Diseases of rhododendrons(rhododendrons) are quite common. This is due to the huge popularity of these shrubs, which are not easy to grow at all. Our climate is not conducive to them and quite oftenmistakes in the care of rhododendronsTherefore, it is worth finding outwhy rhododendrons get sickand how to recognize their diseases. Here are descriptions and photos withsymptoms of rhododendron diseasesand ways to combat them. We recommend the bestrhododendron disease sprays !
Diseases of rhododendrons. Pendulous, discolored leaves may indicate fertilization errors or fungal disease infestation
Why do rhododendrons get sick?
Rhododendrons have quite high cultivation requirementsand our climate is not favorable for these plants. Under natural conditions, where they come from, air humidity is quite high, and rhododendrons grow on slopes where the water flows quite freely. Plants have a lot of moisture in the air and soil but are not susceptible to flooding. In our gardens, the situation is often the opposite - the air is dry, but the soils are often wet.
In our climaterhododendrons are also affected by cold winters and drying winter windsThis especially applies to species with evergreen leaves (these are usually referred to as rhododendron). Water evaporates from their evergreen leaves all the time, and plants cannot replenish it from the soil frozen in winter. In addition,rhododendrons root shallow, so their roots can freeze easilyand are very prone to drying out.
Such weakened bushes can easilysuffer from rhododendron diseases . There are usually 3 types of rhododendron diseases:
- diseases resulting from improper care of rhododendrons , i.e. non-infectious diseases,
- infectious diseases , most often resulting from an attack by a pathogenic fungus (fungal diseases),
- damage related to the attack of pests(their symptoms can sometimes be confused with those of infectious diseases).
Interestingly,the symptoms of rhododendrons are most often seen on the leavesbut we should also observe their shoots, buds and flowers. It is worth finding outhow to distinguish the symptoms of rhododendron diseasesfrom changes resulting from incorrect care, improper fertilization or pest attack. Otherwise, we will unnecessarily use plant protection products that will not help the plant at all.
Non-infectious diseases of rhododendrons
Yellowing of the rhododendron leaves and numerousleaf stainsmay be related to a nutrient deficiency in the soil or an incorrect soil pH, at which rhododendrons are unable to absorb minerals from the soil.
Here are the most common symptoms that indicate micronutrient and macronutrient deficiencies due to fertilization errors or incorrect soil pH:
- lack of potassium- tissue between the veins turns yellow and small brown spots appear on the edges of the leaves
- lack of boron- numerous brown or reddish spots appear on the edges of the leaves
- lack of iron- in the absence of this component, chlorosis of the leaves occurs, manifested by yellowing of the tissue between the leaf veins, while the innervation itself remains green
How to treat nutrient deficient rhododendrons?
The solution to the problem is usually proper fertilization of the rhododendrons. After noticing the above-mentioned symptoms, a multi-component rhododendron fertilizer with microelements should be applied. In some cases, foliar fertilization (spraying the plant with fertilizer dissolved in water) also helps. The following fertilizers will be helpful here: Bujne Flowering soluble fertilizer for rhododendrons and Magiczna Stiła soluble fertilizer for rhododendrons.
It is also worth measuring the soil pH.The correct pH of the soil for rhododendrons is 4.5 - 6.0Usually it is unlikely that the measurement will show a lower pH than recommended (very acidic soil), but often the pH is too high (soil neutral or alkaline). Measurement of soil pH is very important because rhododendrons have difficulties in extracting nutrients from the substrate if the pH is not correct.
Then the right solution is not to add more minerals, but to improve the soil pH.If the pH of the soil is higher than recommended for rhododendrons, use an acidifying fertilizer An example of this type of fertilizer is ammonium sulphate. You can also use acidifying fertilizers for rhododendrons, blueberries and conifers. A specialist soil acidifier brings very fast results. The substrate pH -
In winter, the dangling and rolling leaves of the rhododendron indicate that the shrub is frosty and the soil is lacking water
Winter rhododendron leaf curl
Leaves hanging and rolling along the main nerve , observed in winter, may indicatefrost and dryness of rhododendronsThis is due to the evaporation of water from the evergreen, fleshy leaves of rhododendrons, while the shrubs cannot replenish the water shortage from the frozen soil. Therefore, the plant tissues dry out. To prevent this, water the plants abundantly in late autumn, and continue watering the plants in winter during the thaws.
Fungi diseases of rhododendrons
Rhododendron phytophthora
The tops of the shoots turn brownand turn brown, and the necrosis extends to the leaf blades. The leaves lose their shine, turn brown, die and roll from the bottom of the bush along the main vein. At the base of the shoot you can see its rot moving gradually upwards. Light brown spots that darken quickly can also be observed on the roots.
These symptoms indicate that the shrubs are attacked by phytophthora - a disease of the rhododendron with a fungal basis. Patients strongly affected by the disease should be removed, and rhododendrons growing nearby should be treated several times with appropriate fungicides, eg Magnicur Energy 840 SL or Proplant 722 SL. To overcome phytophthorosis, rhododendrons should be watered and sprayed with these preparations.
To reduce the use of chemicals in the garden, fungicides should be used alternately with natural preparations, such as Biosept Active, which strengthens the resistance of plants.The biological preparation Polywersum WP also brings very good results. It contains a plant-safe fungus that feeds on the phytophthora-causing fungus. Thanks to its use, we have the ability totreat plants infected with phytophthora without the use of environmentally harmful chemicalsIn place of the removed diseased rhododendrons, it is not allowed to plant new plants easily attacked by phytophthorosis, i.e. rhododendrons and azaleas, yews, cypresses, firs, and pines.
Rhododendron leaf blotch
Leaf blotch is whensmall round brown spots appear on the rhododendron leaves , usually edged with a dark red border. The spots can also be larger (up to 3 cm in diameter), round or oval, initially brown, turning gray with time. Black clusters of fungal spores form on the surface of the spots. This disease of rhododendron leaves can be caused by various pathogenic fungi: Colletotrichum gloeosporioides, Septoria, Myrothecium roridum, Cercospora.
After noticing the first spots on rhododendron leaves, remove diseased leaves or, in case of severe infestation, cut out whole shoots with infected leaves. Spray the remaining he althy parts of the plants with the natural preparation Biosept Active. Ifthe symptoms of leaf spot on rhododendronsreappear, you can use a stronger fungicide, e.g. Topsin M 500 SC
Gray mold on rhododendrons
Rhododendrons and rhododendrons can also be attacked by gray mold. It is a disease quite commonly found on various garden plants and caused by the fungus Botrytis cinerea.The symptoms of gray mold on rhododendronsare most often seen on their flowers and flower buds. As a result of infection with this disease, flower buds turn brown and brown. Gray dusting coating appears on them. Stains appear on the flower petals, which are initially light and then turn brown. Gray, dusty mycelium coating appears on the entire flower buds, as well as within the spots on the flower petals.
Infested with gray mold flower buds and already developed flowers should be removedSpray whole plants with natural preparations already mentioned in the article: Biosept Active or Polywersum WP. Spray it several times at intervals of 10-14 days. In the following years, spray rhododendrons with these preparations as a preventive measure after setting flower buds and before flowering.
Chemical fungicidesTo combat gray mold on rhododendronsyou can use Topsin M 500 SC.
We should also remember that the spread of fungal diseases is favored by excessive plant density and frequent wetting of their shoots and leaves. Therefore,avoid planting rhododendrons too densely
, and do not completely rain them while watering. It is best to deliver water directly to the ground, avoiding splashing it onto the plants.The measures for protection against rhododendron diseaseslisted in the articlecan be ordered in the shop of our guide. We guarantee high quality products, low price and fast shipping.To see the available preparations, press the button below.
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