Chemical use and crop residues

The Australian plague locust (APL) or locust can cause serious damage to crops, gardens and rural environments. This page explains how they spread, how to control them and your responsibilities as a landowner or land manager.

Managing Australian plague locusts

Locusts occur infrequently in Victoria. Populations can come from migrations in New South Wales and Queensland but can also result from local breeding within the state.

Large outbreaks can harm agricultural crops, horticultural crops and rural environments.

Know the limits of control

Locust control is challenging. Flying adults make them hard to target with chemical spray.

Locusts lay eggs under the soil, which makes it hard for the for the chemicals to reach them. Egg beds which can cover large areas but be tricky to find.

Numbers can build rapidly when eggs hatch at the same time.

Ground spraying – target early nymph stages

Locusts undergo five growth stages (instars) before reaching adulthood. The best time to spray locusts is at the nymph stage. Spray as soon as nymphs begin forming groups on the ground before they start flying.  This happens at the second and third instar stages, about 2 weeks after hatching in warm weather (Fig. 1).  For more information See Agriculture Victoria’s website on ground-based spraying.

Australian plague locust life cycle

Aerial spraying

Large outbreaks are often managed with aerial spraying. The Australian Plague Locust Commission (APLC) teams up with state government when aerial spraying is needed.

However, careful thought should be given to where to spray as it can be harmful to populated, mixed crop and forested areas.

Choosing appropriate chemicals

Locust control chemicals have various active ingredients and come under different brand names.

You should always read the product label and check that the chemical is suitable for your situation (see Table 1).

Chemical groups

Carbamate and organophosphate insecticides

These chemicals act in similar ways and break down quickly after use.

Common active ingredients include:

  • carbaryl
  • fenitrothion
  • malathion.

Fenitrothion is widely used for locust control. It is approved for use on cereal crops and sorghum. Residue levels on plants reduce by half each day and access should be restricted to treated areas for 48 hours after spraying where possible. If you must enter treated areas, wear protective clothing.

Fenitrothion is toxic to some animals and aquatic life. Avoid spraying near beehives and waterways.

Phenylpyrazoles

Fipronil is the most common chemical in this group. It affects the insect nervous system and works through contact or ingestion.

Key points:

  • Low doses are effective on locusts
  • Risk to mammals is lower due to low use rates
  • It is highly toxic to bees, termites and aquatic life

Do not use near waterways or when bees are active.

Biological products

Metarhizium is a naturally occurring fungus that can be used as a biological insecticide. It works when spores attach to the locust and grow inside the insect. Death occurs after 8 to 21 days.

It works best in warm conditions and on early nymph stages.

Metarhizium is available in:

  • liquid concentrate mixed with water
  • ground application mixture with oil and additives
  • ultra-low volume form for aerial or mister use.

Table 1: Chemical actives and formulations registered for use for APL in Victoria.

 Crop
Product

Cereals

Pastures

Forage crops

Pasture seed crops

Sorghum

Maize

Grapes

Carbaryl 500 SC1

Y

Y

Y

Y

Y

Carbaryl 800 WP2

Y

Y

Y

Carbaryl 800 WDG3

Y

Y

Y

Y

Y

Fenitrothion 1000 EC4

Y

Y

Fipronil 200 SC

Y

Y

Fipronil 800 WG5

Y

Y

Malathion EC

Y

Y

Malathion EW6

Y

Y

Malathion ULV7

Y

Y

Y

Y

Metarhizium SC

Y

Y

Y

Metarhizium ULV

 

Y

Y

    

Notes:
1 – SC: Suspension concentrate – liquid formulation with fine particles suspended in water, needs shaking before use.
2 – WP: Wettable powder – powder mixed with wate before spraying.
3 – WDG: Water dispersible granules- dry granules dissolve in water.
4 – EC: Emulsifiable concentrate – oil-based milky liquid mixed with water.
5 – WG: Water dispersible granules (see WDG).
6 – EW: Oil-in-water emulsion (see EC).
7 – ULV: Ultra-low volume – very high concentration, produces very fine droplets, used for aerial control over large areas.

Details provided are correct at the time of publishing.

Follow registration and permit rules

The Australian Pesticides and Veterinary Medicines Authority (APVMA) provide databases of the registered products, permits and residue limits.

All agricultural chemicals you use must be registered by the APVMA.

You must follow label instructions. These include:

  • withholding periods
  • crop protection instructions
  • pollinator protection
  • environmental protection
  • spray drift controls.

For more information on how to read and understand chemical labels see the APVMA Understanding pesticide chemical labels booklet.

Understand off-label use

Off-label use means using a registered chemical in a way not listed on the label. In Victoria, this is allowed in limited cases, but you must manage risks such as:

  • effectiveness
  • human health
  • residues in produce
  • environmental harm.

For more information visit Off-lable chemical use.

Manage chemical residues

Chemical residues are small amounts left on or in produce after treatment. They can occur from:

  • direct spraying
  • spray drift
  • chemicals in soil.

A maximum residue limit (MRL) is the highest allowed level in food or animal feed. Crops with residue concentrations below MRL are safe for sale. Note that off-label use may increase residue risks and export markets may have different levels of acceptable MRLs.

For more information see Managing chemical residues.

Follow withholding periods

Withholding periods set the time between spraying and harvest or grazing.

There are 2 types of withholding periods:

  • Harvest withholding period for crops
  • Grazing withholding period for livestock

Strict rules apply to the sale of crops, livestock or livestock products (meat, milk, eggs) if the withholding period has not passed.

For more information see Withholding periods.

Protect pollinators

Pollinators such as bees are essential for crop production and yields. Chemicals can harm them if used incorrectly.

You should:

  • follow label instructions for pollinator protection
  • notify neighbours before spraying
  • check for nearby hives
  • avoid spraying when bees are active.

For more information see Living in harmony: pesticides and bees.

Meet your responsibilities

Manage locust control safely by doing these:

  • Know when spraying is happening nearby.
  • Check which chemicals are used.
  • Follow withholding periods.
  • Follow all ‘do not’ label instructions.
  • Assess risks before choosing chemicals.
  • Read and follow all labels and permits.
  • Keep records of spray activities.
  • Confirm withholding periods before selling produce.
  • Notify neighbours before spraying.
  • Notify beekeepers so they can move hives.
  • Manage spray drift risks.
  • Seek advice if unsure.
Page last updated: 23 Jun 2026