For daily wit & wisdom, get the Almanac newsletter.

How to Identify and Control Rust Plant Disease

Fungal rust disease infiltrates these spinach leaves.

Image Credit:
Rust photo by Howard F. Schwartz via Wikimedia Commons
Written By: Catherine Boeckmann Executive Digital Editor and Master Gardener

What is rust plant disease? This fungal disease looks like you have rust on your plants and affects a wide range of woody and herbaceous flowers and vegetables. Even though it rarely kills plants, it reduces their health, vigor, and flower production.

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 by wind or water, which is why rust disease often spreads after watering. Wet surfaces are also needed to cause infections.

Identification

How to Identify Rust Damage

Rust diseases come in different varieties and can affect a wide range of plants. People often struggle with rust on their roses. It is easy to remember the defining characteristics of this fungus as they match its name. Rust plant disease will look similar to the rust that appears on that old bicycle in the shed.

  • Look for yellow or white spots forming on the upper leaves of a plant.
  • Look for reddish to orange blister-like swellings called pustules on the undersides of leaves.
  • Orange or yellow spots or streaks appear on the undersides of the leaves.
  • Within these spots that form are spores.
  • Usually, leaf distortion and defoliation occur.
rust plant disease on a leaf
Small pustules appear on the undersides, and sometimes the tops, of leaves when a plant is infected with rust.
Photo Credit: Bruce Watt, University of Maine. 

 

Control and Prevention

How to Control Rust Fungi

Unfortunately, there is no easy treatment for rust. Try these tips:

  • Remove all infected parts and destroy them. For bramble fruits, remove and destroy all the infected plants and replant the area with resistant varieties.
  • Clean away all debris in between plants to prevent rust from spreading.
  • Avoid splashing water onto the leaves, as this can help spread rust.

Rust Prevention

  • Dust your plants with sulfur early in the season to prevent infection or to keep mild infections from spreading.
  • Space your plants properly to encourage good air circulation.
  • Avoid wetting the leaves when watering plants.
  • There are many effective rust fungicides you can try. Ask your local nursery for which products you should use.

Plant Disease

About The Author

Catherine Boeckmann

Catherine Boeckmann

Executive Digital Editor and Master Gardener

Catherine Boeckmann loves nature, stargazing, and gardening so it’s not surprising that she and The Old Farmer’s Almanac found each other. She leads digital content for the Almanac website, and is also a certified master gardener in the state of Indiana.

Read more from Catherine Boeckmann

More Like This

Comments

<span>Johnnychew</span> Tue, 03/26/2019 - 20:07
How to clear the flower leaf RUST FUNGI...
<span>Lou</span> Sun, 09/02/2018 - 16:42
Should the soil be replaced in the planters that had rust?
<a title="View user profile." href="/author/editors">The Editors</a> Thu, 06/29/2023 - 16:20

Lou-

Yes, we recommend replacing the soil to prevent to spread of the spores.

 <span>Hilary</span> Wed, 05/31/2017 - 20:42
We have had very wet weather lately in Maryland and my pepper plants have rust spots. The first flowers are just beginning to appear. I have removed all leaves that show signs of rust - the younger leaves seem fine at the moment.. There are some black marks on the stem at the joints. Some nearby tomato plants have some leaf distortion but no rust spots. Should I remove the pepper plants, spray with a fungicide or wait and see what happens?
<a title="View user profile." href="/author/editors">The Editors</a> Fri, 06/02/2017 - 09:12

Pls see our advice above: there is no easy solution. Are your plants well spaced apart? A small matter at this stage, perhaps. But as for the fungicide...maybe try dusting with sulfur instead (as noted above). "Wait and see" may be a disappointment. You might feel better about trying something. Again, see above. Hope it works!

 <span>Camille</span> Sat, 08/06/2016 - 19:28
My white hydrangea blooms have turned brown. Leaves are healthy, when new bloom appears, the white turns brown and die. I have about eight brown blooms now.
<span>Simon Cooper</span> Sat, 06/06/2015 - 10:48
Hi, newly planted Hydranger was doing well for a couple of weeks but has now suddenly wilted with black marks on all the stems at the bend points. It doesn't look under watered, is it possible to overwater a hydrangea?? Thank you!
<a title="View user profile." href="/author/editors">The Editors</a> Mon, 06/08/2015 - 15:54

Black marks on your hydrangea sound like a fungal infection. It's been wet or humid or you're getting water on the plant's leaves. First, get rid of any fallen leaves. Then make sure your plant has good airflow and isn't crowded. Only water at the soil level when the soil is dry 3 to 4 inches down (poke your finger in the soil to check). When it's dry, water deeply enough that you end up watering about twice a week. Also, make sure the soil drains well and the plant's "legs" aren't wet. If this continues, you may need a fungicide spray.

 <span>Clifford Edwards</span> Fri, 05/29/2015 - 13:41
my Canna Lily leaves, turned beige after one month in my pots. Just cut off the leaves I'm told.
<span>Deb Jordan</span> Thu, 11/13/2014 - 19:17
I have several hydrangeas that were planted by the previous home owners. I live in NC. In late August when moved in, all the blooms were dead and dried and most of the leaves had rust spots. It is now November and the plants are developing nice green new growth at the end of the branches. However, almost all of the old leaves have many rust spots and are pale green. I would love to prune the plants way back to remove all the rust and start new healthy growth. Can I do this? When? How short? Will they bloom next year? Is there anything I should do to kill and avoid further rust? Thank you so much for your advice.