Spray for Black Spot: Cornell Mixture
Add to one gallon water 1 tablespoon baking soda, 1 tablespoon horticultural oil (garden centers carry this) or canola oil and a drop of dish soap (not detergent). Mix, spray on roses and other things prone to fungus and mildew such as tomatoes, hollyhocks, cucurbits.
This is a preventive measure so start spraying when the leaves have just emerged before any sign of the disease.
Cornmeal as anti-fungal?
Sadly, cornmeal and cornmeal water are not the wonder remedy for fungus that they have been touted. As often happens on the internet, one small reference to cornmeal working against one kind of fungus that occurs on peanut plants seems to have blossomed into a cure-all for plant fungi. Don't waste your time or money on cornmeal for this purpose. [ The Truth About Garden Remedies: What Works, What Doesn't and Why. by Jeff Gillman]
Neem Oil as anti-fungal and pest repellant? I have some neem oil, but haven't tried it yet. I will keep you posted.
Sure fire squirrel repellant (a teensy bit gross but it works)
I use a biodegradable cat litter made from corn. I take some of the urine clumps (NO POOP!) and sprinkle them around the tomato plants, being careful not to get any on anything that will be eaten like the tomatoes or nearby basil, etc. It works beautifully. If you do not have a cat borrow some from a friend with a cat. It only needs to be done once or twice during the growing season. Use when the tomatoes are starting to ripen. Be sure to use biodegradable litter like the corn or newspapers ones, clay is not great for the garden soil. A little goes a long way.