How to Identify and Manage 7 Common Hosta Diseases

I hate it when everyone tells me a plant is impossible to kill. If it starts to look sick, I feel like a failure.

If you can relate, don’t feel bad. Just because hostas are typically disease-resistant, that doesn’t mean they’ll only get sick if you mess up. Sometimes stuff happens.

This guide will help you figure out what to do if you find your plants looking miserable. Here are the diseases that we’ll cover:

Hostas go dormant in the heat, which leaves them susceptible to diseases. The same goes for those that are stressed by sun scorch or drought.

In other words, do your best to plant your hostas in a spot where they will be protected from too much sun, protect them during extreme heat, and make sure they always have the water they need.

Also, be aware that sometimes what looks like a disease is actually a pest problem. Voles can chomp on the roots leaving them looking sad aboveground with no obvious cause.

Examine your plant and compare your symptoms to those listed below to be sure you know what you’re dealing with.

1. Anthracnose

If you’re going to run into disease problems when growing hostas, this is the one you’ll most likely see. It’s pretty widespread and it’s caused by numerous different fungi (all in the Colletotrichum genus) that exist across the planet.

The good news is that this probably won’t kill your plants, but it can be pretty ugly.

If you know that anthracnose is in your area or you’ve struggled with it in past years, treat your plants with copper as described above as soon as the leaves unfurl and before you see any symptoms.

2. Bacterial Soft Rot

Bacterial soft rot impacts the stems (technically called petioles) and the lowest leaves on the plant. These will turn soft and mushy. If you kneel down and take a big whiff, you’ll notice a rotten smell.

The bacteria that cause this problem (species in the Erwinia genus) often enter through cuts, freeze damage, or insect damage on the stems and leaves.

Poor drainage, high humidity, and temps over 80°F increase the chances that this disease will attack. Unfortunately, there is no treatment, so you’ll have to pull the plants and start over.

3. Cercospora Leaf Spot

Unlike spots caused by anthracnose, which have a black border, those caused by Cercospora have a rust-colored border with a tan or red center. Similar to anthracnose, this probably won’t kill your plant but it will mar the appearance.

This is common in the US south and appears during the hottest part of the summer.

The treatment is identical to anthracnose, so don’t worry if you can’t tell the two apart.

4. Fusarium Rot

If your hosta leaves turn yellow and then brown before withering away, fusarium root and crown rot might be paying your plants a visit. Stunting (both above and below ground) is also common.

Many species in the Fusarium genus cause the disease, but F. hostae is the most common. Unfortunately, once this disease is in your soil, it’s there for a long, long time. So long that you might as well forget ever planting hostas in that same spot again.

The fungus that causes this disease (Sclerotinium rolfsii var. delphinii) thrives when air temps reach 80 to 90°F and there’s lots of rain or humidity.

It starts as a sort of white slime on the petioles. This fungal growth eventually turns tan or reddish-brown. The leaves turn yellow, then brown, then they turn mushy and die. Leaves pull away from the stems easily and eventually the entire plant collapses.

This disease has spread across the US on contaminated nursery plants, so always inspect new specimens before planting them.

‘Halcyon,’ ‘Honeybells,’ ‘Snow Mountain,’ and ‘Tall Twister’ are resistant to this disease. Avoid planting ‘Lemon Lime,’ ‘Munchkin,’ ‘Nakaiana,’ ‘Platinum Tiara,’ and ‘Tardiflora.’

Unfortunately, there isn’t any effective treatment for the home gardener. You’ll need to pull the plants and then dig down at least six inches and remove the soil. Replace it with fresh, clean soil.

6. Phytophthora Foliage Blight

While it’s not as common as some of the other diseases on this list, phytophthora foliage blight is becoming a bigger problem.

This disease thrives in wet soil.

If phytophthora strikes, you’ll notice water-soaked spots on the leaf that start to spread and become larger. Eventually, the center of the spot will turn brown and dry.

Underground, the roots will be unhealthy and start to rot away. The entire plant will grow slowly and be stunted before eventually dying.

The best way to deal with this disease is to avoid it in the first place. If only we could do that with all diseases, right?

To avoid it, check plants when you buy them for any signs of disease. Don’t bring them home if they have any evidence of disease. Once you plant, be sure to water at the soil level and be careful not to overwater. Soggy soil is a quick route to disease.

Remove and destroy any plants that exhibit signs phytophthora foliage blight.

7. Viruses

There are a few different viruses that can attack hostas, including hosta virus x (HVX), tomato ringspot virus (ToRSV), impatiens necrotic spot virus (INSV), and tobacco rattle virus (TRV).

All of the viruses cause brown and yellow spots and discoloration. INSV results in green and yellow bullseyes, ToRSV causes yellow and green spots with faded margins, and HVX can be identified by the angular yellow and light green splotches.

None of these can be treated, so avoidance is your only option. All of these spread easily on tools, plant material, clothing, and weeds. Practicing good garden hygiene is paramount, as is controlling thrips, which can spread some viruses.

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