Fact Sheet: Grains Industry
Australian plague locusts naturally inhabit the far north west of New South Wales and adjacent areas of Queensland and South Australia, an area known as the channel country.
They generally inhabit rural regions in relatively low numbers, but under favourable weather conditions they can multiply and migrate in large swarms to southern agricultural areas in southern Queensland, New South Wales, Victoria and South Australia and cause severe damage to pastures, field crops and vegetables.
Although locusts are not native to Victoria, they may be seen in varying densities from season to season, particularly in northern Victoria. In any given year, it is possible for locust swarms to migrate into Victoria from interstate. The Australian Plague Locust Commission provides forecasts on the likelihood of this occurring.
The following information will help land managers plan their risk management strategies for treating locusts if they are present in regional Victoria.
Risk to grain crops
The Australian plague locust prefers to feed on grasses and/or cereal crops such as wheat. However, when there is little green grass available they will eat a wide range of plants including horticulture crops, pasture, grapevines and trees. Locusts can attack nearly mature crops where the tops are still green, cutting off the heads and eating the grain. They can also eat part of the grain in the standing head and damage it.
Crops at most risk include wheat, barley and especially oats. Lupins, canola, chickpeas, field peas and faba beans are also susceptible while green. It is therefore important to remember that:
- established green crops are susceptible to damage by adult locusts, but tend to be avoided by hoppers
- crops that are drying off when locusts begin to fly are also susceptible to damage
- locusts cause little, if any damage to mature crops that have dried off
- the following crops are at low risk of attack: canola (after leaf drop); lupins (from pod bronzing); pulses (from pod yellowing); and cereal crops (when completely dried off).
What can I do?
You should treat locusts with insecticides when they are in the 'hopper' stage, before they can fly.
When locusts first hatch and emerge from the ground, they are often scattered. Treating locusts at this stage may be inefficient as some locusts may not have yet hatched.
Newly hatched locusts are very sensitive and without food and shelter, they are susceptible to premature death. As these locusts develop, they form high density bands and this is the best time for treatment activities.
What are my treatment options?
The use of chemical insecticides is the most effective method of treating locusts, particularly when they are still in the immature stages (called 'hoppers') and unable to fly. Hoppers may form and move as a 'band' or group, with up to thousands of hoppers for every square metre of the band. Spraying with insecticides at this stage is very effective and can greatly reduce numbers.
There are a number of products available for treating locusts. Farmers should seek expert advice from their chemical reseller or agronomist at to which chemical best suits their situation.
When choosing a chemical, landholders need to consider the following:
Harvest withholding period
This is the minimum time that must elapse between spraying the pasture/crop and harvesting the produce. The withholding period is shown on the chemical label. It is important to note that 24 hours must elapse to observe a one day withholding period.
Unless a withholding period is specifically listed for grazing or cutting, you must ensure that stock do not access treated areas, produce or crop waste.
Grazing or cutting for stock food withholding period
This is the minimum time that must elapse between spraying the pasture/crop and allowing grazing in the area or when the pasture/crop can be cut for hay or silage.
Export animal feed interval
This is the minimum time that must elapse between the application of a chemical and grazing or harvesting the crop/pasture for animal feed.
Export slaughter interval
This is the minimum time that must elapse between removal of grazing livestock to clean pasture or feed and slaughter, prior to expiry of the export animal feed interval.
Export grazing interval
This is the minimum time that must elapse between the application of a chemical and slaughter of the stock, where grazing has continued on the crop/pasture from the time the chemical was applied.
Chemicals should only be used according to the label directions and all withholding periods should be observed.
The biological insecticide containing Metarhizium anisopilae is the safest of the products to use, but can take up to 20 days to kill hoppers under cool conditions, which may be too long to prevent crop damage.
Other chemical products work much quicker than the biological insecticides, causing locusts to stop feeding within a few hours, and to die within two or three days.
Products containing the active ingredient fipronil can provide a degree of residual treatment in situations where use of these products is appropriate.
When should I spray?
The best time to spray locusts is in the second and third instar stage, after the eggs hatch and before they are able to fly.
Warm, moist weather conditions are the most favourable for locust egg hatchings. Locusts are hard to spot when they first emerge as young immature hoppers. They are only about 3mm long and pale in colour. Newly hatched locusts can cause considerable damage and can consume half their body weight in food per day.
As hoppers are wingless and form large, slow moving bands, they provide a clear target for efficient chemical use. Spraying with insecticides at this stage is very effective and can greatly reduce numbers, with the period of about ten days to two weeks after hatching the most effective and cost efficient.
The most effective treatment is achieved when hopper band densities reach or exceed 80 hoppers per square metre. It may be more practical to treat bands at lower densities if they pose a danger to nearby valuable crops.
The locust life cycle diagram below shows where this stage occurs within the complete locust life cycle.
The hopper stage will last for around six weeks in total, depending on temperature, but the third instar stage only lasts for a week or so, making it important to carry out regular monitoring.
The best time of the day to spray hoppers is late morning through to late afternoon when they are most active and most visible.
DEDJTR doesn't recommend spraying flying, adult locusts as it is very difficult to do safely and effectively. Individual landholders may make a business decision to spray flying locusts for the protection of valuable crops - but must obey withholding periods and follow the directions on the label of the chemical product used.
Whilst there is no conclusive data, ploughing egg beds may have some effect on loose, sandy soils. However, it unlikely that ploughing heavier soils will have any great effect on egg beds as pods will be more protected in soil clods.
Landholders should concentrate their efforts on treating locust hoppers after they have hatched and when they form dense bands on the ground.
What equipment should growers use?
Using a properly calibrated boom sprayer will minimise the risk of chemical sprays drifting outside targeted areas.
While misters may appear to apply chemicals efficiently, they present a greater risk of spray drift, increasing the risk of unacceptable residues in nearby crops, livestock, or other areas.
What about marketing produce?
Grain growers must ensure they treat locusts while managing the risk of having chemical residues in their grain. Unacceptable residues can lead to restriction, or closure of export markets to all Australian grain growers.
Grain growers should note that relevant maximum residue limits or import tolerances may not exist in export markets for crops treated with the products listed in this document, or they may be different to those established in Australia for domestic use.
If you are growing grain or fodder for export, check with your peak industry body or the manufacturer of the product for the latest information on maximum residue limits and import tolerances before using chemical products.
All harvest, grazing and cuttings for stock food withholding periods, and export animal feed intervals are based on a chemical product being applied to a crop/pasture that is still growing at the time of application and for the duration of the period or interval. The reason behind this requirement is that the breakdown of chemical residue levels in plants slows, and may stop, once the plant is no longer growing or alive.
Do not apply a chemical product to a crop/pasture, where a withholding period or export animal feed interval applies, unless the crop/pasture is still growing (green) at the time of application and for the entire duration of the relevant period or interval, or if expert advice is sought and this risk is managed, including pre-harvest residue testing.
More advice is available from peak industry bodies, chemical resellers, agronomists or chemical manufacturers.
Are there receival standards for locust parts in grain?
Bulk grain handlers have receival standards for locust body parts in samples, and for grain that has been damaged by locust feeding. Locust body parts may also change the smell and colour of grain.
Locust body parts detected when grain is delivered to grain receival centres may result in the grain being downgraded to feed quality, or rejected.
It is possible to clean grain to remove locust body parts, but this is time consuming and expensive, and may not be logistically possible during the harvest period. Receival standards can be obtained from www.graintrade.org.au or grain traders.
What are my obligations?
Landholders need to be vigilant in monitoring their crops, pastures and known locust egg beds for evidence of activity and crop damage.
While we cannot eliminate the locust threat completely, a collaborative approach with public and private landholders working together can reduce the effect on vital food production areas, the natural environment and rural communities.
All Victorians should report locust activity and known locations of egg beds to the DEDJTR Locust Hotline on 1300 135 559.
Private landholders are responsible for treating locust hoppers on their own property.
All chemical use must be in accordance with State laws and regulations, including record keeping requirements.
Information on the current locust situation can be found at www.agriculture.gov.au/pests-diseases-weeds/locusts/current.
Information on locust biology and management can be found at www.agriculture.vic.gov.au/agriculture-and-food/pests-diseases-and-weeds/pest-insects-and-mites/plague-locusts
Report locust sightings to the DEDJTR Locust Hotline on 1300 13 5559.