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European Red Mite

Ravageurs et maladies
English
European Red Mite eggs.
Photo: University of Georgia Plant Pathology Archive, Bugwood.org

Onglets

Description

Summary

European red mites, also known as red spiders or red spider mites, are not true insects, but tiny arthropods, just like other mites and ticks. With their four pairs of legs, they look like miniature spiders. These tiny parasites are difficult to see, but they leave telltale damage. In a heavy, uncontrolled infestation, leaves and fruit may drop and plants may die back quickly, particularly in hot, dry weather.

Signs and symptoms

  • European red mites are barely visible to the naked eye, but they leave a number of telltale signs.
  • The first sign of damage is on tender, young, sap-filled shoots; the mites use their mouthparts to suck out the contents of plant cells, causing the leaves to become discoloured.
  • In a light infestation, small yellowish dots followed by pale patches appear on upper leaf surfaces.
  • In a heavy infestation, the leaves may turn completely yellow or take on a bronze or silver tinge; unlike two-spotted spider mites, European red mites weave very few webs; severely affected leaves dry out and drop prematurely.
  • Affected plants show delayed growth; fruit is smaller and drops before it ripens; a heavy infestation can interfere with fruit set in the current season and the formation of fruit buds for the following year.

Latin name (genus)

Panonychus ulmi

Host plants

Various ornamental and fruit plants and trees, including apple, ash, buckthorn, cherry, conifers, crabapple, elm, hawthorn, honey locust, locust, plum, rose, strawberry and walnut.

Development cycle

Description and life cycle

European red mites belong to the class Arachnida, like spiders, and the order Acari, along with other mites and ticks. They pass through the egg, larva and nymph stage before reaching adulthood.

Eggs: Spherical, about 0.13 mm in diameter; dark orange to bright red, with a tassel or stalk.

Larvae and nymphs: Resemble adults but smaller; nymphs have eight legs and larvae six.

Adults: Oval, brick-red body. The back is marked with four rows of white dots with long curving hairs. They have four pairs of legs but no wings or antennae. Females grow to about 0.3 mm and males are slightly smaller.

The adults, nymphs and larvae do not survive in winter. Only the eggs overwinter, hidden between the scales on buds, in cracks in bark or on leaves and fruit lying on the ground.

In spring, when the buds begin to swell, the eggs hatch and the young larvae move to the new leaves to feed. They mature in five to twenty days. After mating, the first-generation females lay their eggs on the underside of leaves. They live for about twenty days and each lay about twenty eggs. The rate at which subsequent generations appear depends on the weather, with warmer temperatures shortening the life cycle.

Populations normally reach their maximum in late July and early August. There may be as many as six to eight generations a year.

Starting in late summer (mid-August to October), the females of the latest generations deposit their eggs between the scales on fruit buds, in cracks in bark, on leaves and in the calyx of fruit.

Prevention and control

Favourable conditions

European red mites multiply faster during hot, dry weather, in poorly aerated sites. They tend to proliferate after mild falls and winters and after drastic pruning, heavy feeding with high-nitrogen fertilizer and anything else that promotes the growth of tender shoots.

Identification

Use a magnifying glass to carefully examine the underside of leaves, particularly on young, tender shoots.

Prevention

  • Keep plants vigorous by fertilizing adequately, pruning them properly and watering them during dry spells.
  • Avoid heavy feeding with high-nitrogen fertilizers and drastic pruning, both of which promote the growth of vulnerable tender tissues.
  • Keep your garden free of plant litter.

Physical control

  • During the growing season, rake up leaves and fruit as they drop, to break the insects' life cycle.
  • Remove and destroy heavily infested shoots.
  • Spray the foliage, trunk and branches with a strong, steady stream of water to dislodge the mites and increase humidity levels.
  • During dry spells, spray the leaves of susceptible plants regularly to maintain humidity levels.
  • Water early in the morning, to allow the foliage to dry out during the day; avoid overwatering, however, so as not to encourage fungal infections.
  • In fall, remove all plant litter, to reduce the overwintering population, which is the first source of infestation in the spring; never compost infested plant litter.

Biological control

Encourage the presence of natural predators (plant bugs, ladybird beetles, syrphid fly larvae, predacious mites) by increasing the variety of plants in your garden.

Chemical control

As a last resort, use a low-impact pesticide with insecticidal soap or mineral oil (horticultural oil) as the active ingredient. Read the product label carefully and follow the manufacturer's recommendations.

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