Pests aren’t a gardeners only problem, plant diseases are also one of the most dreaded problems for gardens. Their effects can range from aesthetic ones to death and they can spread very rapidly between plants and can even infect the soil itself. They are very common and herbs are especially susceptible to them. Just about every person who has grown herbs has experienced the destructive power of the plant diseases. I personally had lost a few herbs to diseases like rust. Below is a link to a page from planetnatural.com that lists the different disease and how to treat them. To add, planetnatural.com is a great site for organic gardening. I really recommend that you explore the site.