What is Hosta Crown Rot Disease?

Crown rot is a disease caused by a soil-borne fungus that can survive in the soil indefinitely. This fungal disease is often favoured by wet conditions and heavy soils. Symptoms begin to appear on your Hostas usually after a prolonged period of hot, humid weather. While symptoms may vary from plant to plant, there is often little you can do once the disease occurs.

Signs of Crown Rot Disease

While the crown of the plants affected by this disease may exhibit dry rotting at or near the soil line, most other symptoms often go unnoticed—until it's too late.

The lower leaves begin to turn yellow, then brown, and then they wilt, indicative of dead tissue. The upper leaves will collapse very soon after this. The Hosta dies.

How Do You Stop Crown Rot?

Crown rot treatment is difficult, especially if it's not caught early enough, which is often the case. Usually, there's little you can do to save plants, so prevention is important.

Once the first signs of crown rot are noticed, it's best to simply pull the infected plants and discard them promptly. You'll also need to sanitize the area and surrounding soil to keep the disease from spreading to nearby plants.

Amending heavy, clay soil will help with any drainage issues that normally encourage this disease. Avoiding overly wet soil around plants and trees is important. Water plants only when necessary, allowing at least the top inch (2.5 cm.) or so of soil to dry out between watering intervals. When you do irrigate, water deeply, which will allow plant roots to benefit the most while allowing you to water less often.

The use of fungicide can help prevent the disease but is usually ineffective once it's completely taken hold.

How does Crown Rot get into the UK?

Crown Rot (Sclerotia rolfsii) often gets into the UK, by plants from abroad, without the relevant precautions like plant passports and inspections. Several days in transport will not help.

When the crown rot comes into contact with the Hosta it releases oxalic acids, and this kills the growth at the bottom of the Hosta, and the leaves begin to collapse.

What does it look like?

The plant base, and sometimes several inches of the soil around the plant, are covered with this white fluffy mycelium. It may stay in the soil for years, if not removed quickly & thoroughly.

Fluffy white threads (mycelium) of the fungus are typically present on the rotted tissue and the surrounding soil. It shows small spheres, like mustard seeds, sprinkled over the soil. These tiny spheres called Sclerotia allow the fungus to survive extreme cold winters and other unfavourable conditions. As they mature, their colour changes from white to a light tan or reddish brown.

What can we do to prevent Crown Rot?

Improving heavy, clay soil will help with any drainage issues that normally encourage this disease. Avoiding overly wet soil around plants and trees is important.

Water plants only when necessary, allowing at least the top inch (2.5 cm.) or so of soil to dry out between watering intervals. When you do irrigate, water deeply, which will allow plant roots to benefit the most while allowing you to water less often.

The use of fungicide can help prevent the disease but is usually ineffective once it's completely taken hold.

Captan or Aliette are most often used. Drench the soil (2 tbsp. to 1 gal. of water) while somewhat dry to allow the fungicide to penetrate well. Repeat this twice at 30-day intervals.

One key to avoiding crown rot is careful inspection. Before purchasing or transplanting, examine plants for yellow, wilted lower leaves, sclerotia on the soil surface, softening and browning at the bases of petioles, and white mycelium around damaged tissue. Checking for these symptoms will reduce the risk of Sclerotia rolfsii entering the garden.

What else do I need to know?

Symptoms include yellowing and browning of the leaves, then eventually leaves collapse.

The infected crown and soil surface has a white mat of fungus.

No fungicides are effective against crown rot.

Removal of Hostas with crown rot symptoms, and a great deal of the soil with it, thorough washing and disinfecting of tools used in infested soil, and buying disease-free plants are all ways to prevent crown rot. 

So! Now that I’ve frightened the pants off of you let’s look at reality!

Crown Rot of Hostas is a very rare thing in Hostas. You have much bigger things to think about such as slugs & snails, and vine weevil. Do not go thinking that every rotten leaf is Crown Rot. It isn’t. It’s just a dying bit of foliage which the Hosta offers up from time to time.

Don’t get me wrong! Crown Rot is a serious matter. Prevention is better than cure… particularly as there is no cure.

 Credit in parts to the author, Yard and Garden, and Iowa State University Extension and Outreach 

To learn more about Hostas, you may interested in reading : AI Generated Hosta Photographs, Watering and Feeding Your Hostas, What Are the Common Mistakes to Avoid When Growing Hostas?, Ways to Protect Your Hostas from Slugs and Snails and "Uncovering the Advantages of Bare Root Hostas:

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John Plant

Rewela Hostas

rewelacottage@gmail.com