Basil, like most other herbs have many ages in its leaves. Leaves do not last the lifetime of the plant, nor do they stay green forever. Pull any off that are yellow, as well as reduce the watering as I have mentioned MANY times before. Pull off all the flowers and green buds. They will soon bush out. Again, do not over water. Allow it to get a little wilted, then add a bit of water.

bluefish, Your plant is not that bad looking and can thrive if you make a few changes. Check to see that at least the top layer of the soil has dried out before watering, and then water profusely so that the whole pot is wet. Make sure that the water drains properly from the pot. If the pot sits in a saucer, empty it after watering. Basil is short-lived and a heavy feeder. Fertilize it with a high nitrogen fertilizer such as 30-0-0, but fertilize it only once a week. Pick a day of the week that's more convenient for you, and fertilize it always on that day. Do not fertilize with a general purpose fertilizer (20-20-20 or 15-15-15) or any fertilizer with a high middle number as this will encourage the formation of flower spikes. If flower spikes form, just pinch them off. This will keep your plant looking healthy longer and encourage more and larger leaf growth. Other than that, give it lots of sunlight, but if you get temperatures above 90 degrees, protect it from direct sunlight in the hotest part of the day.

It's had a transplant operation and is still recovering from the shock. To help itself, it is concentrating on some upward growth and getting rid of the older leaves which were using up energy. In a mature basil, the stems aren't green - they become brown and woody - it's only the newest growth which will have green stems. I think your basil is behaving as to be expected. It's difficult to over-water a basil - as long as you've provided adequate drainage. If you're worried - make sure to sit the pot up on little 'feet' which leave the drainage hole(s) free.

Her, fungus gnats thrive outdoors and if plants are outside all summer, then brought indoors, this will carry the infestation indoors where it will get into all indoor plants. The gnats don't really have much in the way of preditors outside, unless there Bt applied to soil as well as benefical nematodes that also live in the soil. I see no outdoor 'bugs' that attack the tiny gnats. There are beneficial insects used outside, but most are for controlling caterpillers and a few other destructive bugs, and have little to no protection for the gnats and their maggots. The maggots are the culprits that do damages to plants, as they feed off tender roots. This can weaken and kill plants. Ever see indoor plants die for no apparent reason? Its usually caused by the fungus maggots and not the gnats, who simply lay their eggs everywhere.