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 crops
Locust hatchings are more likely to occur in plantations that are less than one year old, where bare ground is still available. Plantation managers should regularly monitor paddocks, tracks and firebreaks adjacent to the plantation for hoppers.
Most tree species are susceptible to locust attack, including eucalypts, she-oaks, wattles and pines. Western Australian experience indicates that some species and provenances are more susceptible to damage and death than others (e.g. variation between the provenances of Eucalyptus camaldulensis (red gum).
Damage to trees can be unpredictable and may occur from hoppers that have developed on-site or nearby, or from adults flying to the site. The areas at most risk are those with the highest number of locust eggs.
Younger trees (less than three years old) are at greatest risk of attack and are more likely to be killed than mature trees. Severe defoliation of older trees is possible and can significantly reduce tree growth, which will affect the productivity of plantations. Trees planted individually or in narrow bands are at increased risk of damage from hoppers.
Plantation trees are generally at lower risk of attack from locust hoppers once the trees have developed a closed canopy.
What can I do?
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.
Management options include the following:
- Consider postponing any new tree plantings in high risk areas.
- Monitor for locusts from September onwards.
- Protect tree plantings from hopper invasion by treating a band of pasture or crop around the edge of the plantation, before they attack trees.
- Regularly monitor for the arrival of locusts. Once locusts are mature and flying, it will be difficult and probably uneconomic to treat them. As damage is often swift, treatment would need to occur within hours of locusts arriving.
- As trees remain green, they are susceptible over the entire period that locusts are active, and repeated spraying may be required. Ensure any treatment intervals on the chemical label are observed.
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. Landholders should seek expert advice from their chemical reseller or agronomist at to which chemical best suits their situation.
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
The best time of the day to spray hoppers is late morning through to late afternoon when they are most active and most visible.
DEPI 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 I use?Using a properly calibrated boom sprayer will minimise the risk of chemical sprays drifting along fire breaks and boundaries. However, aerial spraying may be more effective for treating plantations over 12 months of age, especially plantations yet to achieve a closed canopy.
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 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 DEPI 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.