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.
Rust Fungus Identification
Many types of rust fungus disease affect specific annual and perennial flowering plants, but no matter the rust disease, gardeners can recognize this problem by observing the speckled masses that form on the surfaces of leaves. Like the namesake, many of these pustules are rust-colored, but gardeners should also suspect rust if they see brown, orange, purple, red, or yellow dry spots on foliage.
Rust spots are usually tiny and scattered across plant foliage like freckles. Affected plants can have dozens of rust spots on each leaf, and it’s possible for a single leaf to have more than a hundred rust spots.
Commonly Affected Plants
Rust disease often affects Alcea rosea (common HollyHock), but hollyhocks aren’t the only potential victims of this fungus. Pay close attention to the signs of rust fungus in the following plants during the summer months:
Plants with a heavy rust infestation might experience curling or withering of leaves, and the plant can lose its leaves entirely. If this much damage occurs, you can expect to see stunted plant growth.
How to Water Plants to Prevent Rust Fungus
Rust fungi, like many fungal plant diseases, flourish in wet conditions. The most important step you can take to reduce rust in your flower garden is to stop overhead watering. Instead, use a drip irrigation system or a watering wand to deliver water at ground level. If this isn’t possible, water your flower garden early in the morning when the sun’s rays will quickly dry your flowers’ foliage.
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.
Control with Commercial Fungicides
You can choose several commercial fungicides to control rust fungus. Apply the sprays when you see the first signs of disease and continue applications according to package directions through July. Look for commercial fungicides that contain these active ingredients:
If you are unsure about the active ingredients that would work best to control a rust issue in your garden, contact your local Cooperative Extension Service for recommendations.
Choose Rust-Resistant Varieties
Hybridizers are continuously developing new flower varieties resistant to rust fungus. If you’ve experienced rust for multiple growing seasons, it might be time to remove susceptible plants and replace them with these proven varieties:
- New England Asters ‘Honeysong Pink’ and ‘Purple Dome’
- Hollyhock 'Happy Lights’
- Snapdragons 'White Monarch’ and the Rocket series
Even if you plant rust-resistant varieties, you must give them enough room to grow. Proper plant spacing increases air circulation that enables plants to dry more quickly. Overcrowding plants and dampness are the perfect conditions for many fungal diseases.
Snapdragon – Rust.” Umass.Edu, 6 Mar. 2018, https://ag.umass.edu/greenhouse-floriculture/photos/snapdragon-rust
Purdue Agricultural Communications Service. “Purdue Agriculture - Plant and Pest Diagnostic Lab.” Purdue.Edu, https://ag.purdue.edu/btny/Herbaria/Pages/Arthur%20Herbarium/The-Rust-Fungi.aspx
Rust Fungi. Purdue University Extension
“Rust in the Flower Garden.” Umn.Edu, https://extension.umn.edu/plant-diseases/rust-flower-garden