The first sign of leaf disease in azalea is the occurrence of dark spots on the back of the leaf plate, and sometimes the entire stem of the plant.
Typical color spots:
- brown;
- grey;
- dark grey;
- black.
Why do the tips of the leaves or the entire leaf plate turn black in rhododendron? This is possible for several reasons:
The blackening of azalea leaves does not depend on the season. 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 of the azalea: 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 houseplant.
If the leaves are damaged by black thrips, they must be treated with a special chemical preparation, for example, a ready-made karbofos emulsion. Blackening in this case can be either partial, at the tips or along the edges of the sheet plate, or complete, on the entire surface of the sheet.
It is impossible to cure an azalea from Fusarios at a late stage, so you will have to get rid of the missing plant. If the disease is found in early stage, then it is necessary to use the drug fundazol. In the fight against rhododendron mites, the most effective is chemical drug diazinon.
After applying various drugs, it is necessary 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 ground. The air temperature in the room during the recovery period should be about 20 - 22̊ C and lighting without direct sunlight.
Learn more about how to revive a dying indoor azalea, can be found in .
So that the azalea retains its beautiful appearance for a long time and pleases others lush bloom, 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 to 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 drained from the top. The lower layer of water, where there is a harmful sediment, is strictly prohibited for irrigation. From time to time, it is advisable to water the azalea with slightly acidified water with lemon juice. The proportion of liquid for irrigation: 3 drops of lemon juice per 1 liter of warm water.
After the illness, the air around the plant should be even more humid. To increase immunity, the azalea must be sprayed with a special solution prepared from Elina. Watering should be carried out with acidified water at least 3-6 times a week.
For the prevention of diseases in azalea, it is important to consider the following factors:
- light intensity;
- air ionization and watering;
- room temperature;
- soil feature;
- soil fertilizer;
- 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. She feels best on balconies, loggias, where the temperature does not fall below + 5̊ C, on the northern and western windows.
For irrigation, it is necessary to use melted or boiled water, avoiding stagnation of liquid in the pot pan. Maximum comfortable conditions content - above 12 - 15̊С. To plant an azalea, heather soil or a mixture of peat, needles and river sand should be used.
Azaleas need to be fertilized in summer and winter. In the warm season, you can use ammonium sulfate, and in the cold - superphosphate. Pinch and prune the plant - after flowering, in the spring. At the end of summer, the azalea must be thinned out and cut off weak shoots, carefully treating the cut points with a special tool.
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. Different specific conditions required for shrub growth are a great 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. Proponents of homemade methods are advised to add crushed tree bark, natural fertilizers or untreated peat to the base.
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 large 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 near 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 destroy 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 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 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. smash 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 sap from 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 apply 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 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.
If your rhododendrons don't bloom there is clearly something wrong with them. In general, rhododendrons are powerful, plentiful flowering shrubs. But in order for them to grow and bloom well, you must first choose the right place for them. It is desirable 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 closer examination you saw spots on the leaves of rhododendron, then sometimes it is either septoria, sometimes consequences improper care. With the 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, ferrovit.
Very often, novice gardeners growing rhododendrons are faced with the problem of browning buds. , the length of which does not exceed 9 mm, does not harm rhododendrons directly, but by laying eggs from the end of August, transfers the pathogen mushroom 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 in such a mummified form remain on the bushes without falling off all year. It is necessary to carry out measures to combat the rhododendroid 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 for planting rhododendrons, feed them with special fertilizer for rhododendrons, and acidify the soil.
Affected buds of rhododendron should be cut deep and burned or thrown into the trash, but in no case into the compost heap.
Destroy when found larvae of cicadas (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 landing site with suitable lighting conditions.
Rhododendrons love acidic soil, the optimum pH level is 4.5 - 5.
Dig a landing hole to the depth of a shovel bayonet. Add peat or a special mixture for rhododendrons to the ground. The higher the pH value, the more “acidic” additives are needed. You can treat the soil with a special acidifying agent, for example, Rodovital.
Don't plant plants too deep. The upper edge of the earthen coma should be at the level of the soil surface.
Mulch the ground under the bushes with pine or spruce bark, or lime-free compost.
For old plantings of rhododendrons:
Check if the correct location has been chosen. If necessary, transplant the bushes.
Check the pH level of the soil, and if it is high, then reduce its level with the help of a special preparation Rodovital. You can also partially update upper layer soil - take it from under the pines or firs, along with needles and pieces of bark. If not, you can use vinegar or battery acid. A few drops in a bucket of water are enough. If there is nothing on hand, you can take citric acid. Also in Lately many new fertilizers appeared, in addition to rhodovital, designed to acidify the soil.
Loosen the soil.
Mulch the soil under the bushes. It is important that the ground under the rhododendrons is always moist.
Withered inflorescences remove or carefully break off, trying not to damage the kidneys.
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 its extremely small size, it is difficult to see it with the naked eye. Determine presence spider mite the appearance of the plant will help: 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 Russia full cycle development (generation) of a spider mite 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, 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. The most effective spraying of leaves from below with nicotine and oil emulsion spring and autumn.
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. They fight tobacco thrips by spraying plants with a 0.3% nicotine solution, 0.2% karbofos 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 beaver 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. By appearance resemble the larvae of the cockchafer.
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, 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 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. 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 the affected parts of plants, spring spraying a solution of Bordeaux liquid, 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 at normal air humidity 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 of 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 the correct irrigation regime.
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 neck.
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 Bordeaux mixture, 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. Fungal sporulation pads form on the spots gray color. 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 out.
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. 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 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 top dressing. mineral fertilizers with high nitrogen content.
Chlorosis of rhododendrons
Chlorosis 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 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]
Growing Tips for Rhododendrons
Rhododendron is amazing flowering shrub, striking abundance and riot of flowering. As a rule, rhododendrons bloom in May, but there are varieties of rhododendrons with earlier flowering, in the month of March, and the rarest varieties can also please in the summer - in June or July.
Probably, almost every gardener is faced with the capriciousness of these garden aristocrats 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 no clear 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 former are also called azaleas. Agrotechnics of azaleas and rhododendrons differs slightly. Azaleas are sun-loving plants, they are best planted in a sunny place, and rhododendrons love light shading.
The basic principles of growing rhododendrons are as follows:
1. First of all, the level of PH (acidity) of the soil. The soil must be necessarily acidic between 4.5 and 5.5 pH.
Rhododendrons will also not like too acidic soil, and they will not grow at all on neutral soil. If you forget about this whim of the rhododendron, of course, it will not work to grow it. And if he liked the soil, the growth of plants will be 30 cm per year!
Therefore, when planting rhododendrons, only acidic soil is used. The best (native) soil for rhododendron is rotted needles. In their homeland, rhododendrons grow in coniferous forests. You can also mix peat and pine needles in equal proportions. This soil is the key to success. It must also be said that the root system of the rhododendron is very compact, so it is not at all necessary to pour a lot of cooked soil swarm into the pit.
When choosing peat for your pet, pay attention to its PH. Neutralized peat is often sold in stores, and if you don’t pay attention to its pH, the gardener can then suffer a mystery for a very long time, why doesn’t anything grow with me? That's exactly what happened to me.
Lack of acid in the soil causes stunting, and azaleas leaves get yellow
, because the plant cannot absorb iron, which takes part in the photosynthesis reaction and the formation of chlorophyll. This disease is called chlorosis.
Sour peat is riding, it has a reddish color, and it is best to take peat from a reliable place, for example, directly from a swamp.
Some gardeners have adapted even easier to fulfill the vagaries of rhododendrons. Peat can be replaced ... with sour apples, or, for example, Japanese quince, if you mulch the soil with them from above. 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 it is written in the literature - they do not like it. True, when I planted my first seedlings, I didn’t take this into account, and it didn’t seem to have much effect on the health of my plants.
3. Another nuisance - rhododendrons do not like stagnant waters. They even love water very much, but they will not tolerate a wet place. Unfortunately, this is true, and I also had to make sure of this after the death of one of the seedlings, planted with love in a damp place ... Some kind of average soil was needed - neither damp nor dry.
4. For better flowering, faded inflorescences must be removed. This contributes to the formation of buds for another year. And you also need to fertilize 2 times a year, before flowering (in April) and after flowering (in early June). Fertilizer must be bought special - for azaleas or coniferous crops.
5. The soil for rhododendron should be loose, breathable. Dense sandy soil is undesirable.
6. Evergreen rhododendrons love abundant watering before wintering.
In general, following these principles is enough to grow the most beautiful rhododendrons in your area. 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.
Amazing variety of colors of rhododendrons. They are usually white-violet and crimson-red, and azaleas are also orange-yellow.
