Fact Sheet: Citrus 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 citrus 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.
Citrus crops are susceptible to attack from both hoppers and adult locusts. Young citrus trees are especially susceptible to attack, but mature trees, while generally less susceptible, may also be attacked if there is a shortage of alternative feed sources.
Eggs are usually laid in bare ground and often along fence lines or roadsides. This could include headland areas at the ends of rows, and in the inter-row areas if the ground was bare in April. Growers should particularly monitor areas adjacent to their block and grove areas for hopper emergence, in addition to monitoring citrus crops for locust infestation damage. Boundary areas of the grove are more likely to be damaged initially and should be checked closely.
While citrus is not the locusts' preferred feeding option, young trees, in particular, are at risk if green grasses or cereals are not available. Severe damage could set back the trees growth.
Also, there is potential for trees to be defoliated and consequently fruit quality and yields could be affected.
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. Growers should seek expert advice from their chemical reseller or agronomist at to which chemical best suits their situation.
If you use insecticides, be aware of sensitive sites such as beehives or organic properties in your area.
Harvest withholding period
Citrus growers need to make sure withholding periods are observed particularly for crops close to harvest. It is also critical to take this into consideration if land adjacent to crops is being sprayed as there is potential for sprays to drift onto crops close to harvest.
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 to spray hoppers when they are on the ground will minimise the risk of off-target chemical movement (spray drift). If such equipment is commonly used to apply herbicides in the grove area, ensure all herbicide residues are cleaned out before using insecticides.
Canopy spraying of citrus trees can be undertaken using oscillating boom, air blast or other suitable sprayers. Make sure the machine is properly calibrated before undertaking any spraying.
While misters may appear to apply chemicals efficiently, they present a greater risk of off-target chemical movement, 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 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