European red mite, Panonychus ulmi, was first identified in Western Australian apple orchards in 2005 and is now present in all major fruit gowing regions here but is most abundant in orchards in the cooler lower south west region of Western Australia. It has been present in eastern Australia since at least 1954.
It is found in virtually all of the world’s apple production regions and its presence does not restrict exports.
Only the colder regions in Western Australia such as Bridgetown to Pemberton seem to provide suitable conditions for consistently damaging populations. European red mite may have been present in WA for some time but sprays against two-spotted mite, Tetranychus urticae, lack of sufficient winter chill for overwintering egg survival, especially in the warmer regions in Western Australia, and some activity of generalist predators, may have helped keep populations below damaging levels.
Distribution, hosts, damage
European red mite is primarily a pest of deciduous fruit trees. The main fruit affected is the apple. Pears and plums are also hosts but less likely to be damaged. Some varieties have greater susceptibility, for example, Hi-early apples and Wilson plums.
Minor hosts include almond, cedars, citrus, cherry, coffee, cotton, grapevine, peanut and some ornamental trees and shrubs, especially in the Rosaceae family such as roses.
European red mite feeding results in leaf mottling on the upper surface of leaves. This may be confused with similar mottling suspected to be caused by an infection with a mild strain of virus, but the mottling by the virus is bright yellow with large patches often present.
Heavy infestations result in leaf bronzing and premature leaf fall. Prolonged feeding can result in reduced fruit size and colour, and may affect fruit set the following season.
European red mite eggs are red or orange, globular and slightly flattened on top. Each egg looks like an onion, with a white stalk at the top as long as the egg is wide. Bryobia mite eggs are also red but lack the spike.
Eggs of the other common pest mite that occurs in orchards, two-spotted mite, are spherical and pale yellow (see below). Eggs of these mites are about the same size.
From autumn onwards, adult European red mite adults lay batches of eggs in protected situations on the trunks of trees and the calyx end of apples. Because such large numbers are often laid in one location, they are relatively easily seen. European red mite overwinters on host plants in the egg stage.
The immature stage of European red mite is red to orange or green. When they first hatch, the mite is referred to as a larva and has three pairs of legs. Later immature stages are called nymphs and have four pairs of legs, as do the adults.
The red to maroon adult European red mite female is very distinctive, with four rows of small white spots on the back, from which strong spines protrude. It is globular in shape and usually slightly smaller at 0.3‑0.4mm long than female two-spotted mites, the other common pest mite found in orchards. Adult male European red mites are pear-shaped and about a quarter of the size of females, with relatively longer legs and a tapered abdomen. Males are straw-coloured, with a light red or green tint.
Female two-spotted mites are 0.4‑0.5mm long and have two dark patches on each side of the body. Eggs are spherical, pale yellow and lack an apical spine.
European red mites overwinter as eggs which occur in clusters on roughened areas of bark, often on the underside of fruit spurs and at forks of small branches.
Eggs hatch around pink bud to full bloom and young mites feed on opening flowers and developing leaves. They continue to feed on leaves during spring and summer, increasing in numbers in response to rising temperatures. The pattern is a slow build-up from October, reaching a peak between mid-January and mid-February. There may be six or seven generations per year.
Populations generally decline by mid-February and females lay overwintering eggs during February and March.
European red mites usually appear earlier than both their predators and two-spotted mite. Most predators also feed on two-spotted mite and may switch to two-spotted mite later in the season.
Establishment and dispersal
European red mites occur mainly in climates suitable for apple production. Overwintering eggs need chilling for a high percentage hatch, although some strains occur in hot climates.
The main means of spread is transport of nursery stock infested with overwintering eggs and on late season fruit where winter eggs have been laid in calyx and stem ends. They can also be dispersed in all stages on leaves, clothing, picking bins, orchard machinery and other equipment. Good farm biosecurity is very important in preventing spread.
In heavy infestations or reduced food quality, they produce silken threads and can be dispersed by wind. This is known as ‘ballooning’. This dispersal mechanism increases the risk of spread to nearby orchards. Spread can also be through accidental contact and consequent hitchhiking on insects and birds.
Effective monitoring is based on examining leaves. If the presence of mites is based on leaf damage alone, mite populations will be so high that control with miticides will be difficult.
Commence monitoring from green tip.
Select blocks based on susceptible varieties and include areas across the orchard. In each block, examine 25 leaves, for example collected from trees on a 5 x 5 grid. Sample fortnightly, or weekly in hot weather.
Unlike two-spotted mites, European red mites tend to colonise the upper side of leaves and do not produce extensive webbing. Egg laying is concentrated on the main rib and usually starts at the leaf base.
Where European red mite has been important at the end of a growing season, prevention of problems the following season may be achieved by an application of a summer oil near the end of flowering. Otherwise, from mid to late December, monitoring and management European red mite and two-spotted mite should coincide. Miticides currently applied for two-spotted mite are active against European red mite.
To gain full advantage of integrated pest management, include observations on predatory mites when checking leaves. Numbers of pest and predatory mites may be determined by hand lens, or employing a mite consultant.
Various predators, including predatory mites, have been recorded in WA deciduous fruit orchards. The effects of these predators will become clearer with experience. In orchards in the lower souith west of Western Australia, the experience has been that predatory mites cannot be relied upon to protect trees from European red mite.
The main mite predator in eastern Australia is Typhlodromus pyri, which was imported to eastern Australia in the early 1970s. At that time, European red mite was not known to occur in Western Australia, so did not participate in this program. T. pyri is more active against European red mite, but will also feed to a limited extent on two-spotted mite. It is also a pollen feeder and some orchardists include a grass grond cover for this reason, as well as undertake alternate mowing of tree rows to conserve the preators that may be inhabit orchard floor plants. T. pyri will feed on other mites so can sustain itself even if European red mite and two-spotted mite are absent or present in low numbers. A program to import this predatory mite from eastern Australia has commenced. The predator is being cultered in a commercial rearing facility and releases are planned for the 2020/21 season.
Mites have a reputation for developing resistance to miticides so integrated pest management is essential. Monitor mites and their predators, use a spray program based on pest numbers and choose chemicals that minimise the impact on beneficials. Alternate the use of chemicals based on their activity class to slow the development of resistance.
Healthy, well-maintained trees will tolerate higher mite populations than weak or stressed trees, and pears tend to be more susceptible to mites than apples.
Targeting overwintering eggs
Overwintering mite eggs are susceptible to oil sprays near the time of hatching. If European red mite was a problem in one season, check apple trees for the prevalence of overwintering eggs. If easily found, apply summer oil around full bloom the following season.
Correctly timed oil sprays are especially important in integrated pest management because this favours survival of predatory mites. Oil has a physical effect on mite eggs and so is not susceptible to resistance development. A well-applied oil spray can keep mites at a low level until mid-summer.
Only apply a miticide after monitoring.
Where it is expected that European red mite will be a problem, miticides containing abamectin can be applied 2 to 6 weeks after petal fall. Best results are obtained at the earlier timing. In the case of applications based on monitoring leaves for the presence of the mite, abamectin should be applied in the same way as indicated for ovicides mixed with miticides (see below).
Apples and stone fruit
For ovicides alone, apply at around 10% leaf infestation.
For ovicides mixed with miticides that control motile stages, apply at 30‑40% leaf infestation.
For all other miticides, apply at 30‑40% leaf infestation
Pears are less frequently attacked but may be more sensitive to mites. A threshold of 10% leaves infested is recommended.
Recommended identification and management guides
Bower CC & Thwaite WG 1995, The mite management manual - a practical guide to integrated mite control in apples. NSW Agriculture - now Department of Primary Industries, Agriculture.
Malipatil MB, Williams DG & Semeraro L 2009, Pests of pome and stone fruit and their predators and parasitoids - a pocket guide. Department of Environment and Primary Industries.