The main diseases of rhododendrons and their treatment. Rhododendrons
Rhododendrons are affected by many pests and diseases. To avoid the death of plants, it is necessary to regularly monitor the condition of rhododendron bushes and take timely measures to eliminate insect pests and fungal diseases.
Insect pests of rhododendrons
Acacia false shield (Parthenolecanium corni Bouche)
Rhododendron bug (Stephanitis rhododendri Horv)
Rhododendron bug is considered the most dangerous and common pest that affects these shrubs. A sign of its presence can be small black-brown dots on the back of the leaf, places of punctures by the bug of the leaves and their excrement.
In the photo, the larva of the rhododendron bug.
Damage to the leaf blade of rhododendron by the larvae of the rhododendron bug.
You can destroy the bug by spraying with contact-intestinal and systemic preparations - clipper, omayt, aktara, demitan, apolo, fitoverm, Bi 58. The preparations must be changed so as not to cause addiction in insects to the active ingredient of insecticides.
Spider mite (Tetranychus urticae)
The spider mite inhabits rhododendron shrubs in a dry, hot season, feeding on the juices of its leaves. Due to extremely small size it is difficult to see it with the naked eye. The appearance of the plant will help determine the presence of a spider mite: the underside of the leaves, as it were, is entangled with a thin cobweb, and they themselves become brown in color, fade and fall off.
Here it must be added that middle lane In Russia, the full development cycle (generation) of the spider mite is from 7 to 9 days. Behind summer season 22 generations of ticks hatch. To achieve success in the fight against ticks, it is necessary to carry out treatments every 6 days with systemic pesticides: Aktara, Omayt, Apolo, Demitan.
Field slug, or plowed slug (Deroceras agreste)
The arable slug infects the leaves of young rhododendrons, making large holes in them. Its activity can lead to the death of shrubs in the shortest possible time. To prevent this, individuals of the plowed slug will have to be collected by hand, and watering with a solution of TMTD (concentration 0.8%) also contributes to its destruction.
Rhododendron whitefly (Dialeurodes chittendeni)
Whitefly rhododendron, or white rhododendron fly (Dialeurodes chittendeni)
They are found mainly on large-leaved rhododendrons: Caucasian, Pontic and Ketevbinsky and their varieties and hybrids. Spraying leaves from below with nicotine and oil emulsion in spring and autumn is recognized as the most effective.
Tobacco (black) thrips (Thrips tabaci).
Tobacco (black) thrips is an insect of small size and characteristic black color. Damages leaves and buds of rhododendrons.
As a result, the foliage fades prematurely, turns yellow and falls off, and the flowers fade without opening. In addition, this pest greatly inhibits the growth of young shoots and deforms the buds. Struggling with tobacco thrips by spraying plants with 0.3% nicotine solution, 0.2% carbophos emulsion. Also suitable for this purpose are preparations: Aktarv, Omayt, Apolo, Clipper, Fitoverm,
Garden beetle (Phyllopertha horticola)
Garden Asian beetles are the most dangerous pests for rhododendrons. They infect the stems and root system of plants, eat their leaves. The most effective means for the destruction of an insect is: Clipper, Bee 58, Apolo, Fitoverm, Aktelik, Karate.
Furrowed weevil (Otiorrhynchus sulcatus L.)
Corrugated bevel Otiorrhynchus sulcatus L. is one of the most dangerous pests. It affects many cultures, including rhododendrons. It is very dangerous for plants, because adults eat leaves, buds, buds, flowers and even young shoots of rhododendrons, and larvae, while in the soil, eat all the roots up to the root collar. In young shoots, the bevel gnaws the bark to wood, the shoot above the affected area withers and dries. The pest eats leaves and petals in an arcuate manner, starting from the edges. Affected plants lose their decorative effect.
The adult beetle is 8-10 mm long, black, brown-black (young individuals are yellowish-brown), with yellow spots on thick, leathery, ribbed wings and with a short nose. Adults are inactive, flightless. Adults feed only at night, and during the day they hide in the substrate, under soil particles, so they are difficult to notice. On flowering specimens, they hide in inflorescences. If early in the morning they can sometimes be seen, then at the first touch the beetles freeze, fall to the ground and become difficult to distinguish.
The larvae are fleshy, yellowish-pale, 10-14 mm long, 3.5-4.0 mm wide, without legs, with a light brown head and black jaws. In appearance, they resemble the larvae of the May beetle.
They eat the roots and bark of the base of the stem, as a result of which the plants die. In greenhouse conditions, the beaver breeds all year round, but especially intense from July to December. It is during these months that the risk of damage to rhododendrons by larvae is greatest. Adults appear around February.
In the open field, the larvae overwinter in the soil, pupae are formed in spring. Adults appear in May and June. Females lay their eggs in humus-rich soils or in compost heaps.
Even in small numbers, pests can severely disfigure the leaves, flowers and shoots of rhododendrons, and their larvae can completely destroy hundreds of young seedlings growing in greenhouses.
Control measures.
The fight against this pest is very difficult, since it is not always possible to notice damage to the larvae in a timely manner. In addition, older larvae, as well as adults, are insensitive to insecticides. If larvae of the scythe appear in the picking boxes in which young seedlings of rhododendrons grow, the plants should be immediately transplanted into a fresh substrate, and the old one should be burned. During transplantation, care must be taken to ensure that pest larvae do not get into the new substrate, which are usually easy to find near the roots of the affected plant. For the purpose of prevention, the remaining boxes located near should be watered with a 0.1% emulsion of phosphamide (Bi-58; Rogor), 0.2-0.3% emulsion of metaphos, karbofos or chlorophos. The permissible concentration of insecticide in each case is determined individually. During the active life of adults, rhododendrons are pollinated with metaphos dust, sprayed with a 0.2% emulsion of metaphos, phosphamide or a 0.3% emulsion of karbofos or systemic insecticides and acaricides: Apolo, Omite, Demitan, Fitoverm, Flumite. Since adults actively feed at night, spraying should be carried out late in the evening, at night or early in the morning.
Narrow-winged miner moth
Its caterpillars gnaw many holes in the leaves, eat the leaf parenchyma, and then fold the edges of the leaf into a tube for pupation.
As a result of their activity, the leaves begin to dry out, crumble and fall off. To scare away the narrow-winged moth, knowledgeable people recommend fumigating or spraying bushes with sulfur.
Mealybug
rhododendron fly
The rhododendron fly infects the leaves of shrubs, leaving small light spots on them and depleting the plants. To destroy this specific pest, spraying with nicotine sulfate, Apolo, Demitan, Fitoverm is used.
Blue Moth (Arichanna melanaria)
Butterfly, wingspan 36-44 mm.
Blueberry moth caterpillar eats the edges of rhododendron leaves.
Control measures
During the appearance of blueberry moth caterpillars, rhododendron should be processed
- Contact Insecticide: Clipper
- Contact intestinal insecticides: Decis, Senpai, Intra-Vir, Barey, Aktellik, Karate, Karbofos
- Systemic insecticides: Aktara, Konfidor, Kinmiks, Bi-58
rhododendrum sawfly
Sawfly larvae leave intricate patterns on the reverse side of the leaf.
Sawfly larvae, unlike adult insects, cause minor damage to the decorativeness of rhododendrons. Therefore, it is recommended, upon detection, to collect them from the leaves and destroy them.
fungal diseases
Tracheomycosis
Tracheomycosis leads to rotting of the rhizome, as well as significant damage to the vascular system of plants. When painful signs appear, it is necessary to cut and burn the branches affected by the disease, and then spray the shrub with Bordeaux liquid.
Late blight rot
Late blight is caused by pathogenic fungi of the genus Phytophthora. As a result of this disease, stems and root collar bushes are covered with spots of brown or purple color. Then the rhizome of the rhododendron turns brown and begins to rot, which leads to gradual wilting. In the absence of timely and competent treatment, the lesion passes first to the stems, and then to the leaves of the plant, leading to its death. When signs of the disease appear, the affected branches and shoots must be burned, and then the rhododendron bushes should be treated with quadris or 0.2% fundazolo. You can also use drugs: Gamair, Abiga Peak, Topaz, Fundazol.
Septoria spotting (Septoria lycopersici)
Pathogen: mushroom Septoria azaleae Voglino. Symptoms are described by different authors with slight differences.
1. Small rounded reddish spots appear on the leaves, gradually turning white in the center.
Over time, dotted black fruiting bodies of the overwintering stage of the fungus form on the surface of the spots. The leaves turn yellow and gradually dry out.
2. As a rule, greenhouse plants are susceptible to the disease. In countries where rhododendrons are cultivated very widely, this fungus is also found on deciduous rhododendrons in open ground. Yellowish, red-yellowish, later yellowish-gray spots of irregular shape appear on the leaves of plants. By autumn, they become dark brown in the middle, and sometimes even brownish black. At first, the spots appear in the middle of the leaf blade, gradually increase and, having reached the large veins, stop. The fungus grows into all leaf tissues, the leaves die and fall prematurely, so that the plant becomes completely naked. As a result of falling leaves in plants, all physiological processes are disturbed, flower buds are not normally laid. On the spots, one can see small, black, dot-shaped spore receptacles - pycnidia, immersed in leaf tissues.
Control measures: pruning of the affected parts of plants, spring spraying with a solution of Bordeaux mixture, its substitutes or cumulus. If the air is excessively humid, do not spray plants with preparations containing copper, as this leads to burns of leaves and young shoots. Preparations containing copper are used only for normal humidity air and enough high temperature. You can spray only those plants whose leaves have fully grown and developed. In the summer, it is necessary to carry out fungicide treatments: Gamair, Abiga-Peak, Skor, Topaz, Fundazol.
Rot of seedlings and young seedlings of rhododendron
(pathogens - Rhyzoctonia sp., Pythium sp. and Botrytis sp.).
Often, when propagating by seeds and cuttings, one has to observe a sudden mass wilting of rhododendrons, their decay and death. The causative agents of this disease are fungi of the following genera: Rhyzoctonia, Pythium and Botrytis. Affected seedlings fall sideways and die, white hyphae of fungi or brownish mold are visible on the leaves. Pale, cobweb-like threads appear on the surface of the substrate. Fungi usually develop if the substrate is fresh, not yet decomposed, or if the crops are watered with fungus-infected water. Too much planting density, excessive humidity in greenhouses and insufficient air exchange increase the likelihood of disease.
Control measures: Dying seedlings should be sprinkled with finely ground charcoal to stop the spread of the disease. In addition, the disease can be instantly eliminated by sprinkling the affected areas with foundation powder. In order to prevent young shoots and seedlings, it is desirable to spray with a 0.2% suspension of foundationol. Captan and TMTD can be used to combat this disease.
Rhododendron bud rot
Pathogen: fungus Sporocybe azaleae (syn.: Pycnosteanus azaleae)
The disease was first detected on rhododendrons in the United States. The disease is typical for the largest rhododendrons (Rhododendron maximum L.) and Katevbinsky (Rhododendron catawbiense Michx.). Buds affected by this disease turn brown and die. Mushroom from buds can grow into branches and lead to their death. Control measures: during the growing season, plants should be sprayed regularly (every 2-3 weeks) with copper-containing preparations.
Buds "beaten" by autumn-spring frosts. Unlike the buds affected by the fungus Sporocybe azaleae (syn.: Pycnosteanus azaleae), they look clean and do not have pycnidia. But still, the buds "beaten" by frosts (frosts) serve as potential objects for the settlement of Sporocybe azaleae (syn.: Pycnosteanus azaleae), so they should be removed.
Carriers of the fungal disease Sporocybe azaleae (syn.: Pycnosteanus azaleae) are rhododendron bugs and cicadas Graphocephala coccinea, Graphocephala fennahi (rhododendron leafhopper). Cicadas themselves can be the cause of the drying of flower buds and buds of Azalea Pontica.
To prevent infection of the rhododendron by the fungus Sporocybe azaleae (syn.: Pycnosteanus azaleae) in July, yellow panels coated with adhesive are installed in the azalea bushes to catch the flightless green and orange striped cicadas.
In case of serious infestation, systemic and enteric-contact insecticides are used against cicada larvae. Treatments are carried out early in the morning.
In order to minimize losses from the development of fungal diseases, it is necessary to remove all shrunken shoots and dead dark-colored buds.
Gray rot rhododendron
Symptoms: blurry brown spots without bordering appear on leaves, stems, buds and petals, the surface of which quickly dries and cracks.
The death of the shoots of rhododendron
Plants planted in full shade are most susceptible to this disease.
The causative agent is the fungus Phytophtora cactorum Leb. Symptoms: in the affected plants, the apical buds do not bloom, they turn brown, and then completely die off. The shoots also dry out at first, and later die off. Mature leaves curl up, turn brown and dry. Severely affected plants die.
The causative agent is the fungus Physalospora rhododendri. This fungus also infects lilacs. Symptoms: in diseased plants, on some shoots, the leaves turn brown, dry out, and then the entire shoot dies.
Control measures: affected leaves and shoots are burned. After flowering, rhododendrons are regularly sprayed with copper-containing preparations. Spraying is done every 10-14 days.
Rhododendron root rot
The causative agent is the fungus Phytophtora cinnamomi Rands. This fungus most often damages the roots and base of the stem. Symptoms: on individual shoots or on the whole plant they wither, and then all the leaves dry up without externally noticeable reasons. The apical buds turn brown and die. Cross sections of the shoots show that the cambium layer is brown. The roots turn brown and rot, the plant dies. This disease mainly affects rhododendrons growing on insufficiently acidic, highly moist soils. Most often, young and oppressed plants suffer. Plants are infected through the root system or through damage to the bark and roots.
Control measures: affected shoots or the entire plant is burned. To prevent the disease, it is necessary to maintain the acidity of the soil corresponding to the requirements of the plant species or variety and observe correct mode glaze.
Dry white rot of the root neck of rhododendron
The causative agent is the fungus Armillaria mellea (real honey agaric).
Symptoms: diseased plants have mycelial films and flat rhizomorphs under the bark. This disease usually affects those plants that have damage to the root collar. The plant affected by the fungus dies. Strongly growing rhododendrons do not get sick with dry rot of the root collar.
Control measures: affected plants are dug up and burned. Plants near which the disease is found should be transplanted so that the root neck is not covered by mulch (it must be dry).
Wax disease of rhododendron, or swelling of the leaves of rhododendron
Large, rounded or oblong spots of red or red-brown color appear on them. A dense waxy coating of sporulation develops on the surface of necrosis. Over time, the spots dry out and crack. Affected plants lose their decorative effect and bloom weakly. Usually this disease affects alpine species of rhododendrons - Rhododendron ferrugineum L., Rhododendron hirsutum L. and others. With the defeat of rhododendrons by the fungus Exobasidium rhododendri, a change occurs in the metabolism of amino acids.
Exobasidium vaccinii is the causative agent of a very common cowberry leaf disease, causing the formation of white cushion-like growths on young leaves of evergreen rhododendrons (Rhododendron maximum L., Rhododendron catawbiense Michx.) and deciduous rhododendrons in their natural habitats.
Exobasidium burtii forms characteristic spots on the leaves, which at first are small, round, and later, increasing in size, acquire an indefinite shape. White spores are visible on the underside of the leaf. This disease usually affects Rhododendron ponticum L. and Rhododendron luteum Sweet.
Exobasidium vaccinii-uliginosi Bond., the causative agent of a very common blueberry leaf disease, causes the formation of the so-called "witch's broom" in the Carolina rhododendron. The leaves turn yellow-brown, their underside is covered with powdery coating. A year later, the affected leaves die off.
Measures to combat diseases caused by representatives of the genus Exobasidium: pruning of the affected parts of plants, spring spraying with a solution of Bordeaux liquid, its substitutes or camulus.
Exobasidium japonicum attacks leaves and shoot tips. Affected plants develop abnormally thick, large, pale green leaves covered with a chalk-white coating.
These leaves quickly shrivel, grow moldy and dry out. On annual plants the fungus is less common than on older ones. Susceptibility to this disease largely depends on the type and variety of rhododendrons.
Pestalocium blotch of rhododendron
Pathogen: fungus Pestalotiopsis sydowiana (syn.: Pestalotia macrotricha Kleb., Pestalotia rhododendri). Leaves and stems are affected. Small brown spots appear on the leaves irregular shape with a thin brown border.
The spots are often scattered along the edges of the leaf blade, which turns yellow and dries prematurely. Gray sporulation pads form on the spots. The spots on the stems are large, depressed, elongated. The surface of the spots dries up and brightens, numerous small gray pads of sporulation of the fungus are formed. Affected shoots gradually dry up.
In humid weather, all necrotic parts are covered with a fluffy smoky-gray coating of sporulation.
The same rhododendron leaf after the wet chamber.
Over time, brown rounded sclerotia form in the drying mycelium.
Control measures: pruning the affected parts of plants. In industrial cultivation - preventive spraying of plants and watering the root zone with a 0.2% solution of foundationol.
Anthracnose blotch of rhododendron
Pathogen: fungus Gloeosporium rhododendri. On the upper part of the leaves, marginal necrosis appears in the form of brown spots of irregular shape. The leaves gradually dry up. On the surface of the spots, sporulation is formed in the form of numerous rounded fruiting bodies of dark color. If the infection continues to develop, the stems are also affected, which dry out over time. This disease is widespread in Holland and England on young seedlings of the Pontian rhododendron.
Control measures: pruning of the affected parts of plants, spring spraying with a solution of Bordeaux liquid, its substitutes or camulus.
Phyllostic blotch of rhododendron
Mushroom Phyllosticta concentrica Sacc. (syn.: Phyllosticta maxima Ellis & Everh.). Symptoms are described by different authors with slight differences.
1. Large rounded spots with a reddish border appear on the leaves.
2. The spots are indistinct, irregular, dark brown or ash gray, with dark edges. Localized along the edges or at the ends of the leaves. Black balls - sporangia - fall out of the spots. In the vast majority of affected leaves die, and the process begins at the tips of the leaves. Similar spots are formed by the fungus Phyllosticta saccordoi.
Mushroom Phyllosticta rhododendricola.
Symptoms: the appearance on the leaves of reddish rounded spots with a thin brown border.
In the future, the affected areas brighten, crack and fall out. Black dotted bodies of the hibernating stage are formed on the necrotic tissue.
Control measures: pruning of the affected parts of plants, spring spraying with a solution of Bordeaux mixture, its substitutes or cumulus.
Cercosporosis of rhododendron. Pathogen: Cercospora rhododendri Ferraris.
Symptoms: Irregular, angular, dark brown spots with reddish edges appear on the leaves, especially noticeable on the underside of the leaf. In conditions of high humidity, the upper side of the leaf blade is covered with a gray coating of sporulation. Leaves of the lower tiers are more affected. The causative agent is widespread in the United States, especially on Pontic rhododendron and varieties based on this species. Another mushroom of the same genus, Cercospora handelii Bubak, is also dangerous.
Rhododendron leaf mosaic
Leaf mosaic is a disease of a viral nature, the carriers of which are bugs, aphids and a number of other insects. Rhododendrons are most susceptible to this disease. alpine species. Due to the development of the disease, the leaves of the plant turn yellow and thinner, and greenish swellings form on their surface. To prevent infection of all rhododendrons, the affected shrubs are destroyed. To combat insect vectors, it is recommended to use means such as confidor, actellik, etc.
rust of rhododendrons
Rhododendron rust affects both deciduous and evergreen rhododendrons. On diseased leaves, the so-called sporulation of the pathogen is formed, resembling dark-colored pads in appearance. In the fight, spraying with copper-containing preparations is effective. Rust of rhododendrons is a dvukhozyainny fungus. The second stage of development occurs on spruces. Strong damage to spruces by rust can cause spruce forests to dry out.
Bacterial cancer of the roots of rhododendrons
The causative agent is the bacterium Agrobacterium tumefaciens, a Gram-negative, obligately aerobic, rod-shaped soil bacterium of the genus Agrobacterium. Able to transform plant cells using a special plasmid. Phytopathogen, causes the formation of crown galls in plants, conditional pathogenicity is also known in people suffering from immunodeficiency diseases. Chemoorganoheterotroph, obligate aerobe.
Symptoms: large, rounded outgrowths form on the roots and root neck, which gradually darken and become hard. Plants slow down growth and bloom poorly. Over time, the growths and the root neck rot and the plant dies. The infection persists in plant debris, often spreading with planting material.
Control measures: regularly spray weakly affected plants with a solution of Bordeaux mixture or its substitutes; severely affected plants are burned along with the roots.
Nitrogen starvation is typical for plants growing in sandy soil. Its signs are the shallowing of the leaves, reduced flowering, weak ovary of the kidneys. You can fight the disease with the help of regular fertilizing with mineral fertilizers with a high nitrogen content.
Chlorosis of rhododendrons
Chlorosis manifests itself in the appearance of spots on the edges of the leaves of rhododendrons. yellow color. The causes of this disease are increased acidity of the soil or insufficient content of nutrients in the soil and necessary elements. The problem should be dealt with by spraying shrubs with magnesium sulfate and iron sulfate (7 g of the substance per 1 liter of water).
Wetting rhododendrons
Soaking is typical for plants planted in heavy, clayey soil, as well as with excessive soil moisture. At the same time, there is a change in the color of the leaf plate, premature fall of foliage and destruction of the root ball. To prevent a problem, be careful when choosing a site for planting rhododendrons, and also do not overdo it with watering to avoid soil waterlogging.
sunburn of rhododendrons
Large-flowered rhododendrons, especially Yakushimanum hybrids, are the first to suffer from the scorching sun. They are the most famous and popular among gardeners, because already young, small plants are abundantly covered with large flowers during flowering.
In bright sun, the leaves become rusty brown in places, as if burned. This should definitely be avoided. This phenomenon is especially susceptible to rhododendrons, which are planted in young gardens, where there are still no large shrubs and trees that create shade.
Winter drying of rhododendrons
One of the most common diseases of rhododendrons. It is observed after severe frosty winter months. Signs of damage are manifested in browning and drying of the foliage.
Then, after a while, the entire shrub dies. The causes of the development of the disease are a violation of the waterways and excessive loss of moisture by rhododendrons. For the treatment of plants, intensive abundant watering is recommended, as well as daily spraying of shrubs. For prevention purposes, the so-called winter watering is used.
Pecking of buds and rhododendrons by birds
In early spring, the facts of pecking of the buds of rhododendrons by crows were noted, most often Smirnov's rhododendron suffers.
The information was collected and presented to your attention by the head of the plant protection department of the Agro-Industrial Complex "Vitus" Sinelnikov Konstantin Yuryevich
Specialists of the department of plant protection of APK "Vitus" carry out entomological and phytopathological examination of green spaces, develop individual action plans for plant protection, treat green spaces with protective agents and carry out comprehensive plant care.
Department of plant protection APK "Vitus": [email protected]
It would seem that suitable conditions for the development of plants and proper care guarantee success. However, the enemy does not sleep and sometimes he manages to surprise us unexpectedly. Plants that are less resistant and prone to disease are susceptible to the spread of pests. One of these is the rhododendron. The different specific conditions required for the growth of a shrub are a big challenge for the gardener, especially when it comes to pest control. Let's figure out how to defeat rhododendron diseases.
Causes
If the soil for rhododendrons is devoid of any nutrients, the leaves of the plant become discolored. Potassium deficiency signals brown spots on the edges of the leaves And yellowing of tissues. Brown or reddish spots indicate a small amount of boron in the soil. Iron deficiency appears yellowing of the tissues between the veins. When the soil of rhododendrons is overloaded with nutrients, it appears on the leaves chlorosis caused primarily by excess lime in the soil. The leaf blades become yellowish, white or light green, the veins remain dark green. Chlorosis is treated by spraying rhododendron with iron chelate. Use a multi-component fertilizer to strengthen plants. Supporters of homemade methods are advised to add chopped tree bark to the base, natural fertilizers or untreated peat.
Yellowing leaves
Yellowing of the leaves can be a sign of incorrect soil pH in the garden, when planting rhododendrons, you need to take care of the correct pH. Research can be done independently using Helling pH meter can be bought at a garden store. If the soil is not acidic enough, a rhododendron fertilizer can be applied to acidify the substrate. You can mix the substrate with acidic peat. If the soil reaction is alkaline or neutral, it is imperative to apply acidic fertilizer for rhododendrons.
The rhododendron withers and dies also because of physiological drought, occurs when the plant is not able to replenish stocks from frozen soil. Rhododendron loses water through evaporation on sunny days. Physiological drought is especially dangerous for plants with big leaves. To prevent or minimize symptoms, it is worth planting a rhododendron in a calm place where the sun only gently warms up during the midday hours. Better in a place among conifers next to the wall of the building. winter rhododendron shade with agrofibre to reduce the impact of direct sun rays. A thick layer of mulch around the plant limits evaporation.
Fungal and bacterial diseases
Rhododendron is especially prone to fungal diseases. The development of the fungus is facilitated by a violation of the rules of care, the presence of various pests on the plant. A sign of the disease is the darkening of the leaves and buds. Fruiting bodies of the fungus appear in the form of black spots on the affected plants. Treatment of the disease begins immediately when the first symptoms appear. Cut diseased parts off and apply a suitable fungicide.
Regular presence light or dark brown spots on the leaves may indicate fungal disease – leaf spot, the affected rhododendron withers. Leaf spot is caused by fungi and bacteria. Infected leaves dry up and fall off. The fight against spotting is the use of fungicides. Infected leaves should be burned.
A common fungal disease that attacks rhododendron is gray rot, caused by fungi that spread in a humid environment. Mealy appears on leaves, shoots and flowers, gray-white bloom, as a result, the rhododendron turns brown and dies. Gray rot is destroyed chemicals, spray rhododendron with nettle infusion or horsetail decoction. Infected parts should be quickly removed and burned.
Rhododendron under attack rust And flour beetle. Rust is caused by fungal spores that are rusty in color. The leaves become covered with brown or reddish-red spots and the rhododendron slowly dies. Infected parts are removed, the plant is sprayed with chemicals. Flour beetle contributes to the development of fungal diseases in the garden. Causes a fungus that covers plants with mealy, initially white, then gray-brown bloom. The affected rhododendron withers and dies. The plant must be sprayed with a fungicidal drug, you can use a garlic-based drug.
late blight
Dangerous consequences are brought by diseases of rhododendrons, which have their origin in the soil. Diseases of rhododendrons caused in the soil by fungi are sometimes called withering. These include phytophthora root rot, leaves on infected roots light brown, rapidly darkening spots. The diseased plant withers, completely or partially, the leaves curl, become light green or grayish in color, the infected rhododendron stops growing. Action must be taken immediately, step by step. Sick specimens are removed and burned, not forgetting to disinfect the tools after each action, the plant is sprayed with a fungicide.
Pests
A common pest of rhododendron - furrowed weevil, the presence is easy to notice, characteristic passages in the shape of the letter U appear on the leaves. Symptoms of an insect attack are yellowing of the plant and the appearance on the leaves visible holes. It is difficult to find the weevil, the insect hunts at night, during the day it hides in the soil under the trees. Weevil attacks plants in May-June. The females lay their eggs in the soil, and the eggs hatch into larvae that damage the roots. The larvae overwinter in the upper layers of the soil, between the roots of plants. In the spring, they gnaw the root neck, eating small roots. In May, the larvae pupate and turn into adults.
At the initial stage of the attack on the plant, weevils can be caught using a plate with a twig, which are left overnight. Chemical control should be carried out in the evening by spraying the plants with an insecticide. The procedure is repeated every seven to eight days. You need to defeat the pests before they have time to lay their eggs, destroying the larvae is much more difficult. Females can lay thousands of eggs, which will hatch into white larvae with brown heads. You can spray the plants with a solution of tansy. Weevils are also food for moles, millipedes, birds, centipedes and spiders.
Diseases caused by pests
The stubborn destroyer of the rhododendron is rhododendron leafhopper.
Symptoms of the presence of leafhoppers are individual punctures on the leaves, as well as a white molt on the plant. Insect females lay their eggs in September in the buds of the plant; from May to June, yellowish, inactive larvae develop under the underside of the leaves. In July and August, adults feed on the leaves, about a centimeter in length and quite mobile. If the pest is frightened away, it will quickly jump to other leaves. The leafhopper is green, with clear orange elongated pigment spots on the sides. Insects, sucking the juices from the plant, make small damage to the leaves, due to their mobility. spread fungal diseases, leads to the death of flower buds. A plant with symptoms of a disease caused by the presence of rhododendron leafhopper is treated by spraying with an insecticide. Spraying is repeated after ten to fourteen days.
Rhododendron - a delicacy for rhododendron bug, a small winged insect, up to four millimeters in length. The adult specimen has a flat body and transparent wings, the larvae are yellow and small. Large and small individuals feed on leaf juice from the inside. A sign of the presence of a pest is yellowish spots on top of the leaves, in the lower part - dark excrement. Affected leaves fall off over time. Fallen leaves must be collected and burned. Bushes are sprayed with insecticide in May-June, when the time of hatching of the larvae is approaching.
It is necessary to conduct an active fight against pests and diseases of rhododendrons at the first symptoms, we use chemical methods of control. Chemical plant protection products are called: in the fight against fungal and bacterial diseases(fungicides), weed control (herbicides) and insect control (insecticides). Spraying the plant chemical agent the indicated doses must be observed, the dosage should not be exceeded. Spraying is carried out in calm weather, best in the evening, so as not to kill beneficial insects. Spraying is not done in the burning sun and during or before rain. Before performing the procedure, it is necessary to check how long the period that must elapse between the application of the chemical protection product and the moment of harvest after the complete decontamination of the product is. For the prevention of diseases of shrubs, plant nutrition helps.
Foreword
Rhododendrons are extremely attractive and showy plants widely used in the field of landscape design, but, like all the inhabitants of the garden, they have characteristic diseases and pests that are very fond of feasting on this flower. Learn how to treat them.
Causes of typical diseases
Gardeners with experience claim that most of the diseases that affect rhododendrons result from improper agricultural practices and errors in plant care. The most common adverse factors include:
- low level of ground acidity;
- excessive soil moisture;
- direct exposure to sunlight, causing burns;
- incorrect and unbalanced feeding;
- drying of the soil, characteristic of the winter period;
- lack of nutrients;
- freezing and sudden temperature changes;
- clay and sandy soils, leading to wetting and wilting of the plant.
In order to avoid adverse consequences, it is recommended to carefully follow the landing rules and. This is exactly what we have to talk about.
The main pests for rhododendrons
This plant is attacked by numerous garden pests. However, the death of rhododendrons can be avoided if measures are taken in a timely manner. What to do in each case?
Rhododendron bug is considered the most dangerous and common pest that affects these shrubs. A sign of its presence can be small powdery white marks on the leaves. You can destroy the bug by spraying with diazinon.
The spider mite attacks rhododendron shrubs in a dry, hot season, feeding on the juices of its foliage. Due to its extremely small size, it is impossible to see it with the naked eye. The appearance of the plant will help determine the presence of a spider mite: the underside of the leaves, as it were, is entangled with a thin cobweb, and they themselves become brown in color, fade and fall off. In the fight against it, gardeners will be helped by periodic spraying with diazinon or agravertin.
The arable slug infects the crown and leaves of young rhododendrons, biting into them and making large holes. Its activity can lead to the death of shrubs in the shortest possible time. To prevent this, individuals of the plowed slug will have to be collected by hand, and watering with a TMTD solution (0.8% concentration) will also contribute to its destruction.
Tobacco (black) thrips attacks both greenhouse plants and shrubs planted in open ground. An insect of small size and characteristic black color damages the leaves and buds of rhododendrons. As a result, the foliage fades prematurely, turns yellow and falls off, and the flowers fade without opening. In addition, this pest greatly inhibits the growth of young shoots and deforms the buds. They fight tobacco thrips by spraying plants with a 0.3% nicotine solution, 0.2% karbofos emulsion, as well as organophosphorus compounds (aktar, foifon, pyrethroid, etc.).
Garden Asian beetles are the most dangerous pests for rhododendrons. They infect the stems and root system of plants, eat their leaves. Diazinon is considered the most effective insecticide.
Furrowed weevil - little bug black, causes great harm to the plant and, in the absence of time measures taken may cause his death. Its individuals feed on leaves, flowers, buds, and sometimes even the bark of this shrub. The larvae infect the root system. In the summer months, when it is especially active, it is recommended to spray shrubs and soak the soil where they grow with furadan or bazudin.
Narrow-winged miner moth. Its caterpillars gnaw many holes in the leaves, eat the leaf parenchyma, and then fold the edges of the leaf into a tube for pupation. As a result of their activity, the foliage begins to dry out, crumble and fall off. To scare away the narrow-winged moth, knowledgeable people recommend fumigating or spraying bushes with sulfur.
Gastropods are slugs and snails of the genus Helix, they actively infect shoots, foliage and buds of rhododendrons. You can fight them by manually collecting, as well as using special means- molluscicides.
The rhododendron fly infects the leaves of shrubs, leaving small light spots on them and depleting the plants. To destroy this specific pest, spraying with nicotine sulfate is used.
Typical diseases of these shrubs
Tracheomycosis (vascular wilt) refers to diseases of a fungal nature. The causative agents are fungi of the genus Fusarium. The lesion can be recognized by the intense drying of the leaves and stems of rhododendrons, as well as by the appearance of a characteristic gray coating (mycelium) on them. Tracheomycosis leads to rotting of the rhizome, as well as significant damage to the vascular system of plants. When painful signs appear, it is necessary to cut and burn the branches affected by the disease, and then spray the shrub with Bordeaux liquid.
Late blight is caused by pathogenic fungi of the genus Phytophthora. As a result of this disease, the stems and root neck of the shrub are covered with brown or purple spots. Then the rhizome of the rhododendron turns brown and begins to rot, which leads to gradual wilting. In this case, the number and intensity of watering should be reduced, and the shrubs should be treated with fungicides.
Septoria spotting. The causative agents of this disease are fungi of the Septoria family. This disease affects mainly the leaves of rhododendrons, leading to their premature yellowing and falling off. Plant stems also dry out. You can recognize the disease in the initial stages of its development by the characteristic round red spots with a white center on the leaves of rhododendron. Treatment begins with the fact that diseased leaves are cut off and burned. After that, the plants are sprayed with Bordeaux liquid or blue vitriol. The procedure should be repeated after a week.
Leaf mosaic is a disease of a viral nature, the carriers of which are bugs, aphids and a number of other insects. Alpine rhododendrons are most susceptible to this disease. Due to the development of the disease, the leaves of the plant turn yellow and thinner, and greenish swellings form on their surface. To prevent infection of all rhododendrons, the affected shrubs are destroyed. To combat insect vectors, it is recommended to use means such as confidor, actellik, etc.
Rust of rhododendrons affects small-leaved plant varieties, provoking the appearance of brown and yellow spots. On diseased leaves, the so-called sporulation of the pathogen is formed, resembling dark-colored pads in appearance. In the fight, spraying with copper-containing preparations is effective.
The death of shoots leads to drilling, wilting and falling off of unopened buds of rhododendrons. The disease is fungal in nature. The causative agents are fungi of the genus Phytophtora cactorum. In the absence of timely and competent treatment, the lesion spreads first to the stems, and then to the leaves of the plant, leading to its death. When signs of the disease appear, the affected branches and shoots must be burned, and then the shrubs should be sprayed with quadris or a 0.2% baseazole solution.
Nitrogen starvation is typical for plants growing in sandy soil. Its signs are the shallowing of the leaves, reduced flowering, weak ovary of the kidneys. You can fight the disease with the help of regular fertilizing with mineral fertilizers with a high nitrogen content.
Mixed chlorine is manifested in the appearance of yellow spots on the edges of the leaves of rhododendrons. The causes of this disease are increased acidity of the soil or insufficient content of nutrients and essential elements in the soil. The problem should be dealt with by spraying shrubs with magnesium sulfate and iron sulfate (7 g of the substance per 1 liter of water).
Root rot affects the base of the stem and rhizome of rhododendrons, leading to their decay and death of the plant. TO outward signs diseases can be attributed to a sharp yellowing and drying of the leaves of the shrub, as well as the death of the apical buds. Sick branches and shoots must be burned, and with extensive damage, the entire plant should be destroyed to avoid the spread of the disease.
Root rot is difficult to treat, although some gardeners claim that it is possible to slow down the pathological process with the help of phytosporin-M.
Soaking is typical for plants planted in heavy, clayey soil, as well as with excessive soil moisture. At the same time, there is a change in the color of the leaf plate, premature fall of foliage and destruction of the root ball. To prevent a problem, be careful when choosing a site for planting rhododendrons, and also do not overdo it with watering to avoid soil waterlogging.
The causative agent of cercosporosis is a fungus of the Cercospora family. The disease affects the leaves of rhododendrons, forming numerous spots of red-brown color on their surface. outer side leaf plate is covered with a gray bloom. The treatment of this disease is carried out by spraying with alternate use of solutions of fundazole and ditan.
Winter drying is one of the most common diseases of rhododendrons. It is observed after severe frosty winter months. Signs of damage are manifested in the drilling and drying of the foliage. Then, after a while, the entire shrub dies. The causes of the development of the disease are a violation of the waterways and excessive loss of moisture by rhododendrons. For the treatment of plants, intensive abundant watering is recommended, as well as daily spraying of shrubs. For prevention purposes, the so-called winter watering is used.
Rhododendrons are extremely attractive and showy plants that are widely used in the field of landscape design, but, like all garden inhabitants, they have characteristic diseases and pests that are very fond of feasting on this flower. Diseases characteristic of them and non-infectious lesions can interfere with the full development of rhododendrons.
Non-infectious lesions
Winter drying
It is observed after severe winters, with prolonged frosts, the leaves of evergreen rhododendrons, even at positive air temperatures, remain twisted into “tubes” and adjoined to the shoots. This indicates that the leaves during wintering and severe, prolonged frosts lost so much moisture that a large water deficit formed in the plants and the plants themselves are not able to restore normal water circulation. If you do not take any measures, then the leaves dry up, turn brown and eventually the plant dies. What to do in this case, how to save the plant? To eliminate water deficiency in plants in the spring, after thawing the soil, they are watered abundantly and sprayed with water several times a day. This must be done until the turgor is completely restored by the cells and after about 1-2 weeks they acquire a healthy appearance. This means that normal water exchange has resumed in the plants, and they continue to grow normally. To prevent winter drying of rhododendrons, it is advisable to water them abundantly in the fall.
soaking out
Occurs as a result of excessive soil moisture. The leaf blade of rhododendrons becomes grayish-green, matte, leaves without visible external causes fall off. New shoots are soft, the leaves wither, the root ball collapses, although the roots at the root neck are not damaged. Wetting often occurs in heavy, clayey soils due to poor drainage leading to water pooling in top layer soil and insufficient aeration of the root system. Sometimes it happens with abundant and frequent watering after transplantation. Due to insufficient aeration, normal growth and development of the root system and shoots are disrupted in rhododendrons, plants weaken and are affected by fungal diseases. Excessive soil moisture and late top dressing often lead to freezing of rhododendrons in winter, because. under these conditions, they do not stop growing in a timely manner, do not have time to undergo the necessary hardening and prepare for winter.
To create a normal water and air exchange for the root system, it is necessary to ensure good drainage, wetting plants should be transplanted into loose water and breathable soil, watering should be stopped for a while; on hot, sunny days, instead of watering, spray the aerial parts with water. Wetted plants are rather slow to restore their normal appearance.
sunburn
Appear in the spring after severe frosts or at the end of winter with sharp fluctuations in temperature day and night. Brown, dry spots of irregular shape appear on the leaves of rhododendrons. Sunburn can also appear as a brown streak along the main leaf vein. The leaves of evergreen rhododendrons at -3 ° C and below roll up into a tube and slightly fall down the side of the twisted leaf facing the sun, it heats up during the day and freezes at night. In spring, a reddish-brown or brown stripe is visible on the surface of the untwisted leaves along the entire leaf. If the damage is not strong, then with the beginning of the growing season, the signs of freezing disappear, and the color of the leaves becomes normal.
Control measures.
To prevent sunburn, rhododendrons are planted in semi-shaded places or create a light penumbra for them (shelter of plants with spruce spruce branches or non-woven material on the frame). With good agricultural technology, rhododendrons will give a strong increase, and already in the middle of the current summer, the plant can partially restore its decorative effect.
Chlorosis
It often happens when soil pH is above 7. In an alkaline environment, iron and magnesium are in an indigestible form (even if they are in sufficient quantity), which disrupts the synthesis of chlorophyll. The leaf blade between the vascular bundles (veins) becomes light green or yellowish green. At first, the veins retain a dark green color, and then turn yellow. With severe chlorosis, young shoots turn yellow or pale yellow. Plants grow poorly, often get sunburned, get sick and eventually die.
The cause of chlorosis can also be an excess of copper and calcium in the soil. With an excess of calcium, the normal assimilation of other elements by the plant is disrupted. With its lack, leaf blades can sometimes turn yellow. The bronze-violet color of the leaves of rhododendron occurs with a lack of phosphorus, and the reddish-violet color of the leaf surface and twisting of the edges - with a lack of potassium.
To eliminate chlorosis that has arisen in violation of the acidity of the soil, it is necessary to bring the pH of the medium to 4-5 in order to restore the mineral nutrition of plants. With iron deficiency, foliar and root top dressing iron in chelate form (ferovit, iron recomchelate, etc.). With a lack of magnesium, foliar top dressing magnesium sulfate solution. After processing the plants, after 5-6 weeks, the leaves restore their green color. With a lack of other microelements, they are fed with the corresponding microelements in a chelated form. With their excess, it is advisable to replace the planting soil.
nitrogen deficiency
The entire leaf blade of rhododendrons becomes light, new shoots grow weakly, they develop small leaves, flower buds are not laid. In the middle of summer, the leaves of previous years begin to turn very yellow, then turn reddish-brown, and most of them fall off. By the end of summer, only the leaves of the current year remain on the plants. Nitrogen starvation in rhododendrons often occurs when grown on light sandy soils. With abundant regular watering, mineral salts, especially nitrogen compounds, are washed out and a deficiency of nutrients is created.
When the first signs of nitrogen starvation appear, fertilizing with nitrogen fertilizers (ammonium sulphate or potassium nitrate) is carried out.
Necrosis
The main vein of the leaf dies, the upper side of the leaf turns brown. Necrosis can be caused by a sharp drop in air and soil temperature (especially pronounced in insufficiently winter-hardy rhododendron species), strong winds, drought, and high salt content in the soil. So, excessive application of nitrophos creates an excess of phosphorus in the soil, negatively affecting plants (iron is not absorbed).
With a high salt content in the soil, a complete replacement of the soil or transplantation of rhododendrons to another place is required.
Infectious lesions of fungal diseases
leaf spot
Both young seedlings and adult plants are affected. The size, shape, color and location of the spot are diagnostic features.
cercosporosis(pathogen - Cercospora rhododendri) - spots are angular, dark brown with reddish edges, especially noticeable on the underside of the leaf. At high humidity, the upper side of the leaf blade is covered with a gray bloom.
Anthracnose(causative agent - Glomerella cingulata [=Colletotrichum gloeosporioides]) - brown spots on leaves and shoots with orange pads of sporulation of the fungus. Severely affected shoots and leaves dry up.
gray spotting(pathogen - Pestalotia guepini) - the spots are large, dry, light brown or gray, often concentric, limited to dark, later black sporangia. Young shoots are also affected, which leads to their death.
gray spotting(causative agents - Phyllosticta rhododendricola, Ph. con-centrica, Ph. saccardoi) - spots are gray, small, with a narrow brown border. Pycnidia of the fungus are formed on the spots in the form of scattered, small, black dots.
yellow-brown spotting(pathogen - Ramularia tumescens) - spots on both sides of the leaf: on the top - yellowish-brown, on the bottom - lighter, often almost white.
Septoria(causative agent - Phloeospora azaleae [=Septoria azaleae]) - spots are yellowish, red-yellowish, small with black dots of pycnidia in the center.
Control measures.
Collection and burning of diseased and fallen leaves. During the growing season in case of recurring severe leaf damage - spraying 3 times from the moment the first spots appear (end of June) Bordeaux mixture 1% and other copper-containing preparations, fundazol 0.2%. To prevent burns of young foliage, plants with fully matured foliage can be sprayed with copper-containing preparations.
Gray rot(pathogen - Botrytis cinerea). Flowers, stems, leaves are affected, which turn brown and in conditions of high humidity are covered with a gray fluffy coating.
Control measures.
Timely removal of faded flower stalks. Pruning severely affected leaves and buds. When the first signs of the disease appear and favorable conditions for the development of gray rot, fungicide treatments are carried out: sumilex 0.1%, foundationol 0.2%.
powdery mildew(causative agents - Erysiphe rhododen-dri, Phyllactinia guttata). Separate rounded spots appear on the leaves, covered with a white coating, then, merging, they form a powdery coating that spreads to the entire surface of the leaves.
Control measures.
Top dressing with phosphorus-potassium fertilizers, which increase the resistance of plants to powdery mildew, and limit nitrogen fertilizers. Spraying with fungicides: topaz 0.4%, bayleton 0.05%, foundationazole 0.2%, topsin M 0.1%. The first treatment is carried out when a spiderweb mycelium or its small spots appear on the leaves, the next 2-3 treatments - after 2-3 weeks, alternating preparations, until the end of August.
Rust(pathogen - Chrysomyxa rhododendri). In autumn, on the underside of the leaves, on pink or purple spots, yellow powdery pustules of urediniosporing of the fungus appear. If the plants are heavily infected, they shed their leaves prematurely. In spring, dark red velvety pads of teliosporing of the fungus are visible on the leaves.
Control measures.
Collection and burning of affected leaves. Spraying during the growing season with topaz 0.4%, Bordeaux mixture 1%, bayleton 0.01%. The frequency of treatments depends on the nature of the focus and weather conditions season. In a weak focus and in unfavorable weather for the development of rust - in wet and cold summers - 1 treatment in early to mid-July is enough, at the time the first yellowish mosaic spots appear on the lower leaves of the most susceptible plants. In other cases, 2-3 treatments per season are recommended.
wax disease, its other names are exobazidia, leaf swelling, thick leaves. called various types fungus Exobasidium. On diseased leaves and shoots, fleshy, pale, waxy gall-like formations appear in the form of a ball ranging in size from a pea to walnut. On leaves affected by E. vaccinii, large spots are formed, covered with a reddish, waxy coating, representing a layer of basidia with basidiospores.
Control measures.
Cutting and burning the affected shoots along with the leaves. Spraying for prevention with copper-containing preparations in the spring - before flowering and after flowering.
Rot of seedlings and young seedlings(causative agents - Rhyzoctonia sp., Pythium sp. and Botrytis sp.). Sudden mass wilting of seedlings and cuttings of rhododendrons, their decay and death.
Control measures.
Creating conditions favorable for plant growth, providing drainage, moderate watering, slightly acidic reaction of the soil solution. Destruction of affected plants along with a clod of soil, disinfection of these areas with lime or ash. Spilling under the root and spraying with foundationazole 0.2%.
root rot(pathogen - Phytophthora cinnamomi). At the base of the stem lower leaves turn yellow, fade, dry up; apical buds turn brown and die, plant growth slows down. On transverse sections of shoots, a brown layer of cambium is visible. The roots turn brown and rot, as a result of which the whole plant dies. Root rot is also caused by fungi of the genera Fusarium, Cylindrocarpon.
Control measures.
The same as with the rot of seedlings and young seedlings.
Necrosis(causative agents - Phoma azaleae, Myxofusicoccum azaleae). Ring or local necrosis is formed on the branches. In the thickness of the cortex of the affected areas, pycnidia are formed.
Control measures.
Creation good conditions for plant growth. Pruning and burning of drying branches, treatment of pruning sites with a solution of copper sulphate 3-5%. After pruning, crown treatment with Bordeaux mixture 1%. For sleeping kidneys, spraying with a solution of copper sulfate 3-5%.
Viral diseases
leaf mosaic(causative agent - Rhododendron mosaic virus). Mosaic spots and swellings form on the leaves.
Control measures.
Destruction of diseased plants, control of vectors: aphids, bedbugs and other insects.
Control measures.
Rejection and destruction of diseased plants. Soil disinfection.
Information from the website "Magic of Nature":
With a disease like rhododendron spotting, the leaves of the plant are covered with spots. The size, color and shape of these spots can be different, and it depends on the fungus-causative agent: gray, brown, yellow, black, angular, blurry, round, with a black border. A gray coating may appear on the upper side of the sheet. Such a disease as rust on rhododendron appears on the lower part of the leaves in the form of dusty yellow, brown or red pimples.
Diseases of rhododendrons - a real concern for the gardener
Fungal diseases of rhododendrons
Fungi also cause the death of shoots, while the buds of rhododendrons are affected, which first turn brown and then die. Then, the same thing happens with the leaves, and then with the shoots of plants. It is necessary to treat such diseases with drugs based on copper; treatment cannot be carried out in humid air, as the leaves can get burned.
Rhododendron diseases caused by external factors
Rhododendron leaves dry and fall off
The winter drying of rhododendrons looks like the death of shoots, the leaves of evergreen species first curl, then dry up and die, in fact, this is the result of a violation of the plant's water metabolism. It is possible to prevent such a disease if evergreen rhododendrons are abundantly watered before wintering, and if signs of the disease appear in the spring, then after the soil has completely thawed, the plants should be watered and sprayed abundantly.
Rhododendron whimsical plant
Rhododendron leaves turn yellow and fall off
Nitrogen starvation is provoked if rhododendrons are grown on sandy soils - the leaves become much lighter and smaller, the growth of young shoots stops, flower buds are not laid. At the end of summer, the leaves on evergreen species begin to turn yellow, and then fall off. In this case, the plant needs a transplant or the systematic provision of fertilizing with mineral fertilizers, which are based on nitrogen.
Rhododendron root rot
Wetting of rhododendrons resembles a disease such as root collar rot in appearance - the shoots become soft, the leaves of a dull, grayish hue begin to fall off. This disease usually develops if it grows in clay soils with poor drainage. In this case, the rhododendron must be transplanted into a moisture- and breathable soil.
