You should post this over in the tomato forum, they will know best what you should do :>)

I discovered spider mites last season late July, a few weeks before the start of harvest. At the time the plants were big and the mites were impossible to eliminate. My only hope was to slow them down so that new growth outpaced my pruning tick infested branches. By that time it was too late for anti mite oil to work because there were too many of them. Hard water showers every day helped slow them down a lot. This meant spraying the hose directly at the plants at full blast.

At this point in the season when the tomatoes are little the anti mite oils might work. I got these mites on my eggplants and cucumbers as well but the tomato plants suffered the most. It was finding them on eggplants last season that led to my discovery of them killing my tomatoes.

Here is a link that might be useful: Link to my log entry on mites written last July