Fact Sheet: Viticulture 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.
The risk to vines?
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 large numbers all grapevines are at risk, with young tender vines and shoots the prime targets for attack.
Typically, the edges of the vineyard will be affected first and damage may be visible. However don't discount the possibility that the whole vineyard may be at risk.
The extent of damage will depend on the number of locusts present, as large populations can potentially strip grapevines of leaves within hours. The pattern of damage is unpredictable, as adult locusts may fly over vineyards to neighbouring properties, attacking some properties but missing others.
In spring, grapevines are drawing down the carbohydrate reserves in their trunk and root systems. The loss of leaves may impact on the ability of the plants to fully ripen the crop and to put carbohydrates back into the vine. This may affect grape quality and productivity in the current season, and can have a longer term effect into the following season.
Young grapevines are at greater risk than mature grapevines due to retarded establishment and a delay in reaching the bearing stage through to outright death of the vine. Although mature vines will survive a locust infestation, yield and quality could still be affected in later years.
Bunches of grapes may be exposed to increased sunlight and heat due to the loss of foliage that can increase the risk of sunburn and lower grape quality.
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?
It has been suggested that mowing or applying herbicide to the grass between the rows might reduce the feed supply for locusts, but this may be counterproductive and encourage them to climb up the grapevines and inflict greater damage to the canopy.
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 as to which chemical best suits their situation.
Some vine products such as grape marc are fed to livestock as alternative sources of feed.
It is vital to ensure that no unacceptable insecticide residues remain in this feed source and the following withholding periods are observed:
Harvest withholding period
This is the minimum time that must elapse between spraying the pasture/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 crop and allowing grazing in the area or when the 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 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 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 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.
While slide-on engine driven misters (different to vineyard sprayers) can apply chemicals efficiently they present a greater risk of off-target chemical movement, increasing the risk of unacceptable residues in nearby crops, livestock, waterways, dams and other areas.
Look out for bees
Some crops need insects to pollinate flowers and bee hives may be placed near your vineyard to assist the pollination process. If you or your neighbours are in this situation, 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 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?
Viticulturists must ensure they treat locusts while managing the risk of having chemical residues in their produce. Unacceptable residues can lead to restriction or closure of export markets to all Australian grape growers. Wine-grape producers are advised to check with the winery they supply grapes to before using any chemicals listed in the table.
Viticulturists and winemakers should note that maximum residue limits or import tolerances may be different to those in Australia or may not exist in export markets for grapes, vines or wine treated with the products listed in this document.
Dried fruits may also have different tolerances to fresh grapes due to the drying process effectively concentrating any residual chemicals in the drying process.
If you are growing produce 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. 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.