Weather conditions leading to rust outbreak
Rusts, caused by the fungi Puccinia and Uromyces, typically occur where low fertility, shade or other stresses occur. Optimal temperatures for attack are 68 - 86F (20-30C). Yet a rust outbreak occurred in late December, 2008, in the Southern California location above -- even though average temperatures were in the mid 50's. The fescue in question had very low nitrogen, and as important, had just received lots of rainfall. In California's dry climate, the rainfall and accompanying low light were enough to trigger infection, despite the low temps.
