Content
- Discover and combat rhododendron diseases in good time
- The most common causes of rhododendron diseases:
- Identify and prevent site and weather damage
- First aid with sunburn
- What to do in frost damage?
- Balance mineral or nutrient deficiencies properly
- nitrogen deficiency
- Lack of iron and magnesium
- Growth of stunt due to nitrogen deficiency
- Remedy for diseases caused by fungi, bacteria or viruses
- Effectively combat rhododendron wilt, dying and dying
- Powdery mildew on rhododendron
- Bud dying of rhododendron
- No chance for the voracious insects
- Tips & Tricks
Discover and combat rhododendron diseases in good time
Those who take proper care of rhododendrons, discovers diseases and pests in good time and combats them with little work, gets a lot of pleasure. In addition, more protection and habitat for insects and birds is created.
Rhododendrons are considered as robust and uncomplicated ornamental shrubs. However, if the location, water and nutrient supply do not agree, deficiency symptoms or pest infestation may occur.
The most common causes of rhododendron diseases:
Identify and prevent site and weather damage
Rhododendrons love light, half-shady places. They thrive on acidic, humic soils with a pH between 4.5 and 5.5. Location and weather damage such as sunburn or frost are visible on leaves or buds.
First aid with sunburn
Direct midday sun causes sunburn in sensitive strains. Visible on yellow or brown leaves while leaf areas in the shade show no damage.
What to do in frost damage?
Even with winter-proof rhododendrons extremely cold, dry and windy weather causes frost damage. If brown leaves or leaf margins die off and flower buds dry up, the plant needs more wind protection. Fir twigs or reed mats provide sufficient protection.
Balance mineral or nutrient deficiencies properly
nitrogen deficiency
First, older leaves have a uniform light green or yellowish color. Later, younger foliage turns yellow. In summer, there is premature leaf fall.
Soil compaction or insufficient nutrient supply cause the nitrogen deficiency with the typical foliage discoloration. An appropriate nitrogen fertilization compensates for the deficiency symptoms and strengthens the plant.
Lack of iron and magnesium
If young rhododendron leaves lose their dark green color and turn yellow while the leaf veins remain dark, these are signs of insufficient iron or magnesium.
Rhododendrons are sensitive to calcareous irrigation water or a lime-rich soil that is too high in pH. Here, not only "special rhododendron fertilizers" but above all a pH-lowering soil improvement with special rhododendron soil help.
Growth of stunt due to nitrogen deficiency
Growth of cress and yellowed leaves indicate nitrogen deficiency. Especially "the rhododendron variety Catawbiense" is regarded as a nitrogen seizure. It requires a lot of humus, nutrients and horn chips as nitrogen fertilizer.
Nitrogen by artificial fertilizers should only take place in March and May. Fertilize later, the shoots do not mature until winter. They do not lignify and freeze.
Remedy for diseases caused by fungi, bacteria or viruses
The healthy and generally robust crude dodendron rarely infects fungi, bacteria or viruses. In case of weakened plants with fungal attack, it is recommended to immediately remove the infected parts of the plant, burn them or otherwise dispose of them from the garden! This is the only way you can permanently prevent fungal attack in the garden.
Effectively combat rhododendron wilt, dying and dying
The fungal genus Phytophthora includes more than 20 species. They cause root, stem, shoot and Fruchtfäuleaber also turnover diseases on rhododendrons and other plants. The fungal spores need water and light to germinate. Waterlogged conditions and warm, humid weather favor an infestation.
Dry branches, brown terminal buds and brown leaf spots along the leaf midrib indicate an infection with Phytophthora fungi. Also gray-brown discolored leaves curl up without falling off. Among other things, the harmful fungus clogs the pathways and the plant dies completely or instinctively. The bark in the diseased root area is reddish brown when cut. Healthy tissue, on the other hand, appears bright and juicy.
Powdery mildew on rhododendron
About the powdery mildew - Microsphaera azaleae - on rhododendrons is little known. Also, the individual varieties are vulnerable differently. Deciduous rhododendron leaves are gray-white and rarely grow. As a countermeasure special pesticides act.
Bud dying of rhododendron
During the winter, the buds of "hardy rhododendrons" become brown and die. The shrub does not bud out the following spring. The most common cause of this is the harmful fungus Pycnostysanus azaleae. Through small black hair on the fruit body in spring, the fungus becomes visible.
Whether rhododendron cicadas are involved in the fungal attack in bud dying is not clear. Therefore, no chemical control of these animals should be done. Since fungicides against the fungus does not work only to remove suspicious dry buds by April at the latest. Just before the yellowish larvae of the rhododendron cicadas hatch in May.
As a precaution, yellow boards can attract and destroy insects in the summer.
No chance for the voracious insects
Rhododendron cicada (Graphocephala coccinea), Rhododendronhaut- or network bugs (Stephanitis rhododendri) or weevils such as the weevil (Otiorhynchus sulcatus) are among the animal pests. They eat leaves, roots or suck nutrients out of the plant and lay their eggs.
Depending on the pest, there are conspicuous feeding patterns, crippling and soiling on the leaves. The undersides of the leaves appear mostly rusty and you will find black Kottröpfchen. In individual cases, the weevil larvae cause fretting damage to roots.
From the gentle damage control to the destructive weapon of destruction, everything is commercially available to destroy voracious insects. Strong remedies against pests also exert strong side effects on beneficials. Instead of radical poisons, environmentally friendly measures are recommended to keep the population in a manageable, non-damaging framework.
Tips & Tricks
Each Rhododendron variety requires special site conditions. In order to find the right variety for your garden, it is advisable to plant different rhododendron species. After a few months, you can see which Rhododendron grows lush and flourishes without costly soil improvement.