PestFacts south-eastern Conditions this autumn have already resulted in extensive outbreaks of lucerne flea in canola and cereals in many areas.
Where have they been reported?
Lucerne flea (Sminthurus viridis) damage has been reported from southern NSW and northern Victoria.
Lucerne flea has attacked many paddocks of emerging canola and wheat in the NSW Riverina, north of Echuca. Many crops have already been sprayed and parts of canola paddocks needed resowing.
Lucerne fleas have caused damage to a canola crop north of Albury at Walbundrie, where an imidacloprid seed dressing failed to control the insects.
In the Lockhart area of the Riverina, lucerne fleas have damaged canola drilled into an old pasture on heavy soils.
Josh Douglas, a researcher from the University of Melbourne, observes that some growers in this region have come to regard lucerne flea as their most intractable emergence pest over the past several years.
To the south in Victoria’s Northern Country, emerging canola crops near Rochester and Colbinabbin are beginning to experience damage from both nymphs and adult lucerne flea. Typically, damage is often patchy and sometimes severe.
Further west in the southern Mallee, lucerne flea damage has been reported on cereals near Boort and on barley seedlings (3-4 weeks growth) north of Lake Hindmarsh. In a canola crop north of Warracknabeal in the Victorian Wimmera, lucerne flea was observed on seedling canola, but they did not appear to be very active.
About lucerne flea
Lucerne fleas lay eggs in the soil and, depending on temperature and moisture availability, typically have 2-4 generations between autumn and spring. One or two generations occur in the autumn-early winter phase, depending on the timing of the autumn break.
High numbers of lucerne flea are often associated with clay (or heavy) soils that retain moisture and aid egg survival. The growth rate of lucerne flea populations is highly moisture dependent; they do well in moist conditions or under dense canopies of pasture or crop.
Young nymphs feed on the soft tissue on the underside of leaves, resulting in transparent ‘windows’. Adults and older nymphs rasp and chew irregular holes in leaves and can completely defoliate plants.
Our advice
Lucerne fleas are naturally tolerant to synthetic pyrethroids, so avoid these if choosing an insecticide. Spot spraying is often all that is required because lucerne fleas are commonly distributed patchily within crops. Do not blanket spray unless the infestation warrants it.
For more comprehensive information on lucerne flea, including their occurrence, lifecycle, behaviour and management strategies, go to lucerne flea within the new PestNote series.
Acknowledgements
Sources of field reports of lucerne flea
Daniel Andrews – Agronomist, Rodwells (Victorian Northern Country)
Matt Bissett – Consultant, AGRIvision (Victorian Mallee)
Josh Douglas – Researcher, The University of Melbourne (Melbourne)
David Eksteen – Agricultural consultant, Eksteen Consulting (North East Victoria)
Warwick Nightingale – Agronomist, Delta Ag (NSW Riverina)
Rick Rundell-Gordon – Senior consultant, all-AG Consulting and Tech Services (Victorian Mallee)
Greg Toomey – Senior agronomist, Landmark (Victorian Northern Country)
Tyler Nelson (@Nel_farms)
Cover image: Photo by Andrew Weeks, Cesar Australia
