Red Spider Mite
Because we have had a prolonged sunny dry spell, we can prepare ourselves for an outbreak of Red Spider Mite (Tetranychus urticae)in the Greenhouses of the nation.
When active they are pale greeny-brown in colour and can be recognised by the two 2 dark dots on their backs – they are only red in winter. Spider Mites are less than 1mm in size and difficult to see without a lens or microscope unless you have very sharp eyes. They often live underneath leaves, and are only active when it is warm
Identifying Spider Mite
These tiny pests are common in greenhouses and on house plants and can also be found on outdoor plants during the warmer summer months. They are very destructive and attack citrus, tomatoes, cucumbers, melons, vines, carnations and chrysanthemums in the greenhouse and on day lilies, gladioli, conifers etc in the garden.
In a bad case, fine webbing appears on new growth. Spider mites are actually spiders and can spin very extensive fine webs which will lead to leaves turning brown and dropping off because of the cell damage the mites cause. A bad case will look like this.
How can we can control them? Fortunately, these were one of the first pests that commercial biological controls were developed for and predators are widely used in commercial glasshouses growing peppers for supermarkets. The point is control – so it has become common commercially to put the pest in first so that there is a ready made food supply when the predators are released. This sets up a little ecosystem that keeps the glasshouse free of anything more than light damage.
Basically there are three common predators. Phytoseiulius and Amblyseius are both predatory mites, while Feltiella is a tiny predatory midge. More details on these including how to buy them are at our sister site Ladybird PlantCare