Dark spots on rhododendron leaves. Rhododendron: problems and solutions

Rhododendron is a deciduous, semi-evergreen or evergreen plant from the heather family. It has high decorative properties - glossy foliage (in evergreen varieties) of rich green color, lush inflorescences of various colors. There are species that reach 30 meters in natural conditions, there are also creeping dwarf shrubs. Sometimes the crown of the rhododendron turns yellow. The article describes the possible causes of this phenomenon and methods of dealing with it.

The plant is moisture-loving. Insufficient watering will lead to a loss of leaf turgor, they will begin to wither and turn yellow. Check the degree of moistening of an earthen coma by squeezing a handful of earth in your hand under a rhododendron bush. The release of water droplets signals that the plant is flooded. This can lead to root rot. The lump crumbled - watering is required. It turned out to form a lump from the soil - moisturizing is optimal.

Place the bushes near a body of water or in the shade of a taller plant (pine is a good option). This will protect the rhododendron from excessive water evaporation. Moisture will also help support occasional watering with a sprinkler.

Watering is carried out with acidified water, for which oxalic, citric, acetic acid is used.

The root system of plants is sensitive and shallow. When weeding, loosening, overheating the soil, it is easy to damage it, which will lead to yellowing of the crown. Mulching the trunk circles (layer height - about 5 cm) with pine needles, oak leaves, moss, high peat will help to avoid this. It is impossible to loosen the earth under a bush.

Thrips black

The upper side of the sheet is covered with gray holes, the lower side is black. The affected parts of the plant become gray, then yellow, fall off. Spray with nicotine solution (0.3%).

Rhododendrons are also susceptible to damage by other insects: plowed slug, narrow-winged mole miner, spider mite, furrowed weevil.

Rhododendrons are subject to various spotting that cause fungi. The most dangerous of these diseases is septoria.

Septoria in rhododendron

Symptoms: reddish small spots form on the leaf plates in the center, which increase in size and turn white. The leaves turn yellow and dry up. A plant without timely assistance may be left with a bare stem.

Help: remove the affected parts of the bush. Spray with a fungicide (after flowering or in spring).

Prevention: choose healthy plants for propagation.

Chlorosis

Yellow spots appear at the ends and along the edges of the leaves due to a lack of nitrogen in the soil or stagnant water at the roots.
Between the veins on the leaf plate, pale or bright yellow spots form with a too dense root system, a lack of iron or magnesium, and alkalization of the soil.

Control measures: timely application of the necessary fertilizers, normalization of irrigation, thinning of the bush, the use of acidified water.

Foreword

Rhododendrons are extremely attractive and showy plants, widely used in the field of landscape design, but, like all inhabitants of the garden, they have characteristic diseases and pests that are very fond of eating this flower. Learn how to treat them.

Causes of typical diseases

Gardeners with experience say 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;
flaw 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. Determine the presence of a spider mite will help appearance plants: 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 attack stems and root system plants and eat their leaves. Diazinon is considered the most effective insecticide.

The furrowed weevil is a small black bug that causes great harm to the plant and, if not taken in time, can cause its 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 manual collection, as well as the use of special tools - 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 which 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.

Rhododendron rust affects small-leaved plant varieties, causing brown and yellow spots to appear on their foliage. 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 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).

Root rot affects the base of the stem and rhizome of rhododendrons, leading to their decay and death of the plant. The external signs of the disease include 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, clay soil as well as 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. The outer side of the leaf plate is covered with a gray coating. 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.

Plants suffer from severe waterlogging, unbalanced fertilizing, low soil acidity, winter physiological desiccation and sunburn. Can be damaged by fungal diseases ( spots, rust) and chlorosis(an acute lack of iron and manganese, which occurs when the soil is low in acidity and disappears with the correct feeding regimen). By collecting and burning damaged foliage, sanitary pruning, and treating plants with suitable fungicides, many diseases can be resisted.

Rhododendrons are most often damaged by garden snails and slugs (collection and destruction helps), rhododendron bugs, spider mites, mealybugs, weevils, scale insects, rhododendron fly, against which insecticides help well.

Major diseases and symptoms

Vascular (tracheomycosis) wilt caused by fungi of the genus Fusarium ( Fusarium oxysporum). The disease begins with root rot, damages the vascular system. Plants turn brown and dry, starting from the top of the shoots. On dried leaves and stems, a grayish coating forms - mycelium.

Late blight rot caused by fungi of the genus Phytophthora ( Phytophthora). Large purple-brown spots appear on the root neck and on the base of the stems, the roots turn brown and rot, the plant fades.

Gray rot caused by fungi of the genus Botrytis ( Botrytis cinerea). One of the most common diseases of many crops, since the spores of the fungus are carried both with air and with water spray. On all parts of the plant - leaves, buds, stems - vague brown-brown spots appear and quickly grow. Damaged tissues quickly dry out, they form a grayish coating - mycelium.

Septoria spotting caused by fungi of the genus Septoria ( Septoria). Small round reddish spots appear on the leaves, the center of which gradually turns white and black dotted fruiting bodies of the wintering stage of the fungus form on them. Diseased stems shrivel, dry out, the leaves turn yellow prematurely and fall off.

Prevention and control measures

Must be carefully examined planting material when buying, select suitable conditions for plants and follow the basic rules of cultivation.
Severely affected branches and leaves are pruned, in autumn plant residues are collected and burned.
In spring and autumn, as well as after flowering, the bushes are sprayed with Bordeaux liquid or its substitutes (Hom preparation).

Major pests

spider mite (Tetranychus urticae) infects plants in hot and dry summers. Adults are so small that they are very difficult to see (about 0.5 mm). Most often, an attack can be seen when the underside of the leaves is covered with a thin cobweb, and the leaves become lifeless, brownish and fall off.

Acacia false shield (Parthenolecanium corni). The larvae, resembling small shiny brown outgrowths on the bark, stick tightly to the branches and "pull" juices from the plant. As a result, it weakens, gradually dries up.

furrowed weevil (Otiorrhynchus sulcatus). This black small (up to 1 cm) beetle is harmful at all stages of development. The larvae damage the roots, and adults feed on leaves, do not shun buds and bark.

Control measures

Compliance with the rules of agricultural technology.
Plants are sprayed in early spring biological preparation Fitoverm, or chemical: Aktara, Actellik, Arrivo, Iskra, Inta-vir. In case of severe damage, the treatment is repeated after 7-10 days.
During flowering, plants are not sprayed so as not to harm bees and other pollinating insects.
In order to avoid addiction of pests, preparations must be changed.

PROTECTION OF RHODODENDRONS FROM DISEASES AND PESTS

Rhododendrons, like any other plants, are affected by diseases and pests. It should be noted that susceptibility to various diseases and pests largely depends on the type and variety of rhododendrons. Long-term practice shows that evergreen rhododendrons growing in open sunny areas are more susceptible to diseases and pests than those that grow in light partial shade. Weak-growing, emaciated specimens tend to be more susceptible to diseases and pests than vigorous-growing specimens. Therefore, the main thing in protecting rhododendrons from pests and diseases is to create optimal conditions for their growth and development. Compliance with the rules of agricultural technology and a reasonable choice of a landing site are essential.

DISEASES OF RHODODENDRONS

For the Latvian SSR, rhododendrons are a relatively young crop, so the diseases that we had to observe are not specific to this particular plant genus. The causative agents of diseases of rhododendrons can be various microorganisms. In addition, the disease may be the result of unsuitable environmental conditions. An active fight against the disease should begin as soon as its first signs are noticed, otherwise it is impossible to fully count on success in the fight against the disease.

Let us dwell on some diseases of rhododendrons, which, due to the expansion of the cultivation of this crop, are becoming more common.

Mosaic of leaves. The causative agent of this disease is a virus that mainly affects the leaves, which become rough, calloused and ugly. Calluses are usually normal green, with the rest of the leaf becoming greenish-yellow. The light part of the leaf blade is much thinner than in places where there are calluses. Venation on calluses is less noticeable. Leaf mosaic virus is carried by aphids, bed bugs and other insects. In our republic, this disease of rhododendrons has not yet been discovered, however, expanding the culture of rhododendrons, we must be ready to fight it.

leaf spot- the most widespread disease of open and closed ground rhododendrons. The disease affects both young seedlings and adult plants. Its causative agents are various fungi, the type of which can be accurately determined by the shape of the spots.

Cercospora rhododendri Mar. et Verpl. - spots are irregular, angular, dark brown with reddish edges, 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 bloom. Leaves of the lower tiers are more affected. The causative agent of leaf spot is widespread in the United States, especially on Pontian rhododendron and cultivars based on this species. Another mushroom of the same genus, Cercospora handelii Bubak, is also dangerous.

Gloeosporium rhododendri Br. et Cov. - patches are irregular, dry, dark brown or black. This type of disease is widespread in Holland and England on young seedlings of the Pontian rhododendron.

Pestallozzia rhododendri Gube, P. guepini Desm., P. macrotricha Kleb. - the spots are large, dry, light brown or gray. Very often the spots are concentric, limited to dark, later black sporangia. These fungi not only cause spotting, but also affect young shoots, which leads to their death. In our republic, pathogens have also been found on the root neck.

Phyllosticta maxima Ell. et Ev. - spots are blurry, 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 Thum.

Septoria azaleae Vogl. calls one of most dangerous diseases rhododendrons of closed ground (greenhouse azaleas) - small leaf spot. 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. If greenhouse azaleas suffer from this disease for several years in a row, then the branches become thin, long, the number of flower buds sharply decreases every year, the plants lose their decorative effect; with severe infestation, the plant dies. On the spots, one can see small, black, dot-shaped receptacles of spores - pycnidia, immersed in leaf tissues. A mass of spores emerges from the pycnidia in the form of thin, pale filaments. The defeat of this disease is facilitated by insufficient illumination in winter period, high air humidity, excessive watering, excessive and one-sided or late fertilization with nitrogen, late transfer of plants to the greenhouse in autumn, late removal from the greenhouse in spring, late pruning of plants, i.e. the main cause of the disease of rhododendrons of closed ground with fine spotting is non-compliance with agricultural technology.

Control measures. In winter, plants should receive sufficient lighting, moderate watering. To eliminate excess air humidity on warm days, greenhouses should be well ventilated, dense plantings should be avoided. Sick and fallen leaves are collected and burned. During the growing season, the plants are regularly (every 2-3 weeks) sprayed with a 0.4% suspension of 80% cineb or a 0.5% suspension of captan. 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 at a sufficiently high temperature. You can spray only those plants whose leaves have fully grown and developed.

bud rot was first discovered on rhododendrons in the United States of America. The disease is typical for the largest rhododendrons (Rh. maximum L.) and Katevbinsky (Rh. catawbiense Michx.). The causative agent of the disease is the fungus Sporocybe (Pycnosteanus) azaleae (P. K ..), which is spread by the cicada Gnaphoce-phala coccinea Forst. 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 preparations containing copper.

leaf swelling(thickness) of rhododendrons is caused by various types fungus Exobasidium. On leaves and shoots affected by this disease, fleshy, pale, waxy gall-like formations appear, having the shape of a ball ranging in size from a pea to a walnut.

The most common causative agent of this disease is Exobasidium rhododendri Cram. Usually this disease affects alpine species of rhododendrons - Rh. ferrugineum L., Rh. hirsutum L. and others.

Exobasidium vaccinii Woronin, the causative agent of lingonberry leaf disease, causes the formation of white cushion-like growths on young leaves of evergreen rhododendrons (Rh. maximum L., Rh. catawbiense Michx.) and deciduous rhododendrons in their natural habitats. In the Latvian SSR, this disease is found everywhere on lingonberry leaves, but has not yet been observed on rhododendrons.

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 Rh. ponticum L. and Rh. luteum sweet.

Exobasidium vaccinii-uliginosi Bond., the causative agent of swollen blueberry leaves, 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. After a year, these leaves die off.

Exobasidium japonicum Shir 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.

The swelling of the leaves of rhododendrons in our republic has not yet been observed.

Control measures. Affected shoots are cut out and burned along with the leaves. For prevention, plants are sprayed with preparations containing copper.

Rhododendron rust. The causative agent is the fungus Chrysomyxa rhododendri D. C. The disease most often affects small-leaved species - Rh. dauricum L., Rh. ferrugineum L., Rh. kotschyi Simonk, etc. In autumn, yellow, red or brown dusty pimples - sporangia appear on the underside of the leaves of affected rhododendrons. If the plants are heavily infected, they shed their leaves prematurely. In spring, dark red pads are visible on the leaves - winter spores. The spores of this fungus carried by the wind onto the spruce trees cause great harm to the trees.

Control measures. Affected leaves are collected and burned. Sick plants are sprayed with preparations containing copper.

Dry white rot of the root neck of rhododendrons. The causative agent is the fungus Armillaria mellea (Vahl) Quel. (real honey agaric). The disease mainly affects the root neck, as a result of which the plant dies. In diseased plants, the root neck is entwined with a grayish-white ring - mycelium. Strongly growing rhododendrons do not get sick with dry rot of the root collar. This disease usually affects those plants in which the root neck is broken or otherwise damaged, therefore, when transferring plants with a large root ball, you cannot hold them only by the aerial part, you must also support the root ball.

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).

Root rot. The causative agent of the disease is the fungus Phytophtora cinnamoni Rands. This disease most often affects the roots and base of the stem. Outwardly, the disease manifests itself as follows: 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, as a result of which the whole plant dies. This disease mainly affects rhododendrons growing on insufficiently acidic, highly moist soils. It is inherent in weakly growing rhododendrons. Young plants are most often affected. Plants are infected through the root system or through wounds.

Control measures. Affected shoots are cut and burned. If the lesion is severe, then the entire plant is burned. To prevent the disease, it is necessary to maintain normal soil acidity (pH 4-5) and observe the correct water regime (you can not water the plants too much).

Rot of seedlings and young seedlings. Very often, when propagating by seeds and cuttings, one has to observe a sudden mass wilting of rhododendrons, rotting and death. The causative agents of this disease are the fungi Rhyzoctonia sp., Pythium sp. and Botrytis sp. The most dangerous representative of this group of fungi is Rhyzoctonia Solani Kuhn. The disease most often affects young shoots. Seedlings affected by this fungus at the root collar become brown or black, soft, 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. Usually the fungus develops if the substrate is fresh, not yet decomposed, or if the crops were watered with fungus-infected water. The reasons for the spread of the disease can be too high planting density, excessive humidity in greenhouses and insufficient air exchange. Dense crops of rhododendrons should not be sprayed with water too often (daily), because excess moisture contributes to the onset of the disease. It is better to water them rarely, but plentifully. Our experience shows that pots with young seedlings are quite thoroughly soaked once a week.

Control measures. Greenhouses where crops and cuttings of rhododendrons are located should be well ventilated, and sufficient lighting should be maintained in them. Young shoots and seedlings should be watered in the morning, with the expectation that they dry out by evening. Too dense crops should be avoided. It is also not recommended to plant cuttings and young seedlings too densely. Seedlings that begin to die 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. Cuttings of greenhouse azaleas are disinfected by keeping for 10-15 minutes in a 0.15-0.2% suspension of TMTD.

The death of shoots. The causative agent is the fungus Phytophtora cacto-rum Leb. 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 fungus Physalo-spora rhododendri can also cause shoot death. In diseased plants, on some shoots, the leaves turn brown, dry out, and then the entire shoot dies (Fig. 26). V last years this disease is also found in the Latvian SSR. This disease also affects lilacs.

Control measures. The affected leaves are collected, the shoots are cut out, and they are all burned together. After flowering, rhododendrons are regularly sprayed with preparations containing copper. Sprayed every 10-14 days. Rhododendrons should not be planted in full shade.

Let's give some examples. With an incorrectly selected substrate (alkaline environment), the leaves of rhododendrons become pale, i.e., typical chlorosis appears. In an alkaline and even neutral substrate, iron, which plays an important role in the formation of chlorophyll, is in a form that is not absorbed by plants. Plants in this case grow weakly, are more susceptible to diseases and eventually die. With the wrong choice of landing site, rhododendrons suffer from a lack or excess of light, from exposure to cold dry winds, etc. The leaves of such rhododendrons are disheveled, the plants look stunted, although they are still alive and growing.

For sandy soils, excessive moisture is not typical, but with artificial irrigation, mineral elements are often washed out, and the plants show signs of starvation.

Frost and sun damage sometimes referred to as "sunburn". Usually this disease occurs in the spring after severe frosts or at the end of winter with sharp fluctuations in temperature day and night. Brown, dry, irregular spots appear on the leaves of rhododendrons, as a result of which the plants lose their decorative effect. Under the climatic conditions of the Latvian SSR, brown spots on the leaves of evergreen rhododendrons appear in late February - early March, when at night the temperature drops to -15 ° C, and in the daytime in the bright sun the surface of the leaves heats up quite significantly, because the temperature rises above zero.

To avoid sunburn, rhododendrons should be planted in semi-shaded areas. However, if you have to plant rhododendrons in an open area , then you need to create a light penumbra for them. The best material for this purpose is a spruce foot. Rhododendrons are very tenacious and, subject to the rules of agricultural technology, form strong shoots with beautiful foliage, which already in the middle of this summer partially covers damaged leaves.

Sometimes "sunburns" do not appear as spots, but as a brown strip along the main vein of the leaf. As you know, the leaves of evergreen rhododendrons already at a temperature of -3 ° C and below roll into a tube in order to reduce the leaf surface, “hide” the stomata and reduce transpiration to a minimum. That side of the twisted sheet, which is facing the sun, is very hot during the day, and freezes at night. In spring, a reddish-brown or brown belt is visible on the surface of the untwisted leaves, stretching 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. During severe frosts, flower buds of rhododendrons can also suffer. If in the spring the flower buds do not bloom, but turn brown and dry up, it means that they froze during the winter frosts. In the climatic conditions of the Latvian SSR, flower buds usually freeze in less winter-hardy species of rhododendrons.

From rhododendrons natural flora In the USSR, the Daurian rhododendron is the most sensitive to a decrease in temperature. Usually, in the mild climate of our republic, it grows and develops very well, annually in the second half of summer it forms a large number of flower buds, however, if winter is replete with thaws, the buds begin to bloom, and then even at a slight sub-zero temperature they freeze. So, in 1976, when December was very warm, the Daurian rhododendron in the open field began to bloom on December 26, and when the temperature dropped to -10 ° C by the New Year, all the buds that had begun to bloom froze. In the summer of 1977, the rhododendron did not bloom. In 1977, the second half of November and the beginning of December were unusually warm, and on December 4, some Dahurian rhododendron bushes were covered with flowers; On December 6, the temperature dropped to -2 ° C, and the buds froze. The history of the previous year repeated itself. We observed a similar picture with Sikhotinsky and pointed rhododendrons. These observations indicate that rhododendrons originating from regions with a continental climate have high frost resistance, but their winter hardiness is low, and they are of little use for growing in the climatic conditions of the Latvian SSR.

Water shortage in summer and drying up of rhododendrons in winter were the main cause of death in Riga parks of most of the rhododendrons planted in 1958. It should be noted that the water deficit in rhododendrons planted in the parks of Riga was felt not only in winter, but also in summer and autumn. It was due to the fact that groups of evergreen rhododendrons were placed under large old lime trees with a powerful superficial root system. Planting sites of rhododendrons were not isolated from the root system of lindens either by roofing material, or by slate, or by tin. From the point of view of illumination, the choice of a place for rhododendrons was not bad, but a year later the root system of lindens intertwined the entire top layer of soil, as a result of which a large shortage of water and nutrients necessary for the development of rhododendrons was created. Since the roots of rhododendrons are collected in a dense lump, they could not withstand strong competition from the surface root system of lindens and could not provide water and nutrients to the above-ground part of the plants. Being under the powerful roots of lindens, rhododendrons did not receive moisture from precipitation either. In addition, these plantings of rhododendrons were not provided with regular watering. As a result, out of several thousand plants planted about twenty years ago, only a few dozen specimens have survived to this day.

To protect evergreen rhododendrons from drying out in winter, it is recommended to water them abundantly before the onset of frost, saturating all plant cells with water as much as possible.

Chlorosis is caused by an acute deficiency of iron and magnesium, which occurs when the pH of the substrate is above 7. In plants affected by chlorosis, the leaf blade between the conducting bundles (veins) becomes light green or even yellowish green. In the initial stage of chlorosis, the veins still retain a dark green color, and then also turn yellow. With severe chlorosis, all young shoots turn yellow or pale yellow and are easily burned in the sun. The occurrence of chlorosis is due to the high content of calcium in the soil and in irrigation water. For the normal synthesis of chlorophyll, iron and magnesium are necessary, but in an alkaline environment they are in an indigestible form, although they are contained in sufficient quantities. In addition, with an incorrect reaction of the environment, the mineral nutrition of plants in general is disturbed. To eliminate chlorosis, the pH of the medium should be brought to 4.0-5.0, which will help to establish the mineral nutrition of plants that will acquire a normal appearance.

Nitrogen starvation. With a lack of nitrogen, the entire leaf blade of rhododendrons becomes light. New shoots grow weakly, small leaves develop on them, flower buds are not laid. In the middle of summer, around August, 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, although under normal growth and nutrition conditions on an evergreen plant, the leaves remain for four years. These signs indicate that the plants are starving, and, in particular, they feel an acute lack of nitrogen. If rhododendrons are regularly fed annually, then they will not have nitrogen starvation.

Our observations show that nitrogen starvation in rhododendrons occurs when they are grown on light sandy soils that require regular watering throughout the summer. With abundant irrigation using sprinklers, mineral salts, especially nitrogen compounds, are washed out and a deficiency of mineral elements is created.

When the first signs of nitrogen starvation appear, nitrogen supplementation (ammonium sulphate or potassium nitrate) should be immediately introduced.

Wetting rhododendrons. In practice, one has to meet not only with the drying of rhododendrons due to water deficiency, but also with the wetting of rhododendrons as a result of excessive soil moisture. In these cases, the leaf blade of rhododendrons becomes grayish-green, matte. Leaves fall off for no apparent external reason. New shoots become soft, the leaves wither, the root ball collapses, although the roots at the root neck are not damaged. These signs indicate that there is excess moisture at the planting site of rhododendrons, which, due to poor drainage in top layer excess water accumulates in the soil, so that the aeration of the root system is clearly insufficient. Wetting of rhododendrons is usually observed if they are grown on heavy, clay soils with poor drainage, and also if after transplantation they are plentifully and often watered.

In order to create normal water and air exchange for the root system, it is necessary to ensure good drainage, wetting plants should be transplanted into a loose water and breathable substrate, watering should be stopped for a while. On hot, sunny days, watering should be replaced by spraying the aerial parts with water. Wetted plants are relatively slow to restore their normal appearance.

In order to avoid wetting rhododendrons, they should be planted in a specially prepared water and breathable substrate in a well-drained area. Watering during the entire growing season should not be excessive.

KONDRATOVICH "RODODENDRONS", Riga, 1981 (experience of introduction of rhododendrons in Latvia)

Rhododendrons, like any other plants, are affected by diseases and pests. Susceptibility to various diseases and pests mainly depends on the type and variety of the plant. Long-term practice shows that evergreen rhododendrons growing in open sunny areas are more susceptible to diseases and pests than those that grow in light partial shade. Depleted specimens are usually more susceptible to diseases and pests than well. developed plants. The main thing in protecting rhododendrons from pests and diseases is to create for them optimal conditions growth and development. Compliance with the rules of agricultural technology and the choice of planting site corresponding to the requirements of the plant are essential. With proper agricultural technology for growing rhododendrons in culture, plants are only slightly damaged.

Diseases

Fungal diseases on seedlings of rhododendrons appear due to poor soil aeration, which occurs with excessive watering. Often this is one of the reasons for the mass death of seedlings. Plants infected with fungi should be regularly sprayed with a solution of Bordeaux mixture. Sick and weakened plants, as well as stumps, must be burned in order to eliminate the foci of the spread of fungal diseases.

Tracheomycosis wilt of rhododendron

Symptoms: the roots turn brown and rot, the fungus penetrates the vascular system of the plant and fills it, blocking the movement of nutrients. Leaves, starting from the upper parts of the shoots, gradually lose turgor, turn brown and dry. The leaves fall along with the petioles, and a grayish-white mycelium begins to spread from the vessels of the stem along the bark. The infection persists in plant debris and infected plants.

Control measures: timely burning of dead plants along with the roots. In industrial cultivation - preventive spraying of plants and watering the root zone with a 0.2% solution of foundationol.

Phytophthora root rot

Pathogen: Phytophthora cinnamomi fungus. Causes: drift from a nursery with acquired plants, soiling and poor drainage of the root zone. Symptoms: first, the leaves begin to wilt, often not on the whole plant, but on individual branches. At the same time, this wilting is not associated with overdrying; wilted leaves do not restore turgor at night or early in the morning. In the region of the root neck - lesions under the bark. Further - the branch turns yellow, then the whole plant. Roots turn brown, rot, soak. Large brown spreading spots appear on the root neck and the base of the stems, the wood rots. Dense dark gray sporulation of the fungus develops on the spots. Affected plants wither and dry out. The infection persists in the soil and on plant debris.

Bacterial root cancer

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.

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. In humid weather, all necrotic parts are covered with a fluffy smoky-gray coating of sporulation. 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.

Rot of seedlings and young seedlings of rhododendron

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: Beginning seedlings to die 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) which is spread by the cicada Graphocephala coccinea. 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.

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. The disease has been noted in Latvia.

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 cinnamoni 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: in diseased plants, the root neck is entwined with a grayish-white ring - mycelium. 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

Symptoms: there is a slight deformation and thickening of the leaves. 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 - the causative agent of a very common disease of lingonberry leaves, causes 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 places of growth.

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. As of 1981, this disease was not observed in Latvia.

Measures to combat diseases caused by representatives of the genus Exobasidium: pruning of the affected parts of plants, spring spraying a solution of 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. As of 1981, this disease was not observed in Latvia.

Pestalocium blotch of rhododendron

Pathogen: fungus Pestalotiopsis sydowiana (syn.: Pestalotia macrotricha Kleb., Pestalotia rhododendri). Leaves and stems are affected. On the leaves appear small brown spots of 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 out.

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.

Septoria blotch of rhododendron, or azalea septoria, or small leaf spot

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-like receptacles of spores - pycnidia, immersed in leaf tissues.

Control measures: pruning of the affected parts of plants, spring spraying with a solution of Bordeaux liquid, its substitutes or camulus. 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 at a sufficiently high temperature. You can spray only those plants whose leaves have fully grown and developed.

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 liquid, its substitutes or camulus.

cercosporosis

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. V more leaves of the lower tiers are 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 rust

The causative agent is the fungus Chrysomyxa rhododendri D. C. Most often found on small-leaved species and species from the Osmothamnus subgenus - Rhododendron parvifolium, Rhododendron adamsii, Rhododendron dauricum L., Rhododendron ferrugineum L., Rhododendron kotschyi, and others.

Symptoms: in autumn, yellow, red or brown dust-like swellings - sporangia appear on the underside of the leaves of affected plants. Severely infected plants shed their leaves prematurely. In spring, dark red pads are visible on the leaves - the winter form of the fungus.

Control measures: Affected leaves are collected and burned. Sick plants are sprayed with copper-containing preparations. In the early stages of this disease, spraying plants with Bordeaux mixture helps.

Mosaic of rhododendron

The causative agent is the Rhododendron mosaic virus. Symptoms are described by different authors with slight differences.

1. Small mosaic yellow spots and swellings appear on the leaves. Plants are stunted and bloom poorly. The leaves turn yellow, but they retain patches in the form of alternating green and brown spots.

2. Leaves become rough, calloused and ugly. Calluses are usually a normal green color, with the rest of the leaf turning greenish yellow. The light part of the leaf blade is much thinner than in places where there are calluses. Venation on calluses is less noticeable.

Control measures: pruning of leaves and branches, culling of heavily affected plants. Mosaic virus is carried by aphids, bedbugs and other insects.

Pests

Furrowed weevil (Otiorrhynchus sulcatus)

Adults are black, 8-10 mm long, not flying, with an elongated head extended forward, at the end of which there are mouthparts. Elytra with deep punctate beards. The larvae are white, with a brown head, legless, curved, up to 12 mm long. The larvae live from 2 to 12 months, then pupate, and after 20 days the pupa turns into an adult beetle. Females live 5-12 months, laying 100 to 1000 eggs in their lifetime. Eggs are laid in groups in the soil, where after 2-3 weeks the larvae emerge from them and immediately start feeding.

The nature of the lesion. Along the edges of the leaves, characteristic eaten away areas are observed. If the damage is inflicted by larvae living in the soil, then the plant suddenly withers and dies.

Control measures: spraying with decis, splender, actellik, or spark.

Common spider mite (Tetranychus urticae)

Almost invisible, since its dimensions are 0.25-0.43 mm. At the larval stage of development, they are transparent, colored from light green to greenish brown in color with two distinct, large dark spots on the sides, which are formed by transparent blind sacs of the midgut. From late summer until the following spring, overwintering females are orange-red to bright red. In contrast to the six-legged first larval phase, all adult ticks have 8 legs.

Damaged leaves turn yellow, deform, turn brown and dry. Up to 10 generations of ticks develop during the growing season.

Control measures: spraying plants with fitoverm, fufanon, karbofos, actellik, or colloidal sulfur.

Acacia false shield

Acacia false scale, or acacia scale, or hazel scale, or acacia scale insect (Parthenolecanium corni). It is currently ubiquitous. In the north, the range reaches Leningrad region. Sexual dimorphism is pronounced. The body length of females is from 3 to 6.5 mm, width - 2.4 mm, height - 4 mm. There are no wings. Body oval or broadly oval, sometimes almost round, no segmentation. The shape, color and size of the body of the female vary depending on the type of host plant. Young females with a delicate, not very convex body, more oval in shape, light brown, with two black stripes and longitudinal black stripes extending from them. Dead - shiny, painted in dark yellow, brown or dark brown. The body length of males is 1.4-1.6 mm. The body is thin, elongated, with a clear segmentation into the chest, head and abdomen. The head is black with three pairs of simple eyes. Abdomen and thorax red-brown, covered with white waxy coating. Ten-segmented antennae and legs are yellow. At the top of the abdomen there are two caudal filaments, 2-2.5 times longer than the body size. Larvae of the first age (tramps) are 0.36 mm long. The body is flat, elongated-oval, slightly narrowed towards the posterior end. The color of the covers is cream or light yellow. In the second age, the larvae of heterosexual individuals differ from each other in body shape. The nymphal stage of development is observed only in male larvae. Nymphs are dark brown in color, have well-developed rudiments of wings, legs and proboscis. Reproduction in acacia false scales is often parthenogenetic, sometimes bisexual in the south. The larvae hibernate. In the northern part of the range, one generation develops per year, in the southern part - two or three.

Insects pierce the bark of the plant with their proboscis and attach tightly to the branches. Damaged plants weaken, lose their decorative effect and gradually dry out.

Control measures: timely spraying of plants with organophosphorus compounds, neonicotinoids, pyrethroids, fitoverm, fufanon, karbofos, actellik.

Thrips tobacco (Thrips tabaci)

In Russia, it is ubiquitous. Polyphagous, damages about 400 plant species in open and closed ground. The coloration of the female is variable, from light yellow to brown, often more or less yellow, sometimes strongly darkened. Body length 0.8-1.0 mm. The male is smaller and lighter, the chest is bright yellow. Body length 0.7-0.75 mm. The larva, 0.8-0.9 mm long, is very mobile, two pairs of wings are surrounded by a fringe of cilia, the body color is variable - from yellow to almost black. Adults hibernate in the upper soil layer at a depth of 5-7 cm or in plant debris. They emerge after wintering in the first half of April, feed and lay eggs at first on weeds. One female during her life (20-25 days) lays about 100 eggs in the leaf tissue, and their fertility largely depends on the type of host plant. Then the females fly to cultivated vegetation. Is a distributor of viruses. On rhododendrons, buds are damaged, which, if severely damaged, do not open, turn yellow and fall off.

Control measures: timely spraying of plants with organophosphorus compounds, neonicotinoids, pyrethroids, fitoverm, fufanon, karbofos, actellik, actara.

Rhododendron mite or American azalea bug (Stephanitis rhododendri)

It occurs on the Katevbinsky rhododendron, Smirnov's, Ungern's rhododendron and other species and varieties that have felt pubescence on the underside of the leaf.

Adult size is about 3.6 mm. Wings are colorless, reticulate with a sheen. Bedbug larvae reach a length of 0.7 to 2.2 mm, they do not fly, they are yellow in color with dark spots and hairy outgrowths from the sides.

Symptoms: the leaves turn yellow, and black spots appear in their lower part, resembling resin. Damage contributes to curling and drying of the leaves. The bug appears in summer, spreads along with peat and pine needles along with the substrate.

With minor damage, you can collect pests by hand. In addition, in late May - early June, plants should be sprayed with nicotine and soap, or a flavored pyrethrum extract. In case of severe damage, pruning of shoots is recommended.

Greenhouse whitefly (Trialeurodes vaporariorum)

Tropical species. Introduced to all continents. It is noted near greenhouse plants, where the pest persists all year round. The greenhouse whitefly is known as a carrier of many viral infections.

Signs of damage: small white insects are visible on the underside of the leaves. The body of the adult is light yellow, the wings are white, without spots. The size of the female is 1.1 mm, the male is 0.9 mm. In GBS, it is quite often noted on large-leaved rhododendrons (Caucasian, Pontic). To combat the greenhouse whitefly, pesticides are chosen that are of little danger to pollinating insects and entomophages. In recent years, drugs from the group of neonicotinoids have become more widespread.

Whitefly rhododendron, or white rhododendron fly (Dialeurodes chittendeni)

V GBS 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. For preventive purposes, it is recommended to spray adult flies with nicotine dust during the summer. Affected leaves should be cut off and burned.

gastropods

Leaves, buds and young shoots of rhododendrons damage Helix snails and slugs. Control measures: manual collection shellfish, the use of molluscicides.

crows

In GBS in early spring the facts of pecking of the buds of rhododendrons by crows were noted, Smirnov's rhododendron most often suffers.