How to control gray mold in poinsettias? Try these five methods
In a previous article, we introduced the care methods for poinsettias. In fact, poinsettias are quite prone to gray mold. Gray mold not only affects the appearance of poinsettias, but in severe cases, the diseased spots on poinsettias become dry and shriveled, completely losing their ornamental value. Here, we introduce several methods for controlling gray mold in poinsettias.
Poinsettia
1. Select excellent disease-resistant varieties.
2. Strengthen cultivation management, apply more phosphorus and potassium fertilizer to promote robust plant growth and enhance disease resistance; pay attention to shaping and pruning the plant, promptly remove fallen leaves from the pot, and improve ventilation and light penetration.
3. Regulate the micro-environment to suppress the occurrence and spread of pests and diseases. Generally, increasing temperature and reducing humidity are used to control the development and infection of pathogens. Maintain air circulation, reduce environmental humidity, do not place plants too densely, and for household potted plants, they can be moved to a balcony. After disease occurs, control watering to avoid water accumulation on leaf surfaces. Keep the temperature above 16°C as much as possible, especially during the flowering period.
4. Once diseased leaves or branches are found, remove them promptly and burn them in a centralized manner to cut off the source of infection.
5. Chemical control: In spring, spray 1:1:100 Bordeaux mixture two to three times to protect new leaves and flower buds and prevent disease. During the disease period, spray 65% zineb 500 times dilution, 50% thiophanate-methyl wettable powder 800 to 1000 times dilution, or 75% chlorothalonil wettable powder 600 times dilution. Other agents include iprodione, Yili, Huimeisuke, Shijiale, etc. Apply thoroughly, use repeatedly, and alternate several agents. In winter, if the room is well sealed, fumigants can also be used with good results.
Methods for controlling gray mold in poinsettias
Gray mold is the most common disease in poinsettia cultivation. It can appear throughout the entire growing season in greenhouses, and all parts of the plant can be infected. Because it mainly occurs in winter, which coincides with the poinsettia flowering season, once rainy and humid weather occurs, it often gets out of control.
Gray mold mainly damages poinsettia inflorescences, bracts, flower branches, and tender shoots. Young plants sometimes become infected on the surface of the growing medium. Under higher temperature conditions, gray fuzzy mold forms on this rotting tissue. Black rot appears on mature branches and stems, and this black rot develops around the stem, causing the leaves above the damaged area to wilt. When bracts are infected, red bracts turn light purple after infection.
I. Disease pattern Generally, water-soaked lesions first appear on the inflorescence, then gradually expand, and the diseased tissue turns brown to black and rots. In humid environments, a layer of gray to grayish-brown mold forms on the surface at later stages, and the lesions are covered with a layer of pathogen conidia. The pathogen continues to spread to the bracts, initially producing water-soaked discolored spots, which later gradually expand into irregular shapes. After the floral organs are infected, they also turn brown, rot, and fall off. The pathogen then spreads to the branches, producing yellowish-brown to brown lesions on the branches. In later stages, the lesions are clearly sunken and dark brown, and in severe cases, the lesions become dry and shriveled, completely losing ornamental value.
The pathogen survives on dead plant tissue or other organic matter. It is prone to growth and development on succulent, aging, and wounded tissue. It has a wide host range and is prone to occur under low temperature and high humidity (relative humidity 90% to 100%). If the greenhouse is too humid, cold, and lacks light, the pathogen produces large numbers of spores in the air within one or two days and begins to infect plant tissue. Under humid conditions, the diseased parts all form grayish-brown mold layers. This disease mostly occurs in cold, humid weather. The optimum development temperature for the pathogen is around 20°C. When air humidity is high, the disease is severe. The pathogen can spread through wind and rain, and spreads especially rapidly after rain when the sky clears.
Symptoms and control methods of gray mold in poinsettias
Symptoms and control methods of gray mold in poinsettias
Symptoms and damage:This disease occurs commonly. When severe, it causes flower blight and plant wilt, causing loss of commercial value. This disease also damages other poinsettias.
This disease mainly damages flowers, leaves, and tender shoots. The disease first appears on wounded, residual, and necrotic tissue of leaves, stems, and flowers. On leaves, brown water-soaked patches appear at the leaf margins and spread inward; under high humidity, they become brown wet rot. On floral organs, water-soaked brown patches appear on the petals and spread inward; under suitable conditions, the flowers rot and scorch. On tender shoots, elongated water-soaked brown patches appear, and in severe cases, the branches break. Under high humidity conditions, gray mold layers can grow on all diseased parts.
Pathogen: This disease is a fungal disease caused by Botrytis cinerea.
Disease characteristics:The pathogen overwinters on diseased plant debris; it spreads through airflow, wind, and rain.
This disease is prone to occur under conditions of cool temperatures, high humidity, and many wounds. It is generally severe in early spring or late autumn. Double-flowered varieties are more severely affected.
Control methods:
1) Cultivation techniques for disease prevention: Planting density should be appropriate to facilitate ventilation and light penetration and reduce humidity; promptly remove old fallen flowers and dead leaves to reduce the source of inoculum; controlling greenhouse humidity is a key measure for disease prevention, and humidity below 80% can suppress the occurrence of this disease. Drain promptly after rain in the field.
2) Chemical protection: Do forecasting work well and prevent promptly. Forecasting work is mainly based on the temperature and humidity of the weather.
Therapeutic fungicides: 50% procymidone, 16% iprodione·prochloraz, Kaize
Protective fungicides: iprodione, Kebo