Diseases and pests of Cycas or the Japanese sago palm

Aphids

Aphids are one of the most common pests that can infest the Japanese sago. These tiny sap-sucking insects often gather on the underside of the leaves, where they draw nutrients from the plant. An aphid infestation can cause an overall weakening of your Cycas, leaf discolouration and, in severe cases, wilting of the plant. It is therefore important to take immediate action at the first signs of an infestation.

Using soapy water

One of the simplest and most natural methods to eliminate aphids from your Cycas is the use of soapy water. You can prepare a homemade solution by mixing a few drops of black soap into one litre of water. Then spray this solution directly onto the infested areas, focusing on the underside of the leaves where aphids tend to hide. Repeat this treatment several times a week until the aphids are completely eliminated.

Garlic or chilli as a natural repellent

Another natural method is to use plant extracts such as garlic or chilli to create a repellent spray. These extracts contain compounds that are unpleasant for aphids, thus driving them away from your Cycas revoluta. To prepare this spray, blend a few cloves of garlic or some chillies with water, strain the solution and spray it on the affected areas.

Natural predators

Alternatively, more simply, ladybird and hoverfly larvae feed on aphids and thus help regulate their population. Make sure your garden provides favourable conditions for these predators, such as flowering plants to provide nectar for adult hoverflies or slightly wild areas (a nettle corner, piles of branches, unmown areas…) to increase the biodiversity of your garden.

→ To learn more: Aphids: identification, control, treatment and prevention.

Mealybugs

Identifiable by their cottony appearance and the waxy substance they secrete, mealybugs suck the sap from the leaves and stems of the plant. Not only do they weaken the Cycas, but their presence can also lead to the development of sooty mould, a blackish fungus that feeds on the sugary substance excreted by the mealybugs. This twofold attack can seriously compromise the health and appearance of your Cycas.

A mixture of water and rubbing alcohol can be effective for removing mealybugs. Soak a cotton bud in a mixture formed of 70% 90° rubbing alcohol and 30% water, then gently dab each mealybug. The alcohol dehydrates the mealybugs, killing them effectively. Be sure to treat all affected areas, including leaves and stems. Carry out this treatment carefully to avoid damaging the plant’s tissues.

→ To learn more about the mealybugs: identification and natural treatments.

Mites

Mites represent a significant threat to Cycas, particularly in hot, dry conditions. These small arachnids feed on the plant’s sap, which can lead to yellowing of the leaves and an overall decline in the plant’s vigour. Among the types of mites that can affect Cycas are mainly tetranychid mites and eriophyid mites.

An effective natural method to counter mites on your Cycas is the use of an infusion made from garlic or nettle. These plants contain sulphur compounds (in the case of garlic) or minerals (in the case of nettle) that act as natural repellents. To prepare the infusion, soak a few crushed garlic cloves or nettle leaves in water for several hours. Then strain the mixture and spray it onto the affected areas of the plant. Repeat the process every few days until signs of infestation disappear.

Yellowing of the leaves can be caused by mites

The nematodes

Nematodes are microscopic worms that attack the roots of plants, which can sometimes affect their health. By feeding on the sap of the roots, they create entry points for pathogenous fungi, making the plant more vulnerable to diseases such as root rot. This type of infestation can cause yellowing of the leaves, stunted growth and, in the most severe cases, the death of the plant.

One way to naturally combat nematodes is the use of composted horse manure or dung, rich in organic matter and beneficial microorganisms. These microorganisms can help to control nematode populations by competing with or preying on these parasites. To apply this method, incorporate the composted horse manure into the soil around the plant’s root zone, taking care not to damage the roots.

Slugs and snails

The ‘slimy ones’ can cause mainly cosmetic problems to your Japanese sago palm. By nibbling the leaves, they create holes and tears that detract from the plant’s appearance. Damage is particularly visible on young shoots, which are more tender and therefore more attractive to slugs and snails.

A natural and effective way to deter snails and slugs is to use a barrier of crushed eggshells. The sharp edges of the shells make it difficult for the molluscs to cross and reach the plant. To put this into practice, crush the eggshells into small pieces and arrange them in a circle around the base of your young Cycas, newly planted. Alternatively, you can simply ignore these molluscs and let your garden wildlife regulate their population (ground beetles, birds such as thrushes, hedgehogs…).

Root rot

Root rot is often caused by an excess of water in the soil, which creates a damp environment favourable to the development of pathogenous fungi. Common symptoms include yellowing and wilting of the leaves, which can ultimately lead to the death of the plant if the problem is not treated in time.

Preventing root rot requires appropriate cultural practices. Ensure your Cycas is planted in well-drained soil to avoid water accumulation. In addition, moderate but regular watering, according to the needs of the plant and the climatic conditions, will help maintain the proper water balance. Also avoid over-fertilising, as an excess of nutrients can unbalance the soil and favour the development of diseases.

It is not widely known, but cinnamon is an effective natural remedy against root rot thanks to its antifungal properties. To use this method, first remove the plant from the soil and cut away the parts of the roots that appear rotten or diseased. Then, sprinkle powdered cinnamon on the cut areas before replanting the Cycas in fresh, well-drained soil.

The yellowing of the leaves of a Cycas can also be due to root rot

Foliar spot diseases

Foliar spot disease can affect the Cycas revoluta, and is generally caused by various types of fungi (genera such as Cercospora, Colletotrichum and Phyllosticta). Symptoms include the appearance of black or brown spots on the leaves, which can affect the plant’s appearance and, over time, its overall health. If this condition is not treated, the leaves may eventually turn yellow and fall, weakening the plant. As with all fungal diseases, prevention is crucial. Make sure your Cycas is planted in well-drained soil and follow a watering regime suited to the plant’s needs. Also avoid over-fertilisation and ensure good air circulation around the plant to minimise the humidity that favours fungal growth.

A commonly used natural method for treating fungal diseases of plants is a spray based on bicarbonate of soda. This product acts as a fungicide and can help prevent the spread of the disease. To prepare the solution, mix one tablespoon of bicarbonate of soda with one litre of water and add a few drops of black soap to aid dispersion. Spray this solution onto the affected leaves, taking care to also cover the undersides of the leaves where fungi can also develop.

Powdery mildew

Powdery mildew is a fungal disease that can severely affect Cycas revoluta, or Japanese sago. Characterised by a white powdery coating on the leaves, this disease inhibits photosynthesis, which can lead to a general weakening of the plant. If left untreated, powdery mildew can spread to other parts of the plant and even infect neighbouring plants. Prevention is often the best defence against powdery mildew. Make sure your Cycas has enough space for good air circulation, which will help reduce humidity around the leaves. Also avoid overwatering and ensure you water the base of the plant rather than the leaves to minimise moisture.

An effective and natural solution against powdery mildew is spraying diluted cow’s milk. Milk contains fatty acids that can help destroy the fungus. To prepare this solution, mix one part milk with nine parts water. Use a sprayer to apply this mixture to the affected areas of the plant, especially the leaves. Repeat this treatment once a week until signs of the disease disappear.

→ To learn more about the Powdery mildew or the white disease.

Anthracnose

Anthracnose is a fungal disease (which can also be included in the group of foliar spot diseases) a dreaded disease that causes leaves to brown and can lead to the premature death of the plant. Most often caused by fungi of the genus Colletotrichum, this disease develops particularly in damp, poorly ventilated environments.

Cinnamon is known for its antifungal properties and can be an effective natural alternative for treating anthracnose. Prepare an infusion by boiling a few cinnamon sticks in water for about 15 minutes. Once the infusion has cooled, strain the solution and use a sprayer to apply directly to the affected areas of the plant.

→ Worried about anthracnose? To learn more, read Anthracnose: prevention and treatment.

Sooty mould

We briefly touched on it when discussing aphids; sooty mould is a common condition affecting Cycas, often caused by the presence of aphids or scale insects. These insects produce a sweet substance called honeydew, which provides a fertile substrate for the development of this surface fungus. Sooty mould appears as black deposits on the leaves, resembling soot. Although this fungus does not attack the plant directly, it can inhibit photosynthesis by blocking the sun’s light, which weakens Cycas over the long term.

One natural method to eliminate sooty mould is to treat its underlying cause, namely the insects that produce the honeydew. Insecticidal soap is effective at removing these insects without harming the plant. You can prepare a homemade solution by mixing a few tablespoons of liquid organic soap into a litre of water. Use a sprayer to apply this solution to the affected areas of the plant, taking care to thoroughly cover the insects and the sooty mould deposits.

→ Sooty mould: what is it?

Appearance of sooty mould (here on an orange tree leaf)