Control of red spider mite

I have had problems over the last few years with red spider mite infestations on my cucumbers and climbing beans. This year was worse than ever and I am considering what I can do to try to combat the problem before next year. I have a small lean to greenhouse which is against the wall of my house and I garden on a terrace which is surrounded by glass balustrades. Any tips or advice would be gratefully received.

Hello Kerri

I used biological control one year and found it very effective. It’s quite expensive though, but I only used it once at the start of the year - as soon as I saw evidence of spider mite - and the predators kept reproducing. It’s important to add some humidity as well. i can’t remember where I got mine from as it was some time ago and there seems to be more available these days, but this link looks pretty comprehensive: https://www.dragonfli.co.uk/blogs/news/how-to-control-red-spider-mite.

Good luck next year!

Thank you! I tried a biological control the year before last with little success but I might try the Amblyseius andersoni sachets early on in the season. The link you provided is very helpful.

I’m wondering about fumigating the greenhouse too but that seems a bit drastic.

The red spider mite problem is a problem connected with hot and dry summers. They simply love hot and dry weather and loathe everything that’s wet or damp.
So the best thing to do when facing red spider mites is to chance the conditions and thus making it uncomfortable for them to be in your greenhouse.
I suggest spraying the plants with water at least every other day for some time, maybe more often.
This should get rid of them. Worked for me more than once in the past…

Btw. cucumbers love moist climate (don’t know about the beans, but I think they should be ok with it too)

Hygiene over winter is essential in glasshouse spider mite control in my experience. Make sure you get all old canes and pots and plant debris right out, if only for the time you are doing the cleaning, and scrub out all the corners of the frames. The females overwinter in anything they can find to overwinter in. If you have soil beds make sure you weed them thoroughly and I make sure I mist under the leaves of overwintering plants - choose warm sunny weather so you don’t encourage fungal diseases. And then introduce a predator the moment you spot the first sign of infestation in the spring so that your predator keeps breeding along with the mites. And of course make sure you keep misting throughout the growing season, paying particular attention to the undersides of the leaves. It’s a pfaff but hopefully you’ll eventually get rid of them. In my experience it is important always to isolate bought in plants and keep them monitored for pests - particularly white fly, green fly, red spider, scale insects, and mealy bugs, before you add them to existing plant collections. Sounds a bit like scorched earth policy I know but hopefully you’ll only have to do it once and it will quiet the bit at the back of you brain that sometimes screams “spray” no matter how many years you’ve been organic (never been anything else but at times you feel desperate)

Wasn’t reading properly there. Terrace, glass balustrade. Yep, hygiene. Sounds like spider mite heaven. Winter hygiene, summer misting.

Thanks for your advice Kathryn. I’m going to give the greenhouse a good clean and all the pots etc. Also I’ll buy new canes next year and get rid of the old ones. Fingers crossed I can get on top of it!

I tried to damp down the greenhouse each morning this year, particularly when it was hot and left a tray of water in there too. I think maybe I need to mist/spray as well to try to keep up the humidity and maybe twice a day when hot. It’s much harder on the terrace as it dries out very quickly - thinking maybe some wet capillary matting (or something similar) between pots might be worth a try.

Missed this - yes, capillary matting can help with spider mite control, and with powdery mildew control as well