17 November 2022

Customer Question – Spider Mite control in HOT greenhouse?

Q. “Hello – I’m a little confused about the two sorts of biological control for spider mites. For the first time ever my greenhouse plants were decimated this summer. I’ve cleaned all I can, and await advice. I grow tomatillos for making Mexican sauces, and they were wiped out. The cucumbers survived longer, but even they succumbed. I moved the aubergines outdoors, and they were fine. Because it might be another hot summer, do I need to introduce one in spring, for the cooler weather, then another as temperatures exceed 10 degrees? This year my free-standing greenhouse got VERY hot, even with shading and damping. What do you recommend? Thank you so much!” Candy

A. Thanks for the message and spider mite was rampant this summer, so lots of people were in the same boat. Female spider mites overwinter in the cracks and crevices of your greenhouses, so the first thing to do is to clean and fumigate the greenhouse to make sure nothing is over wintering. Our Horticultural Disinfectant and Garlic Greenhouse Candles are ideal. This will ensure the greenhouse is free from pests that have flourished during the summer and from any fungal diseases. Ensuring the glass is clean will also let in as much light during the winter.

There are 2 spider mite predators available Phytoseiulus and Ambly Andersonii, but Ambly Andersonii is the best predator for low and high temperatures as it is much more tolerant of temperatures . As you have not suffered before I don’t think you need to go too mad as you may find you do not get them again, but normally we recommend letting some Ambly Andersonii go in the spring i.e. position their sachets on the plants as temperatures start to rise to combat any over-wintering females that may have survived through the winter. Then if it is looking like a hot summer, then re-introduce at 6 weekly intervals throughout the hot summer (we have programmes available), or monitor the crop and introduce at the 1st signs of any attack, but prevention is always better than cure.

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