Bryobia and balaustium mites

Karla Whittaker (AGnVET Services) has reported bryobia mites (Bryobia spp.) attacking a canola crop near Lockhart, in the South West Slopes of New South Wales. The mites caused significant damage to emerging cotyledons and required chemical control. Mark Harris (Rural Management Strategies) has also reported bryobia mites attacking a number of canola crops around Lockhart. Mark says that in some cases, the feeding damage was quite severe. Bryobia mites cause distinctive feeding damage, characterised by a long trail of whitish-grey spots on the upper side of cotyledons and leaves. Agronomist, Dave Eksteen (NSW DPI), has reported bryobia mites and balaustium mites (Balaustium spp.) causing severe damage to canola crops at Tocumwal, in the Riverina district of New South Wales. A combination of alpha-cypermethrin (300 mL/ha) and omethoate (120 mL/ha) was successful in suppressing mite numbers.

Bryobia mites are an important pest of clovers, canola, wheat and lupins. Often called the ‘clover mite’, bryobia mites are less than 1 mm long with a fawn-orange coloured body and orange legs. In the field they are often misidentified as the redlegged earth mite. Bryobia mites can be distinguished by their long forelegs which are 1.5 times their body length. Unlike most other earth mite species, bryobia mites are most active in warm conditions in autumn, spring and summer. These mites are generally found in low numbers and are unlikely to be problematic over the winter period.

Balaustium mites have recently been identified as emerging pests within the Australian agricultural industry. The damage caused by these mites in Australia seems to have significantly increased in the last decade, with reports in Western Australia indicating that they cause extensive damage to cereal, canola and lupin crops.

Balaustium mites are often confused with other mite pests. Adults grow to be twice the size of the redlegged earth mite, about 2 mm in length. They have a rounded red-brown coloured body, densely covered with stout hairs, with orange-red legs. Leaf damage symptoms can also help to identify different mite species. Balaustium mites cause cupping and leathering of cotyledons, which Dave says was evident on the canola cotyledons at Tocumwal.

Bryobia mites and balaustium mites can be difficult to control with pesticides. They are often reported to persist in the field following chemical applications aimed at other mite species. Recent findings by cesar show balaustium mites are more tolerant to a range of organophosphorus and synthetic pyrethroid chemicals compared with other mites. For Bryobia mites, research indicates organophosphates may provide better control than synthetic pyrethroids. Karla reports an application of omethoate (120mL/ha) achieved adequate control of bryobia mites at Lockhart.

It is therefore important to correctly identify mite species and seriously consider non-chemical control methods for these mites. Research is continuing in both Western Australia and eastern Australia to better understand the biology and control of bryobia and balaustium mites. Reports indicate that crops sown into paddocks with a pasture history and high levels of broad-leaved weeds, especially capeweed, will be most at risk from mite damage.

For images of bryobia mites, click here. For images of balaustium mites, click here.