Sunflower rust

The first signs of rust usually appear when sunflowers are at or past bloom. Conditions are more favorable for infection when sunflower plants have reached maximum size and the plants have formed a dense canopy. Cinnamon-brown pustules (uredia) occur first on lower leaves, then on the upper leaves, and eventually on the petioles, stems, and back of the flower head. Uredial pustules occur on both the upper and lower surface of the leaves, are roughly circular, and measure up to 1/16 inch in diameter. Several pustules may merge into a  much larger, irregularly-shaped aggregate pustule. Pustules may or may not be surrounded by a chlorotic (yellow) border.