Why are my sunflower leaves getting yellow and rusty?

Question

My sunflower plant is about to bloom. Its leaves are getting yellow and rusty. How will I fix it? I had watered it quite high several days ago as I could not understand the problem. Now I have stopped watering and applied neem oil on it. What should I do to revive it quickly?

Answer 1

It sounds like rust.

Compare to the images at the linked page.

Why was they infected:

Favorable conditions for rust infection include frequent periods of leaf wetness (fog, dew) and temperatures between 55 and 85 F.

How to avoid it:

Rust is best managed using multiple tools and techniques, including destruction of overwinter hosts (volunteers, wild sunflowers), avoiding planting next to a field with infested residue, selection of a sunflower hybrid with genetic resistance and application of an efficacious foliar fungicide.

Answer 2

It may be that your plant is a variety that is susceptible to rust or other leaf disease. Here is a photo of my collection of sunflowers this year:

There are 14 plants in this assembly. They are plants sown from a bird seed collection, seeds chosen randomly. Most of the large flowers have set seed and matured and have been removed to deny the birds the food. The one exception to this is the closest plant which had its leader chewed off by a nuisance deer and is only now flowering.

Note the plant to the left of the one with multiple medium sized flowers. Most of the plants have a few leaves drying out and looking yellow, but that one in the middle of the image suffered from rust right from the start. It produced a good head all the same. Just by observation and experience, it seems likely that this one plant was fertilized by a different parent, one that might be susceptible to disease.

In short, you might just be unlucky in choice of seed or plant.