If the flower buds of the rhododendron suddenly wither and fall off, the hobby gardener wonders what could be the problem. In most cases, the rhododendron leafhopper is to blame - an insect that is not a pest itself, but often transmits a dangerous fungal disease from plant to plant. We explain how you can fight the rhododendron leafhopper, what natural enemies it has and how you can make your own spray against leafhoppers.
In contrast to 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 leafhoppers also pose a threat to native rhododendron species.
The infestation is slowly becoming noticeable. The number of cicadas seen on a plant is significantly less thanwith other pests. Accordingly, they cannot cause much damage. They feed on plant sap, which is transported down the stem to the leaves. As a result, little nutrients reach the upper leaves. They turn yellow but do not fall off. The infestation is often overlooked by inexperienced hobby gardeners, is not a major problem in itself and the plant will not die because of the leafhoppers.
This type of cicada feeds exclusively on the sap of the rhododendron and only attacks this type of tree. The cicadas are active from late spring to autumn. However, you can only notice them with the naked eye at the beginning of July, when the adult insects can be seen.
This is what rhododendron leafhopper larvae and adult insects look like
The larvae are small, dark yellow to light green, have no wings, a flat body and live on the lower side of the leaf. In mid to late July you can notice the adult rhododendron leafhoppers. They are light green in color and have orange stripes on their backs. They also prefer to stay on the lower side of the leaves.
Fungal disease of rhododendron: what is bud browning
Much more dangerous than the insects themselves is a fungus that attacks the wood during the cicada's mating season. The damage that the females cause to the petals during egg laying becomes entry points for the fungus. As the pathogen spreads, the flower buds initially turn brown, then black. They dry out and the flowers don't open. Other parts of the plant are spared from infestation.
Combat bud tan
The measures to combat the fungal disease are limited to the immediate removal of affected flowers. It's best to cut them off early in the morning. To prevent this, you can also remove the healthy panicles that are located directly around the affected parts of the plant.
Fight rhododendron leafhoppers: sprays
The next step is to control rhododendron leafhoppers. And do this as quickly as possible, before the cicadas make small slits in the petals to lay their eggs there.
A simple spray with vinegar helps against the cicadas: Dissolve vinegar with water in a ratio of 1 to 5 and spray the lower sides of the leaves with it. It's best to do this early in the morning, between 5 and 6 a.m., when it's still cold outside. The insects are then in a particularly rigid state and they can treat the wood without any problems.
Neem oil against cicadas
The larvae are usually the quickest to combat. But if you missed the right time to do this in May and June, you can combat the adult cicadas in August with a spray containing neem oil. Only use approved products 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 molting problems in the larvae
- it prevents egg laying
- it has a quick effect
- The neem oil penetrates the flower petals and the cicadas absorb it with the plant sap
- Neem oil is not dangerous for bees and other beneficial insects
Spray the entire plant from all sides, preferably in the afternoon or early in the morning.
Fighting the rhododendron leafhopper: It has the following natural enemies
A third way to combat rhododendron leafhoppers in an environmentally friendly way is to attract the insects' natural enemies to the garden. These include, among others:
- Skipping Spinning
- Hedgehog
- various garden birds
- Ants
- Parasitic wasps
To attract natural enemies to the garden, you can build insect hotels, bird houses and bird baths yourself.
The rhododendron leafhopper is not a native insect species. It is considered a pest, even though it doesn't actually cause much damage. However, a fungus that attacks the trees is transmitted by the cicada. You can fight against themFungal disease no measuresother than cutting off the flower buds. The cicada itself can be controlled with neem oil and vinegar and has numerous natural enemies.
