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Plant disease spotlight

Plant disease spotlight

Welcome to our monthly plant disease spotlight! Unpleasant as they may be, we know, but worthwhile to learn more on!

Let’s talk rust. Rust disease is a fungal parasite that grows on many plants that we see and use. Rust doesn’t often kill the plant host, but it can inhibit its growth and whether or not it produces the food we need. *The Irish potato famine was actually caused by a species of rust, and it wasn’t the only one.


- Photo courtesy of the old farmers almanac

 The most common and easily identifiable symptom of rust is orange, yellow, brown or red spore masses on the outside of the plant. They look like raised bumps on the leaves or stems of the plant, but sometimes appear on blooms as well. Rust can cause leaves to fall off, and of course, if too many leaves fall off or there are too many rust spots, the plant will die.

Rust fungus is not a danger to humans or animals, but food with rust on it doesn’t taste right.

It’s not easy to prevent rust fungus in our home gardens because it can affect so many types of plants. Buy your plants from a local and reputable nursery and check the stem and leaves for spots. Even if the plants don’t have any rust spots, you should quarantine them away from the rest of your plants for two weeks before planting them to make sure rust spots don’t appear.

Rust fungus has to sit on a wet plant for 6-10 hours before it can infect it. Overhead watering can help to create the ideal environment for rust fungus, so if you can, try to only wet the soil around the roots and not the entire plant. If you have to use a sprinkler or other overheard watering method, water early in the morning so the leaves aren’t wet overnight. Rust is very prevalent in the Spring and fall as the temperature drops. 

Chemical fungicides are only effective before rust symptoms appear and have to be repeated every 4-5 weeks during the time that the conditions are right for the fungus to grow. One method that we use to treat rust is with a sulphur based spray- or sulphur powder itself! (Available online or in store) Once it warms up, rust can’t reproduce, so treatments aren’t necessary.

Depending on the species of rust, copper or sulfur fungicides can be used if you want to go the organic route. If you’re not sure which is best, come into the plant store and have a chat with our resident plant expert.

If you find rust on your plants, remove the infected plant parts and dispose of them carefully. (Kill it with fire!) Make sure to carefully clean up any fallen leaves and rake out some of the loose soil around the plants to ensure you haven’t left any rust behind. Once you’ve taken care of that, you can use a thick layer of mulch to help prevent the spores from making their way back to the leaves during watering.

Source: Planet Natural Research Centre Blog:

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