This summer of 2011 cannot be called favorable for dahlias. Due to the prolonged cold in spring and early summer in the Moscow region, plants developed slowly, and after that unpleasant signs appeared - yellowing of foliage and spotting. Assessment of the condition of plants must be approached very carefully. Sometimes yellowness on the lower leaves can be caused by physiological reasons - lack of nutrition, including in the case of improper soil acidity (it should be slightly acidic, alkalization slows down the absorption of iron and some trace elements, which leads to yellowing of the leaves, on acidic soils the plants also look oppressed).
However, the main problem of the season can be called an excess of moisture, formed due to weather conditions at the beginning of the growing season of plants, to which dahlias are very sensitive and react to it by the death of the suction roots, and sometimes by the decay of the root tubers themselves. As a result, the lower leaves turn yellow, giving nutrients to the growth of the tops. In this case, you need to help the plant in restoring the root system by watering under the root with Kornevin, Heterooxin or another rooting stimulant. Pay attention to regular feeding, the first of which is a complex mineral fertilizer with microelements, to make foliage (at a concentration of 5 g per 10 l of water). When root dressing, use fertilizers without nitrogen - after all, it is already the middle of summer, and it is impossible to overfeed plants with nitrogen so that the tubers are well stored in winter.
In addition to physiological reasons, dahlias can suffer from many serious diseases and pests.
Gray rot, or botrytis
Fungal disease, causative agent - Botrytiscinerea... Thickened and darkened plantings, excess nitrogen fertilizers, and prolonged heavy rainfall contribute to the development of the disease. Brown spots appear on the leaves, which gradually dry out and fall out. All parts of the plant are affected, the peduncles are bent, the buds do not open and dry out. At high humidity, they are covered with a gray bloom of sporulation. The disease most often develops in spring or autumn, when cold weather is replaced by warm, damp weather. The defeat of flowers in autumn begins with softening of tissues, the appearance of watery spots, then the flowers stick together into a shapeless brown mass. Deep necrosis is formed on the tubers, growing in breadth and in depth; during storage, the affected tubers rot. The infection persists in tubers in the form of mycelium and in plant debris in the form of hibernating fruiting bodies - sclerotia.
White rot, or sclerotinosis
Fungal disease, causative agent - Sclerotiniasclerotiorum... Signs of the disease are wilting of individual shoots, the formation of brown spots on the stems and white felt mycelium with black sclerotia.
Fusarium and verticillary withering
Fungal diseases caused by various pathogens - Fusariumoxysporum and Verticilliumdahliae, but accompanied by similar symptoms - rotting of tubers and root system, browning of the lower parts of the plant, wilting of tops and buds. The affected tissues are covered with a white-pink (with fusarium) or brown (with verticillium) bloom of sporulation. Tubers dry out and shrivel during storage. The infection persists in tubers and plant debris.
Measures to combat fungal diseases. There are no radical methods of treating all these diseases; preventive measures and the culling of diseased plants, and the use of healthy planting material are of primary importance. Affected plant parts and plant debris are destroyed. During winter storage of tubers, excessive moisture and condensation are not allowed.They prevent the development of fungal diseases on vegetative plants with a sunny location, good ventilation of the air, ensuring quick drying of the vegetative mass after rain. Withered flowers can be a source of infection, so their timely removal is necessary. In the case of massive development of the disease on plantings, after the elimination of diseased specimens, fungicides of systemic action are used - Fundazol, Oksikhom. They are also used for preventive treatments. Tubers before laying for storage are treated with 0.2% Maxim for 30 minutes. If necessary, repeat the treatment in spring, before germinating the tubers.
Wet Bacterial Rot Dahlia
Fungal disease, pathogens - Erwiniacarotovoraas well as the characteristic chrysanthemum Erwiniachrysanthemi... It is accompanied by wilting of individual shoots or the whole plant. The stems become soft to the touch, often crack along, at the break there is a visible brown mycelium in the tissues of the vessels. The tubers turn yellow and soften, they are affected by weeping rot, accompanied by an unpleasant odor.
Control measures. Destruction of diseased specimens. When digging in autumn, culling of diseased and damaged tubers. Prolonged exposure of tubers in water, too high humidity during winter storage, which can lead to mass death of planting material, can contribute to the spread of the disease.
Fungal disease, causative agent - Rhizoctoniasolani. Most often it affects cuttings and young shoots, it is expressed in thinning and browning of the bases of the stems. Long filaments of mycelium are often visible under the fallen leaves. Deeper planting contributes to the development of the disease.
Control measures. The use of biological fungicides - Fitosporin-M or a mixture of Alirin with Gamair (2 tablets per bucket of water) for spraying plants and soil surfaces in order to prevent disease. In the event of the appearance of diseased specimens, treatment of the bases of the stems with fungicides - Fundazol, Oksikhom.
Fungal disease, causative agent - Entylomadahliae. It causes the appearance of shapeless spots of yellow-green color, which later turn gray-brown, with a dark brown border. Poor ventilation of plants contributes to the disease. The least susceptible to disease are pompon dahlias.
Control measures. Destruction of diseased specimens and all plant debris. Improving ventilation conditions, if necessary, transplanting healthy specimens.
Ring spot, or spotted wilting
The onset of the disease is similar in symptoms to the previous one, but the causative agent is the tomato spotted wilt virus, which is carried by sucking insects, especially thrips. It begins with the appearance of uneven chlorosis spots on young foliage. Brown necrosis develops along the veins, which eventually fall out. Plants stunted, bloom poorly.
Other viral diseases They are expressed in mosaicism, yellowing of veins, discoloration or browning, deformations and asymmetry of leaf blades, slowing down of plant growth. Plants either do not bloom, or with dwarf growth, disproportionately large flowers develop. Pathogens are carried by aphids, thrips, whiteflies. Viral infections can also spread through tools when cutting flowers and gardening, through contaminated planting material.
Measures to combat viral diseases. There are no effective means of control; diseased plants must be destroyed. As preventive measures, it is recommended to use healthy planting material, disinfect the instrument when dividing, grafting, cutting (in alcohol or flame). Timely control of vectors, attraction of their natural enemies to the garden.
If you find diseases on your plants that require removal of the plants, disinfect the vacated area by sprinkling abundantly with garden lime, and do not plant dahlias on it in the coming years.
Aphid colonies are usually clearly visible to the naked eye. In the absence of pests, signs of damage are curliness and yellowing of foliage, the presence of sticky secretions of aphids - "honeydew". In addition to the fact that these sucking pests feed on plant juices, they can be carriers of fungal and viral diseases.
Control measures. Single colonies of aphids are cut off together with the leaves. With a large number of pests, plantings are treated with a solution of Green soap, or with insecticides - Aktara, Decis, Confidor, Fitoverm.
Chrysanthemum and strawberry nematodes are found on dahlias. Damage to the buds, petioles and leaf blades, on which first light and then dark dropping out necrotic spots appear. They overwinter in the buds of tubers. Root nematodes can also occur, the presence of which is detected by stunting and curvature of the stems.
Control measures. Affected plants are removed with a large clod of earth and destroyed. Plants susceptible to nematode infection are not planted in their place. Preventive measures are of great importance in the fight against the pest, for example, spilling the soil before planting with Ekogel, which strengthens the cell walls of plants due to the chitosan it contains. Some protection is provided by planting next to Tagetes (marigolds), which scare away the nematode.
Herbivorous bugs (Lygussp.)
Eating on leaf blades leads to disruption of the flow of nutrients, in places of feeding they leave yellow, later brown spots on the leaf blades. In the process of further growth, leaf tissue shrinks and tears with the formation of irregular holes.
Control measures. With a small degree of damage to plants, treatment with a Green Soap solution is sufficient. In case of mass, chemical means of control are used, for example, Iskra-M, Mospilan. Processing is carried out in the early morning, when the bugs are still inactive.
This known pest of cabbage crops is the culprit for the appearance of uneven holes in the leaves. Butterflies fly out of pupae that have wintered in the ground in June-July. Eggs are laid on the underside of the foliage, from which green caterpillars emerge, reaching 5 cm in length in adulthood. Caterpillars gnaw leaves, and then go into the soil and end their development cycle, pupated for the winter.
Butterflies fly at night in May-June, at night. They themselves feed on nectar, but lay a huge number of eggs. The caterpillars emerging from them gnaw the roots at the surface of the earth, near the root collar, causing the plants to wilt.
Track control measures. Single tracks are easy to assemble by hand. With a massive appearance, it is preferable to use environmentally friendly biological agents - Lepidocide, Bitoxibacillin. From chemical preparations, insecticides Iskra-M, Fufanon can be used.
Slugs (Deroceras leave anddr.)
Gastropods, active mainly at night, in wet weather and in the shade. They eat out the grooves in the juicy leaves of the dahlia, then gnaw through the leaves, they can destroy the leaf blades entirely.
Control measures. Mechanical collection of individual individuals, laying out traps between plantings - wet boards, rags, potato halves. You can also use wood ash (effective until it gets wet), superphosphate, red ground pepper, which irritate the soles of the shellfish in the aisles. Similarly, metaldehyde preparations (for example, Thunderstorm) are scattered, which destroy the pest.
Bronzovka furry, or deer(Tropinota hirta)
Quite large (more than 1 cm) black beetle, covered with thick gray hairs and small white spots along the elytra. Eats out petals, stamens and pistils of flowers. Years takes place from May to August. Females lay eggs in rich humus soils, where white, brown-headed larvae hatch, feeding on plant debris and plant roots.
Control measures. The number of the pest is usually small, therefore, it is possible to cope with it by mechanical collection of beetles, as well as larvae during loosening of the soil.
Greenhouse whitefly (Trialeurodesvaporariorum)
Small white butterflies of about 1 mm in length, previously harming only in greenhouses at the stage of growing dahlia planting material, are now rarely found on open ground plants. They hide on the underside of the leaf and lay eggs there. The larvae that hatch from the eggs feed on the leaves, causing the appearance of chlorotic spots, and form cocoons - puparia, where new individuals of butterflies develop.
Control measures. Spraying plants with insecticides - Aktara, Iskra, Mospilan.
Western flower thrips(Franciniellaoccidentalis)
Sucking pest 1-1.5 cm long, dark brown in color, with yellowish wings. Dangerous to dahlias in greenhouses. It reproduces in the leaves and in the middle of the flower, near the stamens. It causes deformations of the growth point, the appearance of whitish spots on the leaves and the browning of the tips of flower petals. Black excrement may be found on the underside of the leaves. In case of severe damage, the plants dry out.
Control measures. Fighting thrips is very difficult. Blue traps are a preventive measure in the greenhouse. You can make them yourself by smearing the blue cardboard boxes with Alt glue. The most affected plants are destroyed, planting for the purpose of prevention and control of the pest is treated repeatedly with insecticides - Aktara, Aktellik, Fitoverm, Fufanon, alternating preparations during the season.
For self-diagnosis, you can use our Catalog of diseases and pests.
Compliance with the rules of agricultural technology, timely feeding is important for good plant growth - read the article How to grow dahlias.