How To Get Rid Of Rust Fungus On Plants

On cars, a little rust can turn into a lot in a short time when affected spots combine into a bigger problem. Gardeners face a similar issue when rust fungus affects plants, and a few speckles run together to form large masses that distort and deform a flower's foliage. Learn how to get rid of rust fungus once and for all.

Rust Fungus Identification

There are many species of the rust fungus disease affecting host-specific plants and flowers, but no matter the species, gardeners can recognize this problem by observing the speckled masses that form on the surfaces of leaves.1 Like the namesake, many of these pustules are rust-colored, but gardeners should also suspect rust if they see dry spots that are brown, orange, purple, red, or yellow.

Rust spots are usually tiny, scattered across plant leaves 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.

Flowers Affected

Rust disease is legendary in hollyhock flowers, but they aren’t the only potential victims of this fungus.1 Pay close attention to signs of rust fungus in these flowers during the summer months:

Aster

Carnation

Geranium

Iris

Lily

Pansy

Primrose

Snapdragon

Sunflower

Sweetpea

Damage Caused

Flowers with a heavy rust infestation may experience curling or withering of leaves, and the plant can lose its leaves entirely. With this much damage to leaves, gardeners can expect to see stunted growth in their plants.

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 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.

Organic Sprays to Use

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 for garden fungus control. The efficacy of baking soda spray may be enhanced by mixing it with light horticultural oil.

Commercial Fungicides to Use

You can choose from several commercial fungicides to control rust fungus.2 Apply the sprays when you see the first signs of disease and continue applications according to package directions through July. Look for these fungicides and brand names:

Chlorothalonil (Daconil 2787)

Mancozeb (Fore, Dithane, or Penncozeb)

Myclobutanil (Systhane)

Trifloxystrobin (Compass)

Rust-Resistant Flowers to Grow

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:

Aster: ‘Crimson Beauty,’ ‘Honeysong Pink,’ or ‘Purple Dome’

Hollyhock: ‘Happy Lights’

Rugosa rose

Snapdragon: ‘White Monarch,’ ‘Orange Glow,’ the Rocket series

Even when choosing rust-resistant varieties, you’ll get the best results by not overcrowding your plants. Proper spacing promotes air circulation which carries disease spores away from the garden.