What are the common control methods for chrysanthemum diseases?

Chrysanthemum diseases mainly come from flower soil, old flower pots, cuttings, seeds and seedlings, so before planting the soil should be exposed to the sun, or the soil and flower pots should be disinfected with a 1:80 formalin solution, or a certain amount of mancozeb should be mixed into the soil. Before cutting or transplanting, spray once with 800 to 1000 times diluted carbendazim. The following introduces the control methods for several common diseases after chrysanthemum seedlings are established.

Spot disease, also called leaf spot disease, is mainly spread through soil. In the early stage of infection, the leaves of the affected plant show yellow and dark brown round or oval spots, then small black dots appear in the center of the lesions, the basal leaves turn yellow and dry up, and the upper leaves and flower buds gradually become affected, affecting flowering. This disease occurs easily during consecutive rainy days, damp waterlogging, and large day-night temperature differences. Control methods include: rational crop rotation, and selecting virus-free plants for grafting; avoid applying too much nitrogen fertilizer, pay attention to drainage and aeration, avoid muddy water touching the leaf surface when watering, and promptly remove diseased leaves; use 80% wettable zineb 500 times solution or 1% Bordeaux mixture, applying 2 to 3 times per month, and once a week when the disease occurs; when transplanting seedlings, disinfect with potassium permanganate or formalin.

Powdery mildew carries bacteria in the dormant buds of the host, mainly on the front and back of the middle and upper leaves. In the early stage there are yellow spots, later a powdery frost-like substance, which gradually expands and joins together into large white powdery patches; in severe cases the leaves and tender shoots curl and deform, and may even wilt and die. This disease mostly occurs from August to October. Control methods include: clearing overwintering weeds, watering and applying nitrogen fertilizer reasonably to prevent sudden excessive growth; pruning branches and removing leaves to ensure ventilation and light penetration; using carbendazim for prevention, or spraying with 1000 times diluted thiram solution, or spraying with 0.3 to 0.5 degree lime-sulfur mixture; when the number is small, spraying with edible vinegar also has a certain effect.

Rust disease comes from seeds and weeds, and mainly harms chrysanthemum leaves and stems, with leaves suffering more severely. The lesions are grayish-white raised small spots, then the lesions crack through the leaf surface from the back of the leaf, with dry yellow fungal powder that can spread with airflow, and later the spots turn black. This disease occurs easily when there is much rain and high humidity. Control methods include: rational fertilization, appropriately increasing phosphorus and potassium fertilizer to improve the plant's disease resistance; potted chrysanthemums should have their drainage holes frequently cleared to strictly prevent water accumulation in the pot; remove weeds and promptly remove diseased leaves to ensure ventilation and light penetration; in rainy seasons, applying 65% zineb 500 times solution or 0.3 to 0.5 degree Baume lime-sulfur mixture can effectively control the spread of this disease, and thiophanate and carbendazim can also be used for prevention.

Root rot causes the root system to rot, appearing as dry rot or tangled hemp-like strands, with leaves turning yellow and wilting. It mostly occurs before and after flowering. Control methods include: appropriate irrigation, draining when waterlogged and irrigating when dry, and loosening the soil; pouring garlic water on the roots of diseased plants and applying quick-acting fertilizer has a certain effect.

Viral disease is mainly transmitted by aphids and green plant bugs. The young parts of the plant shrink and deform, showing “willow-leaf heads” and “yellow mosaic leaves”, which are very difficult to cure. Control methods include: selecting branches and seeds from disease-free plants, and using virus-free root tip and stem tip tissue to culture plantlets; removing “willow-leaf heads” early, using side branches for flowering, and controlling aphids.