Spruce Spider Mite

Oligonychus ununguis

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Changed on: 08.10.2018
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Schadbild
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Schadbild

The spruce spider mite is one of the most common pests on thuja and spruces in gardens and can destroy entire thuja hedges.

Dry, warm weather conditions in big cities are especially likely to provide favourable conditions for the development of pest calamities. 

More information
Schadbild
caption
Schadbild

The spruce spider mite is one of the most common pests on thuja and spruces in gardens and can destroy entire thuja hedges.

Dry, warm weather conditions in big cities are especially likely to provide favourable conditions for the development of pest calamities. 

More information

Symptoms

The mites puncture the epidermal cells on the surface, which then die and turn yellow. The scale-like leaves of thujas appear yellow-mottled from close up and dull-green from a distance when infested.

Heavily infested thujas turn brown and may wither. In the course of mass developments, the mites begin to move slowly from severely infested areas to parts of the tree that are still mite-free.
What remains are parts of the plants with withered needles: often, the last remains of empty egg skins are still visible on such deserted feeding areas. The remains are often the only evidence of spider-mite infestation when diagnosing damage.

The damage is often mistaken for dry-stress damage following a water shortage. A magnifying glass or, even better, a stereomicroscope is required for an exact diagnosis.

 

 

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Spruce spider mite eggs
Eier der Nadelbaumspinnmilbe
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Adult spruce spider mite
Nadelbaumspinnmilbe adult

Wirtspflanzen, Auftreten und Bedeutung

Die Nadelbaumspinnmilbe wird sehr häufig an Fichten, an Thujen sowie an Scheinzypressen in menschlichen Siedlungsgebieten angetroffen. Daneben findet man sie sehr selten auch noch an weiteren Nadelbäumen.

Die Nadelbaumspinnmilbe ist in Österreichs Gärten sehr häufig anzutreffen, was wahrscheinlich mit den dort für Nadelbäume vorherrschenden ungünstigen Bedingungen zusammenhängt.

Control

Basically, dry locations should be supplied with sufficient water. There are also a number of effective products for chemical control (also see Register for authorised plant protection products in Austria).

Products used to combat spider mites are commonly known as acarizides. However, many products have only a limited effect on certain mite development phases -- e.g. eggs, though in nature there is always a mixture of mite instars. Thus, two applications at an interval of seven to 10 days should be made when using such products.

Tests for biological control using predatory mites of the species Typhlodromus americanus were conducted in America.

This control method seems to be suitable for taller false cypresses or spruces, as chemical products are difficult to apply to those trees.

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