Hostas are those plants that can awaken the spirit of a true connoisseur of beauty. However, over time, most hosta lovers encounter diseases that can severely damage the appearance and health of these plants. Today we are going to talk about what is probably the most common disease of hostas.
Quick tips on how to get rid of anthracnose
- Remove badly damaged leaves along with their petioles.
- Spray the hosta with an aqueous solution of copper fungicide. Repeat spraying after 2 weeks.
- Remove any plant debris from around the hosta. Allow the soil surface to dry slightly.
- Avoid overwatering and watering over the leaves.
- Provide good air exchange around the hosta shrub.
Anthracnose is the common name for a group of pathogens that cause approximately the same damage to plants.
Pathogens are usually found on the ground or on other plants. They are also most abundant in fallen leaves and other plant debris. This is where they overwinter and spend most of their time.
However, when warm and wet weather arrives, the pathogens become active. Falling raindrops and wind carry the fungus spores to the leaves and the infestation begins.
This usually happens in spring when the weather is warm. Young, soft leaves are the most affected because the fungus penetrates their tissues more easily. Mature hard leaves are rarely affected.
In addition to hostas, anthracnose affects many other perennials, shrubs, trees, and even vegetables. Pathogens of this disease can parasitize not only leaves but also leaf petioles and branches.
The main sign of anthracnose is leaf spots. As the fungus spore develops, it begins to destroy the living tissue underneath. As a result, a small pale or yellow spot appears on the leaf.
The spot then enlarges and dries out. It becomes a reddish-brown color. It may even turn into a hole, but this should not be confused with slug damage. Slugs make irregularly shaped holes, while anthracnose holes are usually round and small.
If the infestation is considerable, many spots appear on the leaves. Over time, the spots will combine and a part of the leaf or the whole leaf will turn brown. This causes the leaves to droop or become deformed.
Sometimes spots may appear on the leaf petioles. However, the petioles are quite sturdy and the disease rarely does serious damage to them.
It also happens that anthracnose spores settle close to the leaf edge. As a result, it turns brown and gives the impression that the leaf becomes crispy brown only along the edge. This is a symptom of some other hosta problems, but in the case of anthracnose, you can clearly see round brown spots on the edge.
The first thing you should do if anthracnose has attacked your hosta is to remove the damaged leaves. If a leaf has one or more spots it can be left, cut off only those leaves that are badly damaged or dead.
Cut off the leaves together with their petioles as close to the ground as possible but without damaging the crown of the hosta.
Use good quality, sharp pruning shears. Treat them with alcohol before and after work. Unsterilized tools are one way this disease can spread.
Spray the hosta and all surrounding plants with an aqueous fungicide solution. Make sure the fungicide gets on the undersides of the leaves and petioles. Repeat the spraying in 1 to 2 weeks.
Clean all plant debris from under the hosta. Also, remove any mulch if present. Allow the soil beneath the hosta to dry for a while. Ensure good ventilation around the bush.
Water the diseased hosta with an aqueous multipurpose fertilizer. But do this only once. This will give a good boost for faster recovery.
If possible, provide more shade for the hosta while it is recovering. The less sun it gets, the easier it will recover. After the hosta has recovered, the shade can be removed.
What fungicide kills anthracnose?
One of the best fungicides against anthracnose is a copper fungicide. Copper ions are capable of destroying almost all fungal pathogens at the stage of their development.
It is a very affordable and low-toxic product that you can buy in almost any hardware store. At the same time, some fungicides are little or no available for purchase.
Also, some biological fungicides work well against anthracnose. For example, Serenade Opti which contains Bacillus subtilis is quite good against anthracnose and many other fungal diseases.
In addition, products containing chlorothalonil, propiconazole, and thiophanate-methyl can control the development of this disease. However, you should strictly follow the manufacturer’s instructions on the label.
How to avoid anthracnose
The best way to avoid anthracnose is to grow varieties more resistant to the disease. The harder the leaf the hosta has, the harder it will be for the fungus to penetrate its tissue and germinate. Also, vigorous varieties recover better from the disease than slow-growing ones.
Avoid planting hostas too densely. There should be some distance between the bushes so that there is good aeration. Plant the hostas at least the width of the larger one.
Water the hostas only when the soil around them is at least 1 inch dry. Constantly wet soil can lead not only to anthracnose but also to root rot. Avoid watering the hosta over the leaves if possible.
Only mulch hostas with quality mulch that does not cause rot. That is, do not use freshly mowed grass, leaves or other plant debris for mulching. Pine bark nuggets are best for mulching hostas.
Fertilize your hosta once a year with a slow-release fertilizer. This will give it vigorous growth and immunity. Avoid over-fertilizing as it can cause exhaustion and damage to the plant.
Also use a fertilizer with no more than 15 nitrogen, too much nitrogen can cause soft leaves and greater susceptibility to anthracnose.
When planting hostas, use well-drained and nutritious soil. This will help to avoid too much moisture around the shrub. If you have clay soil, improve it with organic matter, such as compost.
As soon as the young leaves unfold in spring, spray them with fungicide. Repeat the spraying once a month and you can be pretty sure that your hostas will thrive.
For more on proper hosta cultivation, see How I Keep My Hostas Healthy.