Dark spots on the leaves of rhododendron. 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 saturated 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 rhododendron crown turns yellow. The article describes the possible causes of this phenomenon and methods of dealing with it.

The plant is hygrophilous. Insufficient watering will lead to the loss of turgor of leaves, they will begin to dry out and turn yellow. Check the degree of hydration of the earthen coma by squeezing a handful of earth in the hand under the rhododendron bush. The allocation of drops of water indicates that the plant is flooded. This can cause root rot. The lump has crumbled - watering is required. It turned out to form a lump from the soil - moisture is optimal.

Place the bushes near the pond or in the shade of a taller plant (pine is a good option). This will protect the rhododendron from excessive evaporation of water. Humidity will also help maintain intermittent watering with a sprinkler.

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

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

Thrips black

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

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

Rhododendrons are susceptible to various spottingthat cause fungi. The most dangerous of these diseases is septoria.

Rhododendron Septoria

Symptoms: Reddish small spots form in the center of the leaf blades, which increase in size and whiten. Leaves turn yellow, dry up. A plant without timely assistance may remain with a bare stem.

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

Prevention: choose healthy plants for propagation.

Chlorosis

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

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

Foreword

Rhododendrons are extremely attractive and spectacular plants, widely used in the field of landscape design, but, like all residents of the garden, they have characteristic diseases and pests that love to enjoy this flower. We will master the methods of their treatment.

Causes of Typical Diseases

Gardeners with experience claim that the majority of diseases affecting rhododendrons arise as a result of improper agricultural practices and errors in caring for plants. The most common adverse factors include:

low level of ground acidity;
excessive soil moisture;
direct exposure to sunlight, causing burns;
incorrect and unbalanced top dressing;
desiccation of the soil, characteristic of the winter period;
disadvantage nutrients;
freezing and sudden changes in temperature;
clay and sandy soils, leading to wetting and wilting of the plant.

In order to avoid adverse effects, it is recommended that you carefully observe the landing rules and. That is 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 timely measures are taken. What to do in each case?

Rhododendron bug is considered the most dangerous and common pest that affects these shrubs. A sign of his presence can serve as small powdery white traces on the leaves. You can destroy the bug by spraying with diazinon.

A spider mite attacks rhododendron shrubs in an arid, hot season, feeding on the juices of its foliage. Due to its extremely small size, it is impossible to make out with the naked eye. Determine the presence of a spider mite will help appearance plants: the underside of the leaves is wrapped in a thin web, as it were, and they themselves acquire a brown color, grow dull and fall off. In the fight against it, gardeners will help periodic spraying with diazinon or agravertine.

Tilled slug infects the crown and leaves of young rhododendrons, biting into them and making large holes. Its activities can lead to the death of shrubs in the shortest possible time. To prevent this, the plowed slug individuals will have to be collected by hand, and it will also contribute to its destruction by pouring it with a TMTD solution (concentration 0.8%).

Tobacco (black) thrips attacks both greenhouse plants and shrubs planted in open ground. The insect is small in size and has a characteristic black color that damages the leaves and buds of rhododendrons. As a result, the foliage prematurely dims, turns yellow and falls, and the flowers fade without opening. In addition, this pest greatly inhibits the growth of young shoots and deforms the buds. They struggle with tobacco thrips by spraying plants with 0.3% nicotine solution, 0.2% karbofosnoy emulsion, as well as organophosphorus compounds (actar, fuafon, pyrethroid, etc.).

Asian garden hrushers are the most dangerous pests for rhododendrons. They hit the stems and root system plants, eat their leaves. The most effective means to kill the insect is diazinon.

Furrow weevil - a small bug of black color, causes enormous damage to the plant and, if no measures are taken in time, can cause its death. Its individuals feed on leaves, flowers, buds, and sometimes even the bark of this shrub. 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 bazudinom.

Narrow-winged moth miner. Its caterpillars gnaw through 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 winged moth, knowledgeable people recommend fumigating or spraying shrubs with sulfur.

Gastropods are slugs and snails of the genus Helix; they actively infect shoots, foliage and buds of rhododendrons. You can fight them through manual collection, as well as the use of special means - molluscicides.

The rhododendron fly infects shrub leaves, leaving small light spots on them and draining the plants. To destroy this specific pest, spraying with nicotine sulfate is used.

Characteristic diseases of these shrubs

Tracheomycosis (vascular wilt) refers to a fungal disease. 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, then spray the bush with Bordeaux liquid.

Phytophthora rot is caused by pathogenic fungi of the genus Phytophthora. As a result of this disease, the stems and root neck of the shrub become covered with brown or purple spots. Then rhododendron rhizome turns brown and begins to rot, which leads to a gradual wilting. In this case, the number and intensity of irrigation should be reduced, and shrubs should be treated with fungicides.

Septorious spotting. The causative agents of this disease are Septoria family fungi. This disease affects mainly the leaves of rhododendrons, leading to their premature yellowing and decay. Stems of plants also dry out. The disease can be recognized at the initial stages of its development by the characteristic round spots of red color with a white center on the leaves of rhododendron. Treatment begins with diseased leaves breaking off and burning. After which the plants are sprayed with Bordeaux liquid or copper sulfate. The procedure should be repeated after a week.

Leaf mosaic is a viral disease, the carriers of which are bed bugs, aphids and a number of other insects. Rhododendrons of alpine species 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 tools such as confidor, actellic, etc.

The rust of rhododendrons affects small-leaved plant varieties, provoking the appearance of brown and yellow spots on their foliage. On diseased leaves, the so-called sporulation of the pathogen is formed, resembling in appearance a dark colored pads. In the fight effective spraying with copper-containing drugs.

The dying off of shoots leads to drilling, wilting and falling 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 sprayed on the bushes with a quadrice or 0.2% base-solution.

Nitrogen starvation is characteristic of plants growing in sandy soil. Its signs are fading leaves, reduced flowering, weak ovary of the kidneys. You can fight the disease with regular fertilizing with mineral fertilizers with a high nitrogen content.

Mixed chlorine appears in the appearance of spots on the edges of rhododendron leaves yellow color. The causes of this disease are increased soil acidity or insufficient nutrient content in the soil and necessary elements. The problem should be combated by spraying shrubs with magnesium sulfate and iron sulfate (7 g of 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 bush, as well as the death of the apical buds. Affected branches and shoots need to be burned, and with an extensive lesion, the entire plant should be destroyed in order 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 characteristic of plants planted in heavy, clay soil, as well as with excessive soil moisture. In this case, there is a change in the color of the leaf plate, premature fall of the leaves and the destruction of the root coma. To prevent problems, carefully consider the choice of a site for planting rhododendrons, and also do not overdo it with watering to avoid soil overmoistening.

The causative agent of cercosporosis is the fungus of the family Cercospora. The disease affects the leaves of rhododendrons, forming numerous spots of red-brown color on their surface. The outer side of the sheet plate is covered with a gray coating. The treatment of this disease is carried out by spraying with alternate use of solutions of baseazole and ditan.

Winter drying is one of the most common diseases of rhododendrons. Observed after severe frosty winter months. Signs of damage appear in the drilling and drying out of the leaves. Then, after some time, the entire shrub dies. The causes of the development of the disease are violation of the waterways and excessive moisture loss by rhododendrons. For the treatment of plants, intensive heavy watering is recommended, as well as daily spraying of bushes. In order to prevent the use of the so-called winter winters.

Plants suffer from severe waterlogging, unbalanced top dressing, low acidity of the soil, physiological winter drying and sunburn. May be damaged by fungal diseases ( spotting, rust) and chlorosis(acute deficiency of iron and manganese, which occurs with low acidity of the soil and passes with the correct feeding regimen). By collecting and burning damaged foliage, performing sanitary pruning and treating plants with suitable fungicides, many diseases can be resisted.

Most often, garden snails and slugs damage rhododendrons (collection and destruction help), rhododendral bugs, spider mites, mealybugs, weevils, scale insects, rhododendron flies, against which insecticides help.

Major diseases and symptoms

Vascular (tracheomycotic) wilting caused by fungi from the genus Fusarium ( Fusarium oxysporum) The disease begins with rot of the roots, damages the vascular system. Plants turn brown and dry, starting from the top of the shoots. On the dried leaves and stems a grayish plaque is formed - mycelium.

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

Gray rot caused by fungi of the genus Botritis ( Botrytis cinerea) One of the most common diseases of many cultures, since fungal spores spread both with air and with splashes of water. On all parts of the plant - leaves, buds, stems - blurry brown-brown spots appear and quickly grow. Damaged tissues quickly dry out, a grayish coating - mycelium forms on them.

Septorious 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 fruit bodies of the wintering stage of the fungus form on them. Sick stems shrink, dry out, the leaves turn yellow prematurely and fall off.

Prevention and control measures

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

Main pests

Spider mite (Tetranychus urticae) affects 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 noticed when the underside of the leaves is covered with a thin web, and the leaves become lifeless, brownish and fall off.

Acacia false shield (Parthenolecanium corni) Larvae resembling small shiny brown outgrowths on the cortex are firmly attached to the branches and “pull” the sap from the plant. As a result, it weakens, gradually dries up.

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

Control measures

Compliance with the rules of agricultural technology.
In early spring, spraying plants biological product Fitoverm, or chemical: Aktara, Actellik, Arrivo, Spark, 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 addictive pests, drugs must be changed.

PROTECTION OF RODODENDRONS FROM DISEASES AND PESTS

Rhododendrons, like any other plant, are affected by diseases and pests. It should be noted that the 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 prone to disease and pest attack than those that grow in light partial shade. Weak, depleted specimens are usually more susceptible to diseases and pests than strongly growing ones. Therefore, the main thing in protecting rhododendrons from pests and diseases is the creation of optimal conditions for growth and development for them. The observance of the rules of agricultural technology and the justified choice of the landing site are essential.

RODODENDRON DISEASES

For the Latvian SSR, rhododendrons are a relatively young culture, therefore, the diseases that we had to observe are not specific to this genus of plants. The causative agents of rhododendron diseases can be various microorganisms. In addition, the disease may be due to inappropriate environmental conditions. An active fight against the disease should begin as soon as its first signs are noticed, otherwise one cannot fully count on success in the fight against the disease.

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

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

Leaf spotting- The most widespread disease of rhododendrons of open and closed ground. The disease affects both young seedlings and adult plants. Its causative agents are various mushrooms, the appearance of which can be precisely 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 sheet. In conditions of high humidity, the upper side of the leaf blade is covered with a gray coating. The leaves of the lower tiers are more affected. The causative agent of leaf spotting is widespread in the USA, especially on the Pontic rhododendron and varieties based on this species. Another mushroom of the same genus, Cercospora handelii Bubak, is also dangerous.

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

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

Phyllosticta maxima Ell. et Ev. - spots are vague, irregular, dark brown or ash gray, with dark edges. Localized at the edges or at the ends of the leaves. Black balls - sporangia fall out of the spots. The vast majority of affected leaves die off, 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 dangerous diseases closed ground rhododendrons (greenhouse azaleas) - small spotted leaves. In countries where rhododendrons are cultivated very widely, this fungus is also found on deciduous rhododendrons of open ground. Yellowish, red-yellowish, later yellowish-gray spots of irregular shape appear on the leaves of plants. By fall, they become dark brown in the middle, and sometimes even brownish black. Initially, spots appear in the middle of the leaf blade, gradually increase and, reaching large veins, stop. The fungus grows into all leaf tissues, the leaves die off and fall prematurely, so that the plant becomes completely bare. As a result of leaf falling 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, the branches become thin, long, the number of flower buds decreases sharply every year, plants lose their decorativeness; with severe affection, the plant dies. On the spots, one can see small, black, dot-like containers of sporpiccnidia immersed in leaf tissue. A mass of spores emerges from the pycnidia in the form of thin pale filaments. The defeat of this disease contribute to poor lighting in winter period, increased air humidity, excessive watering, excess and one-sided or late nitrogen fertilizing, late transfer of plants to the greenhouse in the fall, late removal from the greenhouse in the spring, late crop pruning, i.e., the main cause of the disease of closed ground rhododendrons with small spotting is non-compliance with agricultural machinery.

Control measures. In winter, plants should receive adequate lighting, moderate watering. To eliminate excess air humidity on warm days, greenhouses should be well ventilated, thickened plantings should be avoided. Sick and fallen leaves are collected and burned. During the growing season, plants are regularly (after 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, you should not spray plants with preparations containing copper, as this leads to burns of leaves and young shoots. Preparations containing copper are used only at normal humidity and a sufficiently high temperature. You can spray only those plants in which the leaves have fully grown and developed.

Bud rotfirst discovered on rhododendrons in the United States of America. The disease is characteristic of 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 distributed by the cicada Gnaphoce-phala coccinea Forst. Affected by this disease, the buds turn brown and die. A mycelium from buds can grow into branches and lead to their death.

Control measures. During the growing season, plants should be sprayed with copper-containing preparations regularly (after 2-3 weeks).

Bloating leaves(fatness) rhododendrons caused different kinds fungus Exobasidium. On the leaves and shoots affected by this disease, fleshy, pale, wax-like gall-like formations appear, having the shape of a ball the size of 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. et al.

Exobasidium vaccinii Woronin, a causative agent of lingonberry leaf disease, causes the formation of white pillow-like growths on young leaves of evergreen rhododendrons (Rh. Maximum L., Rh. Catawbiense Michx.) And deciduous rhododendrons in their natural places of growth. 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 initially 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 bloating of blueberry leaves, causes the formation of the so-called “witch's broom” in Karolinsky's rhododendron. Leaves turn yellow-brown, their underside is covered with powdery bloom. A year later, these leaves die off.

Exobasidium japonicum Shir, affects the leaves and tops of shoots. Sick plants develop abnormally thick, large, pale green leaves, covered with chalk-white plaque. These leaves quickly wrinkle, mold and dry out. The fungus is less common on annual plants than on older ones. Susceptibility to this disease largely depends on the type and variety of rhododendrons.

Bloating of rhododendron leaves in our republic has not yet been observed.

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

Rust rhododendrons.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, et al. In autumn, yellow, red, or brown dusty pimples - sporangia - appear on the underside of the leaves of the affected rhododendrons. If the plants are highly infected, they drop the leaves prematurely. In spring, dark red pads are visible on the leaves - winter spores. The spores of this fungus carried by the wind on spruce cause trees great harm.

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. (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 with dry rot of the root neck do not get sick. This disease usually affects those plants in which the root collar is broken or otherwise damaged, therefore, when transferring plants with a large root lump, you can not hold them only by the aerial part, the root lump must be maintained.

Control measures. The affected plants are dug up and burned. Plants near which the disease is detected should be transplanted so that the root neck is not covered by mulch (it must be dry).

Root rot.The causative agent is Phytophtora cinnamoni Rands. The roots and stem base most often suffer from this disease. Externally, the disease manifests itself as follows: on individual shoots or on the whole plant, they wither, and then all the leaves dry out for no apparent reason. The apical buds turn brown and die. On the cross sections of the shoots, it is evident that the cambium layer is brown. The roots turn brown and rot, resulting in the death of the whole plant. This disease mainly affects rhododendrons growing on insufficiently acidic, highly moistened soils. It is inherent in weakly growing rhododendrons. Most often, young plants suffer. 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 whole plant is burned. To prevent the disease, normal soil acidity (pH 4-5) should be maintained and the correct water regime should be observed (plants should not be watered too much).

Rot of seedlings and young seedlings.Very often, when propagated by seeds and cuttings, one has to observe a sudden mass wilting of rhododendrons, decay 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 seedlings. The seedlings affected by this fungus at the root neck become brown or black, soft, fall to one side and die, white fungal hyphae or brownish mold are visible on the leaves. Pale, cobweb-like filaments 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 water infected with the fungus. The causes of the spread of the disease may be too much planting density, excessive humidity in the greenhouses and insufficient air exchange. Thick crops of rhododendrons should not be too often (daily) sprayed with water, because excess moisture contributes to the onset of the disease. It is better to water them rarely, but abundantly. Our experience shows that pots with young shoots are quite sufficient to thoroughly wet once a week.

Control measures. Greenhouses, where crops and cuttings of rhododendrons are located, should be well ventilated, maintain adequate lighting in them. Young seedlings and seedlings should be watered in the morning, with the expectation that by the evening they will dry out. Too thick crops should be avoided. It is also not recommended to plant cuttings and young seedlings too thickly. Sprouts starting 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 foundationazole powder. For prevention purposes, it is advisable to spray young seedlings and seedlings with a 0.2% suspension of foundationazole. To combat this disease, you can use captan and TMTD. Cuttings of greenhouse azaleas are disinfected, keeping for 10-15 minutes in a 0.15-0.2% suspension of TMTD.

The dying off 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. The shoots also dry out first, and then die off. Adult leaves curl, brown and dry. Heavily affected plants die. The death of shoots can also be caused by the Physalo-spora rhododendri fungus. In diseased plants, on some shoots, the leaves turn brown, dry, and then the entire shoot dies out (Fig. 26). AT last years this disease was also found in the Latvian SSR. This disease also affects lilacs.

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

Here are some examples. With an improperly selected substrate (alkaline medium), the leaves of the rhododendrons become pale, that is, typical chlorosis appears. In an alkaline and even neutral substrate, iron, which plays a large role in the formation of chlorophyll, is in the form not absorbed by plants. In this case, the plants grow weakly, are more easily amenable to diseases, and ultimately 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 have a stunted appearance, although they are still alive and growing.

Excessive moisture is not typical for sandy soils, but during artificial irrigation, mineral elements are often washed out, and plants show signs of starvation.

Damage from frost and sun,sometimes called "sunburns." Usually this disease is observed 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 rhododendron leaves, 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 during the day in bright sun the leaf surface heats up quite significantly, because the temperature rises above zero.

To avoid sunburn, rhododendrons should be planted in half-shaded places. However, if you have to plant rhododendrons in an open area , then you need to create a light partial shade 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 running along the main vein of the leaf. As you know, the leaves of evergreen rhododendrons even at a temperature of -3 ° C and below are curled into a tube to reduce the leaf surface, "hide" the stomata and reduce transpiration to a minimum. The side of the twisted sheet that faces 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 untwisted leaves, stretching along the entire sheet. If the damage is not severe, then with the beginning of the growing season the signs of freezing disappear and the color of the leaves becomes normal. rhododendron flower buds may suffer during severe frosts. If in the spring the flower buds do not bloom, but become brown and dry out, then they froze during winter frosts. In the climatic conditions of the Latvian SSR, flower buds usually freeze out in less winter-hardy rhododendron species.

From rhododendrons natural flora The USSR most sensitive to lower temperatures is rhododendron daursky. Usually, in the mild climate of our republic, it grows and develops very well, forms a large number of flower buds every year in the second half of summer, however, if winter is full of thaws, the buds begin to bloom, and then freeze out even at a slight minus temperature. So, in 1976, when December was very warm, the Daurian rhododendron in open ground began to bloom on December 26, and when the temperature dropped to -10 ° C by New Year, all buds that started to bloom froze. In the summer of 1977, rhododendron did not bloom. In 1977, the second half of November and the beginning of December were unusually warm, and on December 4 some bushes of the Daurian rhododendron were covered with flowers; On December 6, the temperature dropped to -2 ° C, and the buds froze. The story of the previous year repeated. We observed a similar picture with rhododendrons of the Sikhotin and genital. 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 shortages in the summer and winter drying of rhododendrons were the main cause of death in the Riga parks of most of the rhododendrons planted in 1958. It should be noted that the water deficit of rhododendrons planted in Riga parks 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 lindens with a powerful surface root system. Places of planting of rhododendrons were not isolated from the root system of linden by either roofing material, slate, or tin. From the point of view of illumination, the choice of place for rhododendrons was not bad, but a root system of lindens twisted the entire top layer of soil within a year, resulting in a large deficit of water and nutrients necessary for the development of rhododendrons. Since the roots of rhododendrons are gathered in a tight lump, they could not withstand strong competition from the surface root system of lindens and could not provide the aerial part of plants with water and nutrients. Being under the powerful roots of lindens, rhododendrons did not receive moisture and precipitation. In addition, these plantings of rhododendrons were not provided with regular watering. As a result of the several thousand plants planted about twenty years ago, only a few dozen specimens have survived to this day.

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

Chlorosis is caused by an acute deficiency of iron and magnesium, which is observed in cases where the pH of the substrate is higher than 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 become yellow or pale yellow and easily burns in the sun. The occurrence of chlorosis is due to the high calcium content 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 undigestible 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 disrupted. To eliminate chlorosis, the pH of the medium should be adjusted 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 mid-summer, around August, the leaves of previous years begin to turn yellow, then become reddish-brown and most of them fall. By the end of summer, only the leaves of the current year remain on plants, although under normal conditions of growth and nutrition on an evergreen plant, the leaves remain for four years. These signs indicate that the plants are starving, and, in particular, 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. During heavy 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, you should immediately apply nitrogen top dressing (ammonium sulfate or potassium nitrate).

Soaking Rhododendrons.In practice, one has to meet not only with the drying of rhododendrons due to water deficiency, but also with the soaking of rhododendrons as a result of excess soil moisture. In these cases, the leaf blade of the rhododendrons becomes grayish-green, dull. Leaves fall for no apparent external reason. New shoots become soft, the leaves wither, the root lump is destroyed, although the roots at the root neck are not damaged. These signs indicate that there is excess moisture at the rhododendron landing site, which is due to poor drainage in top layer excess water accumulates in the soil, and aeration of the root system is clearly insufficient. The soaking of rhododendrons is usually observed if they are grown on heavy, clay soils with poor drainage, and also if after transplanting they are abundantly and often watered.

In order to create normal water and air exchange for the root system, it is necessary to provide good drainage, soaking plants should be transplanted into a loose water and breathable substrate, and watering should be stopped for some time. On hot, sunny days, watering should be replaced by spraying the aerial parts with water. Soaking plants relatively slowly restore their normal appearance.

In order to avoid the soaking of rhododendrons, they should be planted in a specially prepared water- and breathable substrate in a well-drained place. Watering throughout the growing season should not be excessive.

KONDRATOVICH "RODODENDRONES", Riga, 1981 (experience in introducing rhododendrons in Latvia)

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

Disease

Fungal diseases on rhododendron seedlings 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 sprayed regularly with a solution of Bordeaux fluid. Sick and weakened plants, as well as stumps, must be burned to eliminate the foci of the spread of fungal diseases.

Tracheomycotic 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 top 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 cortex. 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 of the root zone with 0.2% solution of baseazole.

Phytophthora root rot

Pathogen: Phytophthora cinnamomi mushroom. Reasons: drift from the nursery with acquired plants, jamming and poor drainage of the root zone. Symptoms: at first the leaves begin to fade, often not on the whole plant, but on separate branches. Moreover, this withering is not associated with overdrying, withered leaves do not restore turgor at night or early in the morning. In the area of \u200b\u200bthe root neck - lesions under the cortex. Next - the branch turns yellow, then the whole plant. The roots turn brown, rot, grind. Large brown, blurry spots appear on the root neck and base of the stems, the wood rots. Dense dark gray sporulation of the fungus develops on the spots. Affected plants wither and wither. The infection persists in the soil and on plant debris.

Bacterial root cancer

The causative agent is the bacterium Agrobacterium tumefaciens, a gram-negative, obligate aerobic rod-shaped soil bacterium of the genus Agrobacterium. It is 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. Chemoorganeterotroph, obligate aerob.

Symptoms: large, rounded growths form on the roots and root neck, which gradually darken and become hard. Plants slow down growth and bloom weakly. Over time, growths and the root neck rot and the plant dies. The infection persists in plant debris, often spreading with planting material.

Control measures: Spray slightly affected plants regularly with a solution of Bordeaux fluid or its substitutes; heavily affected plants burn along with the roots.

Gray rhododendron rot

Symptoms: on leaves, stems, buds and petals, there are blurry brown spots without bordering, the surface of which quickly dries and crackes. In wet weather, all necrotic parts are covered with a fluffy smoky-gray sporulation coating. Over time, rounded brown sclerotia form in the drying mycelium.

Control measures: pruning of affected parts of plants. In industrial cultivation - preventive spraying of plants and watering of the root zone with 0.2% solution of baseazole.

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 the fungi of the following genera: Rhyzoctonia, Pythium and Botrytis. Affected seedlings fall to one side and die, white fungal hyphae or brownish mold are visible on the leaves. Pale, cobweb-like filaments appear on the surface of the substrate. Usually, fungi develop if the substrate is fresh, not yet decomposed, or if the crops were watered with water infected with the fungus. Too much planting density, excessive humidity in greenhouses and insufficient air exchange increase the likelihood of a disease.

Control measures: seedlings starting 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 foundationazole powder. For prevention purposes, it is advisable to spray young seedlings and seedlings with a 0.2% suspension of foundationazole. To combat this disease, you can use captan and TMTD.

Rhododendron bud rot

Pathogen: Sporocybe azaleae fungus (syn .: Pycnosteanus azaleae), which is distributed by the cicada Graphocephala coccinea. The disease was first discovered on rhododendrons in the United States. The disease is characteristic of the largest rhododendrons (Rhododendron maximum L.) and Katevbinsky (Rhododendron catawbiense Michx.). Affected by this disease, the buds turn brown and die. A mycelium from buds can grow into branches and lead to their death.

Control measures: during the growing season, plants should be sprayed with copper-containing preparations regularly (after 2-3 weeks).

Rhododendron shoots die off

This disease is most susceptible to plants planted in complete shade.

The causative agent is Phytophtora cactorum Leb. Symptoms: in the affected plants, the apical buds do not bloom, they turn brown, and then completely die. The shoots also dry out first, and then die off. Adult leaves curl, brown and dry. Heavily affected plants die.

The causative agent is the mushroom Physalospora rhododendri. This mushroom also affects lilacs. Symptoms: in diseased plants, on some shoots, the leaves turn brown, dry, and then the entire shoot dies. The disease is noted in Latvia.

Control measures: affected leaves and shoots are burned. After flowering, rhododendrons are regularly sprayed with copper-containing drugs. Spraying is done every 10-14 days.

Root Rot of Rhododendron

The causative agent is Phytophtora cinnamoni Rands. This fungus most often damages the roots and base of the stem. Symptoms: on individual shoots or on the whole plant wither, and then all the leaves dry out for no apparent reason. The apical buds turn brown and die. On the cross sections of the shoots, it is evident 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 moistened 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 whole plant is burned. To prevent disease, soil acidity should be maintained that meets the requirements of the species or plant variety and the correct watering regimen should be observed.

Dry white rot of the root neck of the rhododendron

The causative agent is Armillaria mellea mushroom (real honey agarics).

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 neck. A plant affected by the fungus dies. Strongly growing rhododendrons with dry rot of the root neck do not get sick.

Control measures: The affected plants are dug up and burned. Plants near which the disease is detected should be transplanted so that the root neck is not covered by mulch (it must be dry).

Rhododendron wax disease, or bloating of rhododendron leaves

Symptoms: slight deformation and thickening of the leaves is observed. Large, rounded or oblong spots of red or red-brown color appear on them. On the surface of the necrosis, a dense waxy sporulation of sporulation develops. 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. When rhododendrons are affected by the fungus Exobasidium rhododendri, a change in the exchange of amino acids occurs.

Exobasidium vaccinii - the causative agent of a very common disease of lingonberry leaves, causes the formation of white pillow-like growths on young leaves of evergreen rhododendrons (Rhododendron maximum L., Rhododendron catawbiense Michx.) And deciduous rhododendrons in natural places of their growth.

Exobasidium vaccinii-uliginosi Bond., The causative agent of a very common disease of blueberry leaves, causes the formation of the so-called “witch's broom” in Caroline rhododendron. The leaves turn yellow-brown, the underside of them is covered with a powdery coating. After a year, the affected leaves die off. According to 1981 data in Latvia, this disease was not noted.

Measures against diseases caused by representatives of the genus Exobasidium: pruning of affected parts of plants, spring spraying a solution of Bordeaux fluid, its substitutes or camulus.

Exobasidium japonicum, affects the leaves and tops of shoots. Sick plants develop abnormally thick, large, pale green leaves, covered with chalk-white plaque. These leaves quickly wrinkle, mold and dry out. The fungus is less common on annual plants than on older ones. Susceptibility to this disease largely depends on the type and variety of rhododendrons. According to 1981 data in Latvia, this disease was not noted.

Rhododendron Pestalium Spotting

Pathogen: Pestalotiopsis sydowiana mushroom (syn .: Pestalotia macrotricha Kleb., Pestalotia rhododendri). Leaves and stems are affected. Small brown spots of irregular shape with a thin brown border appear on the leaves. Spots are often scattered around the edges of the leaf blade, which turns yellow and dries prematurely. Gray spots of sporulation of the fungus are formed on the spots. On stems, spots are large, depressed, elongated. The surface of the spots dries and brightens, numerous small gray pads of sporulation of the fungus are formed. Affected shoots gradually dry out.

Rhododendron Anthracnose Spotting

Pathogen: Gloeosporium rhododendri fungus. On the upper part of the leaves, regional necrosis appears in the form of brown spots of irregular shape. Leaves gradually dry. Sporulation forms on the surface of spots in the form of numerous rounded fruit bodies dark color. If the infection continues to develop, the stems are affected, which eventually dry out. This disease is widespread in Holland and England on young seedlings of rhododendron pontiac.

Control measures: pruning of affected parts of plants, spring spraying with a solution of Bordeaux fluid, its substitutes or camulus.

Septoria spotting of rhododendron, or azalea septoria, or leaf spotting

Pathogen: Septoria azaleae Voglino fungus. Symptoms are described by different authors with slight differences.

1. Small rounded reddish spots appear on the leaves, gradually whitening in the center. Over time, dotted black fruiting bodies of the wintering stage of the fungus form on the surface of the spots. Leaves turn yellow and gradually dry.

2. The disease is usually affected by greenhouse plants. 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 fall, they become dark brown in the middle, and sometimes even brownish-black. Initially, spots appear in the middle of the leaf blade, gradually increase and, reaching large veins, stop. The fungus grows into all leaf tissues, the leaves die off and fall prematurely, so that the plant becomes completely bare. As a result of leaf falling in plants, all physiological processes are disturbed, flower buds are not normally laid. On the spots you can see small, black, dot-like containers of spores - pycnidia immersed in leaf tissue.

Control measures: pruning of affected parts of plants, spring spraying with a solution of Bordeaux fluid, its substitutes or camulus. If the air is excessively humid, you should not spray plants with preparations containing copper, as this leads to burns of leaves and young shoots. Preparations containing copper are used only at normal humidity and a sufficiently high temperature. You can spray only those plants in which the leaves have fully grown and developed.

Rhodedendron phyllostic spotting

Mushroom Phyllosticta concentrica Sacc. (syn .: Phyllosticta maxima Ellis & Everh.). Symptoms are described by different authors with slight differences.

1. Large rounded spots with reddish bordering appear on the leaves.

2. Spots are blurry, irregular, dark brown or ash gray, with dark edges. Localized at the edges or at the ends of the leaves. Black balls - sporangia fall out of the spots. The vast majority of affected leaves die off, 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 spots of rounded shape with a thin brown border.

Subsequently, the affected areas brighten, crack and fall out. Black point bodies of the wintering stage form on necrotic tissue.

Control measures: pruning of affected parts of plants, spring spraying with a solution of Bordeaux fluid, 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. AT a greater degree the leaves of the lower tiers are affected. The causative agent is widespread in the United States, especially on the 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 subgenus Osmothamnus - Rhododendron parvifolium, Rhododendron adamsii, Rhododendron dauricum L., Rhododendron ferrugineum L., Rhododendron kotschyi, and others.

Symptoms: in the fall on the underside of the leaves of the affected plants appear yellow, red or brown dusty swelling - sporangia. Heavily infected plants drop leaves prematurely. In spring, dark red cushions are visible on the leaves - the winter form of the mushroom.

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

Mosaic of Rhododendron

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

1. Small mosaic yellow spots and swellings appear on the leaves. Plants lag behind in growth and bloom weakly. The leaves turn yellow, but they remain areas in the form of alternating green and brown spots.

2. The leaves become rough, calloused and ugly. Corns are usually of normal green color, and the rest of the leaf turns greenish yellow. The bright part of the leaf blade is much thinner than in places where there are corns. Venation on calluses less noticeable.

Control measures: pruning leaves and branches, culling severely affected plants. The mosaic virus is carried by aphids, bedbugs and other insects.

Pests

Furrowed weevil (Otiorrhynchus sulcatus)

The adults are black, 8-10 mm long, not flying, with an elongated head stretched forward, at the end of which are the mouth organs. Elytra with deep pointed beards. Larvae are white, with a brown head, legless, curved, up to 12 mm long. 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 from 100 to 1000 eggs for their lives. Eggs are laid in small groups in the soil, where in 2-3 weeks larvae emerge from them and immediately begin to feed.

The nature of the defeat. At the edges of the leaves, characteristic corroded areas are observed. If damage is caused by larvae living in the soil, then the plant suddenly withers and dies.

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

Common spider mite (Tetranychus urticae)

Almost imperceptible, since its dimensions are 0.25-0.43 mm. At the larval stage of development, they are transparent, painted from light green to greenish brown with two distinct, large dark spots on the sides, which are formed by transparent blind bags of the middle intestine. From late summer to next spring, wintering females are colored from orange red to bright red. Unlike the six-legged first phase of the larvae, all adult ticks have 8 legs.

Damaged leaves turn yellow, deformed, turn brown and dry. During the growing season, up to 10 tick generations develop.

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

Acacia false shield

False shield acacia, or acacia scale, or hazel scale, or acacia worm (Parthenolecanium corni). Currently widespread. In the north, the range reaches Leningrad region. Pronounced sexual dimorphism. The body length of females is from 3 to 6.5 mm, width - 2.4 mm, height - 4 mm. There are no wings. The body is oval or wide oval, sometimes almost round, segmentation is absent. The shape, color and body size of the female vary depending on the type of feed plant. Young females with a tender, not very convex body, more oval in shape, light brown, with two black stripes and longitudinal black stripes extending from them. The dead are shiny, painted dark yellow, brown or dark brown. The body length of the males is 1.4-1.6 mm. The body is thin, elongated, with distinct segmentation into the chest, head and abdomen. Head of black color with three pairs of simple eyes. The abdomen and chest are red-brown, covered with a white waxy coating. Ten-segmented antennae and legs yellow. At the apex of the abdomen there are two tail filaments, 2–2.5 times longer than the body size. Larvae of the first age (tramp) with a length of 0.36 mm. The body is flat, elongated-oval, slightly narrowed to the posterior end. The color of the integument is cream or light yellow. At the second age, 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 pseudomodules is more often parthenogenetic, in the south sometimes bisexual. Larvae overwinter. In the northern part of the range, one generation develops per year, in the southern - two or three.

Insects pierce the bark of the plant with their proboscis and attach themselves 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, phytoverm, fufanon, karbofos, actellik.

Thrips tobacco (Thrips tabaci)

In Russia it is ubiquitous. Multi-species, damages about 400 species of plants in open and closed ground. The color of the female is variable, from light yellow to brown, more often more or less yellow, sometimes very dark. 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. Larva, 0.8-0.9 mm long, very mobile, two pairs of wings are surrounded by fringe of cilia, body color is variable - from yellow to almost black. Adults winter in the upper soil layer at a depth of 5-7 cm or in plant debris. They leave after wintering in the first half of April, feed and lay eggs first on weeds. One female lays about 100 eggs in the leaf tissue during her life (20-25 days), and their fertility largely depends on the type of fodder plant. Then the females fly to the cultural vegetation. It is a distributor of viruses. On rhododendrons, buds are damaged, which, when severely damaged, do not open, turn yellow and fall off.

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

Rhododendron mite or American Azalea bug (Stephanitis rhododendri)

It is found on the Ketevba rhododendron, Smirnov, Ungern rhododendron and other species and varieties in which there is felt pubescence on the underside of the leaf.

The size of the imago is about 3.6 mm. The wings are colorless, mesh with a sheen. The larvae of the bug reach a length of 0.7 to 2.2 mm, they do not fly, are distinguished by a yellow color with dark spots and hairy outgrowths on the sides.

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

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

Greenhouse or greenhouse whitefly (Trialeurodes vaporariorum)

Type of tropical origin. It is brought on all continents. It is noted near greenhouse plants, where the pest persists 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 imago 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 observed on large-leaved rhododendrons (Caucasian, Pontic). To combat the greenhouse whitefly, pesticides are selected that are not dangerous for 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)

AT GBS are found mainly on large-leaf rhododendrons: Caucasian, Pontic and Ketevbinsky and their varieties and hybrids. The most effective is spraying the leaves from below with nicotine and oil emulsion in spring and autumn. For prophylactic purposes, adult flies are sprayed with nicotine dust during the summer. Affected leaves should be torn off and burned.

Gastropods

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

Crows

In GBS in early spring facts of chewing of the rhododendron kidneys by crows are noted, most often the Smirnov rhododendron suffers.