[James Kilkelly]

Red spider mite (glasshouse pest) - Tetranychus urticae
by GPI

Plants affected
Many glasshouse plants, indoor houseplants and garden plants

Season(s) present.
Mid spring to late autumn.

Red spider mite , photo / picture / image.

Appearance of damage.
The upper side of leaves develop a fine pale speckling, whilst the on the under side yellow-green mites are visible under a magnifying lens.
Fine silk webbing may be present between leaves and stems and leaves will change to an off green/yellow colour, dropping in heavy infestations.

Cause
The sap sucking Red spider mite who despite its name is actually yellowish green with two dark spots on its back. They do however become orangey red in the autumn and winter.
These tiny mites are less than 1mm long and sport four pairs of legs.

Trouble?
Yes, the mites breed rapidly (females lay 4-6 eggs a day) and quickly reach almost uncontrollable numbers, especially indoors where they will have no predators. Heavily infested plants loose leaves, become severely weakened and then die.

Organic or cultural control.
Fight mite with mite, and introduce the predatory mite Phytoseiulus persimilis which feeds on the feeds on the Red spider mite and its eggs. Its period of use is from April to October in glasshouses and June to September out of doors, as it needs good light and daytime temperatures if it is to breed faster than the Red spider mite. Phytoseiulus persimilis can be ordered through garden centres or online.
To keep mite numbers down, spraying with garden centre bought fatty acids is quite effective if applied every 5-7 days on both the upper and lower sides of the leaves.
You can also spray with pyrethrum or derris on a similar timescale to the fatty acid.


Other Control.
Chemical control can be achieved through spraying with a product containing bifenthrin such as Scotts Bug Clear or Rose Clear 3.

Please note: Chemical insecticides should not be used in conjunction with the biological control of Phytoseiulus persimilis

Nature notes.
If spraying, do so at dusk to avoid damage to pollinating insects.
Please note that Irishgardeners.com does not advocate the removal of insect life, instead, this forum encourages wildlife preservation. However, there are occasions where a wildlife becomes a problem within the garden for certain people. Be aware that wildlife is a link in the chain of life, benefiting something or someone down the chain. Please at least think about this before you remove wildlife from your site.

DISCLAIMER: The control methods are suggested here as a matter of general information. Under Irish and EU law it is illegal to use any preparation as a pesticide/fugicide/herbicide that is not approved for such use. The author and the website accepts no responsibility for how a user may mix, use, store, or any effects the mixture or its elements may have on people, plants or the environment. The information here is for reference only and does not imply a recommendation for use. If you disregard this warning and make any of the preparations, you do so entirely at your own risk.

Any queries or comments on Red spider mite (glasshouse pest) - Tetranychus urticae, please post below.


Back to Pests of the Garden in Ireland - Prevention and Control.

Images courtesy
David Cappaert, Michigan State University, Bugwood.org
Louis Tedders, USDA Agricultural Research Service, Bugwood.org
Frank Peairs, Colorado State University, Bugwood.org
Clemson University - USDA Cooperative Extension Slide Series, , Bugwood.org
www.forestryimages.org