Small, yellow spots quickly produce typical 'rusty' pustules containing spores. Pustules are not visible for 7-10 days after infection. They are usually found underneath the lower leaves and spread very rapidly. Infections are often first found as a 'hot spot' with a few plants covered in rust.
The spores can blow long distances between crops.
Can cause major crop losses if it starts early and is uncontrolled. Once rust starts in a crop, dews and fogs are sufficient to create a serious epidemic.