My basil started to get black spots when the temps started to drop down. I am not sure what the exact temperature was but the weather forecast called for a possible frost. Which I do not believe we got and if we did it wasn't really severe.

Make sure you pick it before a frost because after a bad frost it will look like it has been dead for weeks.

If you were going to dig some up I would do that right away before there is any damage done to the plants. Better to dig up a healthy plant then a damaged one. I suggest you do not put it off, I did that this year and lost some that I wanted to pull out. I did get to dig out some though so that is better then nothing.

So when picking it, you mention pulling up the plant? or do you just pick the leaves off? I guess it would be easier to cut off larger pieces of the stem leaves and all. I also had the same thing happen last year, we got an unexpected early freeze(and I was not paying attention to the weather channel until it was too late) and I lost a HUGE gorgeous plant. That wont happen this year. I guess I need to get out there soon. I'm just about finished with my greenhouse floor, so I can get all my benches etc moved back in and then the basil I have in containers can go in there. I'm hoping to keep it growing all winter for fresh basil for cooking.

The danger is between 40 and 45 degrees. It depends on how sheltered the plants are, etc. I say if the forecast is 42 or below go ahead and harvest. Make pesto or grind it in the food processor with olive oil and freeze it.

You can also put a bunch in a vase where it will stay fresh for a month, use it as you need it.