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Attack of the Earth Mites

Red legged earth mites (Halotydeus destructor) and Blue oat mites (Penthaleus spp.) are major pests of pastures and crops in the South East Local Land Services region. Whilst they may be small insects (less than 1mm long and 0.8mm wide) they cause significant issues due to their sheer numbers.

Red legged earth mites and Blue oat mites appear very similar. They both have black bodies with eight red legs. Blue oat mites are slightly larger, have blue-black bodies and have a distinctive red mark on their backs. While the two insects both cause the same damage to the pasture plants there are some differences in the control methods required.

Both mites hatch from their over summer eggs in autumn when there is sufficient moisture and declining temperatures. They will rapidly increase in population while ever there is sufficient food available to them. Both mites will actively feed on leaves of grasses legumes and some weeds.

Different species of mites have subtle preferences for varying plants. New plants are particularly sensitive as the damage caused by mites is similar to that of grazing. A new plant with an undeveloped root system will not have the same capacity to recover as a well-established one. For this reason it is especially important to monitor new pastures and crops.

There is a range of tools used for the control of mites. Cultivation used to play an important role in disturbing the egg bed of mites and reducing their early season population. With the modern approach of minimising soil disturbance this tool is rarely used.

Strong argument can be made that the benefits of direct drilling outweigh the benefits of cultivation even when including incest pest control. Insecticides are available and can be very effective and a cheap option. Just remember when using any insecticide to consider if the damage caused to beneficial predators outweighs the benefits of removing the pest.

The use of insecticides is where the difference starts between Red legged earth mites and Blue oat mites.

The Red legged earth mites lay all of their over summer eggs towards the end of their life cycle in spring. For this reason, a targeted spray in a small spring window can greatly reduce the number of eggs which a lain to hatch in the following autumn. The date this occurs is well known, have a look at the Timeright website to find out for your location. It is dependent on where you are in the region.

Blue oat mites are not as effectively controlled though this one time spray. This is due to the fact that every time they lay eggs a percentage is over summer eggs. Constant spraying would do considerable damage to other insects and is not encouraged. This is further complicated by the relatively new knowledge that there are three different species of Blue oat mites in our region and some are naturally resistant to the most common insecticides used.

For more information on the use of insecticides seek the advice of an agronomist.

If you think you may have a problem with either mite a good way to check is to be in your pasture at dawn or dusk. Have a sheet of white paper with you, holding the paper near the ground shake the leaves of plants over it and see what you find. A suspect place to check during day light is under the broad leaves of any thistle, they love this shaded space. If you are finding greater than 50 mites/m² and the pasture is still establishing some control may well be warranted.

Luke Pope
Senior Land Services Officer - Pastures
Cooma
02 6452 1455 
luke.pope@lls.nsw.gov.au