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Michael McManus, Ken Henry, John Hannay, Michael Wurst

The locust problem

During April and May 2010 adult locusts migrated into the north of South Australia, eastern Eyre Peninsula, the Mallee and the Riverland from southwest Queensland and northwest New South  Wales. These adults were in search of green feed to continue their development and may deposit overwintering eggs in suitable areas in these regions during the autumn. These eggs will hatch in the spring (late September – early October).

In spring 2010, it is likely that hopper bands will be seen in proximity to grain crops and pastures. Grain crops and pastures in these areas are at risk from hopper bands from local egg beds deposited by the autumnal incursions of adult insects and possibly new adult locusts flying in from northern pastoral areas later in spring. The extent of these adult invasions and the damage they will cause are impossible to predict. Locust movements are dependent on prevailing weather, particularly northerly winds.

To help prevent damage, regular monitoring of susceptible crops should be undertaken as hoppers and adults have the ability to move many hundreds of metres a day.

Controlling locusts with insecticides may be necessary to protect crops and pastures, but needs to be carefully considered along with other crop management options available for minimising the risk of damage.

Much of SA's grain produce is exported as "pesticide-free". Individual deliveries of grain will be tested for chemical residues, to detect the use of unapproved pesticides and to ensure that withholding periods have been followed, so that the standards demanded by export markets continue to be met.

Physical contamination of grain with locust bodies and body parts must also be managed at harvest time to ensure grain receival standards are met.

The locust lifecycle

The lifecycle of the locust is explained in detail in the Fact Sheet No. 11/79/00/10 "Australian Plague Locusts" and copies are available from the PIRSA website www.pir.sa.gov.au/locust and district offices.

Locust behaviour

Locust behaviour should be observed when making decisions on management. The stage of the crop needs to be taken into consideration as a near-ripe crop may not suffer significant damage and late sprays may breach harvest withholding periods for the insecticide applied.

Locusts can display the following behaviour:
• Hopper bands form 2 to 3 weeks after hatching, mainly along fence lines, road verges, scrub lines, pasture paddocks and, in some instances, crops.
• Hopper bands are likely to move into crops from around the edges. Late instar hoppers can move up to 400 metres in a day.
• Adults are active during warm semi-calm (some breeze) conditions, and settle in cold or windy conditions.
• Adults feed actively on green or partially green crop which can cause significant economic damage.
• Mature crops are less attractive to adult locusts unless green weed growth is present.
• Adults usually settle at night and do not feed.

Management of locusts in grain crops

The decision on how locusts in crops are best managed is affected by a range of factors including:
• Growth stage of the crop (i.e. whether any green plant material remains or whether the crop has completely dried off).
• Ability to harvest early.
• Risk to market from pesticide residues.
• Ability to clean physical locust contamination from harvested grain.

Hoppers are most likely to hatch in pasture paddocks and along roadsides, fence-lines and the non-cultivated ground around the crop perimeter, but some hoppers may hatch from egg beds laid within crops.

Monitoring

As hopper bands form, landowners should regularly monitor pasture paddocks and crops. Monitoring should include crop edges, fence lines and roads, where bands are likely to first occur.

Susceptible crops should be monitored when adults first appear. Adult densities as low as four per square metre may cause economic damage.

Protecting grain markets

Some export grain markets, particularly canola, malting barley and feed barley, have a very low or nil tolerance to insecticide residues. Chemical residue contamination must be avoided by using only registered and permitted insecticides for locust control. Withholding periods and label instructions for these insecticides must be followed at all times.

Management options

The following sections provide information on risks and management options for grain crops. Consider the use of a range of options including non-chemical management to minimise locust damage.

Windrowing

Consider windrowing a portion of crop to hasten even maturity and lessen risk of locust damage. Most cereal, canola and pulse crops can be windrowed successfully.

Risk management and insecticide control

Assess how much of the cropping program and individual crops are at risk. Crops that have completely dried off are not at risk.

Take into account the cost of crop damage from wheel tracks when using a boomspray versus application by a mister or aircraft.

As a general rule, immediate action will be required once crop damage from hoppers and adult locusts is seen.

No insecticides are effective repellents. It is not possible to spray prior to a swarm arriving to prevent the locusts entering a crop.

Spray adults while they are settled in the early morning or late evening. Hoppers may be sprayed as long as the prevailing wind conditions are suitable, ensuring the spray hits the hopper band target.

Cereals

Cereal crops are likely to be more susceptible to damage than other crops. Crops most at risk are those containing green plant matter. Hoppers prefer thinner green crops while dense wellgrown crops tend to be avoided, although the edges of crops can be damaged.

Flying adult locust swarms can directly enter a green crop at any point and begin feeding. As cereal crops ripen, locusts may continue to cause serious crop damage from head lopping, as locusts chew through the last green tissue (node) on the stem just below the head.

Where crops have dried off and no green plant material remains, damage from locusts feeding on the dried crop is unlikely and insecticide control is unnecessary.

Physical contamination from locust bodies or body parts needs to be considered at the time of harvest. Standards allow for up to three whole locust bodies or the equivalent in locust body parts in a half litre grain sample.

Management options at harvest time include selecting paddocks with low locust numbers and delaying harvest for a couple of days where locust numbers are high. This should allow time for locusts to move out of the crop. Cleaning locust-contaminated grain may be necessary to meet receival standards.

Pulses

Pulses are susceptible to attack while they remain green. The susceptibility of pulse crops that are drying off is not known.

Early harvesting of pulse crops should be considered given that industry standards now allow a maximum moisture receival limit at 14%. This may be a useful management option to minimise physical contamination of locusts in harvested grain.

Crop desiccation (1.5 to 3 L/ha diquat, e.g. Reglone®) and crop topping (400 to 800 mL/ha paraquat (250 g/L formulation)) can hasten crop maturity and allow more even ripening of crops which will permit earlier harvesting. This approach is also a useful management tool to reduce weed seed set.

Acceptable receival standards for the pulse industry allow a maximum of 30 dead or live field insects (including locusts) per 400 gram sample or pro-rata for a 200 gram sample.

Canola

In most districts it is anticipated that canola crops will have been windrowed prior to locust swarms flying in.

Physical grain contamination by locusts present at time of harvest is of concern. Canola harvesters should be set up to minimise foreign material contamination, including locusts or locust parts.

The receival standard for large field insects including locusts is a maximum of 10 per half litre. Where locust numbers are high, delaying harvest for a couple of days may allow locusts to move out of the windrowed crop.

Management of locusts in pastures

Hoppers and adult locusts can cause serious damage to pastures. It is estimated that 20 hoppers per square metre eat the equivalent of three to five dry sheep per day.

Green and drying pastures are very susceptible to hopper attack. Pastures that have completely dried off are not preferred.

Adult locusts may fly into a paddock and, although their stay may be short, they can still consume a large amount of pasture. It may not be possible to protect these pastures effectively in these situations. Damage to pastures by locusts will affect both the quantity and quality of pasture.

Perennial pastures such as lucerne, long season annual pastures and newly sown pastures are at greater risk of attack later in the season, since they tend to remain green longer. Summeractive perennial pastures will remain susceptible to attacks for an extended period. Growers need to identify high-value pasture paddocks for special emphasis on control measures.

Degradation to pastures caused by locusts may subsequently result in erosion in susceptible paddocks, thereby reducing grazing capacity.

Treatment of locust swarms will need to be within hours of their arrival and the subsequent onset of visual damage, which means frequent monitoring from early November onwards.

Withholding periods for livestock grazing and slaughter must be observed at all times following insecticide application.

Management options

The following management factors should be considered in decision making.

• Hopper control in pastures is economic if hopper densities (2nd to 5th instar) exceed 20 per square metre (pasture valued at replacement feed cost).
• Adult locust control in pastures is economic if locust densities exceed 10 per square metre.
• Pasture availability - whether there is a surplus or deficit.
• Insecticide application costs and method.
• Observe the withholding period in sprayed paddocks.

• Avoid over-spraying of stock, including wildlife.
• Consider spray-topping or hay-freezing pasture paddocks.
• Consider grazing or spraying established lucerne or other perennial pastures prior to locust attack.

Farmers with stock should develop strategies to cope with reduced dry feed availability. Previous experience suggests producers should plan for the worst case scenario. Strategies to consider include reducing carrying capacity by selling stock or seeking agistment, and supplementary feeding with hay and grain. Other strategies include feed budgeting and lotfeeding.

Grazing stubbles and residues in livestock

Livestock grazing stubbles or failed crops treated with insecticides are also at risk from chemical residues. Export livestock markets are very sensitive to chemical residues and testing of livestock for chemical residues will be occurring. Check withholding periods for livestock from treated crops, to prevent putting export livestock markets at risk.

Insecticides

Where insecticides are necessary to control locusts, a range of registered and permitted products are available for use on grain crops and pastures. Further information regarding the most suitable insecticide for use in your situation, and updates on available products, may be obtained from your local chemical reseller, private consultants, grain representatives, the PIRSA website or PIRSA Offices.

Consider the following factors when assessing insecticide options for control:

• Select registered or permitted insecticides for locust control on your crop. (Do not use unregistered or non-permitted products, as this may put export markets at risk from chemical residues).
• Read the label and all instructions before you buy and before you apply.
• Markets may have a very low or nil tolerance to insecticide residues.
• Check for off-target impacts, including near-by livestock, bees, aquaculture, organic production, dams and waterways.
• Check all withholding periods carefully (harvest and grazing) as they vary between products.
• Insecticides are not effective repellents. It is not possible to spray prior to a swarm arriving to prevent the locusts entering a crop.
• If in doubt, ask for assistance.

Which insecticides to use

Insecticides that may be used for locust control include those registered for use on the crop for locust control or has a permit for locust control in that crop. The insecticides that are currently registered for locust control are:
• Carbaryl
• Chlorpyrifos
• Diazinon
• Fenitrothion
• Fipronil
• Maldison
Each of these active constituents is available under various product names. All label directions must be followed.

Numerous insecticides fall into the category of being registered for use on a particular crop but are not registered for locusts. Active constituents that previously had APVMA permits (now expired) for locust control include:
• Alpha-cypermethrin
• Beta-cyfluthrin
• Cypermethrin
• Deltamethrin
• Esfenvalerate
• Lambda-cyhalothrin

Use of these insecticides, or others in the same category, for locust control in SA is allowed if they are registered for the crop in question in SA or another Australian State. The maximum application rate and frequency of application for the crop must not be exceeded. Be aware of any ramifications to your quality assurance programs and other market requirements.

Table 1: Approximate residual life of insecticidal activity for locusts

Active constituent	Approximate residual life of affect locusts*	Remarks
Carbaryl	2-3 days	Can leave a surface residue that may affect markets for some crops, particularly ornamentals
Chlorpyrifos	1-2 days	Higher rate most effective and also a higher potential hazard for off target organisms
Diazinon	2-3 days
Fenitrothion	2-3 days	kills mostly by direct contact, less on residual activity
Fipronil	7-10 days	Takes longer to kill, has good residual effect
Maldison	1-2 days	Fast knockdown and short residual activity

*Source from Australian Plague Locust Commission

Spraying

Insecticides can be applied to locusts by boomspray, aircraft or mister, with different methods better suiting different circumstances.

In addition consider:
• Limiting swath width of misters to 50 metres.
• Maximum benefit is gained from treating hoppers.
• Spray when hopper bands begin to appear (2nd -3rd instar) including spot spraying bands along crop edges before they enter crops.
• Effective control of late instar hoppers can be achieved, but the area sprayed will be much larger as these hoppers are more active.
• Adults should be treated when they are settled by spraying early in the morning or at dusk, rather than attempting to control flying swarms.
• Spray when there is a steady breeze. Still conditions or gusty variable winds are not suitable for spraying.
• Spray only where locusts are present

All insecticide applications should be directed at the target locust band or swarm. Consider any off-target impacts, particularly of drift onto water courses, dams and neighbouring aquaculture, organic and livestock operations. In many cases, spraying fence lines, roadways and non-crop areas may provide sufficient control depending on actual distribution of locusts.

Bees

Most insecticides are toxic to bees. Consult your apiarists prior to spraying. Avoid praying flowering crops if possible. Late afternoon spraying is less likely to harm bees.

Aquaculture

Most insecticides are toxic to crustaceans such as yabbies and marron and may possibly affect the health of fish.

Any dam or tank containing crustaceans or fin fish may be at risk from insecticde spraying to combat locusts. Consult your neighbouring aquaculturalists prior to spraying.

Organic control

Green Guard is a biological control agent that can be used to control hoppers. It takes around two weeks from application for the fungus to kill the infected hoppers, so crop damage may continue for some time after application. There are no quick-acting organic control methods for organic growers.

Additional information

Additional and updated information on Australian Plague Locusts is available on the PIRSA website www.pir.sa.gov.au. This includes fact sheets, updates on all insecticides, locust movements, control programs, media releases and other information links. For more specific insecticide information, ask your local chemical reseller or consultant.

Last update: April 2010

Agdex: 622

Author:
Michael McManus, Farm Chemicals Program, Ken Henry, Entomology Unit, John Hannay, Biosecurity, Plant Health Policy and Michael Wurst, Rural Solutions Consultant.

Updated by David Lewis, Manager, Grains Industry Development.

Disclaimer

Use of the information in this Fact Sheets is at your own risk. The Department of Primary Industries and Resouces and its employees do not warrant or make any representation regarding the use, or results of the use, of the information contained herein in terms of its suitability, correctness, accuracy, reliability, currency or otherwise. The entire risk of the implementation of the information which has been provided to you is assumed by you. All liability or responsibility to any person using the information is expressly disclaimed by the Department of Primary Industries and its employees.