European red mite

European red mite (ERM, Panonychus ulmi) is a serious pest of apple and pear foliage. Severe infestations can result in defoliation, particularly in pears. The pest is also found in stone fruit trees, but this is less common.

Pest identification

Adult ERM females are about 0.4 mm long and rounded. They are dark maroon with prominent white spines on their body. In contrast, adult males are smaller than females and lighter coloured. They have a less rounded body and a pointed, angular abdomen. ERM eggs are light red, round and have a slight depression on the top. When infestations are heavy, eggs will be found clustered in hundreds around branch angles and buds.

Damage

ERM feeding will cause mottling on the upper leaf surface. Heavy infestations result in leaf bronzing and premature leaf fall, leading to reduced photosynthesis. Prolonged feeding can affect fruit size and colour and might affect bud development for the following season.

There are several ways to quantify the risk posed by mite populations including counts, presence or absence, percentage of leaves infested and cumulative leaf-infested days (CLIDs). Your local IPM consultant should be able to assist with more advice on applying these methods in your orchard.

Monitoring

During the growing season, and particularly as spring and summer temperatures increase, monitor the undersides of leaves for ERM and their eggs. The presence of webbing can also indicate that mite populations are in the canopy, although this is more common with the two-spotted mite. Scouting the orchard for plant damage, such as bronzed or yellowed leaves, can be a quick way to identify pest mite hotspots.

Monitor for ERM fortnightly using a hand lens or by taking a random sample to the office or laboratory for closer inspection under a light microscope. Commercial mite monitoring services might be available in some districts.

When monitoring, record both pest and beneficial insect activity found on the leaves. It is a good idea to record both mites and predators as a percentage of leaves infested. This way, from sample to sample, you will know if the infestation is getting worse or if the beneficials, such as predatory mites, are maintaining control.

Look for ERM eggs among the branches while pruning, especially in winter. This can help identify potential pest pressure and hotspots for the next season.

Management

Cultural and physical: physical management of ERM can include measures to reduce heat and dust in the orchard and ensure adequate soil moisture, thereby minimising any tree stress.

Biological: the predatory mite Galendromus pyri (formerly Thyphlodromus pyri) can be a very effective biological control agent for ERM. G. pyri adults are about the same size as adult ERM but have a pear-shaped body. When combined with the effects of other beneficial insects, including lacewings and Stethorus spp. beetles, and with a soft (selective) insecticide program, full biological control of ERM is possible.

Predatory mites are often found on the underside of leaves close to the mid-vein. Before feeding on pest mites, the adults are an opaque white or cream, similar to their oval-shaped eggs. After feeding, the gut of the predatory mites takes on the colour of their prey and they become more visible.

If predatory mite numbers are low or absent from an orchard, they can be seeded by transferring leaves and shoots from a block known to have a good population.

Chemical: European red mite is a high-profile pest, and there are resistant populations to several key insecticidal groups. CropLife Australia maintains an insecticide resistance management (IRM) plan for European red mite, two-spotted mite and green peach aphid, available online. IRM is essential to maintain the efficacy of valuable insecticides. Preventing resistance from occurring is easier than trying to regain susceptibility.

Early season sprays should use chemistry with a low effect on beneficial insects to conserve predatory mite populations. In contrast, broad-spectrum insecticides or those with a high impact on beneficial insect populations have the potential to flare up mite populations.

Regular monitoring for both predatory insects and pest mite populations to inform spray decisions is critical. Wherever possible, make no more than one application from each registered miticide group per season. Effective mite control spray programs usually incorporate a single horticultural mineral oil during winter or just before bud burst. Consider also chemical rotation and insecticide mode of action to control other pests of pome fruit, such as codling moth, light brown apple moth and woolly aphid. These sprays can promote chemical resistance in mite pests. Refer to the Orchard plant protection guide for chemical suggestions.