New generations of lucerne flea can reinvade crops after spraying.
It’s been a big year for lucerne flea.
We have received numerous reports of extensive damage in establishing crops in the Victorian Mallee, Wimmera and Northern Country, and the NSW Riverina and Central West Slopes and Plains.
Some crops have gotten away from the damage inflicted by lucerne flea earlier in the season, but reports of concerning numbers in some paddocks continue to arise.
Lucerne flea population growth is highly moisture dependent. It is likely that the above average April rainfall received across much of Victoria and southern NSW gave the pest a great kick start to the year.
While there are no known insecticide resistance issues surrounding lucerne flea, the pest is not immune from control challenges.
This season, there have been many cases of growers applying multiple chemical sprays to control lucerne flea in canola, cereal and pulse crops. While the first sprays have been effective, numbers have often bounced back to damaging levels, as early as 10-14 days later.
Lucerne flea can have up to six generations per year between autumn and spring. The first generation often hatches from over-summering eggs in March-April after soaking autumn rainfall. Staggered egg hatching means that generations can overlap and newer generations can ‘reinvade’ if there are enough eggs that have not hatched prior to spraying.
If chemical control is necessary, consider if the infestation warrants a blanket spray.
Lucerne fleas are generally patchily distributed within crops, so spot or border 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 other crop pests.
If only targeting lucerne flea, there is no benefit applying insecticide mixtures or co-formulations.
Bruce Adriaans – Landmark (Mallee, VIC)
Ben Brennan – AGRIvision (Mallee, VIC)
Heath Griffiths – Landmark (Mallee, VIC)
Rob Launder – PB Seeds (Wimmera, VIC)
Hayden Lunn – Landmark (Riverina, NSW)
Jamie Pursehouse – Landmark (Central West Slopes & Plains, NSW)
Angus Skinner – Landmark (Mallee, VIC)
Andrew Slater – Grower (Wimmera, VIC)
Greg Toomey – Landmark (Northern Country, VIC)