How to treat Brown spots on Red Orange tree leaves?
I'm growing a "Blood" Orange tree in a container in Maryland. Recently brown spots have appeared on 4 leaves. I tend to think that this is Alternaria.
It's important to stress that a few days ago (before the appearance of the Brown spots) I discovered Slugs in the container. At the beginning I sprayed the leaves with a product for "insect, disease and Mite control" (which contains Sulfur and Pyrethrins) . After I discovered that it doesn't kill Snails, I killed them with salt (around 3-4 tea spoons overall that didn't touch the leaves). The Brown spots appeared couple of days, after I applied Bayer's product and the salt.
My questions are:
1. Can it be the result of the product that contains Sulful and Pyrethrins?
2. Can it be the result of spreading the salt on the ground?
3. Is it Altenaria or is there another possibility?
4. What is the best solution for this situation?
I enclosed a picture of one of the leaves.
By the way, in order to make sure that there are no Slugs, I used now Elemntals Slug & Snail, and I hope it will prevent any more of them.