Lucerne flea

Conditions this autumn and winter have suited lucerne flea, possibly allowing an additional generation and perceived spray difficulties

Lucerne flea adult (Source: cesar)

 

Where have they been reported?

Reports of lucerne flea damage have been coming from across Victoria (South West, Wimmera, Mallee and Northern Country) and the Central West Slopes & Plains and Riverina districts of NSW since mid May, and are now becoming all the more frequent. Numerous crops have reportedly suffered high levels of lucerne flea damage including barley, beans, canola, lucerne, lupins, oats and pasture. In most instances, obvious patches of lucerne flea damage have been observed within paddocks, which is characteristic of this pest. This makes it relatively easy to spot spray.

Of concern, two growers in the Victorian Northern Country and NSW Central West Slopes & Plains have experienced difficulties or failures in controlling lucerne flea using organophosphate (OP) insecticides, seeing large numbers approximately 3-4 weeks post-spray. ** See below for our advice.

About lucerne flea

Lucerne fleas (Sminthurus viridis) 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 leaving transparent ‘windows’, whereas adults and older nymphs rasp and chew irregular holes in leaves and can completely defoliate plants.

For more comprehensive information on lucerne flea, including their occurrence, lifecycle, behaviour and management strategies, go to lucerne flea within the new PestNote series.

Our advice

Lucerne fleas are naturally tolerant to synthetic pyrethroids, so avoid these when choosing an insecticide. As yet, there have been no confirmed cases of insecticide resistance in lucerne flea, although resistance development is always a possibility.

In the above cases where OP insecticides were thought to have failed, one explanation is that the spray was applied after the females of the first generation laid eggs, but before these had hatched. In this case, the elapsed time between spraying and rechecking (3-4 weeks) may have allowed time for egg hatch (about 2 weeks) and some growth of the second generation. Insecticides will not affect eggs.

From this experience we recommend:

• monitor early, and where the pest populations are above threshold, spray before the first generation adults mature and lay eggs;
• use omethoate rather than dimethoate because of its greater residual activity and hence ability to control emerging second generation nymphs;
• check within 2 weeks of spraying, and
• advise us if you suspect resistance.

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.

To avoid populations building up in subsequent years, consider grazing with livestock. Control broadleaf weeds (e.g. capeweed) that are favoured by lucerne flea.

 

Sources of field reports of lucerne flea

Matthew Bissett – Consultant, AGRIvision Consultants (Victorian Mallee)

Chris Dunn – Agronomist, Landmark (Victoria’s Northern Country)

Matthew Gready – Agronomist, Lipp’s Bulk Super (Victoria’s Northern Country)

Simon Mock – Consultant (Victorian Wimmera)

Craig Muir – Agronomist, AGRIvision Consultants (Victoria’s Northern Country)

Dr Michael Nash – Researcher, SARDI (Adelaide)

Phil Stoddart – Consultant, Stoddart Agriculture (NSW Central Tablelands)

Elissa Strong – Agronomist, Delta Ag (NSW Riverina)