The spider mites invaded my coriander first rendering it totally useless so I had to throw it all away (it was bolting anyway). It infected my other plants but at lower levels: the holy basil (high infestation), sweet basil (low), and black peppermint (very low).
I was at my wits' end so I opted to use a pesticide I found at the gardening store （ベニカ・ファインX）which seemed to work with only one application. I didn't see the spider mites come back for weeks.
But NOW they are back.
I'm really tempted to go the easy way and just use the pesticide I used before, but as I'm growing mainly herbs for consumption, I'd like to minimize use of pesticides. I tried using neem oil and I'm not sure it really works (it requires continuous application anyway and does not kill on contact). The neem oil does work wonders for my itchy scalp though.
Reading about spider mites on the web made me realize these are tough little creatures that easily adapt and have very short life cycles, making it very hard to get rid of them completely.
My current ideas on how to control the problem:
1) Buy コロマイト which is usually effective and is even counted as 'safe' for normal use. But applications are only limited to 2 per year to prevent the spider mites from developing immunity. This option is very appealing, but I don't know if I'd like to spend money on the product + shipping on top of all the money I've already spent on gardening supplies and whatnot.
2) Throw away all infected plants. I just did that with the holy basil (it has run its course anyway). I'm having second thoughts with the black peppermint (the most infested one this time) because it's still thriving and I'm attached to it -- I grew it from a lanky nursery plant with all but 4 tiny leaves into a lush plant that has already crowded its container! And I thought peppermint was a natural repellant? The spider mites seem to love sucking on its juices! The black peppermint variety is particularly strong, and the unfortunate thing for me is that I associate the peppermint smell with the insecticide BAYGON. So every time I eat the peppermint leaves, I feel like I'm drinking insecticide!
The red rubin basils also seem to have light infestations -- though I can't really tell because of the yellowish bottom leaves. I think I will get rid of them anyway because they have totally lost their purple color and their strong basil-y smell. (I suspect due to lack of sunlight).
Thankfully, the spider mites have stayed away from my eau de cologne mint.
3) Diligent spraying of neem oil 2 times a week for prevention.
I found a few stray spider mites on my hydroponically grown kangkong (water spinach) but I don't think the damage is extensive yet. I want to prevent it before I am forced to take extreme measures on the kangkong!
Fall will be here in a few weeks just in time for me to grow new plants so I don't feel so bad throwing some of them away. I plan to do a thorough cleaning before planting my new batch of seeds. I've decided to start everything from seed from now on to prevent contamination. I'm also going to stay away from the brand of potting soil I first used, which seemed to harbor insects right out of the bag.
Goodbye, Holy Basil. 頑張ったね。