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pests - spider mite


Spider Mite - Pests


Commonly asked question(s):

- How do I get rid of spider mite?
- What are the little red spots on my Lotus, Black Eyed Susan, Yucca and Gloriosa?
- What are the spider webs on my ginger lilies?


How do I get rid of spider mite?

Spider mite is a particularly difficult pest to eradicate as it readily develops tolerance to chemical controls and generally requires several applications of chemicals in order to eradicate all stages of the lifecycle (mites, nymphs and eggs).

Therefore biological controls such as the predatory mite Phytoseiulus persimilis are the most effective control against spider mite. This particular predator reproduces at twice the rate of spider mite. It is highly active under hot dry conditions, where just one mite of P. persimilis can consume 20 eggs or 5 adults per day! However, it requires a minimum temperature of over 16ºC (although daytime temperatures of 21 ºC are preferable) and there needs to be sufficient numbers of spider mite present for the predatory mites to feed on. Obviously, if you choose to use biological control then you cannot also use chemical control as this will kill the predatory mites!

There are a number of cultural practices that you can also use to help prevent and reduce outbreaks. Spider mite thrives in warm dry conditions, so damp down greenhouse floors and paths to increase the humidity. Regular inspection of the undersides of leaves will also help to detect the problem before it spreads. Pick off and burn any infested leaves when you find them. Finally, at the end of the growing season, make sure that you take time to really clean out your greenhouse properly as spider mites like to spend the winter hidden in dry crevices and plant debris until the weather warms up again in spring.



What are the little red spots on my Lotus, Black Eyed Susan, Yucca and Gloriosa?

It sounds like red spider mite. This is a common glasshouse and conservatory pest at this time of year, and it is a particularly difficult pest to eradicate. Spraying with Provado should help but spider mite readily develops tolerance to chemical controls and generally requires several applications in order to eradicate all stages of the lifecycle (mites, nymphs and eggs).

Biological controls such as the predatory mite Phytoseiulus persimilis are the most effective control against spider mite. This particular predator reproduces at twice the rate of spider mite. It is highly active under hot dry conditions, where just one mite of P. persimilis can consume 20 eggs or 5 adults per day! However, it requires a minimum temperature of over 16C (although daytime temperatures of 21 C are preferable) and there needs to be sufficient numbers of spider mite present for the predatory mites to feed on. Obviously, if you choose to use biological control then you can’t use chemical control as well because this will kill the predatory mites! There are a number of cultural practices that you can also use to help prevent and reduce outbreaks. Spider mite thrives in warm dry conditions, so you can try misting your plants to increase the humidity. Regular inspection of the undersides of leaves will also help to detect the problem before it spreads. Pick off and burn any infested leaves when you find them. Finally, at the end of the growing season, make sure that you take time to really clean out your conservatory properly as spider mites like to spend the winter hidden in dry crevices and plant debris until the weather warms up again in spring.



What are the spider webs on my ginger lilies?

Ginger lilies range from frost hardy to frost tender and are best kept inside in most parts of the UK. It sounds like your ginger lily could be suffering from spider mite. Spider mite thrives in the warm, dry conditions of a conservatory and will cause discolouration to the leaves. Have a look for these tiny creatures on the underside of the leaves. If you do spot any spider mites then it is important to control them, either by misting your plant daily to increase humidity (spider mites don’t like humid conditions but ginger lilies do!), introducing a predatory mite: Natural Pest Control - Red Spider Mite, or by spraying with a chemical spray which will be available at all good garden centres.

If you can’t see any sign of insects then the shrivelled leaves may be a sign of over-exposure to sunlight, which causes the leaves to curl and brown. Try placing your ginger lily in a position that receives lots of light, but not direct sunlight. You’ve done the right thing in feeding your ginger lily; ideally it should be fed monthly in the spring and summer with a balanced liquid feed: Chempak® Fully Balanced Feed - Formula 3. Also make sure you keep the soil moist (but not wet) during the growing season - these plants originate from moist woodland and will suffer if kept too dry. Ease off watering in the winter and keep the soil just moist.