This might help.
Your peas should be planted out in the sun in the cool months of the year and have good air circulation. Which means they should not be near a solid wall. A lot of people with small home gardens like to put their garden bed up against a solid fence or wall. The wall blocks air circulation and shades plants so they will lean away from the wall. It is better for the garden bed to be able to be accessed on all sides so not up against a fence or wall and far enough out that it won't get shaded by the wall.
Fungal diseases are hard to control once they get a foothold, so prevention is key. Make sure all of the garden debris and infected plants are taken out and destroyed. When the weather is conducive to fungal growth and before symptoms appear, you need to start spraying the plants preventively.
You can use horticultural oil or sulfur but not both.
If I know it is going to rain and probably rain for a few days, I find it easier to use the horticultural spray. I like ultra fine or summer spray. Neem is has anti fungal properties and is a good preventive but not effective after fungal disease takes control. I don't like neem my self it gives me a headache and it may not be good for bees. Horticultural oils leave a coating on the leaves that helps to wick off moisture and prevent fungi from getting a foothold on the plants. It does not wash off with rain unlike sulfur. Milk spray also works the same way by coating the leaves. I prefer to use milk that has some fat in it or mix some oil with the milk which will act as a sticker. I would spray the plants every 5-7 days.
I use a drip watering system and I mulch with newspaper to prevent splashing up back onto the plant. Any leaves that are heavily infested should be removed and bagged to prevent spread. Make sure the plants are well spaced so that air can move between them. For damping off problems cinnamon is a natural fungicide. Steep cinamon overnight in hot water, strain and spray on plant leaves and the soil. Make sure the cinnamon is strained well through a couple of coffee filters or it will clog your sprayer.
Other natural fungicides are made from Hydrogen peroxide, and baking soda spray which helps to dry the leaves.
Sometimes if fungal problems are aggressive I will double up and use a fungicide with chlorothalonil (daconil- you need to check what is listed) Daconil by itself usually can't control fungi issues but when used in conjunction with another fungicide it is synergistic.
Powdery mildew can usually be controlled if it is caught early. Take off the damaged leaves from the bottom of the pea plant. They don't do any good any way.
AACT actually can help plants by making them more resilient and better able to fight off problems.