Balaustium mites

Is this pest slowly replacing the redlegged earth mite or blue oat mite in some areas as the pest to watch?

Where have they been reported?

In recent years, Balaustium mites have become the most pressing mite problem at the University of Melbourne’s Dookie campus in Victoria’s Northern Country. The mites have been the most consistent and retractable mite pest on the property, the niche that redlegged earth mite once held. The 2014 season has been no exception, with reports of Balaustium mites having a significant impact on emerging canola crops. The problem is expected to abate with cooler temperatures. Balaustium mites have been reported in a canola crop southwest of Hopetoun, in the Victorian Mallee. Some leaf distortion has occurred as a result of mite feeding, but the damage is fairly patchy and does not warrant control. Balaustium mites have been observed in several canola crops near Kaniva, in the Victorian Wimmera. Reports suggest numbers are greater than seen in previous years. Balaustium mites have also been damaging canola in a property near Lockhart in NSW’s Riverina district, immediately following the removal of a long-term lucerne crop. The PestFacts SA team also report Balaustium mites in a range of crops in the mid-north of South Australia and in the Victorian Wimmera. In the latter case, the mites were particularly difficult to control. (Thanks for these reports*).

Balaustium mite habits and behaviour

Balaustium mites (Balaustium medicagoense) typically first appear early in autumn, with eggs hatching well ahead of redlegged earth mites and blue oat mites. They may be present in highest numbers in May and June, and tend to decrease after this time peaking again in spring through a second annual generation. Balaustium mites tend to be more day-active than other mites and are relatively easy to observe. Crops that are most vulnerable to attack include canola, lupins and cereals, as well as various pasture types. However, they have a preference for canola, grasses, cereals and weeds, particularly barley, wheat, oats, barley grass and capeweed. Even in pastures, Balaustium mites tend to have a preference for grasses and weeds over clovers and other medics.

Our advice

Correct identification of mite species is critical before using insecticides. In addition to wasting time and money, the inappropriate use of chemicals can lead to issues with resistance and change the pest species dynamics. Early control of late-summer weeds and grasses is probably the most appropriate option for preventing Balaustium mite problems. Reports such as that from Lockhart (above) indicate that crops sown into paddocks with a pasture history and/or with high levels of broad-leaved weeds will be most at risk from damage. The repeated annual use of synthetic pyrethroids for control of mites, aphids and caterpillars in a paddock is likely to provide a selective advantage to Balaustium mites by removing both predators and other competing mite species.

Control options

There are currently no chemicals registered for the control of Balaustium mites. In addition, Balaustium mites are considerably more tolerant to a range of insecticides and will generally survive applications aimed at other mite pests in crops and pastures. Seed treatments do not appear to be effective against this species.

Description

Balaustium mites are often confused with other mite pests. Balaustium mites reach about 2 mm in length as adults, which is about twice the size of other earth mite species. They have a rounded dark brown coloured body that is densely covered with stout hairs giving them a velvety appearance, and eight orange-red legs similar to other pest mites. They also have distinct ‘pad-like’ structures on their front legs and move more slowly than redlegged earth mites and blue oat mites. Balaustium mite damage appears as cupping and leathering of cotyledons, which is quite characteristic, or irregular white spotting on cereals and grasses.

Click here for further information on Balaustium mites, or alternatively you can download the GRDC Back Pocket Guide - Crop Mites.

 

* Sources of field reports of Balaustium mites

Greg Dearman – Agronomist (Victorian Wimmera)

Simon Mock – Agronomist, Clovercrest Consulting (Victorian Wimmera)

Warwick Nightingale – Agronomist, Delta Ag (NSW Riverina)

Paul Wallace – Farm Manager, Dookie College (Victorian Northern Country)

PestFacts SA team – SARDI