Spider Mites Theo 22 October 2022

Spider Mites

Spider Mites
Red or Two-Spotted Spider-Mites feed by puncturing cells and draining the contents, producing a characteristic yellow speckling of the leaf surface. They also produce silk webbing which is clearly visible at high infestation levels. At very high infestation levels, reddish-brown masses of mites can be seen hanging from the tips of leaves. When populations of spider mite are this high, the pest can be transferred accidentally to clothing, and spread around the crop by workers.
Spider mites are common pests on many vegetable and ornamental crops, including tomatoes, cucumbers, peppers, strawberries, roses, Gerbera and many other species.
In genereal, mites enter an over-wintering state known as diapause in autumn, and seek hiding places in the glasshouse structure or on equipment. They will emerge from diapause in the spring and can re-infest the crop. Occassionally, however, spider mites may also enter diapause in February in greenhouses not just for winter. Over-wintering forms are usually bright red, but red forms also occur later in the year.
Certain strains produce more severe ‘hyper-toxic’ damage, leading to severe leaf damage and leaf loss at low population densities. The exact cause of this damage is unknown, but these ‘hyper-toxic’ mites are usually considered to belong to the species Tetranychus cinnabarinus, or Carmine Mite, and are generally red in colour. Recent research also shows that these more damaging mites are able to lay more eggs than standard forms. Green forms of T. cinnabarinus are now known to occur, but do not appear to cause the same type of damage. Distinguishing between the species is not easy, and some taxonomists still consider T. cinnabarinus to be a form of T. urticae.
Other species of Tetranychus, such as T. evansiT. turkestani and T. pacificus also cause crop damage in some countries. Related mites such as the Fruit Tree Red Spider Mite, Panonychus ulmi, and Citrus Mite, Panonychus citri, are also important pests.


Broad Mite (Polyphagotarsonemus latus)
Cyclamen Mite (Phytonemus pallidus)
These tiny mites can cause immense damage to plants, and yet are difficult to see, and often not present on the leaves that show the damage symptoms. This is because they occur in the very middle of the growing point of the plant, where new leaves are being formed but have not yet expanded. They feed on this delicate leaf tissue, and as the leaf expands it becomes distorted. Some types of plants show less distortion, but affected leaves often appear glossy and discoloured.
Heavily infested plants can become severely distorted, and infestation can rapidly spread through a crop from an initial focus.
The pest can be controlled biologically with high doses of Amblyseius cucumeris applied onto and around the foci of infestation. Lower rates must be applied around the area of visible damage, as the pest is almost certainly present in lower numbers, even when no damage is yet apparent. Amblyseius californicus has also been shown to offer control, but this is not available for use on outdoor crops in some countries. It is also an expensive option compared to A. cucumeris.


Tomato Rust Mite (Aculops lycopersici)

This minute mite forms huge colonies on the stems of tomato or aubergine plants, which show up as a ‘rust-coloured’ mass which spreads along the stem. It belongs to the family Eriophyidae, which are characteristically tiny and ‘worm-like’ in appearance. Other species in the same family cause russetting on apples and citrus fruits.
Until recently, there were no adequate biological controls for this pest. Trials had shown that Amblyseius cucumerisAmblyseius californicus and Typhlodromips montdorensis were able to feed on the mite, but that none gave adequate control of the pest in glasshouse situations. The best results were obtained from the use of Amblyseius cucumeris CRS sachets (Amblyline cu CRS), which slowed the spread of infestation on individual plants but did not stop it.
Amblyseius andersoni, a predatory mite recently introduced into commercial production, has now changed that situation. This predator is available in our Gemini sachets (Anderline aa), which release several hundred predators onto the crop over a period of several weeks.
The Gemini sachets should be hung as high as possible on the plants, so that the predators are released in front of the advancing Rust Mite infestation. Trials in commercial tomato crops have shown that predators colonise the entire plant, and are able to prevent severe damage when used early enough.
— Information © Syngenta Bioline