Sean there is no Rust in the U.S. yet, all that has been a scare by the Chemical companies to sell their product, it is still only in South America, if a wind storm brings it up we will start spraying when it hits N. Carolina. Rust is going to be a tiny white grain of salt like on the leaf that will increse in size as is mastitizes, If you said you had wet weather it could be pithium, it could could be magnesium deficiency or it could be caused by spider mites, does the leaf have tiny holes in it. Try spraying it with a mix of 10 lbs of Epsom salts and 20 gallons of water to the acre, see what happens. If you have ever had 2=4=D in your sprayer dont use it for anything but the weed killer. You can never get 2-4-D out of the sprayer in it's lifetime... Use another sprayer.... Keep me posted ... the color is not synonomous with the fungus Rust.. Hope this helps a little