Bryobia mites

Bryobia mites has benefited from the mild conditions, but damage should be on the decline once cooler conditions set in. Some unexpected control failures are of concern.

Where have they been reported?

Bryobia mites have been reported widely across NSW and Victoria, in most cases, attacking canola. In the high rainfall areas of the Victoria’s Central district, the milder conditions have suited Bryobia mites, but crop impacts have been tolerable (although border sprays were applied in some cases). Near Dookie in the Northern Country district of Victoria, Bryobia mites were an early season problem. The heavy infestations warranted control, which was achieved with registered insecticides. Bryobia mites have been found in canola crops south of Elmore, also in the Northern Country district. The crops, which are at the 2-leaf stage, are struggling to outgrow the mite feeding damage.

In Victoria’s Mallee and in areas to the west of Lockhart in the NSW Riverina, Bryobia mites have needed control. In these cases, the mites have been easily controlled with omethoate but registered rates of bifenthrin have not proved as effective. In the Central Tablelands and Central West Slopes & Plains districts of NSW, Bryobia mites have been seen in high numbers and much earlier in the season than is usual in pasture and canola crops. (Thanks for these reports*).

Bryobia mite habits and behaviour

Bryobia mites are most active in the warmer conditions of autumn, spring and summer. In seasons such as 2014 where summer and autumn weeds (green bridge) have been encouraged by early rains, pre-crop populations can be large. Bryobia mites are an important pest of clovers, canola, wheat and lupins, and are often confused with other species of earth mite. However, unlike other species that spend a lot of time on the soil surface, Bryobia mites are mostly found on the lower and upper leaf surfaces of plants. These are also a lot less active than other earth mite species.

Our advice

It is likely that Bryobia mite numbers will naturally decline in most areas with the onset of cooler late autumn and winter conditions. It is important to distinguish Bryobia mites from other mite species before deciding on control options. Look for mites and evidence of feeding damage (below) on newly established crops and pastures. Established crops can tolerate moderate infestations of Bryobia mites. It is a possible that some reports of control failures with bifenthrin are associated with particular species of Bryobia, which are numerous in cropping systems. Last year there were several reports of chemical control failures after alpha-cypermethign was applied to paddocks. This insecticide should not be used to control Bryobia mites.

Control options

Early control of summer and autumn weeds within and around paddocks, especially broadleaf weeds such as capeweed and clovers, can help prevent mite outbreaks. If chemicals are required, application rates need to be higher than for other pest mites, such as redlegged earth mites and blue oat mites. This is because Bryobia mites have a higher natural tolerance to some chemicals. For example, Bryobia mites have a high tolerance to some synthetic pyrethroids. Further, insecticide seed treatments may not be effective against this pest although research is needed to assess this thoroughly.

Description

Often called the ‘clover mite’, Bryobia mites (Bryobia spp.) are comprised of a group of species. There is very little known in Australia about individual species. Adult mites are less than 1 mm in length with a fawn-orange coloured body and orange legs, but they are often misidentified as the redlegged earth mite. Bryobia mites can be distinguished by their long forelegs, which are about 1.5 times their body length. With a hand lens, you may also be able to recognise their slightly flattened bodies in comparison to other earth mites which are globular shaped. Another way of recognising Bryobia mites is by the leaf damage they cause; characteristic white trails on cotyledons and leaves rather than the general silvering caused by other mites.

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

 

* Sources of field reports of Bryobia mites

Neil Hives – Entomologist (Victorian Central District)

Warwick Nightingale – Agronomist, Delta Ag (NSW Riverina)

Emma Robinson – Agronomist, Landmark (NSW Central West Slopes & Plains)

Phil Stoddart – Consultant (NSW Central Tablelands)

Greg Toomey – Agronomist, Landmark (Victorian Northern Country)

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

Kent Wooding – Agronomist, AgriVision (Victorian Mallee)