Fungal rust disease is one of the most common fungal diseases that affects plants. Rust can spread fast to other plants nearby, so it's good to act fast to try and prevent this from happening.
WHAT IS FUNGAL RUST?
Fungal rust actually refers to quite a large group of fungi that can affect plants - there are currently over 5,000 known types. As with most types of fungi, rust usually thrives in mild and moist conditions - with warm temperatures and low light intensity - where leaf surfaces stay wet for a prolonged time. Once an infection occurs, it can then spread easily from plant to plant, as the spores are carried by the wind or are passed from infected to healthy plants during watering. Rust can sometimes kill plants - but the most common damage is that it will reduce your plant's overall health, which can, in turn, leave it more vulnerable to other problems.
Orange-brown or yellow (rust-colored) pustules develop on the leaf surface - often on the underside. These pustules contain fungal spores. (Note: they can also be white in color)
The pustules may also spread to the plant’s stem
Yellowing of the leaves
Premature leaf drop
WHAT TO DO NOW
Unfortunately, there's not an easy way to treat rust, especially as you may not notice symptoms until the infection has become quite severe. In these cases, it may do more harm than good to try and treat it. For example, if the majority of a plant’s leaves are affected, then removing all of these leaves will make it difficult for the plant to survive afterwards. Therefore, you may want to consider throwing the plant away to stop the spread and make sure your other plants won't get infected.
If you want to give it a try nevertheless:
Carefully remove all damaged parts and leaves and dispose of them properly. Remember that the spores can still be spread easily, so it’s important to fully destroy any removed material. Don’t compost it or leave it lying around near your plants
Thoroughly clean around the infected plant to ensure that no spores are left behind
Make sure that your plants aren't placed too close together to help stop spreading
Avoid misting and splashing water on the leaves for a while, as this could also spread any leftover spores
As a last resort, consider using fungicides. These can be quite harsh on your plant, and the environment, so shouldn’t really be used unless it’s strictly necessary
Alternatively, you can try using Neem oil
HOW TO PREVENT THIS FROM HAPPENING AGAIN
Fungal rust disease is definitely one of those ‘prevention is key’ cases. Spacing your plants apart and ensuring that they have good air circulation will help to discourage the fungus from setting in. Similarly, make sure to avoid overwatering - along with the other types of damage this may cause your plant, such as root rot, an excess of water creates an ideal environment for fungus.
Do your best to encourage strong growth in your plants, but bear in mind that overfertilizing can also contribute towards a repeat fungal infestation. This is because when a plant takes in plentiful nutrients, it results in lush green growth, which in turn attracts fungus.
Ensure that your plant pots have good drainage, and avoid allowing leaves to stay overly wet for a long time.
Finally, keep an eye on your plants - check them every now and then for any symptoms or any decline in overall health. This will make it a lot easier to treat if you manage to catch the signs early.