Two-spotted mite

Two-spotted mite (TSM, Tetranycus urticae) is the most common pest mite species affecting all temperate fruit. It is more likely to become a problem in warm to hot, dry summers and when sprays for other pests and diseases disrupt predatory insects.

Pest identification

Adult female TSM are approximately 0.6 mm long and, while they can be seen with the naked eye, are best viewed with a 10× hand lens or light microscope. They are opaque, cream, and have 2 distinctive dark patches (spots) on either side of the upper and forward part of the body. Adult males are smaller and less distinctive than females. Eggs are also opaque, cream and very small, about 0.1 mm. TSM activity is often associated with webbing over the affected foliage.

Damage

TSM damages crops by feeding mostly on the underside of leaves, causing cells to turn yellow–white and lose their photosynthetic capacity. Heavy feeding causes severe speckling of the foliage, giving the trees a bronzed look. Leaf bronzing can significantly affect normal tree function and can lead to premature leaf drop, negatively affecting fruit development and colouring in red fruit varieties. With TSM, this feeding damage is usually first noticed in the inner and lower third of the tree canopy.

Monitoring

During the growing season, and particularly as spring and summer temperatures increase, monitor the undersides of leaves for TSM and their eggs. Webbing can indicate that mite populations are in the canopy. TSM should not be confused with other orchard pest mites, such as European red mite or Bryobia mite. Scouting for plant damage, such as bronzed or yellowed leaves, can be a quick way to identify pest mite hotspots. There are several ways to quantify the risk from mite populations, including mite counts, presence or absence, percentage of leaves infested and cumulative leaf-infested days (CLIDs). Your local IPM consultant should be able to help with applying these methods.

Management

Cultural and physical: similar to most mite pests, TSM seems to prefer dusty conditions and often thrives in orchard trees adjacent to unsealed roads. Any method that reduces dust arising from such sources will help decrease TSM activity. Maintaining good soil moisture and minimising tree stress, particularly through the hottest part of the season, will help trees resist damage and recover from mite attack.

Biological: the predatory mites Galendromus occidentalis (formerly Typhlodromus occidentalis), Phytoseiulus persimilis and Neoseiulus californicus can be effective biological control agents for TSM if seasonal conditions and crop protection chemical selection are favourable. G. occidentalis is established in the key apple-growing regions and can be effectively seeded into blocks via leaves and cuttings. P. persimilis is reared commercially for purchase and release.

There are many other naturally occurring predators of TSM including lacewings and Stethorus beetles, which will help control TSM populations, provided they are not killed off by sprays used for other orchard pests.

Chemical: two-spotted mite is a high-profile pest, and there are resistant populations to several key insecticidal groups. CropLife Australia maintains an insecticide resistance management 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.