When suddenly the flower buds of the rhododendron wither and fall off, the amateur gardener wonders what could be the reason. The culprit in most cases is the rhododendron cicada – an insect that is not itself a pest, but often transmits a dangerous fungal disease from plant to plant. We explain how you can fight the rhododendron cicada, what natural enemies it has and how you can make a spray against cicadas yourself.
Table of Contents
- How to fight rhododendron cicada: damage pattern.
- Fighting rhododendron cicada: sprays
Fighting the rhododendron cicada: pest symptoms
Unlike other pests in German gardens, the cicada species with the Latin name “Graphocephala fennahi” is not native. The insects arrived in Europe at the beginning of the last century and settled here. Like other alien species, rhododendron cicadas pose a threat to native rhododendron species.
The infestation is slowly becoming noticeable. The number of cicadas seen on a plant is much smaller than other pests . Accordingly, they can not cause much damage. They feed on the plant sap, which is transported through the stem to the leaves. As a result, few nutrients reach the upper leaves. They turn yellow, but do not fall off. The infestation is often overlooked by inexperienced amateur gardeners, is not a major problem in itself, and the plant will not die because of the cicadas.
This species of cicada feeds exclusively on the sap of the rhododendron and attacks only this type of woody plant. The cicadas are active from late spring to autumn. However, they can be noticed with the naked eye only in early July, when the adult insects can be seen.
This is what the rhododendron cicada larvae and adult insects look like.
The larvae are small, dark yellow to light green, have no wings, a flat body and stay on the lower leaf side. In mid to late July, you may notice the adult rhododendron cicadas. They are light green in color and have orange stripes on their backs. They also prefer to stay on the lower leaf side.
Fungal disease of rhododendron: what is the bud blight.
Much more dangerous than the insects themselves is a fungus that attacks the woody plant during the cicada’s mating season. The damage that females do to petals while laying eggs becomes entry points for the fungus. As the pathogen spreads, the flower buds turn brown, then black. They dry out, and the flowers do not open. Other parts of the plant are spared from infestation.
Combat bud browning
Measures to combat the fungal disease are limited to the immediate removal of infested flowers. It is best to cut them off early in the morning. As a preventive measure, you can also remove the healthy panicles located directly around the affected parts of the plant as well.
Fighting rhododendron cicada: sprays.
The next step is to fight the rhododendron cicada. And do it as soon as possible, before the cicadas make small slits in the petals to lay their eggs there.
A simple spray with vinegar will help against the cicadas: Dissolve vinegar with water in a 1 to 5 ratio and spray it on the lower sides of the leaves. It is best to do this early in the morning, at 5 to 6 am, when it is still cold outside. The insects are then in a special state of rigidity and you can easily treat the woody plant.
Neem oil against cicadas
The larvae can usually be controlled the fastest. But if you missed the right time for this in May and June, then in August you can fight the adult cicadas with a spray containing neem oil. Use only approved means from the trade, homemade sprays are banned throughout Europe. Neem oil is environmentally friendly and has a broad effect:
- it drives away the pests
- it leads to moulting disorders of the larvae
- it prevents egg laying
- it has a fast effect
- Neem oil penetrates into the petals and the cicadas absorb it with the plant sap
- neem oil is not dangerous for bees and other beneficial insects
Spray the whole plant from all sides, preferably in the afternoon or early morning.
Fighting the rhododendron cicada: it has the following natural enemies.
A third way to combat the rhododendron cicada in an environmentally friendly way is to attract the insects’ natural enemies to the garden. These include:
- Jumping spider
- various garden birds
- ichneumon wasps
To attract natural enemies to the garden, you can build your own insect hotels, birdhouses and birdbaths.
The rhododendron cicada is not a native insect species. It is considered a pest, although it does not actually cause much damage. However, a fungus that affects the woody plants is transmitted by the cicada. You cannot take any action against the fungal disease other than cutting off the flower buds. The cicada itself can be controlled with neem oil and vinegar, and has many natural enemies.