Blight Injury on Milkweed Leaf
Can you see the grayish-brown bands of dry, dead tissue on this leaf? This is a fungus attacking the milkweed leaf. See the concentric rings? As the leaf grows and ages, and as weather conditions change over the summer the infection can grow slowly or rapidly depending on the conditions. The infection grows more quickly when conditions are favorable.
While the leaf spots are often ugly, the damage is often just that, ugly. They don't really affect the plant too much. Infected plants often bloom and set seed. But, heavily infected leaves may die earlier than uninfected leaves. Do you think blight can affect the plant's growth?