Locust and grasshopper update and risk outlook for 2022
Recently there have been reports of immature Australian plague locust (APL hoppers) activity in northern areas of the WA grainbelt (see location list below).
- Southern Cross
There have been dense bands of APL hoppers reported either crossing roads or in patches in pasture paddocks and on crop edges.
Both APL hoppers and sand grasshoppers (Urnisa spp) are active in the Coorow area.
Recent substantial rainfall in the regions, combined with mild weather, is expected to increase the availability of green feed present along roadside verges and paddock edges. This will lead to the APL hoppers having sufficient food reserves to reach the next instar growth stage. If green feed remains, these hoppers are expected to reach the adult stage.
With crops being close to harvest, in many cases grasshoppers and/or locusts will not pose a risk to crops. Hoppers tend to be restricted to crop edges and do not enter dense thick crops.
Crops that are beginning to dry off when locusts begin to ﬂy are especially susceptible to damage. Later sown crops will be most at risk as these are more likely to coincide with adult APL.
Identification of APL hoppers
Immature grasshoppers/locusts, known as hoppers, can easily be confused with other grasshopper species. Some grasshopper species have different registered insecticides rates compared to APL so correct identification is important.
APL hoppers have a distinct X-shaped mark on their thorax, the bottom half of the X is more pronounced in younger instars. They also have three distinct bands on their femur and black knees. The side surface of their head and thorax is mottled and a dark red hind tabia.
Adult APL are between 24-40mm long. They vary in colour from light to dark shades of green to brown. Plague locusts have a dark blotch at the outer edge of the hind wing, and the inside of the hind legs are red in colour. Both adults and hoppers all have a distinctive cross on the thorax (that is, on their neck).
For more information to help you identify APL refer to DPIRD’s Australian plague locust: identification field guide page. .
Management in crops
For crops, hopper and adult locust numbers should be closely monitored and if any damage is seen then consider applying insecticides. Be mindful of harvest withholding periods if applying insecticides.
Management in pastures
For pastures, implement control measures if hopper densities exceed 20 per square metre, or there are more than 10 APL adults per square metre, and if the feeding value of pastures is equivalent to the cost of replacement feed for livestock.
Applying insecticide over entire paddocks may be necessary to prevent extensive damage from locusts. To achieve effective control, the best time to apply an insecticide is when locusts are hoppers.
Treating small areas of dense masses of hoppers immediately after hatching can also be worthwhile but will only control a relatively small proportion of the total numbers within a paddock and may involve several sprays as hatching times are staggered.
If locust swarms do form, they should be controlled when they first fly into an area where their feeding will cause damage. It is important that you are aware of the likelihood of locusts flying onto your property and to stay vigilant.
Sprays must be applied directly onto the locusts and the vegetation on which they are feeding. Barrier spraying to keep locusts out of an area is not effective. Pastures that tend to remain greener longer such as lucerne and long-season annual pastures are at greater risk of attack.
Adult locusts may fly into a paddock and although their stay may be short, they can still consume a considerable amount of pasture. If there are 25 or more locusts inflight this suggests high locust numbers. It may not be possible to effectively protect pasture in these situations, as locust swarms will need to be sprayed aerially within hours of them arriving. Monitor frequently from spring onwards, if large infestations are in your area.
For more insecticide information, visit DPIRD’s Australian plague locust control: registered insecticides.
Locust and grasshopper risk for 2022
The potential risk of APL to WA crops next year will depend on how much rainfall is received over summer.
If there is summer rainfall inspect paddocks in early autumn for grasshoppers and APL.
Managing summer weed hosts (green bridge) over summer will decrease the risk of APL and grasshoppers being present at seeding.
Only consider control measures if APL and grasshoppers will be present at the same time as summer crops or autumn crops crop germinate.
DPIRD will be conducting targeted surveillance this summer and will inform industry of risk of APL movement in autumn.
Please report any APL hatchings to the PestFax team by using DPIRD’s PestFax Reporter app.
More APL information can be found at DPIRD’s:
- 2021 PestFax Issue 14 article Australian plague locust: spring hatchings predicted
- Diagnosing locusts and grasshoppers in crops page
- Australian plague locust: overview page.
Previous APL activity reports received by the PestFax team this season can be viewed on the PestFax map or read in DPIRD’s:
- 2021 PestFax Issue 16 article Locust hatchings have started
- 2021 PestFax Issue 5 article Locusts are still on the move
- 2021 Issue 1 article Locusts can damage emerging crops.
For more information contact Research scientist Svetlana Micic, Albany on +61 (0)8 9892 8591.
Article author: Svetlana Micic (DPIRD Albany).