Diseases and Parasites of Acanthus

Powdery mildew: the most common disease among bear's breeches.

Description and Symptoms of the Disease

Powdery mildew is a fungal disease, which means it is caused by a fungus. This type of disease is among the most common in the garden, whether in the vegetable garden, orchard, ornamental garden, or even when growing in pots. It is often a combination of heat and humidity that promotes their appearance and spread, which is why they mostly occur from spring to autumn.

Powdery mildew is also known as “white disease.” This name refers to one of its main symptoms: a white or grayish powdery appearance. In acanthus plants, it can appear on the leaves, stems, and even on the flower buds. All aerial parts can be affected.

It is a contagious disease: neighboring plants can easily be affected in turn. Moreover, powdery mildew spores can remain in the soil for a long time, sometimes for several years, making it difficult to get rid of this disease.

The damage caused is primarily aesthetic, but over time, the disease can lead to the drying out of the aerial parts. It results in leaf drop, flower deformation, and new shoot wilting.

Prevention

When it comes to fungal diseases, prevention is the best approach. Curative treatments are not always effective. To prevent the appearance of powdery mildew, certain actions are recommended:

1. Take care of the growing conditions by providing your acanthus plants with a suitable environment for their needs. Plant them in full sun or light shade (especially in the hottest regions of southern France), sheltered from strong winds. Ensure that the soil is well-drained to prevent water from stagnating. Add gravel or clay pebbles at planting time if necessary. Opt for deep soils that never completely dry out. A healthy plant is more resistant to diseases and pests. Also, avoid growing acanthus in an area previously infected with powdery mildew.
2. If you grow multiple acanthus plants, ensure good planting distances to promote natural ventilation. For the larger varieties, allow at least 1 meter between each plant. Remember that acanthus plants do not like to be moved, so it is important to choose the right location from the start.
3. When watering, avoid wetting and splashing the foliage as much as possible.
4. If you need to prune certain parts of the plant (damaged leaves, flower stalk…), always use a sharp cutting tool that has been previously disinfected with alcohol. This reduces the risk of disease spread between plants.
5. Acanthus plants prefer fertile soils. Avoid using fertilizers too rich in nitrogen, as they can weaken the plant and make it more susceptible to diseases.

Some gardeners also use plant-based infusions preventively. Their effectiveness is not scientifically proven, but these 100% natural recipes still have a reputation for boosting plant immune defenses. This helps increase their resistance to diseases. For powdery mildew, nettle and horsetail infusions are preferred. You can buy them in garden centers or make them yourself by following our recipes:

• tutorial on making nettle infusion;
• tutorial on preparing horsetail infusion.

Natural Treatments for Powdery Mildew

To prevent the spread of a disease, regular plant observation is essential. This allows for quick action at the first sign of a identified symptom. If you notice a white powdery appearance on your acanthus plants, start by immediately cutting the infected parts. Dispose of the pruning waste at a waste disposal site (do not leave them on-site or put them in the compost, as spores may survive). Disinfect your cutting tools thoroughly after use.

Bordeaux mixture can be used preventively and curatively. It is a powder based on copper sulfate, which must be diluted in water before being sprayed. It is suitable for organic farming. However, to prevent it from becoming counterproductive by promoting soil imbalance, it is important to use it punctually and judiciously. There are also sulfur-based treatments to combat powdery mildew.

Finally, nettle and horsetail infusions can also be used here, due to their attributed antifungal properties. They should be diluted in water (preferably rainwater) before being sprayed on the affected parts in the early morning or late afternoon.

Additionally, explore our articles “Powdery Mildew or White Disease” and “Everything You Need to Know About Fungal Diseases“.

Powdery mildew creates a grayish film on the leaves

Slugs and Snails: The Main Pests of Bear's Breeches

Description and Symptoms

Every gardener is familiar with the devastating appetite of gastropods. The lush foliage of acanthus plants can suffer as a result. Snails and slugs indeed target young shoots from the beginning of spring. While they may not cause the decline of an adult plant, they can hinder the growth of younger ones.

Prevention against Slugs and Snails

There are numerous preventive solutions against gastropods. Each gardener has their own technique. You can choose from:

• beer traps;
• natural barriers made of ash, diatomaceous earth, or eggshells (which work in dry weather and particularly well on small varieties of slugs and snails);
• repellent plants (whose effectiveness seems to vary);
• manual removal of unwanted pests, especially at dusk (time-consuming, but effective).

If you wish to treat your plants against slugs and snails, you can opt to spread granular treatments from early spring. Made of iron phosphate ([Ferramol](https://www.promessedefleurs.com/soins-et-luttes-biologiques/anti-limaces-naturel-ferramol-neudorff.html)), they are suitable for organic farming and are known to be non-toxic to pets and predators of gastropods (birds, hedgehogs, etc.). By acting as an appetite suppressant, this product encourages slugs and snails to isolate themselves and stop feeding, leading to their decline.

If you live with chickens or Indian runner ducks, you can also make use of their skills as gastropod hunters (while ensuring to protect your youngest acanthus plants, just in case…).

Lastly, remember to promote the natural predators of snails and slugs in the garden: birds, hedgehogs, or even toads. To do this, avoid any use of chemical products in the garden, set up shelters and water sources, maintain wild areas, etc.

Slugs and snails love acanthus foliage

Aphids: Other occasional pests of bear's breeches

Description and Symptoms

They are among the other common garden pests. Aphids are these piercing-sucking insects that feed on the sap of plants. They can cause the leaves of the acanthus to curl and a slowdown in its growth. Most importantly, their honeydew (the sticky substance they secrete) promotes the development of sooty mould. This is a fungal disease that can be identified by the black deposit resembling soot that it leaves on the aerial parts, which will reduce the natural photosynthesis process.

Natural Treatments Against Aphids

Here again, we advise you to regularly observe your acanthus plants in order to act as soon as the first unwanted pests are spotted. If the infestation is mild, simply manually remove the aphids.

If you need to treat your plant, opt for a natural insecticide. Black soap proves to be quite effective. It is used diluted in warm water, at a rate of one to two tablespoons per litre of water. Place this mixture in a sprayer and spray it on the affected parts in the late afternoon.

Remember that it is necessary to leave some aphids in the garden in order to maintain the presence of their natural predators, such as ladybugs or lacewings. This is what allows for a naturally balanced garden that self-regulates with little or no human intervention. For this, you can grow plants like the nasturtium, which will naturally attract aphids and divert them from the crops to protect.

Additionally, feel free to check out our article: Aphids: Identification and Treatment

Aphids are found on the underside of leaves