Good weed control is essential, because the crop will not compete well in the early stages of growth, although it will when established.
Post-emergent herbicides are limited, particularly for grass weeds, so they should be controlled at or before sowing. Suitable herbicides are shown in Table 1.
Pest control:
Problem pests include soil insects, cutworm, armyworm, heliothis (budworm), locusts or grasshoppers, and sorghum midge. Soil insects such as false wireworm and earwigs need to be prevented from destroying seeds and seedlings.
Seed dressings containing imidacloprid, thiamethoxam or thiodicarb are registered and can be used. Alternatively, chlorpyrifos can be sprayed into the furrows at planting, or spread on the soil surface in bait form immediately after planting.
Heliothis
can cause damage between flowering and grain fill, but does not normally warrant spraying. Large numbers of small grubs in early grain fill should be monitored closely. Spray with registered chemicals such as synthetic pyrethroids (e.g. Fastac Duo®, Dominex 100®), Nuclear Polyhedrosis Virus (NPV - Gemstar), endosulfan or methomyl if grub numbers build to damaging levels.
Armyworm
feed on young leaves and may defoliate young plants. Chlorpyrifos and methomyl are registered for control in WA.
Cutworm
damage the plant as it is emerging or defoliate young seedlings. Carbaryl and chlorpyrifos are registered for control.
Grasshoppers
(locusts) can be controlled by carbaryl, chlorpyrifos, diazinon, maldison and fiprinol. Avoid sowing in areas or seasons where locust plagues are predicted.
Midge
is a common pest in the eastern States. The female midge lays eggs on the flowers just prior to and during flowering with a susceptible period of five to seven days. Many new varieties have a level of midge resistance indicated by a rating system.
Chemicals for control include synthetic pyrethroids, chlorpyrifos, diazinon, endosulfan, maldison, methomyl and carbaryl. Midge has not been identified as a major pest in WA to date.
Rutherglen bug
is an occasional pest that can cause yield loss in the head at flowering and grain fill. Both carbaryl and maldison can be used, however effectiveness may be limited on the nymphs if they are well hidden in the head.
Disease control:
Current varieties have good disease resistance (but not immunity) to the major diseases, and so far there have been no significant problems. The main diseases in growing areas of the eastern States are root and stalk rots and leaf rust. Others include ergot, Johnson grass mosaic virus, head smut and leaf blight.
The most economical way to control disease is through good agronomy and management, and the use of resistant varieties. As the area sown increases, it is likely that disease incidence will increase.
Harvesting:
Grain sorghum is a perennial and will continue growing after the seed has matured. Chemical desiccation with glyphosate (when most seed reaches maturity and contains 25% or less moisture) is normally required before harvesting.
The seed is mature when the base of the grain goes black, even though the plant may remain green. Do not wait for all the secondary heads to mature before desiccating, because you may lose ripe seed from the primary heads through shattering.
Grain sorghum can be harvested with an open front header fitted with sorghum fingers, and should be taken off at a moisture content of 13.5% for delivery, and 12% or less for long-term storage.
In eastern States, desiccation with reglone or a lower rate of glyphosate will allow the crop to ratoon (continue growing to produce a second crop the following season). For a ratoon crop, harvest at 10 to 15 cm with a sharp knife (shattered and split stalks may not re-shoot) and apply fertiliser on the first rain to stimulate growth. The second crop will usually only produce 50 to 60 per cent of the first crop yield.
Marketing:
The market for grain sorghum is very small, so a market should be secured and contract arranged before planting. Sorghum is marketed both domestically and internationally, with domestic markets fetching the best prices (similar to feed wheat and barley).
In Australia most grain sorghum is used in intensive animal industries (lot feeding, batteries). A small amount is sold as birdseed and commands a higher price, but quality standards are higher. Grain sorghum normally fetches $140 to $180 per tonne.
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