Fact Sheet: Nursery Ornamentals Cut Flowers
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 plants and cut flowers
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. Horticultural nurseries producing seedlings are also potentially at risk of attack from adult locusts when in large numbers.
In permanent plantings, the main risk of damage may stem from crops being covered rather than from locusts damaging the flower or buds.
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. Horticultural business owners and managers should seek expert advice from their chemical reseller or agronomist at to which chemical best suits their situation.
When choosing a chemical, growers need to consider the following:
This is the minimum time that must elapse between spraying the crop and the harvest date. The withholding period is shown on the chemical label.
Chemicals should only be used according to the label directions and all withholding periods must be observed. Re-entry periods are also specified on the product label, and it is critical for the health of workers to observe these periods.
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 is the impact on my integrated pest management program?
Using chemicals to treat locusts will have an impact on integrated pest management programs. The extent of the impact will depend upon the 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.
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 equipment should growers use?
Using a properly calibrated boom sprayer will minimise the risk of sprays drifting outside the targeted areas.
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 about marketing produce?
Nursery managers and growers must ensure they treat locusts while managing the risk of having unacceptable chemical residues in their crops. Unacceptable residues can lead to restrictions on, or closure of export markets to all Australian growers.
Contact your nursery industry body to check whether chemicals to be used are acceptable for target markets.
Growers should note that relevant maximum residue limits or import tolerances may not exist in export markets for crops 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 maximum residue limits and import tolerances before using chemical products. Your chemical reseller or agronomist may also be able to provide advice.
Specific market advice can also be provided by your peak industry body, chemical reseller, agronomist or chemical manufacturer.
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.