Red legged earth mite and Lucerne flea monitoring
Cooler weather and wet conditions are a breeding ground for pests in crops and pastures.
In South Australia’s mid-north, the Red legged earth mite (RLEM) and Lucerne flea are proving particularly bothersome. Elders Jamestown graduate agronomist Zoe Fulton discusses the two pests and what you can do about them.
Red legged earth mites (RLEM)
RLEM are a common pest found right across the Australian wheat belt. In Southern Australia they can be active from autumn through to spring depending on environmental conditions.
Summer-laid eggs tend to hatch once there is substantial rainfall and daily temperatures consistently sit below 21°C.
With the late start to the season in South Australia, RLEM were not observed until early winter this year.
RLEM are approximately 1 millimetre in length with an oval shaped black body. They are easily identified by their namesake eight orange-red coloured legs. You’ll typically find RLEMs in packs of approximately 30 on the leaf surface, stem and ground around the plant. Any plant can be a host to RLEMs, including weeds.
RLEMs damage appears as silvering discoloration of the leaves, and in severe infestations, leaves will shrivel.
High RLEM populations early on can also cause seedlings to die at emergence.
Care needs to be taken in damage identification as RLEM symptoms can look very similar to hail damage.
Monitoring for Red legged earth mite
RLEMs can be expected where it is cold and wet. You are best to monitor in the morning or on overcasts days as this is when RLEMs are most active.
Look at the leaves of the plant first, and if mites cannot be spotted, move to observing the soil surface as RLEMs will be sheltering in leaf sheaths and under soil debris when conditions are warmer. Observing the same few plants or patch of ground for 10-15 seconds should be enough time to spot mites moving around if they are present.
A garden blower with a fine sieve covering the suction pipe is also an effective method to find RLEM. RLEM move in from weeds on the fence line and are usually found spread across whole paddocks as opposed to in patches.
Much like the RLEM, Lucerne flea is also a common pest found right across the Australian wheat belt. They are more problematic on loam/clay soils but can cause issues elsewhere.
Higher numbers are found in the winter rainfall zones of Southern Australia. Lucerne flea require moisture for eggs to hatch and will die when conditions become warm and dry, so you can expect to see population from autumn to spring.
Despite being called a flea, the Lucerne flea is a springtail. Springtails are characterised by having six or fewer body segments with a furcula under their abdomen that allows them the ‘hop,’ hence receiving the name flea.
The Lucerne flea is approximately three millimetres in length and light green in colour. The arthropod will also often have mottled patches of brown on the back of its large globular abdomen and head.
Lucerne fleas work in patches and can be found on both the plant and the ground. They will target all crops and pastures, but broadleaf plants are particularly susceptible to attack. Like RLEMs, weeds can also play host to Lucerne flea.
Lucerne flea damage appears as ‘windows’ in the leaf tissue due to the rasping process by which they feed. In severe infestations, the Lucerne flea can consume all the plant tissue which can stunt or kill plant seedlings.
Monitoring for Lucerne flea
You should start monitoring for Lucerne flea at the emergence of crop or pasture, when the plants are most susceptible to damage. Plants should be checked every two weeks however where there is Lucerne flea history, monitoring should occur more frequently.
Lucerne flea work in localised patches and therefore careful monitoring of the entire paddock is required to ensure no potential sites of infestation are missed. Sighting of the Lucerne flea itself can be made by swiping your hand over the crop and watching for the jumping of the arthropod as it reacts to the movement. A garden blower with a fine sieve covering the suction pipe is also an effective method to find them.
Threshold and Control
Depending on the crop, there is a different economic threshold for RLEM.
In canola, the threshold differs depending on the crop stage. At first true leaf stage, 10 mites per plant warrants treatment. At second true leaf stage, treatment is only warranted if there is less than 30 plants/m2 and mites present, or if majority of plants show visual symptoms when there are more than 30 plants/m2.
Once that plants are beyond third leaf stage, there is no benefit in spraying unless the plants are under severe stress. In wheat, barley and pulses, 50 mites per 100cm2 is considered the threshold to act.
The Lucerne flea economic threshold is determined by the level of damage. A guide of 20 small holes per trifoliate on a legume leaf will warrant action.
Chemical control is considered the most effective when implemented appropriately. In some areas of Western Australia and South Australia, resistance to synthetic pyrethroids and organophosphates has been detected.
Lucerne flea also has a high natural tolerance to synthetic pyrethroids, therefore should be avoided in the treatment of RLEM or Lucerne flea. The following actives can be considered in the control of both*:
*Ensure the label is followed regarding crop choice, rate of application and timing of application.
Timerite® is an online tool by GRDC that can be used by growers and advisors to ensure chemical application occurs prior to the laying of diapause eggs in RLEM. This strategic application will help to reduce the number or surviving eggs over summer, which will in turn reduce RLEM populations in the following season.
It is important to not be reliant on chemical control and to consider other biological and cultural options such as predators, grazing management, crop selection and weed control.
Elders offers a range of crop protection products including pest control options.
For advice you can trust regarding your crops, speak to your local Elders agronomist.