Lucerne flea

Researcher, John Roberts (cesar), reports finding lucerne flea (Sminthurus viridis) nymphs in several pasture paddocks around Colac, in the Western district of Victoria. Lucerne flea 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. John says judging by their size, the lucerne fleas appear to have hatched quite recently and have not yet built up to numbers where significant damage is evident. With the recent rainfall experienced across much of south-eastern Australia, lucerne flea are now likely to also be hatching in other regions. They are generally a problem in regions with loam/clay soils.

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’. Click here for images of the lucerne flea.

There are several options available to growers for controlling lucerne flea in crops and pastures.

Foliar insecticides should ideally be applied approximately three weeks after lucerne flea 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 flea are often distributed patchily within crops, spot spraying is generally all that is required; do not blanket spray unless the infestation warrants it.

Cultural control techniques such as clean fallowing and effective weed management within crops and around perimeters, especially of capeweed, can help to reduce lucerne flea numbers. In paddocks which have a history of lucerne flea damage it is best to avoid sowing highly susceptible crops such as lucerne and canola. Crops are more likely to have problems where they follow a weed infested crop or pasture in which lucerne flea have not been controlled.