Spores are very light and spread by winds or passing animals. Simply touching the diseased tree will attach spores the toucher and will flick spores into the atmosphere.
Spores move from the ground up to the leaves during rain periods.
Spores will also move up the plant from rain. Spores last a long time on the ground. An area affected by Hemileia Vastatrix may never recover. This disease is temperature related. The spore gets on the leaf, germinates, and sucks nutrition out of the leaf.