"Diseased" Rosemary and Basil?

I have a lovely rosemary plant and two basil plants that I wintered indoors this past year. All of them were doing quite well. However, because they were growing larger in a very sunny window, I transplanted them, using some new potting soil (don't know if this is the cause of the problem). I planted the rosemary (standard variety) in the same pot as the basil (standard variety) and alongside a separate pot with the Queen Siam basil. The rosemary began to develop the white powdery fungus, and I treated it effectively with a spray of soap and baking soda. However, in time, the standard basil and then the Queen Siam basil began to develop white spots and the lower leaves, including new shoots (sadly), began to turn brown (texture was not completely dry) and to fall off. The rosemary, although slower to develop a similar problem, has become brown and rusty on some of the lower leaves, which dry-up and sometimes fall off. I've begun picking off anything that looks suspicious, but to no avail (have continued to try to use the soap spray). There are no insects in evidence and the tops of the plants are still growing decently, although the basil is quick to develop the brown rust (which I've named the creeping crud). I'd certainly be willing to start from scratch with the basils, but I'd like to know what this is and how I can prevent it in future. Also, if it's possible to save the rosemary, I'd like to try. I'm wondering if the problem is some sort of disease in the potting soil (which I have not used again) and I'm wondering whether planting the basil and the rosemary in the same pot and/or keeping them nearby was such a great idea. These plants are in quarantine on my balcony now, far away from any other plants.

Potting soil that has been standing around in a shop is often contaminated with all kinds of micro-organisms. Before using any soil, it should be sterilized by pouring boiling water over it. Use right after it cools. The plants may recover by being out in the fresh air and in the sun. This will harden off their exterior and make them more able to withstand an attack of a disease.
I wonder if a contributing factor was the shock of repotting. The rosemary in particular may have become a bit too dry and the brush with death weakened it. Make sure to not let it dry out. Check out our web-site as we have answered similar questions before and posted the answers on our web-site. Go to www.richters.com under the "Q&A" heading in the "News & Info" section of the site. Click on "Search Question & Answers" and type in"rosemary", to find the topics that sound as if they would answer more of your question.