Just like I don't like to use toxic products on our skin, I don't like to use it in my yard or in my vegetable garden, either. But occasionally, I do find the need to use something to help ward off bugs, fungus, mildew, etc.
The following is a recipe I use to try to keep the plants healthy and to help fight off "plant sickness." You could probably use more essential oil than what I did, but I once burned the leaves of my roses with a "too strong" blend. So I use this milder version first to see if it does the trick, before moving to a stronger one.
Test it on your plants first before spraying the whole thing. And I personally do not spray the parts of the vegetable plants that we will be eating in the next few days.