When the rhododendron is in full bloom, it beautifies every garden. Occasionally, however, one finds small, grasshopper-like insects on it, the rhododendron planthoppers.
The rhododendron can be a gardener's pride and joy, especially when it begins to open its bright, vigorous flowers in May. Unfortunately, however, it occasionally falls victim to pests or diseases, so that flowering is inhibited or does not occur at all. We will tell you how to recognize the rhododendron leafhopper and what options for action and preventive measures there are.
Rhododendron Leafhopper: Detect Infestation
For every rhododendron owner, May is a real highlight in the garden. Because then the flowering period of the rhododendron begins (Rhododendron) and the flowering splendor is overwhelming, especially with larger plants. Occasionally, however, the magnificent plant can be attacked by the rhododendron cicada (Graphocephala fennahi, synonym also Graphocephala coccinea). From May, the small, yellow to pale green larvae of the cicada can already be observed on the underside of the rhododendron's leaf. At this point, the larvae are dependent on the rhododendron as their sole food source. They feed on the sap of the young, soft shoots.
The adult cicada resembles a grasshopper. It is green in color with two typical red vertical stripes on the forewings. Also striking is their yellow underside, on which you can recognize the approximately 1 cm large insects between July and November. The cicadas on rhododendrons usually sit on the upper side of the leaf, but occasionally retreat to the underside of the leaf to flee or fly away from the rhododendron.
The damage caused by the rhododendron leafhopper shows itself in the event of a severe infestation by blotching of the leaves, some of which even fall off. In contrast to rhododendron larvae, adult rhododendron leafhoppers are no longer solely dependent on the rhododendron as a food source. The plant suckersare not a direct threat to your rhododendron or other plants and the damage is negligible. However, a problem arises between August and October when laying eggs: small slits are cut into the scales of the rhododendron buds, in which the cicada then lays the eggs. These slits can also serve as a gateway for some fungi and plant viruses to enter the plant.
Rhododendron leafhopper as a vector of bud dieback
Occasionally it happens that the flowering of the rhododendron is much smaller than usual in one year. But what could be the reason for that? First of all, it is worth taking a close look at the buds. If these look dark and dead, it is not about frost damage from the previous winter. The real culprit is usually the fungus Pycnostysanus azaleae, which forms countless small, brown or black, spiky spores on closer inspection of the buds. The buds covered with the black fungus threads have already died by this time and any help would be in vain. For a long time, the small slit cut into the rhododendron buds by the rhododendron leafhopper to lay eggs was considered the direct and only entry point for the fungal spores of Pycnostysanus azaleae. According to new scientific findings, some points speak against a direct connection. An infestation can be favored by the cicada, but it also occurs independently of the insects. Unfortunately, the fungal infestation will not be seen until next spring, around February. Because over the winter the buds show no noticeable symptoms.
Tip: If the rhododendron develops brown or black buds, these should be collected early in the spring and disposed of with household waste before they can form any more spores.
Prevent Rhododendron Leafhopper
In order to be able to recognize the rhododendron cicada before it lays its eggs, it is worth taking a look at your rhododendron from time to time. The underside of the leaf in particular should be examined closely for the pest. Glued yellow boards that are hung in the rhododendrons can greatly simplify observation. The cicadas caught on the board indicate an infestation at an early stage and enable appropriate countermeasures to be taken. In addition, the yellow panels contribute to a slight decimation of the adult animals.
Note: Yellow panels are very good for early detection of cicada infestation on rhododendrons, but not for controlling insects. Further, timely action is therefore necessary. Yellow panels trap numerous beneficial insects in addition to the pests. The panels should therefore only be hung outdoors for short periods between July and November in order to detect a possible infestation.
Fighting Rhododendron Leafhoppers
Anyone who has noticed an infestation by the rhododendron leafhopper should act promptly to prevent later consequences. Natural predators of the rhododendron leafhopper and the right choice of location are primarily suitable for this. Biological control of the rhododendron leafhopper is also possible in the event of a heavy infestation.
Natural enemies of the rhododendron planthopper
In the wild, the rhododendron leafhopper also has a number of natural enemies such as lacewing larvae, chalcid wasps, ground beetles, predatory mites, parasitic wasps, as well as some spiders and birds. With a natural garden design and the promotion of beneficial insects, the rhododendron can be kept in check. Simple measures are, for example, setting up nesting boxes, insect hotels and bird baths, seeding a flowering meadow or garden design with native plants. Beneficial insects, especially parasitic wasps of the species Anagrus atomus, against the rhododendron plant hopper are now commercially available. However, their effect is partially controversial.
Biological control of rhododendron leafhoppers
In the event of a heavy infestation, natural pesticides can be used to combat the rhododendron planthopper. But when should you spray your rhododendron against cicadas? Because cicada oviposition is causing the problem, insecticide application should occur between May and August during the young larvae and larvae stages. Means that contain the natural ingredient azadirachtin, which is obtained entirely from the seeds of the neem tree, are particularly suitable against cicadas. The agent can be evenly distributed on the top and underside of the leaves by a thorough spray application all over the plant and can be picked up by the insects. With our Plantura organic pest-free neem, you can greatly curb the proliferation of cicadas and protect your plants. ThatMeans obtained from the seeds of the neem tree ensures that the cicadas are less fertile - it can thus prevent the damaging egg laying. In addition to the important active ingredient azadirachtin, it also contains a natural, plant-based surfactant and a plant-based oil. This increases the wetting of the leathery rhododendron leaves, so that the effectiveness against the cicada can be increased. In addition, the active ingredient in our organic pest-free neems is more tolerable for beneficial insects than other alternatives and of course not harmful to bees (B4). However, the adult rhododendron leafhoppers are extremely resistant, so that the active ingredient only takes effect after some time and reduces their fertility. The cicadas will remain active for some time - but then there is no reason to panic.
Tip: It is best to apply a plant protection product against cicadas in the early morning hours, the insects are still immobile at this time due to the night cold and cannot jump away.
Home remedies against rhododendron planthoppers
The best prevention against rhododendron planthopper infestation is the right location. Above all, you should avoid waterlogged and damp soil as well as dense sandy soil. In our special article you will learn how to transplant the rhododendron if it grows in a bad location. You can also find other diseases and pests that can seriously affect your rhododendron in our special article on rhododendron diseases.