The part that the Primitive forgot to mention is that the reason for the threat in the first place is that this summer is unusually cold and wet. Stem Rust likes wet conditions, and about 70F temperature. --Pretty much the same as most molds and fungi.
In other words, the main reason the stem rust threat exists as much as it does this year is the planet stubbornly refuses to be globally warm, and plagued with drought, as Lord Gore decreed.