Rhododendron - common diseases and pests


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The rhododendron is a wood that can be found in many gardens. This is due to the fact that it has a beautiful inflorescence and therefore brings a lot of color in the garden. On the other hand, he is quite straightforward in nursing, which also promotes his popularity with certainty. Because if the location fits and the rhododendron gets enough water, it grows and thrives by itself.
However, if the location and the supply of water or nutrients are not right, then even this uncomplicated woodland sometimes causes problems. Because then the rhododendron is susceptible to diseases that are caused in many cases by pests.
Best possible conditions for Rhododendron
Diseases and pests can only occur more frequently if the rhododendron does not feel well in its environment and with its supply. For this reason, you should pay attention to the following things when you want to plant a rhododendron in your garden:

  • Make sure the rhododendron is in partial shade.
  • The location should be protected from wind.
  • The soil should be acidic, loose, low in lime and rich in humus.
  • Rhododendron should be poured daily. However, there must be no waterlogging.
Tip: Since rhododendrons are fairly flat, deep rooting should be one of the shady neighbors. So the roots do not get in the way and pull each other's nutrients out of the ground. Suitable would be, inter alia, pine or oak.
Pay attention to these things during the planting and the care, then you have already created a good basis for the prosperity of the rhododendron. Despite all this, you should always pay attention to the following diseases.
Deficiency symptoms and their effects
With rhododendron, two deficiency symptoms can lead to serious damage to the wood. First, this is the lack of nitrogen. If this is present, a light green or partly yellow color can be found on the older leaves of the wood. The further the nitrogen deficiency progresses, the more leaves have fallen into it. At an advanced stage also the young leaves. In addition, the rhododendron early loses its leaves and flowers drive little or no.
As a countermeasure, it is recommended to use nitrogen fertilizer, which restores the balance in the soil and thus helps the trees to regain their strength.
In addition, an iron deficiency (iron deficiency chlorosis) can lead to damage to the rhododendron. This deficiency manifests itself among other things in the young leaves, which are very bright from the leaf surface, but have very dark leaf veins. The specialist calls this condition chlorosis. In iron deficiency, the pH of the soil is too high. The plant can not absorb the iron from the soil and suffers.
Remedy can be provided with a correction of the pH. There are special iron-containing preparations for fertilization, which contain many trace elements and thus optimize the soil again. The best possible pH is between 4.5 and 6.
Special Pest: Rhododendron web bug
Pests too are a major contributor to rhododendron. Pay special attention to the rhododendron bug. The little bug lays her eggs on the underside of the leaves. This usually happens in the fall. There they spend the winter and in May of the next year the bug larvae hatch. The rhododendron reacts with speckled leaves that gradually wither away. If you want to do something about it, sprinkle the rhododendron after flowering with Spruzid Pest Control, which helps against sucking insects. This remedy is biological, so the "chemical leg" does not have to be taken out.
Frayed weevil
The furrowed black weevil also shows great interest in rhododendron. He eats the leaves - preferably from May. The nibbling of the leaves is not that bad. Much worse are the larvae of the little beetle. Because they go to the roots of rhododendrons and can thus ensure that he enters. Therefore, bend in advance and pour the soil with nematodes. These are thread worms, which are simply put into the irrigation water. Tip: The beetles, which can grow up to 1.3 cm, are nocturnal. Therefore, occasionally check your Rhododendron in the evenings. If you discover beetles, then collect them.
Rhododendron cicadas and bud dying
Rhododendron cicadas are small flying beetles that can cause bud dying on rhododendrons. The little crawlers bring the fungus Pycnostysanus azaleae to the flowers, which dry them and die off. This always happens when the cicadas lay their eggs in the flowers. They scrape this for it and bring so also the mushroom into the flower buds.As a measure, it is recommended to remove the affected flower buds as quickly as possible, so that the fungus can not spread. A treatment against the bud dying with chemical agents is unfortunately not possible because no one can say exactly if the cicadas are really the reason for the bud dying. However, the cicadas can generally be kept away from the wood by chemical means. Among other things, with pest-free-plus or Neudosan New aphid. Always keep in mind when using the funds that you only act against the cicadas and the bud dying can not be stopped.
twig blight
And also the branches can die off by pathogens like mushrooms. Here, the end bud of the branch is attacked first, which then lead the fungus further and further into the branch. The affected branches along with the leaves on it die off. As a countermeasure it is advisable to remove the affected branches from the rhododendron. The casting with appropriate poisons against this disease is unfortunately no longer allowed. Tip: Do not throw the affected branches on the compost. The fungus can survive there. It is better to dispose of them with the household waste.
Powdery mildew
Mildew on the leaves and shoots of the rhododendron are limited in their growth. In a deciduous rhododendron, the coating appears in gray and white. In a year-round green rhododendron, the affected leaves and branches are covered with yellow spots. Mildew is a fungus that can be treated quite well with pesticides. The treatment is recommended, among others, fungus-free Ectivo, Duaxo Universal Mushroom-free or net sulfur WG. Tip: Most pesticides are used preventively. You should therefore water regularly so that the mildew can not infest their trees.
General remark
How long a plant protection product is used usually depends on the success of the treatment. If this happens quickly, the remedy can be discontinued quickly. If the infestation is quite advanced, then please be patient and use the remedy over a longer period of time.
frequently asked Questions
  • Where is the best location? - The rhododendron likes it slightly shady. A partially shaded place, which offers sun, but also enough shade, is ideal.
  • Can harmful substances and diseases be prevented? - Yes. Always make sure that the pH of the soil is right. Fertilize regularly to provide the most important nutrients.
  • Can diseases kill all the trees? - Very persistent pests and diseases can do this. Therefore, look at your Rhododendron regularly and remove affected areas immediately, so that a spread of the disease can be avoided.
Worth knowing about rhododendron diseases and pests
prevent diseases
In order to protect a rhododendron from diseases and pests, the correct soil condition is very important. In general, most plants grow best on a neutral pH soil, but rhododendron is an exception. He needs an acidic soil with a pH between 4 and 5.5. If this condition is not present in the garden, the soil can be prepared by adding peat or by using a special rhododendron soil.
fungal diseases
  • The Phytophthora cactorum is a fungal infection of the rhododendron.
  • This is due to fungal spores that spread over the ground and find ideal conditions, especially in hot and humid weather.
  • Then first the buds, later also the leaves and the branches turn brown, wither and fall off.
  • Often only individual shoots are affected, so fungal attack can be combated by removing the affected branches as early as possible.
  • However, to prevent re-spreading of the fungal spores, the clippings should never be disposed of on the compost.
Fight pests
  • The Fringed Stout-toed Marsh occurs from April to May, damaging the rhododendron leaves by eroding parts of them.
  • He has a size of about ten millimeters when fully grown and a black body with dark brown spots.
  • Mostly he is only active at dusk and at night. Their eggs lay these beetles in the ground, where larvae hatch within two to three weeks.
  • These larvae cause further damage to the rhododendron by eating the roots.
  • A large population of these larvae can even lead to the death of the plant.
Tip: Naturally, the larvae of the weevil can be fought with nematodes. With a mixture of water and the nematodes the infested plant is poured.
  • The rhododendron cicada is especially feared because it transmits a mushroom when her eggs in the buds of rhododendron.
  • Through this fungus the flower buds turn gray or brown, but they do not fall off the shrub.
  • From the buds then grow small rods, which are about two millimeters long.
Tip: cicadas can be fought with yellow boards. These are boards made of cardboard or plastic, which are provided with adhesive and to which the cicadas stick and die.

Video Board: Lesson 7 Diseases and Insects Affecting Rhododendrons.

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