Rust

Symptom

It can readily be recognized when the orange colored pustules or uredia appear on the lower surfaces of the leaves and rupture to expose masses of reddish brown urediospores. In highly susceptible cultivars, the original pustules may be surrounded by colonies of secondary pustules. The pustules may later be formed on the upper surface  opposite those of the lower surface. The pustules are usually circular. They may be formed on all aerial plant parts apart from flowers and pegs. In contrast with the rapid defoliation associated with leaf spots, leaves infected with rust become necrotic and dry up, but tend to remain attached to the plants.