Common name : Glashouse red spidermite
Latin Name :Tetranychus urticae .
Type of organism : Mite
Season : Mid-spring to late autumn
Encouraged by: Hot dry conditions –a particular problem in greenhouses and conservatories but may infest outdoor plants during hot summers.
These little pests may be tiny, but they have power in numbers. Breeding incredibly rapidly particularly in hot,dry conditions they can soon do a lot of damage. To be honest it is hard to grow plants in a greenhouse or conservatory without coming across the red spider mite at some stage. Indeed you are likely to find it is a regular visitor!
The leaves become mottled with numerous tiny yellow flecks as the mites feed and if numbers are allowed to build up leaves may become sucked dry, turning dry and shriveled and ultimately going brown and crispy. They may even form a series of webbing or silken ‘ropes’ over the infested plants,these providing miniature escape routes so that they can move off and on to fresher, greener plants. The real problem is that if you only notice the problem at this late stage, you have already got yourself a severe problem, so it is well worth keeping an eye out for those first signs of flecking.
The mites themselves are hard to see unless you have extremely sharp eyesight : each measures less than 1mm in length, is a yellow-green colour with two dark markings on its back. Now these camouflage colours may come as a surprise when you consider its common name,but in fact this mite only turns a reddish orange colour during autumn and winter, when the females are hibernating. (NB they are NOT red at this time of year, see v enlarged image!!)
To say that control is not easy would be a huge understatement. Indeed I would always recommend binning heavily infested plants. Many of the mites have now developed resistance to some of the most commonly used pesticides – so however much and frequently you spray, it will have no effect. You could try using my preferred option, biological control, where, crazy as it may sound, you introduce another mite. But this mite is round, orange-red and is a rampant predator of the so-called red spider mite and rushes around the infested plants, providing excellent control as it eats its way through the pest mites. If you do decide to try this option, do make sure that you know the greenhouse is not contaminated with pesticide residues (as these could prove lethal to the predatory mites) and that the temperatures are high enough . We have them waiting to send out to you at www.pippagreenwood.com/products/protect-your-crops , just click on ‘New Products Available’ on the home page! Provided these conditions are met, biological control works really well as long as the infestation has not become too heavy before you introduce the predators – and of course the great thing is, the predators get on and do the job for you…..whilst you sit back and relax!
Keep conditions as cool as is practicable for the plants.
In creasehumidity – try misting the plants regularly, damping down the greenhouse .
Always inspect newly purchased plants thoroughly to avoid introducing the pest.
If in any doubt,keep them in a ‘quarantine’ area for a couple of weeks.
Clearing up infested plants is very difficult so dispose of them wherever possible.
Introduce biological controls, the predatory mite Phytoseiulus persimilis works well and means no unpleasant chemicals and no chemical residues, especially significant if you’re growing edible crops! We can send them out to you promptly, just look in the Protect Your Plants Section of the Products area of this website.