Hostas are resilient plants that can take a lot of abuse and pests without an issue, making them a popular ornamental garden plant. However, although hostas are relatively infection-resistant, there are a few fungal infections that can take over your hostas and threaten their lives.
To treat fungus on hostas, you must identify which fungus it is, remove the hosta from the infected soil, prune it, and treat it with a fungicide. Then, keep the hosta in quarantine in clean, sterile soil while it recovers.
In this article, I will teach you the most effective way to eliminate fungal infections from hostas and tell you more about how to identify and prevent the most common diseases. So, let’s walk through the steps together and save your plants!
1. Identify the Fungal Infection on Your Hostas
Not all fungal infections are the same. Some are curable, others are not, and some aren’t even fatal to hostas. So, to understand how to best treat and eliminate the infection, you’ll need to investigate the plant and find out what kind of fungus has infected your plant.
The most common fungal infections for hostas are:
Petiole rot — also called sclerotinia or crown rot — can be fatal to your plants.
When your hosta has this disease, the lower leaves will turn yellow and become light brown and crispy. You may notice white fan-shaped mycelia on the soil or small, round yellow-orange mushrooms in the plant’s stem and leaves. These seed-sized mushrooms will spread over time and may change color from white to orange to brown.
Petiole rot thrives in warm, wet conditions, making it a summertime disease for hostas. If the infection continues to develop, the rest of the leaves will gradually wilt and die off from the base of the plant to the top.
Fusarium Root and Crown Rot
Fusarium wilt occurs when the roots of your hostas do not get enough aeration, causing them to decay and soften. As this happens, your hosta will not get enough water since the roots are dying off, resulting in leaves with dark brown tips, soft yellowing leaves, and leaves falling off until the plant dies.
Anthracnose, which appears during warm periods with high humidity and rainfall, causes rust-colored spots on hosta leaves. Since it only thrives in hot, humid environments, it is most common in the southeastern USA. This fungal disease is not fatal but will discolor your hosta’s leaves.
Phytophthora Foliage Blight and Root Rot
Phytophthora only thrives in wet conditions and infects hostas due to overwatering, increased rainfall, or improper soil drainage. Phytophthora only occurs in the southeastern US since it only became a problem for hostas due to widespread infection in plant nurseries in the southeast.
When this rot infects the crown of your hostas, you will notice rotted, light brown to yellow holes in your hostas’ leaves. When the decay infects the roots, the roots will cease growing, causing stunted growth and eventual death in your plant.
If the phytophthora has infected your hostas’ roots, you must destroy the plant. However, if the infection is not severe and only extends to the leaves, you may be able to save your plant.
2. Destroy Hostas With Incurable Diseases
Unfortunately, some of the most common fungal infections in hostas are incurable. The two diseases that you will never be able to eliminate are:
- Phytophthora root rot
- Fusarium root and crown rot
So, if your hosta shows signs of extensive root damage, it’s best to destroy your plants and get new ones for later. If your plant is beyond saving, most or all of the roots will be brown and mushy, and they may also smell bad.
If you find the roots are infected and dying, get rid of the hosta to prevent the disease from spreading. To responsibly dispose of the plant, place it in a plastic bag and throw it away.
It’s well worth mentioning that the spores of phytophthora and fusarium rot can stay dormant in your soil for years, waiting for you to plant something new in the area. The infection will return if you plant hostas or any other plant in the infected ground.
So, once you have these issues with your hostas, you should stop planting anything in the same area and drench the soil with bleach regularly for a few weeks to kill off the fungus.
3. Remove Your Hosta From the Soil and Prune It
If your hosta only has crown rot, minor root rot, petiole rot, or anthracnose, you will likely be able to save your plant with a bit of TLC.
To complete this disinfection step, you’ll need some tools to prevent the infection from spreading. Here’s what you’ll need:
- A plastic sheet, tarp, or tray.
- Clean pruning shears or a pruning knife.
- A disposable plastic bag, like an old grocery bag.
- A clean container or bucket of water.
- An empty, sterile glass container large enough to fit your hosta in it.
To start treating the plant:
- Lay out your tarp or tray. This barrier will keep the infected soil in one place, ensuring that the spores do not spread to your healthy plants or lawn.
- Next, dig up your hosta or remove it from its pot; take care not to damage the roots or displace the soil too much.
- Hold your hosta by the base of the plant, then hover the roots and soil over your disposable plastic bag.
- Remove the leftover soil from the plant’s roots using your fingers, shaking it off directly into the plastic bag. Be careful not to spill too much dirt since it will contain fungal spores.
- After removing the soil, dip the hosta’s roots into your water container to rinse any remaining soil particles. Gently massage the roots to get as much dirt and spores off as possible.
- Now, lay out your plant on your tarp. If there are brown, mushy roots, pinch them off with your fingers; take care not to break the healthy roots. The rotten roots should practically fall off on their own.
- If there are no rotten roots, you can remove the rotten leaves from your plant and leave anything that’s still green on the plant. Your hosta will still need healthy foliage and plenty of light to recover from the infection. However, if the roots are infected, do not prune the plant at this stage. Cutting the stems and leaves could introduce a root infection to the plant’s crown, making things worse.
- Place your hosta in your clean, empty glass container with the roots facing down.
Now that you have pruned and de-soiled your hosta, you can tie up your plastic bag and throw it away. Dispose of the water in your sink, and do not pour it anywhere outdoors. Then, sterilize your hands, pruning shears/knife, and bucket with a disinfectant such as isopropyl alcohol, hydrogen peroxide, or bleach.
4. Soak the Hosta in Hydrogen Peroxide
Now that you have isolated your infected hosta, it’s time to kill the fungus on the plant. A hydrogen peroxide soak will displace the spores and fungi on your hosta’s roots and leaves and kill most of the fungus.
To prepare a hydrogen peroxide soak, follow these steps:
- Mix four parts of water with one part of 3% hydrogen peroxide.
- Pour the solution into the container holding your hosta and let it soak for 5 to 10 minutes.
- After the time’s up, swirl the plant around in the liquid to displace any remaining spores.
- Pull the plant out of the peroxide water and lay it out to dry in a shady, well-ventilated spot for around 10 minutes.
5. Pot Your Hosta in Sterile Soil
The next step is to pot your hosta in a container with sterile-well draining soil.
Even if you do not plan on keeping it in a pot, placing the hosta in a container will help you control the soil humidity and ensure that there are no spores or fungi in your plant’s environment. Keeping your hosta in a “quarantine pot” will also prevent the infection from spreading to healthy plants in your garden.
If your plant has any yellow or wilted leaves, you can prune them off during potting. Ensure you leave at least three larger leaves to help the plant recover.
After potting, place your plant in a warm spot with partial shade far away from other plants. If the infection returns, you won’t want it to infect anything else. Do not water the hosta; let it stay dry for one week. Most fungi that live on hostas can only thrive in soggy, damp conditions, so drying the plant will “starve” the fungus.
6. Treat the Hosta With a Fungicide
When it comes to fungicides, there are many options.
However, in my hostas, I have seen a lot of success using regular treatment with a neem oil spray like Bonide Captain Jack’s Neem Oil Spray (available on Amazon), which comes pre-mixed and ready to use in a convenient spray bottle. I love this neem oil because it’s all-natural, gentle on delicate leaves and roots, and smells fantastic.
When I use neem oil, I apply the treatment once a week for around two months. Then, I give my plants a good spray every month or two as a preventative measure, especially when it’s warm and rainy.
If you do not want to use neem oil, you can use a commercial-grade fungicide such as mancozeb, which is very effective for fusarium, anthracnose, and petiole rot. Mancozeb is stronger than neem oil, which makes it suitable for heavily infected plants, but you must follow the instructions carefully. It can be harsh on a hosta if you use too much of it.
Conditions that promote fungal growth may also attract fungus gnats whose larvae will feed on your vulnerable hosta plants. To learn more about this problem, check out my article: How to Deal With Fungus Gnats in Your Soil
To eliminate fungus from your hostas, you’ll need to remove it from the soil, prune and clean the plant, and follow up by repotting it in sterile soil and treating it with a fungicide regularly.
After a few months of nurturing your hosta back to health, it can go back outside. Just be sure to avoid planting it in its old spot since spores can live in the soil for years unless you drench the dirt with fungicides. In addition, ensure that your hosta has plenty of drainage and never gets soggy since those conditions cause fungal infections.