Difficult to say for sure. I have seen similar, but smaller marks due to minor insect damage from leaf hoppers (kind of like very small grasshoppers), but you say no insects. My second guess would be a fungus of some sort. Try not to get the leaves wet or let them stay wet overnight i.e. water early in the day. It wouldn't hurt to spray with Neem oil-it acts as both an insecticide and a fungicide.

Your otherwise beautiful plants look like they need to be cut back even further, I see some flowers forming.

F. DeBaggio

Thanks, I appreciate the help. yeah, they definately need to be pinched back a bit more, I stopped paying attention to them when they started looking bad. I did have some insects at one point, most likely spider mites (tiny, red), but it was never an infestation, and I haven't seen any in a couple of weeks at least.

Basil seems to be more prone to leaf spot diseases than other herbs. I believe that that is what your plants are suffering from. It would be worthwhile to try the neem, but I would do a leaf test first, I think, at this time of year. Some neem products can cause burning in hot temperatures.

My apologies for a complete beginners questions here... I get the idea of a leaf test, but can you give a hint of how or where I could get a leaf tested?

I think what rhizo_1 means is to test the Neem spray on a small section of the plant first before spraying the whole plant. Very good advise indeed-thanks for clarifying. Also, spray in the evening when it is cooler and the sun is not as likely to burn Don't spray when the air temperature is above 80ºF just to be safe.

F. DeBaggio

Ah, apparently I fail on reading comprehension. Thanks for the help all.

You read it perfectly. We just needed frances to clarify. :-)

Well, this spring something actually ate huge holes in my basil AND my mint! Not sure what the critter was that did the damage, but suddenly, nothing is eating the plants any more. Whatever did it is gone!

My basil was sending up blooms like crazy, and I read it roots easily in water, so I picked 6 stems with leaves, stuck them in a glass, changed the water daily, and after 7 days roots appeared. Now the roots are legion!! I am going to plant my new basil plants under the drip system for my grapevines, and I notice that after the big cut back on my original basil, it has tons of new leaves!

Ain't growin' basil grand?