Lucerne flea and other collembolan

Research Consultant, Samantha Strano (cesar), has reported high numbers of lucerne flea (Sminthurus viridis) in several paddocks around Colac, in the Western district of Victoria. Samantha says lucerne fleas are attacking established lucerne stands. Hatchings of lucerne flea have also been observed around Shepparton, in the Northern Country 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.

Adult lucerne fleas are approximately 3 mm in length and appear yellow-green to the naked eye, although their globular abdomens are often a mottled pattern of darker pigments. Lucerne fleas are ‘collembola’ and spring-off vegetation when disturbed. They 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’.

Lucerne fleas are generally a problem in regions with loam/clay soils. Paddocks are most likely to have problems where they follow a weed infested crop or a pasture in which lucerne flea has not been controlled. There are several options to control lucerne flea. Foliar insecticides can be applied approximately three weeks after lucerne flea have first been observed. 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.

In addition to lucerne flea, there have been several reports of small insects that have been found in canola crops in some regions. These may be a different species of collembolan also favoured by wet autumn conditions. A collembolan species has been found by Research Agronomist, Simon Craig (BCG), who observed them in a canola paddock near Birchip, in the Mallee district of Victoria. Agronomist, Bob Ronald (Landmark), has reported small insects that have caused some damage to about 100 acres of canola near Albury, in the South West Slopes district of New South Wales. Agronomist, Allan Edis (Landmark), has found similar insects in a paddock near Temora, also in the South West Slopes district. They have been observed in the crown of canola seedlings at the 3-5 leaf stage.

Although unconfirmed, these insects could be the collembolan Entmobrya unostrigata, which can be problematic on rare occasions. Researcher, John Roberts (CSIRO), says this species belongs to the Family Entomobryidae and is known to be an occasional pest of field crops and pastures. It is a slender insect, approximately 2-3 mm long when adults.  They have long antennae, and prominent hairs. It is unclear whether insecticides are effective against this species.