Red spider mite, often better described as two spotted mite (Tetranychus urticae)due to the small black dots on their backs, attack a wide variety of plants. They extract sap from plants and normally feed on the underside of leaves. The damage caused can be severe, infested leaves will turn yellow and plants can die completely. When the spider mite builds up they create threads or webbing, which they use to transport themselves either by air flow or on clothing as people brush past infested plants. Spider mites can also be transported when plants or plant material is moved.
Spider mite leaf damage Two spotted mites
Spider mites can reproduce very quickly at higher temperatures. At 25.c spider mite populations can double in less than three days. Warm and dry conditions favour spider mite development. The time when spider mites appear red is when they are entering or coming out of diapause, this is triggered by shorter day length, falling temperatures and lack of food. Diapause is when the mites find somewhere to hide and are dormant. During this phase they do not feed or reproduce and are not easily found or fed on by predatory mites. Once day lengths and temperatures rise, the spider mites come out of diapause/hibernation and start feeding and reproducing. If growing under artificial lights, spider mites can occur all year round.
The best way to control spider mite is by seeing it early, so make regular checks of plants, especially under leaves and in the growing heads of plants. Look for leaf speckling or yellowing leaves. Purchasing a small hand lens will help not only find spider mite but also to check on predator levels once introduced.
Prevention treatments begin with the introduction of Amblyseius andersoni predatory mites. This predator can feed on pollen and a variety of mites and can be supplied in slow release breeder sachets, which release predators onto the plants for 3-4 weeks. If introduced once a month, this will ensure predators are already on plants ready to tackle any new spider mite infestations. This predator is also more tolerant of lower humidity than the traditional Phytoseiulus persimilis predators and can survive longer without spider mite as a food source. However Phytoseiulus persimilis is more efficient as a predator when spider mite numbers and temperatures are higher.
A new link in the biological control chain for the control of red spider mite is with the introduction of Spider Mite Killer Propagation sticks. These small breeder sachets can be inserted into rockwool blocks, propagation blocks, seed trays etc when the plants are very young. They will release predators onto the plants at an early stage to help prevent early spider mite attacks. Once the plants are larger hooked sachets of Amblyseius andersoni can be hung on plants. To ensure good coverage, apply one sachet per plant.
New Propagation sticks [ Amblyseius andersoni ]
If spider mite is not observed until high numbers are already present (when leaves are already yellowing or webbing is present) then it is best to apply Spider Mite Killer Phytoseiulus persimilis . This is the most efficient predator and thrives in warm, humid conditions. At 20.c female Phytoseiulus lays more eggs than a female spider mite and eat 5 adult spider mites and 20 young larvae or eggs a day.
This predator can be used in conjunction with other predatory mites and should be introduced by sprinkling over infested leaves or by pouring into distribution boxes and hung onto plants, as close as possible to the spider mite infestations.
When there is webbing on plants this normally means there are very high numbers of spider mite present, repeat applications of Spider Mite Killer predators could be required to fully irradicate the pests. Spider mites always head towards the growing points of plants, ensure predators are applied there. In very hot dry conditions, predators may stay lower down the plant, so misting or raising the humidity where possible will help with predator movement and disrupt the spider mites. If webbing is present and predators cannot be applied quickly, it is also good practice to apply SB Plant invigorator to the worst affected areas. This physical acting spray will kill spider mite adults but not leave harmful residues that may harm future predator introductions. Cease applications once predators are applied.
Plants recovering from spider mite attack often first show new green growth that is not showing spider mite damage. It is also good practice to keep checking predator levels on the plant with a hand lens after application. They do reproduce faster than spider mite in the right conditions but also need some time to establish. If severe levels of spider mites are present, keep applying predators until you can easily find them or spider mite damage reduces or disappears.
Biological control with predators of red spider mite will win the battle with enough numbers and the right environment. Avoid using pesticides before or during those times when relying on predators.