Lucerne flea

There have been several reports of lucerne flea (Sminthurus viridis) hatchings in parts of Victoria and southern New South Wales. Researcher, John Roberts (cesar), reports finding lucerne flea nymphs in several pasture paddocks around Colac, in the Western district of Victoria. Agronomist, Greg Parker (Mangoplah Farm Centre), has found lucerne flea in two paddocks of established lucerne south of Wagga Wagga, in the South West Slopes district of New South Wales. To date, there has been little feeding damage observed but the paddocks will be closely monitored. Agronomist, John Jervois (Tarcutta Rural Supplies), has also reported lucerne flea hatchings near Tarcutta, in the South West Slopes of New South Wales. Most hatchings have occurred in low-lying areas within newly emerging pastures and older established lucerne stands. John says some paddocks are likely to need some control to protect young seedlings.

Lucerne fleas hatch following periods of good soaking autumn-winter rainfall and can cause significant damage to emerging crops and pastures at this time of year. They can also cause considerable damage to older crops if numbers build up under favourable conditions throughout the season. With the lack of recent rainfall experienced across much of south-eastern Australia, lucerne flea hatchings may be delayed and somewhat staggered in many regions.

Adult lucerne fleas are approximately 3 mm long and appear yellow-green to the naked eye, although their globular abdomens are often a mottled pattern of darker pigments. They ‘spring off’ vegetation when disturbed. Lucerne fleas have a wide host range and will attack most broad-acre crops, including canola, lucerne, pastures, cereals and some pulses. Feeding results in the appearance of distinctive transparent ‘windows’. They are generally a problem in regions with loam/clay soils. Click here for images of the lucerne flea.

Crops should be inspected frequently at and immediately following emergence, when they are most susceptible to damage. Paddocks are most likely to have problems where they follow a weed infested crop or a pasture in which the lucerne flea has not been controlled. There are several options available to growers for controlling the lucerne flea. Foliar insecticides can be applied approximately three weeks after lucerne fleas have been observed in a newly emerged crop. This will allow for further hatching of over-summering eggs but will be before lucerne flea reach the adult stage and begin to lay winter eggs. If spraying is required, do not use synthetic pyrethroids.

In paddocks where damage is likely, a border spray may be sufficient to prevent movement of lucerne fleas into the crop from neighbouring paddocks. As lucerne fleas are often distributed patchily within crops, spot spraying is generally all that is required; do not blanket spray unless the infestation warrants it. Snout mites (which have orange bodies and legs) are effective predators of lucerne fleas, particularly in pastures, where they can prevent pest outbreaks. The complex of beneficial species (including snout mites) should be assessed before deciding on control options.