WestVic Dairy News - October 2010 Edition
The current situation
Victoria is facing what could potentially be the biggest locust plague for 75 years. During April this year adult locust population levels increased in northern Victoria, with migrations from New South Wales and within Victoria. Dense swarms and egg-laying activity occurred in the Swan Hill, Mallee and Wimmera districts of the Northwest, along the Murray River and in areas around Bendigo and Shepparton. Swarms were also reported as far south as Horsham.
Locust eggs now hatching
Large numbers of locust eggs have hatched from late September and early October, beginning in far northwest Victoria and progressively moving south. Additional locust swarms could also migrate into Victoria from northern New South Wales, southwest Queensland and South Australia.
Warm, moist weather conditions are the most favourable for locust egg hatchings. Locusts are hard to spot when they first emerge as young immature locusts (called 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.
Hoppers, which are wingless and unable to fly, 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.
Treatment of the hoppers is needed in spring to prevent another egg laying period in December and January 2011. Based on spring weather forecasts, it is expected the vast majority of hatching locusts will survive and grow into adults unless chemical treatment is undertaken.
Appearance
The locust is similar in appearance to grasshoppers. It can be identified by the large dark spot on the tip of the hind wings and the distinctive red shanks on the hind leg. The body colour varies; it can be grey, brown or green. Male locusts are 25-30 mm long while females are 30-42 mm long.
Immature plague locusts are referred to as hoppers or nymphs. Their wings are not fully developed and the red colour of the hindleg shanks is less developed than in adults. This makes it hard to distinguish them from immature stages of other locusts and grasshoppers.
Picture: Plague locust adult showing the black spot on the hind wing (source Plague Locust Commission)
The Australian Plague Locust is a native Australian insect. It occurs naturally in the far north west of New South Wales and adjacent areas of Queensland and South Australia, an area known as the channel country. The eggs of the locust are laid in the ground at depths of up to 8cm. They hatch into very small “hoppers” which can move short distances but which cannot fly.
Like all insects, the locust develops through discrete stages called instars until it becomes adult. Only the adult can fly. When the locust is present in small numbers it behaves as a solitary insect and causes little or no damage, feeding primarily on summer grasses. When numbers increase, it can become gregarious and form very dense bands of hoppers or swarms of adults.
Migration
Migratory flights of up to 700 km occur only at night, generally on strong warm winds associated with fronts or low pressure systems. Mass take-off after sunset usually only occurs when the surface temperature is above 25°C. The locusts can fly at heights of up to 3000m. Migration flight is usually, but not exclusively, to the south or south east. Migration flight causes locusts, in very large numbers, to appear literally overnight in locations that were previously free from locusts. Migration is important both in the origin of outbreaks, and often in their collapse as it does not necessarily lead to locusts arriving in areas (where there is rainfall) suitable for successful breeding. There are reports that locust swarms have overshot continental Australia and drowned in Bass Strait.
What crops are at risk?
Victorian dairy farmers need to be vigilant in monitoring their pastures, fodder crops, and known locust egg beds for evidence of activity and crop damage. Pastures and fodder crops are potentially at high risk from locust attack. While locusts prefer to feed on tender, green vegetation, experience shows that they are still capable of causing extensive damage to pastures and crops.
Locusts are ravenous feeders of fresh, green vegetation. Green pasture and fodder crops are highly susceptible to locust attack. Newly sown grass pastures are particularly vulnerable, as are the shorter pasture species. Young annual legumes may also be attacked. When locusts are present in massive numbers, all pasture and fodder crops are at risk.
Lucerne is typically green for longer than other crops, making it a prime feeding target. Damage is generally restricted to the stripping of leaves, but this may not always be the case. Established lucerne pastures (up to the 5th trifoliate leaf stage) may be less susceptible if paddocks have green grass weeds or there are alternative crops nearby.
What are dairy farmers’ treatment options?
Chemical application is the most effective method of treating locusts. There are a number of products eligible under the Victorian Government's Locust Insecticide Rebate Scheme. Dairy farmers should seek expert advice from their chemical reseller or agronomist as to which chemical best suits their situation.
The factsheet Locust Chemicals for Pastures and Fodder Crops lists the chemical products suitable for pastures and fodder crops and eligible for the Victorian Government's Locust Insecticide Rebate. Chemicals should only be used according to the label directions. All restraint and ‘DO NOT’ statements, WHPs and export intervals (EI’s) 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 pasture or fodder crop damage.
When should dairy farmers 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.
At this stage the locusts, then known as hoppers, are wingless and form large, slow moving bands, providing 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 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.
Diagram of a locust life cycle. (source DPI)
What are my obligations?
Livestock producers in Victoria need to be vigilant in monitoring their pastures, fodder crops and known locust egg beds for evidence of activity and crop damage.
The Australian Plague Locust has been declared an exotic pest under the Plant Health and Plant Products Act 1995, and this declaration places two important obligations on all land managers. All land managers must notify DPI of the presence of locust activity on their land. Notifications can be made by calling the DPI Locust Hotline on 1300 135 559.
All land managers must treat locust hoppers on their land when numbers reach or exceed 80 locust hoppers per square metre. This must be completed before locusts grow wings and are able to fly. Failure to notify or treat locusts is a breach under the legislation.
All chemical use must be in accordance with State laws and regulations, including record keeping requirements. For information, visit the DPI Chemical Standards website at www.dpi.vic.gov.au/chemicalstandards
Information on the locust situation and locust biology and management can be found at www.dpi.vic.gov.au/locusts
Report locust hatchings or contact the DPI Locust Hotline on 1300 13 5559
