Symptoms of gray mold in flowers and integrated control, and fertilization techniques for edible fungi
Gray mold in flowers is one of the most common diseases in production, occurring frequently during the growing season of flowers, especially during the growth period of flowers in greenhouses in winter and spring, when the pathogen can infect any part of the plant. If cultivation management is neglected, it further favors the occurrence and spread of the disease, and in severe cases it can cause mass flower drop and leaf drop, affect plant flowering, reduce ornamental value, cause great damage to flower quality and yield, and severely restrict the economic benefits of flower production.
I. Affected flower species
Gray mold damages many herbaceous and flowering plants, such as Rieger begonia, New Guinea impatiens, cyclamen, cineraria, Phalaenopsis, poinsettia, Chinese primrose, China aster, begonia, dahlia, fuchsia, calceolaria, gloxinia, geranium, gladiolus, bird of paradise and more than 50 species of flowers.
II. Damage symptoms
The disease damages leaves, flowers, pedicels, petioles and tender stems, and also damages fruits. It causes leaves and flowers to rot and tender stems to break, reducing or losing the commercial value of the flowers. When gray mold infects leaves, dark green water-soaked spots (like scalding by boiling water) often appear at the leaf margin or leaf tip and continuously spread inward; under high humidity they cause brown rot covered with gray mold. When humidity decreases, the diseased parts become dry and withered in brown, light brown or withered yellow (depending on the flower species), and water-soaked patches of brown, light brown or white appear on the petals (depending on the flower species), followed by rot. Brown patches appear on tender stems or stems with high water content; if temperature and humidity are suitable, the lesions expand very quickly, causing brown rot of the diseased parts, breaking or lodging of branches and stems, and wilting, blighting and death of the parts above the diseased area, with the whole plant dying in severe cases. No matter which part of the flower is affected, under high humidity conditions the growth of gray mold on the diseased parts is their common feature and also an important symptom of the disease.
III. Pathogen and disease pattern
The pathogen is Botrytis cinerea of the Hyphomycetes among the Deuteromycetes, order Moniliales; the gray powdery substance appearing on the diseased parts consists of the conidiophores and conidia of the pathogen. The conidiophores are slender, upright and branched, 1.3 mm long, with the terminal cells swollen like spheres bearing many small sterigmata, on which conidia are produced; the conidia gather into grape-like clusters, are oval or elliptical, a few spherical, and colorless to pale. The pathogen overwinters as mycelium or conidia and sclerotia attached to diseased residues or left in the soil. The suitable temperature for the development of this fungus is 10-32°C, the minimum is 4°C, and the relative humidity should be maintained at 90%.
The large number of conidia produced on the diseased parts when moist is the main source of secondary infection. Warmth and moisture are the main conditions for the epidemic of gray mold. The pathogen overwinters on diseased residues in the soil, and mature conidia are spread by air currents, rain, irrigation water, dripping water in greenhouses and agricultural operations. The pathogen has strong pathogenicity to flowers and leaves, mainly infecting through plant wounds, and can also directly infect and cause disease from faded flowers, necrotic tissue and the epidermis; robust plants are less likely to be infected. Under conditions of relative humidity maintained at about 90% and temperature at about 18-25°C, gray mold is most likely to occur. When air humidity is high, the disease develops rapidly; when the air is dry, development is slow and there is little gray mold. In greenhouses where flower pots are placed too densely and ventilation is poor, the disease occurs severely. With excessive nitrogen fertilizer, plant tissues are tender and weak, and the disease is severe. Continuous rainy weather, insufficient light, excessive nitrogen fertilizer, poor soil drainage and many years of continuous cropping all make plants susceptible to infection and severe disease. After continuous cloudy low temperatures, when the weather clears and humidity rises, gray mold is prone to outbreak. The old leaves of some flowers are relatively sensitive to gray mold; fallen leaf layers and flowers are often places where large numbers of gray mold spores breed, and large numbers of spores fly into the air and cause disease when suitable temperature and humidity conditions are encountered. Spray irrigation in greenhouses also helps the spread of the pathogen. During cutting propagation, because film is used as an arched shed, the humidity inside is very high, and if too much condensation appears on the shed film, it will also aggravate the occurrence of the disease. In poorly ventilated, shaded and humid environments, plants are prone to the disease. Usually in the north in winter and spring, when the temperature in greenhouses is not high enough and humidity is high, plants suffer more severe disease.
IV. Control techniques and methods
Control techniques and methods include variety selection, cultivation techniques for disease prevention and chemical protection.
1. Variety selection
Selecting disease-resistant varieties for cultivation is the most economical means of controlling flower gray mold. For example, red-flowered varieties of carnation are more disease-resistant than yellow-flowered varieties; under the same conditions, red-flowered varieties develop lighter disease than yellow-flowered varieties.
2. Early-stage treatment
(1) Seed disinfection
To kill fungi attached to the surface of flower seeds, the seeds can be soaked in a 10% trisodium phosphate solution for 20 minutes and used after rinsing with running water for 40 minutes. They can also be soaked in 52°C warm water for 30 minutes and used after drying.
(2) Substrate disinfection. The pathogen mainly overwinters in the soil; therefore, whether for field planting or pot planting, the soil must be disease-free new soil, and flower pots and seed bulbs must be disinfected.
(3) Reduce infection sources. To reduce sources of infection, remove diseased flowers, diseased leaves and other residues at any time, and faded flowers should also be cut off promptly.
(4) Other treatments. For those planted with bulbs and seedlings, remove diseased plants before planting, soak in 0.3-0.5% copper sulfate for 0.5 hour, wash with water, dry and then plant.
3. Field management
Apply sufficient base fertilizer when planting to promote plant development and strengthen resistance. Apply fully decomposed organic fertilizer as much as possible, increase the application of phosphorus and potassium fertilizer, and at the same time pay attention to controlling the amount of nitrogen fertilizer to avoid excessive vegetative growth and aggravated disease, so as to keep plants robust and improve disease resistance. In the early stage of disease, promptly remove the diseased parts; they must not be piled directly in the greenhouse or placed on garbage heaps, but should be gathered for high-temperature composting or deep burial. Strengthen the cultivation management of potted flowers, pay attention to ventilation and light transmission, and leave sufficient space between flower pots. Water according to the principle of "water when dry, stop when wet"; the potting soil should not be too wet, and waterlogging should be avoided. In the field, pay attention to ventilation and light transmission between plants, and drain promptly after rain. During management, minimize plant damage, avoid wounds and prevent pathogen invasion.
4. Improve environmental conditions and control the occurrence of the disease. Increase indoor light to improve host disease resistance. Greenhouses should pay attention to ventilation and light transmission, reduce humidity, avoid placing potted flowers too densely, avoid excessive watering and fertilizing, avoid spray irrigation, and preferably water by pouring from the edge of the flower pot, so as to prevent high leaf surface humidity from favoring the disease. Avoid watering on cloudy and rainy days; when watering stops, ventilate to remove moisture; after disease occurs, control watering, and if necessary, carry out sprinkling around the rhizomes. It is best not to mix different flowers in the same greenhouse. Reduce humidity and reduce condensation on the shed roof and leaf surfaces. Greenhouses should be ventilated and aired in time to reduce humidity below 80%, especially when the temperature rises on sunny days after continuous cloudy weather; this work should be done even more promptly. Pay attention to operational hygiene to avoid transmitting the disease during management.
The suitable temperature for the occurrence of gray mold is between 20-25°C; above 32°C the pathogen stops infection, growth, development and reproduction. Using this principle, in protected cultivation the development and infection of the pathogen can be controlled by raising the temperature, and this method has obvious effects when used in autumn. Usually, ventilation is delayed in the morning to raise the temperature in the greenhouse to between 31-33°C; ventilation begins when it exceeds 33°C. If it is still above 25°C near noon, ventilation can be continued, but in the afternoon the temperature needs to be maintained at 20-25°C; when it drops to 20°C, the vents must be opened, and the nighttime temperature should be maintained between 15-17°C. If this method is well controlled, it can achieve the goal of controlling gray mold without using chemicals. 5. Chemical control. There is currently no specific chemical for controlling this disease, so prevention should be the main approach, and chemical control should be carried out at the right time. Leaf spraying, fumigation and dust application can all be used. (1) Before disease occurrence and in the early stage of disease, spray with 1:200 Bordeaux mixture once every two weeks. (2) After disease occurrence, promptly cut off diseased leaves and spray chemicals for control. (3) Chemical fumigation. (4) Dust application.