Fact Sheet: Fruit and Nut Industries
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
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. When locusts are present in massive numbers, all crops are at risk.
Locust eggs are usually laid in bare ground, often along fence lines or roadsides. Fruit and nut growers should monitor paddocks adjacent to orchard areas for hopper emergence in addition to monitoring trees for infestation damage. Boundary areas of orchards are more likely to be damaged initially and should be checked closely.
Foliage will experience more damage than fruit or nuts, depending on the time of the year. This makes immature trees more susceptible to damage. If young trees are stripped of foliage in spring, it may affect emerging shoots and consequently, trees shapes may need to be re-training the following spring.
Due to the reduction in foliage, it is likely that yield and size will be affected, with fruit or nuts also sustaining some damage. Quality of fruit and nuts may also be affected through direct exposure to the sun given the reduction in foliage from locust damage.
While mature trees are likely to experience little damage, any emerging buds, fruitlets or green nuts may be susceptible to damage from locusts. Mature trees usually recover from locust infestation and normal production can be expected to return by the next year.
It will be a particularly critical time if locust treatment is being carried out when trees are flowering because these chemicals may impact on pollinators (see section on Bees). Non-chemical treatments such as bird/hail netting may provide some protection, particularly to fully enclosed orchards, however there have been reports of locusts damaging some netting.
Damage to orchards can be extensive as adult locusts can strip trees within hours. The extent of damage is unpredictable, as locusts may fly over some orchards and feed on others, giving a 'hit and miss' effect.
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.
Treating locust eggs through cultivation of egg beds is generally ineffective. It is recommended that livestock managers concentrate their efforts on more regular monitoring and applying chemicals while hoppers are in a concentrated band.
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.
When choosing a chemical control option, landholders need to consider the following:
Harvest withholding period (WHP)
This is the minimum time that must elapse between spraying the crop and harvesting the produce. The WHP is shown on the chemical label. Note that 24 hours must elapse to observe a one day WHP. Unless a WHP is specifically listed for grazing or cutting, you must ensure that stock do not access treated areas, produce or crop waste.
Fruit and nut by-products such as pomace, seconds, hulls and shells are quite often used as alternative feed options for livestock. If you are supplying fruit or nut by-products for stock feed, you should ensure that you supply a commodity vendor declaration (CVD) to your client so they can avoid any potential issues with unacceptable chemical residues and can consider the following:
Grazing or Cutting for Stock food (WHP)
This is the minimum time that must elapse between spraying the pasture/crop and grazing that feed or when the pasture/crop can be cut for hay or silage.
Export Animal Feed Interval (EAFI)
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 (ESI)
This is the minimum time that must elapse between removal of grazing livestock to clean pasture or feed and slaughter, where the livestock have been grazing the crop/pasture prior to expiry of the export animal feed interval
Export grazing interval (EGI)
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. All restraint and 'DO NOT' statements, WHPs and export intervals 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.
How will treating locusts impact on my integrated pest management (IPM) program?
Using chemicals to treat locusts will have an impact on a grower's IPM program. The extent of the impact will depend upon the individual chemical used by the grower.
Some locust treatment chemicals may impact on beneficial species, but it is a mandatory requirement that growers treat locusts on their property.
Monitoring insect levels (e.g. mites, thrips) after spraying is critical to ensure growers can quickly respond to any harmful insects that may arise.
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 I use?
Using a properly calibrated boom sprayer to spray hoppers will minimise the risk of off-target chemical movement (spray drift). If such equipment is commonly used to apply herbicides, ensure all herbicide residues are cleaned out before using insecticides. Herbicide sprayers should preferably only be used for ground spraying, not onto vine foliage.
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.
Bee hives may be placed within or near nurseries or crops to assist the pollination process of trees from nearby orchards. In such cases where crops or land adjacent to nurseries and flower farms require insecticide spraying, consideration needs to be given to bee hives in the area.
Apiarists should be contacted and informed of your intention to spray, which will enable 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 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.
What about marketing produce?
Fruit or nut growers must ensure they treat locusts while managing the risk of having unacceptable chemical residues in their produce. Unacceptable residues can lead to restrictions on, or closure of export markets to all Australian fruit and nut growers.
WARNING - Export of Treated Produce
Growers should note that relevant Maximum Residue Limits (MRLs) or import tolerances may not exist in export markets for fruit and nuts 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 crops for export, check with your peak industry body or the manufacturer of the product for the latest information on MRLs and import tolerances before using the product. 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 13 5559.