When it gets around 90 degrees, rust tends to back off and wait for cooler weather.
I've had good luck spraying with Green Magic (not Simple Green) that you can buy off Ebay or the Lily Auction.
This is probably the least toxic.
I try to water early enough that plants can dry off before going into the night.
Also plants that get early sun tend to have less rust than those getting morning sun later.
Adding minerals to soil (like Azomite) can help make plants stronger and more rust resistant.
High nitrogen fertilizers can flame rust. I try to use long lasting organic fertilizer.
I try to buy plants with good rust ratings.
I'm hybridizing for plants with good rust resistance too.
