on June 10, 2016
These creatures are members of the Acari family Tetranychidae, live on the undersides of leaves, and tend to spin protective silk webs there, or just about anywhere in your greenhouse and surrounding areas.
Spider mite can be an intimidating pest, hiding over winter and creating explosions of webbing on plants in the greenhouse, making their leaves change colour and even causing some to perish or drop, if left unchecked.
Luckily, there are a couple of things that can be done to be rid of them which worked for us.
- Clean, clear and scrub!
The mites seem to relish dark (and not so dark) corners, hidden spaces and crevices. So to open the first line of attack, and defence, clear and thoroughly cleanse anything that is not being used, or is simply messy, from the greenhouse: stacks of plastic pots, old labels, bags of compost, worse-for-wear plants, weeds in plant pots, etc. This reduces the number of hiding places and, more importantly, places which you cannot reach or see into easily.
The most practical time for doing this is early spring, when there are not many plans in the way and the greenhouse is at its most accessible for a deep clean. After a general clear out, I simply got a bucket of water with a bit of washing up liquid, a large yellow sponge, and got to work, – scrubbing and sloshing everywhere I could reach.
- High humidity
In the glasshouse (or conservatory, for that matter) spider mite is king. There is never enough time to keep up with the watering and the sun bakes the air relentlessly (in a good year!). Just the kind of thing that these pests enjoy. A regular regime of watering (the pots together with the floor, if possible), misting and airing brings the humidity of the air up, and dampens their spirits.
- Phytoseiulius
A very effective spider mite predator without side effects as far as we can tell! This is an organic way to control pests which is both more rewarding and more fascinating than squirting pesticide around. It can be ordered online from a number of reputable suppliers and released onto the affected plants. The key is just making sure that it is warm enough for the creatures to survive. And keep misting!
This is not a substitute for the first bullet point, however, and the area needs to be kept clean at all times as general good practice and to avoid re-occurrence of the invasion.
Good luck!