If you want a healthy plant, you should of course take good care of it. And proper care begins with the right time of planting and an appropriate location. Is everything else OK, but you still notice a problem with your rhododendron bush? Then a disease or a pest infestation could be the cause. So that you can recognize them correctly and then treat them, we have put together the most common rhododendron diseases, pests and problems with their characteristics. The following are noticeable on leaves, buds and flowers and can largely be remedied if you address them in a timely manner.
Rhododendron diseases – problems with the buds and flowers
Plant produces fewer buds than usual
If the flower buds are defective, this can either be because the plant is doing too well (as strange as that may sound) or because it isLocation doesn't getor there is a lack of nutrients or incorrect care:
- too little potassium
- too little phosphorus
- low temperatures in summer
- too much moisture in summer
- Lack of light due to too much shade: although some varieties are less sensitive to shady locations, the rule of thumb is that more sun produces more buds, but can also cause burns and dry out the plant
- Cutting at the wrong time: The buds are already formed at the end of summer to the beginning of autumn the previous year, which is why the plant should no longer be cut
- Oversupply of nitrogen, which promotes the growth of leaves and shoots, but not flowering
- the bush is still too young: cuttings only bloom after 2 to 3 years at the earliest, bushes grown from seeds even need 1 to 2 years longer
Rhododendron Diseases – Brown Buds
Did the flowering bush form plenty of buds, but they turned brown? This happens in sudden cold weather after a milder period, i.e. when frost occurs late in the spring or the previous autumn was particularly cold and immature buds froze. The plant gets confused and thinks the weather is getting warmer, causing it to start opening its flower buds early and the buds fall off.
The rhododendron leafhopper also produces brown to black buds in some cases. More specifically, this Pycnostysanus can transmit azaleae, which can be recognized by a dark, spiny coating. Remove affected buds in spring and if you notice leafhoppers near the plant in June, treat them immediately with a suitable insecticide to prevent fungal infestation next spring. Be careful when combating and pay particular attention to the undersides of the leaves.
Rhododendron diseases – flowers do not open
The many promising rhododendron flowers are not blooming? First of all, check whether they are actually future flowers and not leaf buds. Causes for missing flowers could be:
- too low temperatures and the buds are frostbitten (recognizable by the brown discoloration, as described above): normally the rhododendron is hardy, but under certain circumstances it can suffer frostbite; winter protection can prevent frostbite
- Lack of phosphate and potassium: these increase the plant's resistance to low temperatures
- the soil is not acidic enough: you can improve the pH with powdered sulfur
The opposite problem, that of flowers opening earlier than they should, is the result of a warmer period that causes the plant to believe that spring has arrived. Since the weather then gets colder again, many flowers freeze and typical rhododendron diseases could occur until the next season.
Spotty flowers
The so-called ovulinia is a blossom rot that can be recognized by brown spots on the flowers. What is typical is that these spots look like they are wet and get bigger and bigger until the entire flower is brown and rotten. There is nothing you can do about it, but you should cut off the rhododendron flowers and take preventive measures in the future. If you expect a very wet spring season, it is worth using a suitable fungicide before the flowering period.
Characteristics on the leaves
Rhododendron Diseases – Curled leaves during extreme weather
If periods of strong heat, cold and/or lack of water are the cause, curling of the leaf sides is a normal reaction that also occurs in other plants. Fix the problem by watering more, using sunscreen, or as appropriatewinter protectionset up. If you water more, however, be careful not to overdo it (once the soil is actually dry) to avoid fungal infections on the roots that are encouraged by too much moisture. We list a few typical fungal diseases at the end.
Rhododendron has yellow leaves
Light yellow color evenly distributed
This is a sign that the plant is lacking nitrogen. So you should provide them with appropriate fertilizer as quickly as possible.Also horn shavingsare suitable for this purpose.
Uneven yellow colored leaves
The larger areas of theLeaves turn yellow, but the leaf veins remain green? This means that your rhododendron is iron deficient, even though iron is found in sufficient quantities in the soil. Although these shrubs are known to like acidic soil, soil that is too acidic is counterproductive because it causes the problem known as chlorosis, which prevents the plant from absorbing the nutrient. It is best to water or spray young plants with suitable preparations (magnesium deficiency could be another cause). However, it is then important to improve the pH value of the soil in order to finally solve the problem.
Brown leaves on rhododendron bush
Brown leaf edges that die off
This is a sign that the plant has been damaged by stronger winds and cold weather. If the rhododendron has brown leaves of this type, this could also be caused by a lack of boron.
The middle areas of the leaf turn brown
Sunburn is a possible cause because these areas are particularly exposed to the sun, in contrast to the edges of the leaves. On the one hand, you can of course remedy this with sun protection. But a windbreak that prevents it from drying out too quickly after watering also proves to be a good and quick measure. Also try to provide the plant with plenty of water before the first frost occurs.
Further discoloration and coating on the rhododendron leaves
- Leaf spotas Rhododendron Diseases - irregular spots spreading from outside to inside (reddish brown/ash gray/dark brown, black in the center of the spots); the death of the leafstarts at its top; Fungicides are suitable agents
- Gray mold rot – moldy coating on about two-thirds of the surface of a leaf, which gradually migrates to the stem; usually in June or July on relatively fresh leaves; treat with fungicide
- Rhododendron diseases likemildew– also with a grayish-white, but rather powdery coating, more often on the undersides of the leaves
White coating in combination with deformed leaves can also be a sign of earlobe disease (only insome Japanese azaleas) - Rhododendron-Wanze– Leaves are pale green, yellowish or tending towards white, although the undersides may be brown to black and the leaf edges may curl; May, June and July are peak seasons for these pests; treat in a timely manner with a suitable insecticide
- Rhododendron Diseases – Sticky LeavesWhiteflies(whitefly); leaves a sticky coating on the leaves (honeydew), but is more likely to affect indoor or greenhouse plants. If you nevertheless notice them on the undersides of the leaves, you should take action. The honeydew itself weakens the plant, but also promotes the formation of the so-called sooty mold fungus. The scale insects lay their eggs on the undersides of the leaves, from which harmful larvae then hatch and, together with the adult animals, damage your shrub.
- Rhododendron andAphids– Aphids also produce honeydew, so these pests also have an increased risk of the plant becoming ill with sooty mold fungus. If the infestation is severe, the leaves will begin to curl or curl. As a rule, treatment is not absolutely necessary or necessarywith the help of home remediessufficient. However, if the infestation is severe, you can apply an insecticide.
- Algaeon the rhododendron leaves - Especially in shady locations, a coating of algae can form on the leaves. If the weather is humid, formation is even more favored. This is not a cause for concern in itself, but rather an aesthetic problem that you can eliminate with the help of a preparation between February and April. This is an oily agent that settles on the algae and suffocates it.
Problems with twigs, branches and roots of the rhododendron bush
Rhododendron diseases – The black weevil causes plants to suddenly die
This pest can be seen in many different ways on the plant, with the infestation of larvae in the roots and at the base of the trunk being the most feared. The larvae separate the flow of plant sap and in this way kill the plant.
However, if the leaves are eaten, it is the beetle that only visually affects the plant, but there is little you can do about it. The use of nematodes even before the beetles hatch in early May is considered quite successful.
Fungi on individual parts of plants
Phytophthora, Botryosphaeria and Phomopsis cause fungal diseases that are difficult to treat. The good news is that they usually only affect some parts of the plant and it is extremely rare for the entire plant to die. You should preventatively treat your rhododendron bush with fungicides against these fungal infections.
Rhododendron diseases – fungal attack by the following fungi
- Botryosphaeria – primarily affects twigs and branches that begin to die back; Reducing stress reduces risk of infection; Discard diseased parts, but this is no guarantee that the plant will survive
- Pestalotia – Leaves turn brown with white spots; can be treated immediately, but is usually unsuccessful
- Phomopsis – similar to Botryosphaeria, more common in azaleas
- Phytophthora – on the roots, buds and/or leaves; Peat or bark humus prevents and prevents waterlogging
- Pycnostysanus azaleae – on the buds; is brown-black and has a spiky appearance; Remove and dispose of diseased buds as soon as possible
Prevent fungal infections and pest infestations through proper fertilization
Fertilizer is good and important, that's clear. However, you should do it right, otherwise it can even cause damage. For example, it is not a good idea to continue to have high nitrogen levels in the summerApply fertilizer. This promotes plant growth when they should actually be slowly approaching the rest period. During growth, a plant develops so-called bark cracks. These cracks then have a much harder time healing in the colder season, which not only makes your shrub more susceptible to fungi and pests, but in extreme cases can even lead to its death.
