Pest Problems Explained - RED SPIDER MITE (Two-Spotted Mite)
Red Spider Mite Description
Small yellow/olive mites which have dark patches on either side of the body, red spider mite are less than 1mm long. Also known as "two-spotted mite" they can be found in large numbers on the underside of leaves.
In bad infestations they can produce fine webs.
As day lengths reduce in the autumn, they become deep red in colour and leave the plants to overwinter.
Red Spider Mite Damage:
The mites suck sap from cells on the underside of plant leaves, in the early stages, characteristic white speckles can be seen from the upper leaf surface.
As mite numbers increase these white speckles will increase in number, the leaf will take on a bleached appearance and die.
The mites are found in highest numbers on the underside of leaves although you may need a magnifying glass to see them!
As the population builds you will start to see webs and aggregations of mites at certain sites, usually the growing points of the plant.
Red Spider Mite Life Cycle:
The mites go through 5 development stages. Egg to adult takes about 14 days at 21ºC, or less than a week at 30ºC.
Eggs are laid on the underside of leaves. Each adult female can produce more than 100 eggs in 3 weeks. They reproduce at alarming rates - 10 spider mite in May are capable of becoming 1,000 by June & 100,000 by July!
High humidities can reduce the egg laying rate of the mites.
During the autumn, when day lengths shorten the mites turn deep red in colour and migrate from the plants to hibernate in crevices within the glasshouse structure.
Red spider mite can overwinter without feeding and re-emerge in the spring and summer to re-infest plants.
NB. Artificial lighting may stop the mites from hibernating.
Biological Control of Red Spider Mite
Red spider mite can be controlled biologically indoors or outside by using their natural enemy, the predatory mite Phytoseiulus persimilis which is unable to control any other mite species.