The first sign of leaf disease in azaleas is the appearance dark spots on the back side of the leaf blade, and sometimes on the entire stem of the plant.
Characteristic color of spots:
- brown;
- grey;
- dark grey;
- black.
Why do the tips of the leaves or the entire leaf blade of rhododendron turn black? This is possible for several reasons:
The blackening of azalea leaves does not depend on the time of year. The following factors influence this process:
- Not proper care behind the plant (excessive watering);
- the appearance of fungal infections;
- viral diseases;
- ticks.
IMPORTANT. Improper care for azaleas: the use of poor-quality drainage, excessive substrate moisture, low or very high temperatures - all this provokes the development of fungal infections, which ultimately lead to blackening and falling of the leaf plates of the indoor plant.
When leaves are damaged by black thrips, they must be treated with a special chemical, for example, ready-made karbofos emulsion. Blackening in this case can be either partial, at the tips or along the edges of the leaf blade, or complete, over the entire surface of the leaf.
It is impossible to cure an azalea from Fusarium at a late stage, so you will have to get rid of the missing plant. If the disease is detected on early stage, then it is necessary to use the drug foundationazole. In the fight against rhododendron mites, the most effective is chemical drug diazinon.
After using various drugs, you need to get rid of the affected parts of the plant. It is necessary to remove all remaining damaged leaves without touching the branches, even if they have become completely bare. Then check the condition of the root system and transplant the azalea into new soil. The air temperature in the room during the recovery period should be about 20 – 22̊ C, and lighting without direct sun.
Learn more about how to resuscitate a dying person. indoor azalea, you can find out in .
So that azalea retains its beautiful appearance for a long time and pleases others lush flowering, it is very important to monitor the intensity of its watering and water temperature. The ideal water temperature for irrigation is the same as indoors or a maximum of 1 - 2 degrees higher. Such water is easily absorbed by the root system and saturates it with useful elements.
Water for irrigation should be soft. Before watering, it must be boiled, cooled and the upper part drained. The lower layer of water, where harmful sediment is located, is strictly prohibited for irrigation. From time to time, it is advisable to water the azalea with slightly acidified water and lemon juice. Proportion of liquid for irrigation: 3 drops of lemon juice per 1 liter of warm water.
After suffering from the disease, the air around the plant should be even more humid. To increase immunity, azalea must be sprayed with a special solution prepared from the drug Elina. Water with acidified water at least 3-6 times a week.
To prevent diseases in azaleas, it is important to consider the following factors:
- light intensity;
- air ionization and watering;
- room temperature;
- soil feature;
- soil fertilization;
- special care during the flowering period.
Azalea should be kept in a light or semi-dark room where there is no access to direct sunlight. It feels best on balconies and loggias, where the temperature does not drop below +5̊ C, on northern and western windows.
For watering, it is necessary to use melted or boiled water, avoiding stagnation of liquid in the tray of the pot. Maximum comfortable conditions content – above 12 – 15°C. To plant azaleas, you need to use heather soil or a mixture of peat, pine needles and river sand.
It is necessary to fertilize azaleas in summer and winter. In the warm season, you can use ammonium sulfate, and in the cold season, superphosphate. Pinch and trim the plant after flowering, in spring. At the end of summer, the azalea needs to be thinned out and weak shoots cut off, carefully treating the cut areas with a special product.
It would seem that suitable conditions for plant development 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. These include rhododendron. Different specific conditions The nutrients required for shrub growth 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 rhododendron soil is deprived of any nutrients, the plant's leaves will become discolored. Potassium deficiency signals brown spots along the edges of leaves And yellowing of fabrics. Brown or reddish spots indicate a small amount of boron in the soil. Iron deficiency manifests itself yellowing of the tissue between the veins. When the soil of rhododendrons is overloaded with nutrients, 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. Proponents of homemade methods are advised to add crushed tree bark, natural fertilizers or untreated peat to the base.
Yellowing of leaves
Yellowing of the leaves may be a sign of incorrect soil pH in the garden; at the stage of planting rhododendrons, care must be taken to ensure the correct pH. You can do the research yourself using Helling pH meter, can be bought at a garden store. If the soil is not acidic enough, you can use fertilizer for rhododendrons, which acidifies the substrate. You can mix the substrate with acidic peat. If the soil reaction is alkaline or neutral, it is necessary to apply an acidic fertilizer for rhododendrons.
Rhododendron withers and dies also due to physiological drought, occurs when the plant is not able to replenish reserves from frozen soil. Rhododendron loses water through evaporation on sunny days. Physiological drought is especially dangerous for plants with large leaves. To prevent or minimize symptoms, it is worth planting the rhododendron in a windless place where the sun only gently warms up during the midday hours. It is better in a place among coniferous trees near the wall of a building. Rhododendron in winter shaded 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 susceptible to fungal diseases. The development of the fungus is facilitated by violation of the rules of care and the presence of various pests on the plant. A sign of the disease is darkening of the leaves and buds. The 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. Diseased parts should be trimmed and a suitable fungicide applied.
Regular presence light or dark brown spots on leaves may indicate fungal disease – leaf spot, the affected rhododendron fades. Leaf spotting is caused by fungi and bacteria. Infected leaves dry out and fall off. The fight against spotting involves the use of fungicides. Infected leaves should be burned.
A common fungal disease that attacks rhododendron, gray rot, is caused by fungi that spread in moist environments. A powdery, gray-white coating, as a result, the rhododendron turns brown and dies. gray rot destroy chemicals, spray rhododendron with nettle infusion or horsetail decoction. Infected parts should be quickly removed and burned.
Rhododendron is under attack rust And flour beetle. Rust is caused by fungal spores characterized by a rusty color. The leaves become covered with brown or reddish-red spots and the rhododendron slowly dies. Infected parts are removed and the plant is sprayed with chemicals. Mealworm promotes the development of fungal diseases in the garden. Causes a fungus that covers plants with powdery, initially white, then gray-brown coating. The affected rhododendron withers and dies. The plant needs to be sprayed with a fungicidal preparation; you can use a garlic-based preparation.
Late blight
Diseases of rhododendrons that originate in the soil have dangerous consequences. Diseases of rhododendrons caused by fungi in the soil are sometimes called withering. These include late blight root rot, which leaves light brown spots that darken quickly. The diseased plant withers, completely or partially, the leaves curl, acquire a light green or grayish color, and the infected rhododendron stops growing. Action must be taken immediately, step by step. Diseased specimens are removed and burned, not forgetting to disinfect instruments after each action, and the plant is sprayed with a fungicide.
Pests
Common pest of rhododendron - grooved weevil, the presence is easy to notice, characteristic U-shaped passages appear on the leaves. Symptoms of an insect attack are yellowing of the plant and the appearance of visible holes on the leaves. It is difficult to detect the weevil; the insect hunts at night and hides in the soil under trees during the day. The weevil attacks plants in May-June. Females lay 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 collar, eating small roots. In May, the larvae pupate and develop into adults.
At the initial stage of attack on the plant, you can catch weevils using a plate with a twig, which is left overnight. Control with chemicals should be carried out in the evening, spraying the plants with an insecticide. The procedure is repeated every seven to eight days. It is necessary to defeat the pests before they have time to lay eggs; destroying the larvae is much more difficult. Females can lay thousands of eggs, which hatch into white larvae with brown heads. You can spray the plants with tansy solution. Weevils are also food for moles, shrews, birds, centipedes and spiders.
Diseases caused by pests
A stubborn destroyer of rhododendron is rhododendron leafhopper.
Symptoms of the presence of a leafhopper are individual punctures on the leaves, as well as white molting on the plant. Female insects lay 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, adult individuals, about a centimeter in length and quite mobile, feed on the leaves. If the pest is scared away, it will quickly jump to other leaves. The planthopper is green in color, with clear orange elongated pigment spots on the sides. Insects, sucking juices from the plant, cause minor damage to the leaves due to their mobility spread fungal diseases , leads to the death of flower buds. A plant with symptoms of disease caused by the presence of rhododendron leafhopper is treated by spraying with an insecticide. Spraying is repeated after ten to fourteen days.
Rhododendron is a delicacy for rhododendron bug, a small winged insect, measuring 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 the juice of leaves from inside. A sign of the presence of a pest is yellowish spots on top of the leaves, and dark excrement in the lower part. Affected leaves drop over time. Fallen leaves need to be collected and burned. The bushes are sprayed with insecticide in May-June, when the time for the larvae to hatch is approaching.
It is necessary to actively combat pests and diseases of rhododendrons at the first symptoms, we use chemical methods struggle. Chemical plant protection products are called: in the fight against fungal and bacterial diseases (fungicides), in the fight against weeds (herbicides) and against insects (insecticides). Spraying a plant chemical agent The indicated dosages must be observed and the dosage should not be exceeded. Spraying is carried out in calm weather, preferably in the evening, so as not to kill beneficial insects. Spraying should not be done in hot sun or during or before rain. Before performing the procedure, you need to check how long the period that should elapse between the use of the chemical protection product and the time of harvest after complete decontamination of the product. To prevent diseases of shrubs, fertilizing plants helps.
If your rhododendrons don't bloom, then something is clearly wrong with them. In general, rhododendrons are powerful, abundant flowering shrubs. But in order for them to grow and bloom well, you must first choose the right place for them. It is advisable that the roots of rhododendrons be in the shade and the above-ground shoots in the sun. The soil should be rich in humus and (pH 4.2-5.5).
If, upon careful examination, you see spots on the leaves of the rhododendron, then sometimes this is either septoria, sometimes it is consequences improper care. During development chlorosis Rhododendron leaves at the top first turn yellow, then their tips turn black. In most cases, the cause is unfavorable soil conditions. It is necessary to increase the acidity of the soil and feed the rhododendron with iron chelate, ferrovite.
Very often, beginning gardeners growing rhododendrons are faced with the problem of browning of the buds. , the length of which does not exceed 9 mm, does not harm rhododendrons directly, but by laying eggs from the end of August and transmitting the pathogen fungal disease. The fungus penetrates the buds and buds, destroying them from the inside, causing them to turn brown. Then the buds turn black, become ugly and remain in this mummified form on the bushes, not falling off all year. It is necessary to take measures to combat the rhododendron cicada, as well as spraying with copper-containing preparations to prevent the spread of the disease.
What can be done against browning of rhododendron buds?
Choose the right place to plant rhododendron, feed it with special fertilizer for rhododendrons, and acidify the soil.
Affected rhododendron buds should be deeply cut out and burned or thrown into the trash, but under no circumstances into the compost heap.
When detected, destroy cicada larvae (from May) and adult insects (from the end of August) with Decis or other systemic insecticide. You can catch insects with yellow glue traps by hanging them near rhododendron bushes.
For new plantings of rhododenrons:
Choose a planting site with suitable lighting conditions.
Rhododendrons love acidic soil, the optimal pH level is 4.5 - 5.
Dig the planting hole to the depth of a spade bayonet. Add peat or a special mixture for rhododendrons to the soil. The higher the pH value, the more “acidic” additives are needed. You can treat the soil with a special acidifying preparation, for example, Rodovital.
Don't plant plants too deep. The top edge of the earthen ball should be level with the soil surface.
Mulch the ground under the bushes with pine or spruce bark, or compost without lime.
For old rhododendron plantings:
Check if the location was chosen correctly. If necessary, replant the bushes.
Check the pH level of the soil, and if it is high, then reduce its level using the special drug Rodovital. You can also partially update upper layer soil - take it from under pine or spruce trees along with pine needles and pieces of bark. If you don't have it, you can use vinegar or battery acid. A few drops per bucket of water is enough. If you don’t have anything like that on hand, you can take citric acid. Also in Lately Many new fertilizers have appeared, in addition to Rodovital, designed to acidify the soil.
Loosen the soil.
Mulch the soil under the bushes. It is important that the soil under rhododendrons is always moist.
Remove faded inflorescences or carefully break off, being careful not to damage the buds.
Rhododendrons are affected by many pests and diseases. To avoid plant death, 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 scale (Parthenolecanium corni Bouche)
Rhododendron bug (Stephanitis rhododendri Horv)
The rhododendron bug is considered the most dangerous and widespread pest that affects these shrubs. Signs of its presence can be small black-brown dots on the back of the leaf, places where the bug pierced the leaves and their excrement.
The photo shows a rhododendron bug larva.
Damage to the leaf blade of rhododendron by the larvae of the rhododendron bug.
The bug can be destroyed by spraying with contact-intestinal and systemic preparations - clipper, omaite, actara, demitan, apolo, fitoverm, Bi 58. The preparations must be changed so as not to cause addiction in insects to the active substance of insecticides.
Spider mite (Tetranychus urticae)
Spider mites inhabit rhododendron bushes during hot, dry seasons, feeding on the juices of their leaves. Due to its extremely small size, it is difficult to see with the naked eye. Detect presence spider mite The appearance of the plant will help: the underside of the leaves seems to be entangled in a thin cobweb, and they themselves acquire a brown color, fade and fall off.
It must be added here that middle lane Russia full cycle development (generation) of spider mites from 7 to 9 days. During the 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, Omite, Apolo, Demitan.
Field slug, or crop slug (Deroceras agreste)
The slug slug infects the leaves of young rhododendrons, making large holes in them. Its activity can lead to the death of bushes in the shortest possible time. To prevent this, individuals of the cultivated slug will have to be collected by hand, and its destruction is also facilitated by watering with a TMTD solution (0.8% concentration).
Rhododendron whitefly (Dialeurodes chittendeni)
Rhododendron whitefly, or white rhododendron fly (Dialeurodes chittendeni)
They are found mainly on large-leaved rhododendrons: Caucasian, Pontic and Katevbinsky and their varieties and hybrids. Spraying the leaves from below with nicotine and oil emulsion in spring and autumn.
Tobacco (black) thrips (Thrips tabaci).
Tobacco (black) thrips is a small insect with a characteristic black color. Damages leaves and buds of rhododendrons.
As a result, the foliage fades prematurely, turns yellow and falls off, and the flowers wither without opening. In addition, this pest greatly inhibits the growth of young shoots and deforms the buds. Tobacco thrips is controlled by spraying plants with 0.3% nicotine solution and 0.2% carbophos emulsion. The following drugs are also suitable for this purpose: actarv, omaite, apolo, clipper, fitoverm,
Garden beetle (Phyllopertha horticola)
Asian garden beetles are the most dangerous pests for rhododendrons. They infect the stems and root systems of plants and eat their leaves. The most effective means for exterminating insects is considered to be: Clipper, Bi 58, Apolo, Fitoverm, Aktelik, Karate.
Grooved weevil or corrugated weevil (Otiorrhynchus sulcatus L.)
The corrugated mower Otiorrhynchus sulcatus L. is one of the most dangerous pests. It affects many crops, including rhododendrons. It is very dangerous for plants, because adults eat leaves, buds, buds, flowers and even young shoots of rhododendrons, and the larvae, while in the soil, eat all the roots up to the root collar. In young shoots, the mower gnaws the bark down to the wood; the shoot above the affected area withers and dries up. The pest eats away leaves and petals in an arched manner, starting from the edges. Affected plants lose their decorative properties.
The adult beetle is 8-10 mm long, black, brown-black (juveniles are yellowish-brown), with yellow spots on thick, leathery, ribbed wings and a short nose. Adults are sedentary and 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 you sometimes manage to see them early in the morning, 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. By appearance resemble chafer larvae.
They eat the roots and bark of the base of the stem, as a result of which the plants die. In greenhouse conditions, the mower reproduces all year round, but especially intense from July to December. It is during these months that the danger of damage to rhododendrons by larvae is greatest. Adults emerge around February.
In open ground, the larvae overwinter in the soil and pupae form in the spring. Adults emerge in May and June. Females lay eggs in soils rich in humus 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, like adults, are less sensitive to insecticides. If mower larvae appear in the picking boxes in which young rhododendron seedlings grow, the plants should be immediately transplanted into fresh substrate and the old one should be burned. During transplantation, you need to carefully ensure that pest larvae, which are usually easy to find near the roots of the affected plant, do not get into the new substrate. For preventive purposes, the remaining boxes located nearby 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 the insecticide in each case is determined individually. During the active life of adult rhododendrons, they are pollinated with metaphos dust, sprayed with 0.2% emulsion of metaphos, phosphamide or 0.3% emulsion of karbofos or systemic insecticides and acaricides: Apolo, Omite, Demitan, Fitoverm, Flumite. Because adults feed actively at night, spraying should be done 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 roll 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 repel narrow-winged moths, knowledgeable people It is recommended to fumigate or spray the 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.
Blueberry moth (Arichanna melanaria)
Butterfly, wingspan 36-44 mm.
The blueberry moth caterpillar eats the edges of rhododendron leaves.
Control measures
When the blueberry moth caterpillars appear, rhododendron should be treated
- Contact insecticides: Clipper
- Contact-intestinal insecticides: Decis, Senpai, Intra-Vir, Barey, Actellik, Karate, Karbofos
- Systemic insecticides: Aktara, Konfidor, Kinmiks, Bi-58
Rhododendron sawfly
Sawfly larvae leave intricate patterns on the back of leaves
Sawfly larvae, unlike adult insects, cause minor damage to the decorative appearance of rhododendrons. Therefore, it is recommended, if detected, 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. If painful signs appear, it is necessary to trim and burn the branches affected by the disease, and then spray the bush with Bordeaux mixture.
Late blight rot
Late blight is caused by pathogenic fungi of the genus Phytophthora. As a result of this disease, the stems and root collar of the bush become covered with spots of brown or purple color. Then the rhododendron rhizome turns brown and begins to rot, which leads to gradual withering. In the absence of timely and competent treatment, the damage spreads first to the stems and then to the leaves of the plant, leading to its death. If signs of the disease appear, the affected branches and shoots must be burned, and then the rhododendron bushes must be treated with quadris or 0.2% foundationazolo. You can also use the following drugs: Gamair, Abiga Peak, Topaz, Fundazol.
Septoria lycopersici
Pathogen: Septoria azaleae Voglino fungus. 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, pinpoint 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. Greenhouse plants are usually susceptible to the disease. In countries where rhododendrons are cultivated very widely, this fungus is also found on deciduous rhododendrons open ground. Yellowish, red-yellowish, and later yellowish-gray spots of irregular shape appear on the leaves of plants. By autumn they turn dark brown in the middle, and sometimes even brownish-black. At first, the spots appear in the middle of the leaf blade, gradually increase in size and, reaching large veins, stop. The fungus grows into all leaf tissues, the leaves die and fall off prematurely, so that the plant becomes completely bare. As a result of the falling leaves in plants, all physiological processes are disrupted, and flower buds do not form normally. On the spots you can see small, black, point-shaped spore containers - pycnidia, immersed in the leaf tissue.
Control measures: pruning of affected parts of plants, spring spraying a solution of Bordeaux mixture, its substitutes or cumulus. If the air is excessively humid, you should not spray plants with preparations containing copper, as this leads to burns of leaves and young shoots. Preparations containing copper are used only at normal air humidity and sufficient high temperature. You can spray only those plants whose leaves have fully grown and developed. In the summer, it is necessary to carry out treatments with fungicides: Gamair, Abiga-Pik, Skor, Topaz, Fundazol.
Rot of shoots and young seedlings of rhododendron
(pathogens: Rhyzoctonia sp., Pythium sp. and Botrytis sp).
Often, when propagating by seeds and cuttings, one has to observe sudden massive wilting of rhododendrons, their rotting and death. The causative agents of this disease are fungi of the following genera: Rhyzoctonia, Pythium and Botrytis. Affected seedlings fall to one side and die; white fungal hyphae or brownish mold are visible on the leaves. Pale, cobweb-like threads appear on the surface of the substrate. Typically, fungi develop if the substrate is fresh, not yet decomposed, or if the crops are watered with fungal-infected water. Too much planting density, excessive humidity in greenhouses and insufficient air exchange increase the likelihood of disease occurrence.
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 foundationol powder. For preventive purposes, it is advisable to spray young shoots and seedlings with a 0.2% suspension of foundationazole. Captan and TMTD can be used to combat this disease.
Rhododendron bud rot
Pathogen: fungus Sporocybe azaleae (syn.: Pycnosteanus azaleae)
The disease was first discovered on rhododendrons in the United States. The disease is typical for the largest rhododendron (Rhododendron maximum L.) and Katevbinsky (Rhododendron catawbiense Michx.). Buds affected by this disease turn brown and die. Mycelium from buds can grow into branches and cause them to die. Control measures: during the growing season, plants should be sprayed regularly (every 2-3 weeks) with copper-containing preparations.
The buds are “beaten” by autumn-spring frosts. In contrast to the buds affected by the fungus, Sporocybe azaleae (syn.: Pycnosteanus azaleae) look clean and have no pycnidia. But still, buds “beaten” by frosts serve as potential objects for the spread of Sporocybe azaleae (syn.: Pycnosteanus azaleae), so they should be removed.
The carriers of the fungal disease Sporocybe azaleae (syn.: Pycnosteanus azaleae) are rhododendron bugs and cicadas Graphocephala coccinea, Graphocephala fennahi (rhododendron leafhopper). Cicadas themselves can cause the flower buds and buds of Pontine azalea to dry out.
To prevent infection of rhododendron by the fungus Sporocybe azaleae (syn.: Pycnosteanus azaleae), yellow panels coated with adhesive are installed in azalea bushes in July to catch non-flying green and orange striped cicadas.
In case of serious infestation, systemic and enteric 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 dried shoots and dead dark buds.
Gray rot of rhododendron
Symptoms: blurry brown spots without a border appear on the leaves, stems, buds and petals, the surface of which quickly dries out and cracks.
Dying of rhododendron shoots
Plants planted in full shade are most susceptible to this disease.
The causative agent is the fungus Phytophtora cactorum Leb. Symptoms: the apical buds of the affected plants do not bloom, they turn brown and then die completely. The shoots also dry out first and then die. Adult leaves curl, turn brown and dry out. Severely affected plants die.
The causative agent is the fungus Physalospora rhododendri. This fungus also affects 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: individual shoots or the entire plant wither, and then all the leaves dry out for no externally noticeable reason. The apical buds turn brown and die. Transverse sections of shoots show that the cambium layer is brown. The roots turn brown and rot, the plant dies. This disease mainly affects rhododendrons growing in insufficiently acidic, highly moist soils. Most often, young and depressed plants suffer. Plants become infected through the root system or through damage to the bark and roots.
Control measures: the affected shoots or the entire plant are burned. To prevent the disease, the acidity of the soil should be maintained in accordance with the requirements of the plant species or variety and the correct watering regime should be observed.
Dry white rot of the rhododendron root collar
The causative agent is the fungus Armillaria mellea.
Symptoms: diseased plants have mycelial films and flat rhizomorphs under the bark. This disease usually affects those plants that have damaged root collars. The plant affected by the fungus dies. Strongly growing rhododendrons do not suffer from dry rot of the root collar.
Control measures: affected plants are dug up and burned. Plants near which the disease is detected should be replanted so that the root collar is not covered with mulch (it must be dry).
Rhododendron wax disease, or swelling of rhododendron leaves
Large, round 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 stains dry out and crack. Affected plants lose their decorative properties and bloom poorly. Usually this disease affects alpine species of rhododendrons - Rhododendron ferrugineum L., Rhododendron hirsutum L. and others. When rhododendrons are infected by the fungus Exobasidium rhododendri, a change in amino acid metabolism occurs.
Exobasidium vaccinii, the causative agent of a very common disease of lingonberry leaves, causes the formation of white cushion-shaped 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 are initially small and round, and later, increasing in size, take on an indeterminate 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 disease of blueberry leaves, causes the formation of the so-called “witch’s broom” in Carolina rhododendron. The leaves become yellow-brown, their undersides become covered with a powdery coating. After a year, the affected leaves die.
Measures to combat diseases caused by representatives of the genus Exobasidium: pruning affected parts of plants, spring spraying with a solution Bordeaux mixture, its substitutes or camulus.
Exobasidium japonicum, attacks leaves and shoot tips. Diseased plants develop abnormally thick, large, pale green leaves covered with a chalky white coating.
These leaves quickly wrinkle, become moldy and dry out. On annual plants the fungus is less common than on older ones. Susceptibility to this disease largely depends on the species and variety of rhododendrons.
Pestalocia spot 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 out prematurely. Fungal sporulation pads form on the spots gray. The spots on the stems are large, depressed, and elongated. The surface of the spots dries out and becomes lighter, and numerous small gray pads of fungal sporulation are formed. The affected shoots gradually dry out.
In humid weather, all necrotic parts are covered with a fluffy, smoky-gray coating of sporulation.
The same rhododendron leaf after a humid chamber.
Over time, round-shaped brown sclerotia form in the drying mycelium.
Control measures: pruning of affected parts of plants. For industrial cultivation, preventive spraying of plants and watering of the root zone with a 0.2% solution of foundationazole.
Anthracnose spot 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 out. On the surface of the spots, sporulation forms in the form of numerous rounded fruiting bodies 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 rhododendron ponticus.
Control measures: pruning the affected parts of plants, spring spraying with a solution of Bordeaux mixture, its substitutes or camulus.
Phyllostictosis spot of rhododendron
Mushroom Phyllosticta concentrica Sacc. (syn.: Phyllosticta maxima Ellis & Everh.). Symptoms are described by different authors with slight differences.
1. Large round spots with a reddish border appear on the leaves.
2. Spots are vague, irregular, dark brown or ash-gray, with dark edges. Localized along the edges or ends of leaves. Black balls - sporangia - fall out of the spots. 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 round spots with a thin brown border.
Subsequently, the affected areas lighten, crack and fall out. Black dotted bodies of the overwintering stage are formed on the necrotic tissue.
Control measures: pruning the affected parts of plants, spring spraying with a solution of Bordeaux mixture, its substitutes or cumulus.
Cercospora 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 high humidity the upper side of the leaf blade is covered with a gray coating of sporulation. The leaves of the lower tiers are more affected. The pathogen is widespread in the United States, especially on rhododendron pontica 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 viral disease transmitted by bugs, aphids and a number of other insects. Rhododendrons are most susceptible to this disease. alpine species. As the disease develops, the leaves of the plant turn yellow and thin, and greenish swellings form on their surface. To prevent infection of all rhododendrons, affected bushes are destroyed. To combat insect vectors, it is recommended to use products 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, which resembles dark-colored pads in appearance. Spraying with copper-containing preparations is effective in the fight. Rhododendron rust is a two-host fungus. The second stage of development occurs on spruce trees. Severe damage to spruce trees by rust can cause spruce forests to dry out.
Bacterial canker of rhododendron roots
The causative agent is the bacterium Agrobacterium tumefaciens - a gram-negative, obligate aerobic rod-shaped soil bacterium of the genus Agrobacterium. Capable of transforming plant cells using a special plasmid. A phytopathogen that causes the formation of crown galls in plants, it is also known to be conditionally pathogenic in people suffering from immunodeficiency diseases. Chemoorganoheterotroph, obligate aerobe.
Symptoms: large, round growths form on the roots and root collar, which gradually darken and become hard. Plants slow down and bloom poorly. Over time, the growths and root collar rot and the plant dies. The infection persists in plant debris and is often spread with planting material.
Control measures: regularly spray lightly 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 considered to be smaller leaves, reduced flowering, and weak bud ovary. You can fight the disease with regular feeding. mineral fertilizers with a high nitrogen content.
Chlorosis of rhododendrons
Chlorosis manifests itself in the appearance of yellow spots on the edges of rhododendron leaves. 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 combated by spraying the bushes with magnesium sulfate and iron sulfate (7 g of substance per 1 liter of water).
Soaking rhododendrons
Soaking is typical for plants planted in heavy, clayey soil, as well as with excessive soil moisture. In this case, a change in the color of the leaf plate, premature leaf fall and destruction of the root ball are observed. To prevent this problem, carefully choose 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, suffer primarily from the scorching sun. They are the most famous and popular among gardeners, because even 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. Rhododendrons that are planted in young gardens, where there are no large shrubs and trees that create shade, are especially susceptible to this phenomenon.
Winter drying of rhododendrons
One of the most common diseases of rhododendrons. Observed after harsh frosty winter months. Signs of damage appear in browning and drying out of the foliage.
Then after a while the entire bush dies. The causes of the development of the disease are disruption of the water supply and excessive loss of moisture by rhododendrons. To treat plants, intensive heavy watering is recommended, as well as daily spraying of shrubs. For preventive purposes, so-called winter watering is used.
Pecking of buds and rhododendrons by birds
In early spring, cases of crows pecking at the buds of rhododendrons were noted; Smirnov's rhododendron most often suffers.
The information was collected and presented to your attention by the head of the plant protection department of the Agro-Industrial Complex “Vitus” Konstantin Yuryevich Sinelnikov
Specialists of the plant protection department of AIC "Vitus" carry out entomological and phytopathological examination of green spaces, develop individual action plans for plant protection, treat green spaces with protective agents and provide comprehensive plant care.
Plant Protection Department of AIC "Vitus": [email protected]
Tips for growing rhododedrons
Rhododendron is wonderful beautiful flowering shrub, amazing with abundance and riot of flowering. As a rule, rhododendrons bloom in May, but there are varieties of rhododendrons with earlier flowering, in March, and the rarest varieties can please you in the summer - in June or July.
Probably almost every gardener is faced with the capriciousness of these aristocrats of the garden when growing them. The fact is that without knowing the characteristics of this wonderful culture, it is simply impossible to grow it. Plants will get sick and refuse to grow for some unknown reason...
But before I tell you how to please rhododendrons, let's figure out what they are.
It turns out that rhododendrons have 2 forms: deciduous and evergreen. The first ones are also called azaleas. The agricultural technology of azaleas and rhododendrons differs slightly. Azaleas are sun-loving plants, they are best planted in a sunny place, and rhododendrons love light shade.
The basic principles of growing rhododendrons are:
1. First of all, the PH (acidity) level of the soil. The soil must be acidic between 4.5 and 5.5 pH.
Rhododendrons will also not like too acidic soil, and they will not grow at all in neutral soil. If you forget about this whim of the rhododendron, of course, you won’t be able to grow it. And if he likes the soil, the plants will grow by 30 cm per year!
Therefore, when planting rhododendrons, only acidic soil is used. The best (native) soil for rhododendron is rotted pine needles. In their homeland, rhododendrons grow in coniferous forests. You can also mix peat and pine needles in equal proportions. Such soil is the key to success. It should also be said that the root system of rhododendron is very compact, so it is not necessary to pour a lot of prepared soil into the hole.
When choosing peat for your pet, pay attention to its PH. Stores often sell neutralized peat, and if you don’t pay attention to its pH, the gardener can then be tormented for a very long time by the mystery of why nothing grows for me? This is exactly what happened to me.
Lack of acid in the soil causes growth to stop, and azalea leaves acquire yellow
, because the plant cannot absorb iron, which takes part in the photosynthesis reaction and the formation of chlorophyll. This disease is called chlorosis.
Acidic peat is raised peat, it has a red color, and it is best to take peat from a safe place, for example, directly from a swamp.
Some gardeners have adapted to cope with the whims of rhododendrons even more easily. Peat can be replaced... with sour apples, or, for example, Japanese quince, if you mulch the soil with them. Regular watering of the soil with a weak solution of vinegar, citric acid and even aspirin also helps.
2. When planting rhododendron seedlings on permanent place, do not bury it too deep into the ground. As they say in the literature, they don’t like it. True, when I planted my first seedlings, I did not take this into account, and it seems that it did not particularly affect the health of my plants.
3. Another nuisance - rhododendrons do not like stagnant water. They even love water very much, but they will not tolerate a wet place. Unfortunately, this is so, and I also had to be convinced of this after the death of one of the seedlings, lovingly planted in a damp place... Some kind of average soil was needed - neither damp nor dry.
4. For better flowering, you need to remove faded inflorescences. This promotes the formation of buds the next year. And you also need to apply fertilizer 2 times a year, before flowering (in April) and after flowering (in early June). You need to buy special fertilizer - for azaleas or coniferous crops.
5. The soil for rhododendron should be loose and breathable. Dense sandy soil is undesirable.
6. Evergreen rhododendrons like to be watered deeply before wintering.
In general, following these principles is enough to grow the most beautiful rhododendrons on your site. And I am sure that in the spring your site will turn into a real paradise, and the neighbors will not be able to take their eyes off such beauty.
The variety of colors of rhododendrons is amazing. They are usually colored in white-violet and raspberry-red tones, and azaleas are also orange-yellow.
