Dahlia disease prevention and control methods

Dahlia mosaic disease

symptom

  When the leaves are infected, spots appear, the veins on both sides turn brown-green, and translucent "clear veins" appear. Light yellow spots appear on the diseased leaves, the leaves shrink, growth stagnates, and the plants become short. Plants grown from virus-infected roots rarely grow to a normal height.

Prevention and treatment methods

The tubers or sprouts of diseased plants cannot be used as breeding materials.

Observe carefully and remove and burn diseased plants in time.

Spray 1000 times diluted 50% malathion, 1500 times diluted 40% dimethoate, or 800 times diluted 25% carbaryl to prevent and control poisonous pests.

Botrytis cinerea

symptom

The flowers are easily infected and turn brown, and then soft rot occurs. In severe cases, the flower buds cannot open and gray mold ( fruiting bodies of the pathogen ) grows on them. Therefore, gray mold is also called blossom end rot. When the disease occurs on the leaves, large, nearly circular to irregular spots will occur. The spots often occur on the leaf edges, and are light brown to brown, sometimes showing ring patterns and water-soaked shapes. Gray mold will grow when the humidity is high. The lesions on the stems are brown, sometimes with ring patterns and water stains, and gray mold will grow when the humidity is high. The spots on the stems are brown and irregular in shape. In severe cases, the stems soften and break. This is the main disease of dahlias.

Prevention and treatment methods

Since Botrytis cinerea is both parasitic and saprophytic, diseased flowers and leaves must be cut off and buried deep in time.

Strengthen cultivation management and avoid over-dense planting to facilitate ventilation and light transmission. When watering, do not pour water on the plants to avoid splashing and spreading germs. Be careful to drain away stagnant water after rain.

Dahlia powdery mildew

symptom

  Powdery mildew of dahlias harms leaves, young shoots, pedicels and flower buds. A layer of white powdery substance, namely the spores, appears on the surface of the diseased part. Several small spots on the leaves can connect into a large spot. After being attacked, the plants become short, the leaves become uneven or curled, and the young shoots become deformed. When the flower buds are damaged, they cannot bloom or only produce deformed flowers. In severe cases, the leaves may dry up or even the entire plant may die. In autumn and winter, gray mycelium and a few small black spots are produced. The small black dots are the cleistothecia.

Prevention and treatment methods

Prune out and destroy diseased plants.

During the disease season, spray 1500 times diluted 15% triadimefon wettable powder, 700 times diluted 70% thiophanate-methyl wettable powder, or 500 times diluted 50% carbendazim wettable powder for prevention and control.

Dahlia bacterial wilt

symptom

  After being infected by the bacteria, the roots and tubers turn brown and rot, and the above-ground leaves wilt, droop and die. When the diseased roots and stems are cut cross-sectionally, the woody part is yellow-brown and bacterial pus is oozing out.

Prevention and treatment methods

Cultivate disease-free seedlings and avoid selecting stock from diseased areas.

Do not plant in soil that has had this disease. Strengthen management to avoid wounds. Watering should be appropriate and prevent irrigation water from diseased areas from flowing to healthy plants. If diseased plants are found, they should be removed and burned.

In the early stage of the disease, spray with 4000 times diluted streptomycin, 500 times diluted 30% DT ( copper succinate ) wettable powder, 500-600 times diluted 70% DTM wettable powder, or 500 times diluted 77% Coumadin wettable powder. Spray once every 7-10 days, for 3-4 times in a row.

Dahlia dark vein disease

symptom

Circular or semicircular dark green ring-like spots appear on the leaf surface and leaf edges. The spots later turn dark brown with gray-green in the center. There are small black spots scattered on the surface of the lesion. When the disease is serious, the leaves wilt and droop.

Prevention and treatment methods

After harvesting, diseased and damaged parts should be completely removed and burned in a centralized manner to reduce the source of initial infection.

At the early stage of the disease, spray 500 times diluted 75% thiophanate-methyl wettable powder, 500-600 times diluted 40 % polysulfur suspension, 500 times diluted 50% mixed sulfur suspension, 1 : 1 : 200 Bordeaux mixture, 500 times diluted 77% chlorothalonil wettable powder, 400-500 times diluted 50% copper succinate (DT) wettable powder, once every 10 days or so for prevention and control 1 or 2 times.

Dahlia flower blight

symptom

When the disease occurs, the top part of the petals turns light brown, and circular or nearly circular spots appear, which then spread to the petals. The petals wither from the diseased area, gradually turn brown and die. The disease of the outer corolla spreads to the inner corolla, causing the petals to rot and droop.

Dahlia Sclerotium

symptom

Wet rot occurs at the base of the plant, which is initially brown-black, and later produces white silky mycelium and forms sclerotia the size of rapeseed.

Prevention and treatment methods

Remove diseased plants, burn the sclerotia in the soil, spread lime on the diseased holes, or fill them with poisoned soil made of 70% pentachloronitrobenzene powder and 100 times the amount of new soil for disinfection.

In the early stage of the disease, water the base of the stem of the diseased plant with 500 times diluted 50% thiophanate-methyl wettable powder or 500 times diluted 50% carbendazim wettable powder, and water again after 7-10 days.