The most heartbreaking occurrence in a garden is the loss of a cherished plant, often due to diseases. Just like any other plant, hostas are susceptible to various pathogens such as fungi, bacteria, and viruses.
In today’s discussion, we will delve into the realm of hosta diseases and how to combat them. I have gathered comprehensive information on this subject, and I am eager to present it to you in an accessible format. Additionally, we will provide images illustrating the key diseases for you to compare with your own observations.
To begin, I will provide a concise overview of each disease in a tabular format, outlining their symptoms and treatment methods. Following that, we will explore each of these cases in-depth.
|Anthracnose (Colletotrichum)||Red-brown spots on leaves.||Prophylactic spraying with fungicides.|
|Petiole rot (Sclerotium rolfsii)||Yellowed leaves, broken petioles at the base.||Removal of the damaged part of the plant, treatment with fungicide.|
|Fusarium root and crown rot (FRCR Fusarium hostae)||The center of the crown and the rhizome are light brown.||Removal of the damaged part of the plant, treatment with fungicide.|
|Bacterial Soft Rot (Pectobacterium)||The petioles and center of the crown become soft and watery, with a bad smell.||Remove the damaged part of the plant and treat it with a fungicide.|
|Hosta Virus X (HVX)||Green spots on leaves, twisting leaves, slowing growth.||Remove infected plants.|
|Nematodes (Aphelenchoides spp.)||Dry stripes on the leaf.||Remove infected leaves.|
|Phytophthora Foliar Blight||The leaves are partially turning brown. The bush is falling apart.||Remove the damaged parts of the hosta. Treat it with copper fungicide.|
|Phyllosticta Leaf Spot||Brown spots with holes.||Spray hosta with cooper fungicide.|
|Cercospora Leaf Spot||Brown spots with a reddish-brown center.||Spray hosta with cooper fungicide.|
During the warm and rainy summer months, conditions become ideal for the development of anthracnose, a disease caused by various fungal spores that can inflict significant damage upon hostas. While it is a common ailment, it rarely results in the demise of the plant.
- Anthracnose manifests as brown spots on hosta leaves.
- The center of these spots becomes dry.
- Over time, the spots can expand and merge with others, potentially leading to leaf death.
To combat this disease effectively, start by promptly removing the infected leaves and disposing of them properly; do not let them decompose in your yard.
In the initial stages, if the plant is not severely affected, employ the fungicide Phyton. Apply the product to the entire plant and its surroundings. With time, your hosta should recover.
In more advanced stages, turn to systemic fungicides recommended for anthracnose control, particularly those containing chlorothalonil.
For prevention, regular spraying with systemic fungicides is highly effective.
Read more: How Do You Get Rid Of Anthracnose?
2. Petiole rot (Southern Blight)
Petiole rot stands as one of the most formidable adversaries of the hosta, capable of swiftly decimating the plant. Thus, the key to success lies in prevention and early detection.
The spores of this fungus can remain dormant in the soil for extended periods without manifesting any symptoms. However, when favorable conditions arise—typically when temperatures soar beyond 80°F with high humidity—the disease proliferates rapidly, targeting the base of petioles.
- Indications of this disease include the yellowing of leaves.
- Petioles snap at ground level and drop off, often displaying a reddish hue in the early stages.
- Yellow granules around the rhizome can also be observed.
The spores of this fungus thrive in moisture-rich environments, making mulch beneath hostas an ideal breeding ground. Maintain a gap of at least 1 to 2 inches between petioles and the mulch.
Upon early detection of this fungus, meticulously cleanse all parts of the plant. Additionally, remove the top layer of soil surrounding the hosta and replace it with fungus-free soil.
Apply a fungicide specially designed to combat this type of fungus (such as Fungo or products containing tebuconazole) to the plant, rhizome, and the surrounding soil.
The most effective control strategy involves regular application of various systemic fungicides to all plants within your garden.
If you realize the disease has taken hold too late, and the plant is severely compromised, your only recourse is to uproot the hosta and relocate it, along with the soil, far from your yard. Then, thoroughly disinfect all tools and the area where the hosta was previously located.
Read more: How Do You Treat Petiole Rot On Hostas?
3. Fusarium root and crown rot (FRCR)
This is yet another highly perilous and widespread disease, and once it takes hold, it is nearly impossible to save the plant. The spores of this fungus primarily reside in the soil, and any open wound on the hosta is an open invitation for infection.
At the outset, the symptoms of FRCR can be elusive. Hosta leaves tend to emerge later in the spring, and affected plants exhibit slower growth compared to their healthy counterparts. Additionally, the number of leaves and their size may be noticeably reduced.
- In the advanced stages of infection, the leaves take on a yellow hue and gradually wither.
- The center of the crown acquires a light brown discoloration.
Prior to purchasing, thoroughly inspect the roots for signs of FRCR. Additionally, ensure you use clean tools when dividing hostas and treat any wounds that may occur during this process.
If the disease is detected early, you have a chance to salvage the plant by trimming away the affected portions and immersing them in a water-based solution of a fungicide containing thiophanate methyl.
Replant the hosta in a pot using sterile peat-based soil. Over time, there’s a possibility that the plant may recover.
However, if the entire plant succumbs to this disease, it is imperative to excavate and either dispose of it or remove it from your yard.
4. Bacterial Soft Rot
Bacterial soft rot has the potential to completely devastate a hosta plant. As depicted in the image, the core of the crown undergoes decomposition, leaving no chance for the plant’s recovery.
Like many diseases, the pathogens responsible for bacterial soft rot lie dormant in the soil, awaiting the right conditions to proliferate. Most often, infestation occurs when hostas endure severe frost damage during the winter, providing an entry point for bacteria to infiltrate and infect the plant.
Another common source of infestation is during rhizome division. Failing to adhere to strict sterility requirements during this process significantly increases the risk of infection.
The bacteria responsible for this disease can remain latent within a plant, only revealing themselves when favorable conditions emerge. These conditions typically involve high humidity and warm temperatures exceeding 80°F.
- Symptoms of bacterial soft rot include the yellowing of leaves, with petioles becoming limp and resting on the ground.
- The center of the crown becomes mushy and watery.
- A distinctive feature of this disease is the peculiar odor reminiscent of rotting fish.
To combat bacterial soft rot, carefully excavate the hosta from the soil. Thoroughly clean and wash the plant with water. Utilize a sterile knife to remove any compromised sections.
Allow the hosta to sit in the shade for a few hours before immersing it in an aqueous solution of a fungicide like Phyton 35, allowing it to soak.
Transplant the hosta into a new location or pot, ensuring the use of fresh, uncontaminated soil.
5. Hosta Virus X (HVX)
Unfortunately, once a hosta is infected with HVX, there is no known cure. This virus was initially identified in 1996, and its origin remains a mystery.
HVX cannot survive outside of a host plant or insect. Infection spreads from an infected plant to a healthy one through several means. The primary mode of transmission occurs when pests damage an infected plant and subsequently move on to a healthy one. Another method is through the use of the same tool to cut stems from both infected and healthy plants.
HVX is particularly insidious because it remains inconspicuous during the first year of infection, allowing for the multiplication of infected plants and the inadvertent spread of the disease.
- Indicators of this disease include the presence of green spots on the leaves.
- Alongside the spots, leaf deformation is a common sign of infestation.
- In some affected plants, leaves may become yellow and curl.
- The size and growth rate of the hosta bush are typically reduced.
Regrettably, there is no known cure for HVX once a hosta is infected. Thus, the first line of defense is to safeguard against purchasing diseased plants. If you observe similar symptoms on a plant you intend to buy, it’s advisable not to proceed with the purchase.
In cases where the virus has severely compromised the plant, the only course of action is to excavate the hosta, remove it from your yard, and burn it.
Read more: Hosta Virus X
6. Leaf Nematodes
Leaf nematodes are diminutive worms that navigate through liquid environments. Infestations primarily occur during rainy periods. When these nematodes are in proximity to a hosta shrub, raindrops can dislodge them onto the plant.
Subsequently, they infiltrate the plant through openings or damaged areas. Once inside, the nematodes assail the plant’s cells and commence reproduction.
- Dry streaks become visible on the leaves, often extending along the entire length of the leaf.
- In cases of severe infestation, multiple streaks may manifest, leading to leaf decay.
- Symptoms typically become apparent a few months following infestation.
Upon detecting the initial signs of infestation, promptly eliminate the affected leaves, including the stems. Do not leave the discarded leaves in your yard; instead, incinerate them immediately. It’s essential to note that these pests can endure for an extended period within decaying leaves. Additionally, thoroughly disinfect all tools used for pruning.
Another effective method to manage leaf nematodes is to trim the stems and leaves of the hosta in late summer while they are still green, without waiting for them to yellow. These removed leaves should also be disposed of. This approach significantly reduces the nematode population.
Read more: How do you treat foliar nematodes?
7. Phytophthora Foliar Blight
Phytophthora foliar blight is a relatively common fungal disease that can affect a wide range of plants, including hostas. This disease thrives in conditions of high humidity and temperatures exceeding 70°F, posing a significant threat to the hosta and potentially leading to its rapid demise.
- Distinctive large brown spots begin to appear on the leaves, steadily expanding and ultimately causing the affected leaf to wither and die.
- In some cases, the leaf petioles may partially turn brown, and the hosta plant may become notably frail and vulnerable to falling apart.
Avoid excessive watering of hostas; only water when the soil has dried more than 2 inches deep.
In the event of an infection, carefully excavate the afflicted hosta and trim away any rotting portions. Cleanse the wounds with a copper fungicide solution, allowing them to air-dry for no more than an hour in a dry, shaded location.
Eliminate any severely damaged leaves and apply a broad-spectrum fungicide to the remaining foliage.
Replant the hosta in well-drained soil, ensuring it is situated in an area where excessive moisture is less likely to accumulate.
8. Phyllosticta Leaf Spot
Phyllosticta Leaf Spot
Phyllosticta Leaf Spot is a fungal disease that damages the leaf plate. In addition to hostas, it can affect a wide variety of plants.
It begins when the air temperature reaches 77°F (25°C). At this time, the pathogens begin to attack the leaf. After a while, brownish spots appear on the leaf in the center of which a whitish fungal body can be seen.
The spots then turn into holes with a brown edge. The disease progresses until it destroys the entire leaf.
- Brown spots on the leaves turn into holes. The number of spots constantly increases until the leaf dies.
- The stems can also be susceptible to this disease and brown areas can appear on them.
Avoid overwatering the hosta. Allow the soil to dry 2 inches between waterings.
Do not plant hostas in areas with poor air exchange and high humidity.
If disease occurs, spray the hosta with an aqueous solution of copper fungicide. Repeat the spraying a week later. Remove any badly damaged leaves.
9. Cercospora Leaf Spot
Cercospora Leaf Spot is yet another fungal disease that primarily targets hosta leaves, as implied by its name. This ailment tends to manifest more frequently during exceptionally hot weather conditions.
As with most diseases of this nature, Cercospora Leaf Spot primarily affects the foliage, leaving the stems and crown relatively unscathed.
- Leaves exhibit brown spots surrounded by a yellow border, with the center of the spot often taking on a vivid reddish-brown hue.
- The number of these spots continues to multiply until the leaf succumbs and dies.
Copper fungicide is the most effective solution for combatting Cercospora Leaf Spot. Copper ions have the capability to eliminate a wide range of fungal pathogens.
Regularly spray the hosta with an aqueous fungicide solution until the disease begins to recede, ensuring a minimum interval of 7 to 10 days between applications.
Additionally, it’s essential to diligently remove any dead leaves to help mitigate the spread of the disease.
There are also several other diseases that can afflict hostas. Let’s briefly explore them.
Impatiens Necrotic Spot Virus (INSV)
Impatiens Necrotic Spot Virus, or INSV, is another infection that can impact your plants. It is transmitted by various species of thrips.
Symptoms may not become immediately evident. The most common indicator is the appearance of white patterns on the green leaves, with leaf necrosis also being possible.
Control methods involve the sterilization of tools and the application of insecticides to the plants.
Tomato Ringspot Virus (ToRSV)
Tomato Ringspot Virus, or ToRSV, induces leaf yellowing similar to chlorosis. It is transmitted when hostas are propagated through division and can also be spread by nematodes.
Unfortunately, there are no highly effective methods for controlling this virus. The best course of action is to remove infected plants to prevent the spread of the virus.