If establishing crops aren’t getting away from the burden of lucerne flea, there are a few considerations to be made before spraying.
Lucerne flea (Sminthurus viridis) population growth is very moisture dependent. The above average April rain received in much of Victoria and southern NSW has resulted in high infestations in pastures, canola and cereals crops.
Lucerne flea feed through a rasping process, leaving behind a thin clear layer of leaf membrane that appears as transparent ‘windows’ through the leaf. In severe infestations, this damage can skeletonise the leaf and stunt or kill plant seedlings.
Seed treatments registered against lucerne flea are one important tool preventing damage to crops during establishment when they are at their most vulnerable.
However, it is likely that the wet conditions have given lucerne flea a head start and seed dressings alone aren’t effectively combating the pest in all paddocks.
If chemical control is necessary, consider the following questions:
Does the infestation warrant a blanket spray?
A border spray may be sufficient to prevent movement into crops from neighbouring paddocks.
Lucerne fleas are generally patchily distributed within crops, so spot spraying may be sufficient.
In addition to saving on chemical costs, this approach limits the impact of insecticides on beneficial invertebrates (particularly predatory mites which are predators of lucerne flea) and reduces the selection for insecticide resistance building up in crop pests.
Are you also spraying for redlegged earth mites?
When both lucerne fleas and redlegged earth mites are present, it is recommended that control strategies consider both pests, and a product registered for both is used at the highest directed rate between the two to ensure effective control.
Remember, lucerne fleas have a high natural tolerance to all synthetic pyrethroids and should not be treated with insecticides from this chemical class.
When did lucerne flea first emerge?
If the damage warrants control, treat the infested area with an insecticide three weeks after lucerne fleas first emerge in autumn.
This will allow for the further hatching of over-summering eggs but will be before they reach maturity and begin to lay winter eggs.
Where there is a consistent pattern of lucerne flea damage in autumn/early winter, spray four weeks after the first significant rain of the season.
For more information on lucerne flea, including their occurrence, lifecycle, behaviour and management strategies, visit lucerne flea with our PestNote series.
Sources of field reports
James Challis – Rodwells (Northern Country, VIC)
David Eksteen – Eksteen Consulting (North East, VIC)
Hayden Lunn – Landmark (Riverina, NSW)
Greg Toomey – Landmark (Northern Country, VIC)
Kate Wilson – AGRIvision (Mallee, VIC)