Deficiency Diseases
Deficiency diseases first show up in leaf discoloration. Only if the cause is not eliminated after the first signs, stunted growth or deformed shoots, leaves and flowers - although the latter can also fail to appear.
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Iron deficiency chlorosis
The chlorosis is shown by the yellowish discoloration of the leaves. Typically, however, the leaf veins remain bright green. Iron deficiency is very common when the Soil pH is too high and the roots can therefore not absorb enough of the mineral - calcareous soil interferes with the absorption and metabolism of iron.
Nitrogen deficiency
With insufficient fertilization and / or if the soil is too firm, impermeable to air, a strong yellow coloration of the leaves rather indicates a lack of nitrogen. This can be eliminated with the gift of blue grain.
Fungal or viral infections
Leaf spot diseases are also quite common on azaleas. These are shown by yellowish or dark brown, mostly irregularly round spots that spread quickly and can also pass onto the shoots. Various fungi or viruses can be used for this phenomenon, the mosaic virus in particular. In all cases, only the pruning of infected parts of the plant helps.
Beware of the wilt disease
The dreaded Verticillium wilt also occasionally attacks azaleas. In this case, quick action can sometimes save the plant. However, it is not enough just to prune back the affected plant; you also have to dig it up and carefully remove the soil adhering to the roots. The pathogen sits in the ground and attacks the azalea from there. As a rule, however, only the disposal of the diseased azalea helps. Make sure not to plant or grow any Verticillium-sensitive plants at this point. to undertake a generous soil replacement.
Common pests
Pests do not stop at the Japanese azalea either.
Rhododendron bug
The rhododendron bug (Stephanitis rhododendri and Stephanitis obertii) is initially noticeable through yellowish or greenish leaf spots. Remove infested leaves in the event of an infestation - especially before winter.
Rhododendron cicada
Cicadas are leaf sap suckers, but basically do not cause too much damage. They are only dangerous as Carrier certain pathogens such as bud rot. Put up yellow boards in June / July to combat it.
Tips
Due to the shady and therefore often moist location of the Japanese azalea, the leaves can occasionally be covered with a greasy, green coating. This can be easily wiped off. These are algae. To combat these, you need to get more light.
