Weed control
Weeds compete for nutrients and water, create harvesting problems and may lead to cleaning charges with a grain crop. Weeds need to be controlled during the first four or five weeks after planting. After this time shading from the crop will prevent weed germination.
Cultural control
Zero-tillage maize uses the cane trash to suppress weeds.
Chemical control
There are some relatively cheap and effective herbicides available for use with maize:
One strategy would be to apply Atrazine post-plant / pre-emergent at a rate of 1.1 kg/ha and another 1.1 kg/ha 25 days later when top-dressing.
Always read the label and check registrations before spraying.
Diseases
Common diseases include rots, leaf blights, rusts, smuts and viruses. Selecting resistant varieties is the best way to reduce the incidence of disease.
Pests
Corn earworm
Corn earworm
Soil insects can be a problem for maize but this has not been experienced in northern sugarcane fields to date.
Corn earworm (Helicoverpa armigera) is a moth which lays its eggs on the top two-thirds of the plant and can damage the tassels and the silks, and so reduces pollination and grain set. Spraying is rarely worthwhile as the caterpillars are protected inside the cob and spraying will destroy any beneficial insects present.
Aphids will often be found on maize but do not warrant control measures.
Irrigation
Most coastal growers will not apply irrigation to summer crops but winter-grown maize would benefit from extra water. Maize requires 4 - 8 ML/ha depending on seasonal conditions. This equates to 400 - 800 mm of rainfall. Summer rainfall is far in excess of this in the north tropics and the crop will tolerate extra rainfall if it is on well-drained soil and the grain is immature at the time of the rainfall.
Mild water deficits during vegetative growth stages will decrease leaf area and more severe moisture deficits will reduce leaf number. Both will reduce the plant’s photosynthetic ability and have severe consequences on grain yield.
Flowering is the critical stage for determining final crop yield, and irrigated crops should be well watered from three weeks before flowering through to physiological maturity.
Moisture stress at flowering can slow pollen shed and sustained moisture stress will increase the interval between pollen shed and silk emergence, decreasing pollination rate and therefore grain formation.
Excessive soil moisture at seedling and flowering stages can have disastrous effects on maize establishment and yield. Selecting a well-drained paddock is crucial.
Harvest time
Grain
Different varieties have different times to maturity. Under optimal growing conditions, slower varieties will yield more than quick varieties. A slower variety will also stretch the harvest time further into the drier months.
The target moisture content of the grain for storage is 14% but the grain can be physically harvested up to moisture content of 25%. This is not recommended as grain drying is expensive. Crops harvested at 17-18% moisture content will attract a drying charge of around $15/t.
Silage
Silage maize is normally sold direct to feedlots and dairies at an agreed in-field price per tonne. Farmers growing for stock-feed grain and silage need to be aware of the stringent requirement of most buyers in relation to chemical residues.
The best indicator of dry-matter yield and silage quality is in the milk line score. At late grain-fill stage, there is a visible line of separation between the starchy tip and the milky base of individual grains. The line moves down the grain towards the core of the cob over a period of up to six weeks.
When this milk line is half way down the length of individual grains, its milk line score is said to be 2.5. Prior to the line being visible the milk line score is zero and once the line is at the base of the grains the score is 5. For most corn silage buyers, a milk line score of 2.5 is ideal. This occurs between three and four and a half months after planting, depending on the variety grown and seasonal conditions.
Gross margins
The gross margin for a crop is the gross income earned, less the variable costs incurred. For machinery operations, only include the cost of fuel, oil, repairs and maintenance.
The sensitivity analysis shows how returns would vary with a change in yield and price.
Market price maize
Gross margin/ha at different maize prices and yields (not including levy)
