Red Spider Mite - Plant Pest

Signs - Leaves become speckled, as though covered with hundreds or thousands of pale yellow dots giving a rather ill-looking and "dusty" appearance. Heavily  infested plants may become covered with fine webs. The red spider mites themselves are eight legged animals less than 1mm long and can be difficult to see.

Leaves dry up and fall leaving only young leaves at the ends of shoots. More often affect plants under glass, but will also attack many ornamental plants outdoors in a hot dry summer.

Damage - Sap feeders which weakens the plant. Usually a problem in house and greenhouse plants as they like a dry atmosphere, can be a problem outside in hot, dry summers.

Treatment - Red spider mites breed in hot and dry places. If you can increase the humidity around the plant you decrease the pest's reproduction rate. In greenhouses and patio areas the floors can be damped down. For house plants a short holiday somewhere cooler and more humid - the bathroom or even outside in the warmer months may help get rid of the infestation.

You could try giving them cold water baths, they hate them. Spray them with water that is between 0°C and 5°C (make sure the plant won't also hate it though!). If you find an infested plant, attack it with ice water. Keep a spray bottle in the refrigerator and mist once or twice a day until the mites are all gone.

Another option is to go for biological control. Biological control of a pest relies on introducing a predator species so "fighting nature with nature", if chosen carefully, the predator will stop damage to your plants without damaging the environment. Such biological controls are safe for the user, children and pets. They will not harm other beneficial garden insects and are biodegradable.

They do rely on the predator always having some food though, or they will die out, so like other organic practices it is a question of maintaining a small population of pests to allow the predators to be ready for them, in this case though the balance is skewed away from the problem.

Biological control for red spider mites is a predatory mite; Phytoseiulus permilis. This insect reproduces at twice the speed of red spider mite at 18°c (64°f). The Phytoseiulus mite eats only Red spider mite and each can eat many hundreds of them. Whilst feeding on Red spider mite, Phytoseiulus will also reproduce laying many eggs which will hatch into more predators. Phytoseiulus is similar in appearance to red spider mite but is more red in colour and moves much faster.

Phytoseiulus is suitable for glasshouse or conservatories and can be used on strawberries and fruit from May to August outside.