Listed below are several homemade sprays that I have used for years. I believe that my grandfather also used these and left the recipes in one of his gardening journals
Seaweed spray is rich in nutrients and minerals. It provides protection from many fungal diseases and can be used to prevent damping-off.
How to make Seaweed spray:
Use 2/3 cup of kelp or seaweed concentrate to 1 gallon of water, spray. You can get kelp or seaweed and many gardening centers or a health store. And if you live near a lake you can harvest your own.
Chamomile tea is an excellent preventative for damping-off. This is my most important spray in the spring when I am starting seedlings. Use the chamomile spray on seed starting soil, seedlings and in any humid planting area. 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.
How to make a Chamomile spray:
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. Tip: If you don’t have access to Chamomile blossoms, Chamomile tea will work just as well.
Apple Cider Vinegar Spray
This works well for leafspot, mildew, and scab.
How to make Apple Cider Vinegar Spray:
Mix 3 tablespoons of cider vinegar (5% acidity) with one-gallon warm water and spray in the morning on infested plants. Spraying in the morning gives the plant and soil a chance to dry during sunlight hours.
I use a diluted cider vinegar mix to clean my plant leaves. I also rinse my pots in cider vinegar after I have washed them.
I prefer homemade sprays to most store bought sprays. They have fewer chemicals and when I need a spray, I just mix up what I need. This way I have lees bottles of garden and plant sprays sitting around.