Fact Sheet: Vegetable and Herbs
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 vegetable and herb 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. Seedlings and younger crops are more at risk because they will need to recover and some plant loss may be experienced. Crop varieties that require drying off and are already at that stage of production will be at a much lower risk.
When locusts are present in large numbers all vegetable and herb crops are at risk.
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. Vegetable and herb growers should seek expert advice from their chemical reseller or agronomist as to which chemical best suits their situation.
If vegetable crop waste and by-products like leaves, stalks and skins is fed to livestock it is vital to ensure that no unacceptable insecticide residues remain in this feed source and that the following with holding periods are observed:
Harvest withholding period
This is the minimum time that must elapse between spraying the crop and harvesting the produce. 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 in accordance with directions and all withholding periods must 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 control 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 I use?
Using a properly calibrated boom sprayer to spray hoppers will minimise the risk of chemical sprays drifting outside targeted areas.
If boom sprayers are commonly used to apply herbicides, it's important to ensure all herbicide residues are cleaned out before using insecticides. Herbicide sprayers should preferably only be used for ground spraying, not onto vine foliage.
Look out for bees
Some vegetable crops need insects to pollinate flowers and bee hives may be placed within crops or nearby to assist the pollination process.
Apiarists should be contacted and informed of your intention to spray enabling them to manage the risk to their hives. Other options include waiting for suitable weather conditions, when hives are upwind of the treatment area or during times of low bee activity for example in the early evening.
Some chemicals contain 'DO NOT' label statements that specifically prohibit the use of the chemical when bees are foraging in the crop to be treated. Complying with these statements is a legal requirement.
Managing other pests
If an integrated pest management (IPM) program is used by growers there is only one biological option for hopper control; however, this can take up to 20 days. If high-value crops are at risk this may represent too long a time period. Other broad-spectrum controls will disrupt an IPM program. This may be critical in situations where key pests have resistance to some broad-spectrum chemicals and other control options for these pests may need to be considered if possible.
What about marketing produce?
Vegetable and herb growers must ensure they control locusts while managing the risk of unacceptable chemical residues in their produce. Unacceptable residues can lead to restriction or closure of export markets to all Australian vegetable and herb growers.
Maximum residue limits in export countries may differ or be non-existent for vegetables or herbs treated with the products listed in this document.
If growing crops 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 control chemicals. Your chemical reseller or agronomist may also be able to provide advice.
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 135 559.