Dahlia Pest and Disease Control
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Dahlia, also known as dahlia, Chinese peony, tuberous peony, sweet potato flower, Dali flower, passion fruit and chrysanthemum, is a perennial herbaceous plant in the Compositae family. Dahlia has colorful colors, with red, yellow, orange, purple, white and other colors, very attractive. Dahlias adapt to different climates and soil conditions across the country, have few pests and diseases, are easy to manage, and are the best for breeding. However, they are often affected by the following pests and diseases:
Dahlia Flower Leaf Disease
SYMPTOMS After the leaves are damaged, spots occur, brown and green along both sides of the leaf veins, and semi-transparent "clear veins" appear. Light yellow patches appear on the diseased leaves, the leaves become wrinkled, growth stagnates, and the plants become stunted. Plants grown from virus-infected roots rarely reach normal height.
PATHOGEN Dahlia Mosaic Virus (Dahlia Mosaic Virus), the virus particles are icosahedral, spread by aphids and leafhoppers, and can also be transmitted through grafting. This virus can also infect zinnias, marigolds, coreopsis, and petunias. In addition, cucumber mosaic virus (CMV), tobacco necrosis virus (TSV) and tomato spotted wilt virus (TSWV) can also cause dahlia to have viral diseases.
Control Methods
1. Diseased tuberous roots or germinated buds cannot be used as breeding materials.
2. Observe carefully and remove and burn diseased plants in time.
3. Spray 50% malathion 1000 times dilution or 40% Rogor 1500 times dilution, 25% carbaryl 800 times dilution to control virus-carrying pests.
Dahlia Gray Mold
SYMPTOMS The flower is prone to be invaded and turn brown, followed by soft rot, severe flower buds cannot open, and gray mold-like substances (pathogenic fungal fruiting bodies) appear. Therefore, gray mold is also called flower rot. On the leaves, large round to irregular large spots occur, the spots often occur at the leaf margin, light brown to brown, sometimes showing ring patterns, water-soaked, and gray mold grows when the humidity is high. The stem lesions are brown, sometimes with ring patterns, water-soaked, and gray mold grows when the humidity is high. The stem lesions are brown and irregular in shape, and the stem softens and collapses in severe cases, which is a major disease of dahlia.
PATHOGEN Gray Botrytis [Botrytis cinerea Pers.], belonging to the subphylum of Deuteromycetes. Conidiophores are slender and branched, sometimes dichotomous near the top, with conidia on short stipes, ovoid, usually producing black, irregular sclerotia.
INFECTION PATHWAY The pathogen mainly overwinters with sclerotia in diseased plant residues. Under suitable conditions, sclerotia grow into conidiophores, produce conidia, and cause secondary infections. Conidiophores produced on diseased spots produce conidia, causing primary infections. Conidia produced on diseased spots are transmitted by wind and rain, causing secondary infections. It is more harmful in rainy seasons and has a wide range of hosts.
Control Methods
1. Since Botrytis cinerea has parasitic and saprophytic properties, diseased flowers and leaves should be cut off and buried deeply.
2. Implement crop rotation or use new soil free of pathogens.
3. Strengthen cultivation management, avoid planting too dense to facilitate ventilation and light transmission. Do not pour water on the plants when watering to prevent the spread of pathogens by water droplets. Pay attention to drain accumulated water after the rain.
Dahlia Powdery Mildew
SYMPTOMS Dahlia powdery mildew damages leaves, tender buds, flower stems, and flower buds. A layer of white powdery substance, that is, conidial spores, appears on the surface of the diseased part. Several small spots on the leaves can connect into large spots. After being damaged, the plants become stunted, the leaf surface becomes uneven or curled, and the tender shoots develop abnormally. Diseased flower buds cannot bloom or only open abnormal flowers. In severe cases, the leaves can dry out, and even the entire plant can die. In autumn and winter, gray mycelium and a few small black spots appear. The small black spots are closed ascocarps.
PATHOGEN Erysiphe polygoni DC., class Ascomycetes, order Erysiphales. The hyphae grow on both sides of the leaves.
INFECTION PATHWAY The hyphae overwinter. When the temperature rises to 18℃-25℃ the following year, the hyphae begin to grow and produce a large number of conidial spores. When the environmental conditions are suitable, hyphae grow out, produce haustoria, and absorb nutrients from the tissue. High temperature and humidity are conducive to the occurrence of the disease.
Control Methods
1. Cut off and destroy diseased plants.
2. During the onset season, spray 15% wettable powder of myclobutanil 1500 times dilution, or 70% wettable powder of thiophanate-methyl 700 times dilution, or 50% wettable powder of carbendazim 500 times dilution to control.
Dahlia Bacterial Wilt
SYMPTOMS After the roots and tubers are infected by the pathogen, they turn brown and rot, and the above-ground leaves wither, droop, and die. The xylem turns yellow-brown when the diseased roots and stems are cut transversely, and bacterial pus oozes out.
PATHOGEN Pseudomonas solanacearum E.F.smith.
INFECTION PATHWAY The pathogen can survive in diseased plant residues or soil, and breed in large numbers under high temperature and high humidity conditions, and invade from wounds when encountering hosts. It is most likely to occur during the transplanting season of high temperature and heavy rain, if the soil or fertilizer contains bacterial wilt pathogens.
Control Methods
1. Cultivate disease-free seedlings and avoid selecting breeding materials in diseased areas.
2. Do not plant in soil where the disease has occurred. Strengthen seedling management to avoid wounds. Watering should be appropriate, and prevent irrigation water from flowing to healthy plants from diseased areas. Diseased plants should be pulled out and burned.
3. Improve the soil: apply 100-150 kg of quicklime per mu, apply enough decomposed manure, turn the soil, make the soil fertile, loose and slightly alkaline to inhibit the breeding of pathogens, and enhance the resistance of plants.
4. Chemical control:
1) Remove and burn diseased plants in time, pour 2% formaldehyde solution or 20% lime water for disinfection into each hole, or sprinkle lime powder.
2) At the beginning of the onset, spray 4000 times dilution of streptomycin, or 30% wettable powder of DT (copper ethylene diamine tetraacetate) 500 times dilution, 70% wettable powder of DTM 500-600 times dilution, or 77% wettable powder of copper oxychloride 500 times dilution. Spray once every 7-10 days, for 3-4 consecutive times.
3) The above-mentioned agents can also be used for root irrigation, with 0.5 kg of liquid per plant, combined with spraying, once every 7-8 days, for 3-4 consecutive times.
Dahlia Dark Stripe Disease
SYMPTOMS Circular or semicircular dark green ring-shaped lesions occur on the leaf surface and leaf margin. The lesions later turn dark brown, with gray green in the center. Black spots appear on the surface of the lesions. When the disease is severe, the leaves wither and droop.
PATHOGEN Phyllosticta dahliaecola Brunaud. is called Dahlia Leaf Spot Fungus, belonging to the subphylum of Deuteromycetes.
INFECTION PATHWAY The conidiomata overwinter with the diseased residues on the ground. The following year, conidia germinate and produce germ tubes to infect the host. Then, conidiomata and conidia are produced on the diseased parts, and spread and spread through wind and rain to cause secondary infections. The temperature of 21℃ is conducive to its occurrence or prevalence.
Control Methods
1. After harvest, thoroughly remove the diseased residues and burn them or turn the land deeply to reduce the initial source of infection.
2. At the beginning of the onset, spray 75% wettable powder of chlorothalonil 500 times dilution, 40% wettable suspension of sulfur 500-600 times dilution, 50% wettable suspension of mixed sulfur 500 times dilution, 1:1:200 Bordeaux mixture, 77% wettable powder of copper oxychloride 500 times dilution, 50% wettable powder of copper ethylene diamine tetraacetate (DT) 400-500 times dilution, once every 10 days or so, for 1 or 2 times of prevention and treatment.
Dahlia Flower Blight
SYMPTOMS The corolla is affected. The top part of the petals turns light brown and has circular or nearly circular spots. Then, the spots spread on the petals, the petals wither from the affected area, gradually turn brown and die. The outer corolla develops inward, leading to the decay of the petals and drooping.
ONSET CONDITIONS The pathogen can grow at 5-25℃, and 20-25℃ is the most suitable for growth. Flower blight occurs more severely in autumn with heavy rain and large double flowers.
PATHOGEN Itersonilia perplexans Derx belongs to the subphylum of Deuteromycetes, order Hyphomycetes, genus Helminthosporium, flower blight Helminthosporium. The hyphae of the pathogen easily form clamp connections, and some cells of the hyphae form small stipes with asymmetrical colorless blastospores, which can be strongly emitted. The pathogen surviving on the diseased flower residues is the source of infection.
Control Methods Refer to the control methods for chrysanthemum black spot.
Dahlia White Silk Disease
SYMPTOMS Wet rot occurs at the base of the plant, initially brown-black, and then white silk-like mycelium appears, and sclerotia the size of rapeseed are formed.
PATHOGEN Sclerotium rolfsii Sacc., belonging to the subphylum of Deuteromycetes. The hyphae are white, loose or gathered into linear and tightly attached to the substrate to form sclerotia, which are small (diameter 0.5-1.0 mm) and neat, initially white, then turn yellow-brown, and the interior is grayish white.
INFECTION PATHWAY The pathogen survives for many years in the soil and plant residues with hyphae and sclerotia, and invades the host from the root neck. The pathogen has a wide range of hosts, and iris, orchids, peonies, pyrethrum, peaches, pears, etc. are also often affected, causing damping-off, root rot, basal rot, and fruit rot.
Control Methods
1. Pull out the diseased plants, burn the sclerotia in the soil, sprinkle lime in the diseased holes, or fill in the soil mixed with 70% pentachloronitrobenzene powder 100 times to disinfect.
2. At the beginning of the onset, pour 500 times dilution of 50% wettable powder of thiophanate-methyl or 500 times dilution of 50% wettable powder of carbendazim around the base of the diseased plant stem, and pour again after 7-10 days.
Willow Bat Moth
Willow Bat Moth, also known as Oriental Bat Moth, belongs to the order Lepidoptera and the family Bat Moth.
DISTRIBUTION AND DAMAGE Distributed in Heilongjiang, Jilin, Liaoning and the former Soviet Union, Japan and other places. It damages many kinds of flowering trees.
DAMAGE SYMPTOMS The larvae bore into branches and trunks, and the entrance of the burrow is often sunken and ring-shaped, and the wood shavings are filled with silk web to form a wood shavings bag.
MORPHOLOGICAL CHARACTERISTICS Adult body length 35-44 mm, wing span 66-70 mm. The body is powdery brown to brownish red. Antennae are short and linear. The front wing has a ring-shaped pattern on the front edge, a dark green triangular pattern in the center, and 2 wide brown oblique bands on the outer edge of the pattern. The hind wings are narrow and the abdomen is large. Eggs are spherical, 0.6-0.7 mm in diameter, black, slightly glossy. Larvae are dark brown, with dirty white chest and abdomen, cylindrical, with yellowish brown tubercles, and the mature larvae are 44-57 mm long.
LIFE HISTORY AND HABITS In Liaoning, most have one generation per year, and a few have two generations per year. They overwinter with eggs on the ground or with larvae at the base. They begin to hatch in mid-May the following spring. They turn to fruit trees, forest trees, or weeds in early June to feed on stems. They begin to pupate in early August and end in late September. They become adults in late August. The peak of eclosion is in mid-September, and they are seen until mid-October. Adults mate and lay eggs immediately after eclosion. They overwinter with eggs. Some larvae hatched later, or larvae that develop slowly due to other disturbances overwinter as larvae. They begin to become adults in July the following year, and lay eggs immediately after becoming adults, completing one generation in two years. Most adults eclose between 16-18 o'clock. During the day, adults often hang motionless on tree trunks, lower wood, or weeds, and only begin to fly, mate, and lay eggs after sunset. Adults have a photophobic property. After mating, they lay eggs immediately, and there is no fixed place for laying eggs. Most of them are laid one by one with the tremor of the two wings, and some lay eggs while mating; most lay eggs without mating. The number of eggs laid by female insects varies from hundreds to thousands.
Control Methods
1. Cut off seedlings and branches with wood shavings bags.
2. Chemical control: from late May to early June, when the young larvae are active on the ground, spray 50% parathion 1000 times dilution on the ground. When the middle-aged larvae enter the trunk, drip 10 times dilution of 50% DDVP into the worm hole.
Short-horned Grasshopper
Grasshoppers, commonly known as grasshoppers, are widely distributed and damage flowers such as Impatiens, Celosia, Salvia splendens, Viola tricolor, Snapdragon, Amaranthus, Marigold, Zinnia, Daisies, Chrysanthemums, Echinacea, Roses, Jasmine, Hibiscus, Dahlias, Gardenias, etc.
DAMAGE SYMPTOMS Young nymphs like to gather and feed on leaves, causing the damaged leaves to show a net-like appearance. After a while, they scatter to feed, causing leaf notches and holes. In severe cases, only the main veins are left on the entire leaf.
MORPHOLOGICAL CHARACTERISTICS Adult body length 21-31 mm, light green to brown and light yellow in color. The head protrudes forward. The hind legs are developed for jumping. The forewings are green. The base of the hind wings is red and the tip is green. Eggs have yellowish brown secretions on the outside of the egg mass. Single eggs are milky white and elliptical. The nymphs are initially light green, dotted with white spots, resembling adults, wingless, only with wing buds. Life history and habits: The insect occurs twice a year in the Yangtze River Basin and other regions. They overwinter with eggs in the soil. The eggs hatch in May and June the following year. In early July, the first generation of adults begin to lay eggs. The peak of egg laying is in mid- to late July. The second generation of nymphs begin to hatch from late July, and the peak of hatching is in early and mid-August. From mid- to late September to early November, the second generation of adults begin to lay eggs, and the peak of egg laying is from late October to early November.
Control Methods
1. When young nymphs gather and damage, they can be manually caught and killed.
2. Spray 50% fenvalerate emulsion 1000 times dilution, or 25% imidacloprid 1000 times dilution.
Here is a comprehensive introduction to the prevention and control of Dahlia pests and diseases, hoping to bring some knowledge about green plants to green plant lovers.