that has been heavily fertilised with nitrogen and potassium. The highest levels of oxalate occur at night, and the lowest in the mid-afternoon. The problem often shows itself in the morning when the dairy farmer goes to get the milkers in.

If there are doubts about the potential toxicity, monitor stock closely and remove them from the pasture immediately if problems develop. Problems with dairy cows have been very sporadic and infrequent; however, the possibility of subclinical effects on high-genetic-merit dairy cows should not be ignored.

As well as the acute hypocalcaemia syndrome, a more chronic syndrome called oxalate nephrosis can be associated with ingestion of forage which is high in oxalates. This syndrome is only occasionally reported in beef and dairy cattle on the North Coast.

Pests and diseases

Setaria pastures are attacked by the common pests of North Coast pastures. Outbreaks of armyworm and pasture webworm can be controlled by insecticides registered for that purpose.

Buffel grass seed caterpillar (Mampava rhodoneura) has been present on the Far North Coast since 1989. It causes considerable damage to seed crops from late January onwards. The caterpillars tunnel through sections of the developing seed head, eating out the caryopsis from each fertile seed and webbing the damaged material as they go.

The main disease is a leaf spot fungus Pyricularia trisa, which is prevalent under hot humid conditions and can retard the growth of ungrazed stands.

Further information

See Agnote DPI-293 Setaria.

Acknowledgments

The author gratefully acknowledges the contributions of:

Dr Phil Sharman, private veterinarian, Casino
Kerry Moore, District Agronomist, Kyogle
Warren McDonald, Technical Specialist (Pastures), Tamworth
Dr Chris Bourke, Senior Research Scientist (Poisonous Weeds), Orange.