There's no reason not to eat it now it has been picked.

The idea of not picking rhubarb after July is to give the plant a rest so that next year's growth is vigourous.

Somewhow, this became the idea that the leaf blades became poisonous, rather than just the leaves, later in the year and many people believe this is why you shouldn't eat it and, of course, if you aren't going to eat it you wouldn't harvest it.

So, from the plant's point of view, it would be better if it hadn't been picked but, since it has, go ahead and enjoy it.

I find our rhubarb gets rather woody by this time of year.

I picked and ate my last crop this weekend, leaving about 5 stems on each plant, and won't crop again this year now.