Mr. Savel,

Thank you for your question about the white substance on your Jalapeno pepper plant and the decline of your plant.  The two options that come immediately to mind are powdery mildew (which you have addressed with the sulphur spray), and mealybugs.  While mealybugs are soft bodied insects with a waxy covering on their body, they create long white filaments that can look like flakes or white patches.  The adults can usually be found in the leaf midrib section or on the veins.  Females lay eggs sacs with as many as 600 eggs in them, and when the crawlers hatch they are extremely small and can be blown leaf to leaf or plant to plant by breezes.

Mealybugs can be very difficult to control because they live in hard to access and inspect parts of the plant, because their waxy covering protects them, and because there are consecutive generations.  If you are just treating one or a small number of plants the adults can be washed off or rubbed with a cotton swab dipped in rubbing alcohol.  You can try filling a sink with a solution of two teaspoons of mild dish detergent (not soap) per gallon of water, covering or holding the soil in place, and swishing your plant in the solution.  This will help dislodge the mealybugs.

There are also houseplant insecticides that are labeled to treat mealybugs.  Both the plant you want to treat and "mealybugs" must be listed on the label.

Unfortunately, it is recommended that heavily infested plants be disposed of because of the difficulty of successful treatment and the possibility of spread.

You will want to take a magnifying glass (if needed) for a positive identification of mealybugs on your plant.

Here's a good article on mealybugs from the University of Maryland Extension:

https://extension.umd.edu/hgic/topics/mealybugs-indoor-plants

Here is a good article on powdery mildew on houseplants from the Clemson Cooperative Extension:

https://hgic.clemson.edu/factsheet/powdery-mildew/

From your photo it looks like your infestation is extensive.  For both powdery mildew and mealybugs it is recommended that severely infested leaves be removed.  Along with any remediation you should incorporate good growing practices--make sure the plant is in a sunny well ventilated site, water when dry (don't let the plant remain wet or dry), lightly fertilize for optimum grown (but don't overfertilize--more is not better here), and make sure plants are properly spaced from each other to optimize air circulation and reduce infections.

Good luck with your pepper plant.