The fungaluglies are best treated prophylactically - much more difficult to eradicate than prevent. Also, given that you're on the organic forum, your options are further limited if you're to stay within organic principles. IOW, those fungicides that DO work as fixatives DON'T work with an organic mindset.
You could try sprays with chamomile tea or sulfured molasses in them. You could also try milk sprays, but I have found these concoctions to be far less than stellar as fixatives. Neem oil also has anti-fungal + insecticidal properties and in my estimation is probably your best bet. A cold-pressed product (virgin neem oil) is much preferred over some of the other products that tout neem extracts as an ingredient but use steam or solvents as extraction methods, which destroys most of neem's beneficial properties.
Neem is GREAT, but will burn if applied too heavily, or improperly mixed, it needs to first be emulsified, then added to your spray.
Your plants may "burn" or have a reaction to what you are using in excessive heat.
Organic Recipe for Mildew
1 tbs. Baking Soda
1 tbs. Olive Oil
1 tbs. Liquid Coconut oil soap
1 gallon water
Apple Cider Vinegar Fungicide: For leafspot, mildew, and scab
Mix 3 tablespoons of cider vinegar (5% acidity) with one gallon water and spray in the morning on infested plants.
Baking Soda Spray: for anthracnose, early tomato blight, leaf blight and spots, powdery mildew, and as a general fungicide:
Mix 1 tablespoon baking soda, 2 1/2 tablespoons vegetable oil with one gallon of water. Shake this up very thoroughly. Cover upper and lower leaf surfaces and spray some on the soil. Repeat every 5-7 days as needed.
Chive Spray: For preventing apple scab and downy mildew on cucumber, pumpkin and zucchini.
To make: Put a bunch of chopped chives in a heat proof glass container, cover with boiling water. Let this sit until cool, strain and spray as often as two to three times a week.
Compost and Manure Teas: Many people have success with manure tea keeping blight and other pathogens away from plant. Soak the area around plants and use as a foliar spray. Do not use on seedlings as it may encourage damping-off disease.
To Make: Fill a 30 gallon trash can with water. Let sit for 24 hours to evaporate the additives (use rain water if you can). Add about 4 shovelfuls of manure to this and cover. Let it sit for 2-3 weeks, stirring once a day. Strain and apply as needed.
Various manures supply nutrients as follows:
Chicken manure: nitrogen rich. Use for heavy feeders such as corn, tomatoes and squash.
Cow Manure: contains potash, use for root crops.
Rabbit manure: promotes strong leaves and stems.
Horse manure: leaf development.
Compost Tea: Make and use just the same as you would the manure tea. This is another terrific reason to compost all those prunings, grass clipping and kitchen wastes.
Fungus Preventative: This blend is surprisingly potent preventative spray to protect your plants.
To make: Gather a handful of corn leaves, clematis leaves (any kind) and as much of the paper like outer leaves of garlic as you can. Process thoroughly in a blender. Then mix with sufficient water to make a thin liquid. Let sit for an hour, strain and spray on plants as a preventative.
Garlic Oil Fungicide Spray: For leaf spot and mildews
To make: Combine 3 ounces of minced garlic cloves with 1 ounce of mineral oil. Let soak for 24 hours or longer. Strain. Next mix 1 teaspoon of fish emulsion with 16 ounces of water. Add 1 tablespoon of castille soap to this. Now slowly combine the fish emulsion water with the garlic oil. Kept in a sealed glass container this mixture will stay viable for several months. To use: Mix 2 tablespoons of garlic oil with 1 pint of water and spray.
Horseradish (preventative for fungal disease)
To make: Process one cup of roots in food processor till finely chopped. Combine this with 16 ounces of water in a glass container and let soak for 24 hours. Strain liquid, discard the solids. Now mix the liquid with 2 quarts of water and spray.
Milk for Mildew
Milk with its' natural enzymes and simple sugar structures can be used to combat various mildews on cucumber, asters, tomato, squash and zinnia foliage. Use a 50/50 mixture of milk and water. Thoroughly spray plants every 3 to 4 days at first sign of mildews or use as a preventative measure.
Milk can also be mixed at a rate of 2 ounces milk to 18 ounces of water and used as a spray every 7 to 10 days to treat for fungal diseases on cucumber, tomato and lettuce.
Tomato Protective Spray
To make: Mix 1/2 teaspoon of antitranspirant (like Cloudcover, Wiltpruf etc.) with 8 ounces of skim milk, and 1 gallon of water. Spray plants. Clean out your sprayer when done and flush with fresh water.
powdered milk may be substituted for the skim milk.
Chamomile Spray: Chamomile is a concentrated source of calcium, potash and sulfur. The sulfur is a fungus fighter. This can also be used as a seed soak prior to planting.
To make: Pour 2 cups boiling water over 1/4 cup chamomile blossoms. Let steep until cool and strain into a spray bottle. Use as needed. This keeps for about a week before going rancid. Spray to prevent damping off and anytime you see any fuzzy white growth on the soil. Chamomile blossoms can be purchased at health food stores and usually grocery stores.
Seaweed Spray: Seaweed spray is rich in nutrients and minerals. It provides protection from many fungal diseases and can be used to prevent damping-off.
To Make: Use 2/3 cup of kelp or seaweed concentrate to 1 gallon of water, spray.
Horsetail Tea (Equisetum arvense)
The common horsetail plant, which is very invasive, is rich in silica and helps plants to resist fungal diseases and can be used to increase plants light absorbing capabilities. Use on most plants to combat powdery fungi, and on vegetables and roses to control mildew. You can use this on seedlings and plants in greenhouses. May prevent damping off.
To make: In a glass or stainless steel pot, mix 1/8 cup of dried leaves in 1 gallon of unchlorinated water. Bring to a boil, then let simmer for at least 1/2 hr. Cool and strain. Store extra concentrate in a glass container. Will keep for a month. Dilute this mix, adding 5-10 parts of unchlorinated water to one part concentrate. Spray plants that show any symptoms of fungal type disease once every 4 days. Spray your seed starting mixtures to prevent damping off.
This kills aphids, small caterpillars and is useful as a fungicide for mildew and blackspot on roses. The toxic agent is hydro-cyanic acid, so in preparing the spray use an old saucepan.
Gather 450g (1 lb) leaves and young stems of elder prefer-ably in spring when the sap is rising. Place in the saucepan and add 3.3 litres (6pt) water. Boil for half an hour, topping up as necessary. Strain through old tights and use the liquid cold and undiluted. It will keep for three months if bottled tightly while still hot.
Twigs of elder, cut in the spring and placed at intervals, inverted V-wise, over early turnip rows, are said to ward off attack by flea beetles.
The oxalic acid in rhubarb leaves is a safe control agent for aphids, particularly those on roses. Cut 450g (llb) rhubarb leaves, place in an old saucepan with 1.1 litres (2pt) water and boil for half an hour, topping up as necessary. When cool, add ldsp soap flakes dissolved in 275ml (l/2pt) warm water. This acts as the wetting agent when added to the strained rhubarb liquid. Stir the mixture thoroughly and use undiluted as a spray
Something I do is lightly sprinkle plain horticultural cornmeal and dry garlic on the soil every 4-6 weeks. This helps with fungus and bug control as the cornmeal helps fight the fungus and the garlic deters the bugs. It's also good for the soil as it gets watered into the dirt.
If you apply it at the right time of the year, it acts as a weed killer, too. Inside, you can use it to soak your hands and feet to make them nice and soft and to get rid of athlete's foot and toe fungus. Very handy stuff!