Q.Gardenia Brown Spots on Leaves
Gardenia bush was fine with a slight powdery mildew at bottom which I treated. Watered on Thursday and light on Saturday. Checked Tuesday and there were brown spots all over the leaves and there is heavy leaf droppage. Have 2 other gardenia bushes and they are fine and were also previously treated for powdery mildew. Home remedy for the powdery mildew from gardeningknowhow: 1 gallon water, 4 teaspoons baking soda, a little non-degreaser dishwashing soap and a little cooking oil. What happened and is there any way to salvage the bush? Do I need to worry about my other bushes?
It sounds like you used the recipe for homemade pesticides.
The recommendation for Powdery Mildew recipe is in the links below.
You do need to avoid spraying any plants with any product during bright sunlight or heat. Early morning is best treatment time.
Also make sure the soap used does not have any bleach additives.
I would just wait it out, washing the plant is not likely an option with the addition of oil to the mixture you used.