On cars, a little rust can turn into a lot of rust in a short time when the rust spots combine into a bigger problem. Gardeners face a similar issue when rust fungus affects a plant; a small outbreak can quickly spread and affect the appearance of an entire plant. Rust disease does not affect a plant’s general health and is usually not fatal, but you should learn how to get rid of rust fungus once and for all.
What is Rust?
Rust is caused by fungi that belong to the order Pucciniales. There are about 168 rust genera with approximately 7,000 species. Why so many? Because each fungi species is unique to a specific plant family. Which means that the rust that infects my hollyhocks will not infect anything else in my garden. It only grows on hollyhocks. It will also only infect a certain part of its host. So in the case of my hollyhocks, it will only infect the leaves. Other species of fungus will infect only the leaves or petioles (leaf stems) or the plant stems or fruits. No other part of the plant is infected.
How did it get its name rust? Because the spores of the fungi are brown or rust colored. The fungi doesn’t just cause rusty patches on plant surfaces, they can also cause cankers, galls or what is known as witches brooms which is when a mass of shoots grows out of a single spot on a tree. They look like giant birds nests or brooms, hence their name.
Rust fungi are obligate parasites which means they need a living host. Although they can stunt a host plant’s growth or severely damage the leaves, they will not kill their host plant.
Rust is a huge problem in agriculture where they can ruin entire crops of grain or fruit. It is also a big problem for the home gardener where it can attack fruit and nut trees, ornamental trees and shrubs, roses and other flowering plants.
What Causes Rust?
Rust disease is caused by a fungal parasite that needs living plants to survive. Rust diseases occur most often in mild, moist conditions. Rust is spread by spores that are transferred from infected plants to healthy plants. These spores can be transferred either by the wind or by water, which is why rust disease often spreads after watering. Wet surfaces are also needed to cause infections.
Symptoms Of Plant Rust
Rust fungi are easy to identify on the plant. Here are some signs to look out for:
- The appearance of pale leaf spots eventually turns into spore-producing structures called pustules.
- The pustules normally appear on the lower leaf surface producing massive numbers of microscopic spores. They can also form on leaf stalks, stems, flowers, and fruit.
- These pustules can be yellow, orange, black, brown, or white. Some have a rusty brown color, giving the rust fungal disease its common name – brown patches.
- In some cases, you will notice dozens of pustules on each leaf. Severely affected leaves could turn yellow and die prematurely
Rust Treatment for This Plant Disease
For rust fungi, prevention is the best defense. Rust thrives in a wet environment, so do not overwater your plants. Also, make sure your plants have good air circulation inside the branches and around the plant itself. This will help it dry its leaves faster.
If plant rust does affect your plant, remove affected leaves at the first sign of rust color on plant leaves. The faster the affected leaves can be removed, the better chance your plant has for survival. Be sure to dispose of these leaves. Do not compost them.
Then treat your plant with a fungicide, such as neem oil. Continue to remove leaves and treat the plant until all signs of the plant rust are gone.
Control by Organic Methods
A weekly dusting of sulfur can prevent and treat rust fungus. Neem oil, a botanical fungicide and pesticide, also controls rust. Some organic gardeners swear by baking soda to control garden fungus. The efficacy of baking soda spray might be enhanced by mixing it with light horticultural oil.