Growers urged to monitor for crop mites

SOUTHERN region grain growers and graziers are being advised to monitor for redlegged earth mites (RLEM) this winter, with experts warning environmental conditions have been ideal for mass hatchings, potentially putting emerging winter crops and pastures at risk.

Dr Garry McDonald from the University of Melbourne said rain in some southern regions followed by cooler conditions in May had been conducive to population increases of the pest, which could affect canola, lupins, cereals and legume seedings, as well as pastures.

“RLEM, or Halotydeus destructor, only hatch in autumn under specific conditions, like those we had in May where areas received at least five millimetres of rain accumulated over five consecutive days or less, followed by 10 days of average daily temperatures below 16°C,” he said.

“Our predictive modelling suggests the peak egg hatch would have occurred in mid-May in some areas.

“So the time to monitor crops, and where necessary enact management strategies for RLEM, is now.”

RLEM is traditionally active from autumn until mid-spring in southern cropping regions, with pest hatching often coinciding with crop emergence.

Dr McDonald said the pest feeds on the crop causing silvering or white discoloration of leaves and distortion or shriveling in severe infestations.

“Affected seedlings can die at emergence with high mite populations, feeding symptoms can also be mistaken for frost damage.

“RLEM have been found to be directly responsible for a reduction in pasture palatability,” he said.

RLEM are approximately 1mm in length with a velvety black body and eight orange-red coloured legs.

They can often be found on the leaf surface in feeding aggregations, of up to 30 individuals. In the warmer part of the day, they tend to gather at the base of plants, sheltering in leaf sheaths and under debris.

“Growers should be regularly monitoring crops, mites are best detected feeding on the leaves in the morning or on overcast days.

“If mites are not observed on plant material, inspect soil for mites,” Dr McDonald said.

Growers and advisers can also access a service to determine if RLEM populations within their paddocks are resistant to insecticides.

This service is being made available through a Grains Research and Development Corporation (GRDC) investment.

Knowing the resistance status will assist in implementing appropriate and effective management.

For more information go to: cesaraustralia.com/sustainable-agriculture/pestnotes/insect/Redlegged-earth-mite.