How to prevent and control gray mold in plants? What specific pesticides are available?
Gray mold is a fungal disease that is common in open-field and protected cultivation crops and is relatively difficult to control. It is a low-temperature and high-humidity type of disease. The growth temperature of the pathogen is 20 to 30°C. When the temperature is 20 to 25°C and the humidity remains above 90%, it is a high-incidence period for the disease. It is caused by infection with Botrytis cinerea. Flowers, fruits, leaves, and stems can all be affected. Now let us take a look at what specific pesticides there are for preventing and controlling gray mold!
Pyrimethanil
Pyrimethanil is a new type of fungicide belonging to the anilinopyrimidine class. Its mechanism of action is unique. By inhibiting the production of enzymes that infect the pathogen, it prevents infection and kills the pathogen. Its mechanism of action is unique, and it is effective against gray mold pathogens that have developed resistance to commonly used non-anilinopyrimidine fungicides (benzimidazole and carbamate types).
Procymidone
Procymidone mainly inhibits the synthesis of triglycerides in the fungal body. It has both protective and therapeutic effects, has good systemic activity, and works well under low-temperature and high-humidity conditions.
Carbendazim
A fungicide with negative cross-resistance to carbendazim. After the agent enters the fungal cells, it binds to tubulin within the fungal cells, thereby affecting cell division. This mode of action is very similar to that of carbendazim, but the two do not act at the same site. If Botrytis develops resistance to carbendazim, it is very sensitive to diethofencarb. Conversely, for Botrytis that is sensitive to carbendazim, diethofencarb shows no antifungal activity.
Diethofencarb
After diethofencarb enters the fungal cells, it binds to tubulin within the fungal cells, thereby affecting cell division. It has cross-resistance with carbendazim and negative cross-resistance with carbendazim. Botrytis that is resistant to carbendazim is also very sensitive to diethofencarb. It is generally not used as a single agent.
Iprodione
Iprodione is a broad-spectrum contact fungicide that acts on spores, mycelium, and sclerotia simultaneously, inhibiting spore germination and mycelial growth. It can hardly penetrate into plant tissues and is a protective fungicide. It has good fungicidal activity against Botrytis, Sclerotinia, Streptomyces, Sclerotium, and Monilia.
Dimethachlon
Dimethachlon is a highly effective fungicide exclusively developed by experts targeting the "fungi, bacteria, and viruses" to which crops are susceptible. It has the characteristics of broad spectrum, sterilization, systemic action, penetration, treatment, and long duration. It has dual systemic and conductive effects. Foliar spraying can quickly conduct it to the diseased site, thoroughly sterilizing from the surface inward and eliminating multiple pathogens at once.
Fludioxonil
Fludioxonil inhibits the transfer related to glucose phosphorylation and inhibits the growth of fungal mycelium, ultimately causing the pathogen to die. Its mechanism of action is unique, and it has no cross-resistance with existing fungicides.
Polyoxin
Polyoxin is a metabolite produced by Streptomyces aureus. It belongs to the broad-spectrum antibiotic fungicides and has good systemic activity. It interferes with the biosynthesis of the fungal cell wall and can also inhibit pathogen sporulation and lesion expansion.
Integrated control of gray mold in flowers
Gray mold in flowers is one of the common diseases in flower production. It frequently occurs during the flower growing season. In mild cases, it affects leaves; in severe cases, it can cause a large number of fallen flowers and leaves, affect flowering, cause great harm to flower quality and yield, and seriously restrict the economic benefits of flower production.
Pathogen and damage
The pathogen of gray mold is Botrytis cinerea, a fungus of the genus Botrytis in the order Moniliales of the class Deuteromycetes. The gray powdery substance appearing on diseased parts consists of the conidiophores and conidia of the pathogen. The pathogen overwinters as mycelium, conidia, or sclerotia attached to diseased plant residues or left in the soil.
The large number of conidia produced on diseased parts is the main source of secondary infection. Warmth and humidity are the main conditions for the epidemic of gray mold. Mature conidia are spread by airflow, rainwater, irrigation water, dripping water in greenhouses, and agricultural operations. The pathogen mainly infects through plant wounds, and can also directly infect from faded flowers, necrotic tissue, and the epidermis. Under conditions of about 90% relative humidity and a temperature of 18°C to 25°C, gray mold is most likely to occur. When air humidity is high, the disease develops rapidly; when flower pots are placed too densely and ventilation is poor in a greenhouse, the occurrence is severe; when there is excessive nitrogen fertilizer and plant tissues are tender and weak, the disease is severe.
Gray mold harms many kinds of herbaceous and woody flowers, such as Cyclamen, Rieger Begonia, Begonia, New Guinea Impatiens, Cineraria, Fuchsia, Phalaenopsis, Calceolaria, Poinsettia, Primula obconica, China Aster, Dahlia, Gloxinia, Pelargonium, Strelitzia, Gladiolus, and more than 50 other flower species.
Gray mold mainly harms leaves, and also harms branches, petioles, sepals, petals, fruits, and seeds. In the early stage of the disease, nearly circular purple-brown spots with a diameter of 1 to 5 mm appear on the leaves, later expanding into irregular large spots with a diameter of 7 to 12 mm, with a pale yellowish-brown center and purple-brown edges. The lesions have obvious concentric rings. The lesions expand and connect into patches, and in severe cases the entire leaf scorches and withers. When the leaf margin is affected, the leaf becomes somewhat distorted. On green stems, there are purple-brown oblong small spots, somewhat raised, and the lesions expand slowly. The symptoms on petioles are similar to those on stems, but are elongated strips, on which dark green moldy material grows.
Integrated control
To prevent and control gray mold in flowers, the following multiple measures should be taken.
Choose disease-resistant cultivars for cultivation, such as carnation. Red-flowered cultivars are more disease-resistant than yellow-flowered cultivars. Under the same conditions, red-flowered cultivars are less affected than yellow-flowered cultivars.
Pay attention to pre-treatment. Soak seeds in a 10% trisodium phosphate solution for 20 minutes, rinse with running water for 40 minutes, and then use. They can also be soaked in 52°C water for 30 minutes, then dried for later use.
The pathogen mainly overwinters in the soil. Therefore, whether for garden planting or pot planting, the soil must be disease-free new soil, and the pot soil, flower pots, and bulbs must be disinfected.
To reduce sources of infection, diseased flowers, diseased leaves, and other residues should be removed at any time, and faded flowers should also be cut off promptly.
When planting with bulbs or seedlings, remove diseased plants first, soak in 0.3% to 0.5% copper sulfate solution for 30 minutes, wash with water, dry, and then plant.
(1) Strengthen field management
Apply sufficient base fertilizer in a timely manner to promote plant development and enhance resistance. Apply fully decomposed organic fertilizer as much as possible, increase phosphorus and potassium fertilizer, pay attention to controlling the amount of nitrogen fertilizer, prevent excessive vegetative growth, and improve disease resistance. In the early stage of the disease, promptly remove diseased parts. They must not be directly piled in the greenhouse or placed on garbage heaps; they should be centrally composted at high temperature or deeply buried. Strengthen the cultivation management of potted flowers, pay attention to ventilation and light transmission, and leave sufficient space between flower pots. Watering should follow the principle of "see dry, see wet"; the pot soil should not be too wet, and water accumulation should be prevented. In the field, attention should be paid to ventilation and light transmission between plants, and drainage should be done promptly after rain. During management, plant damage should be minimized to prevent pathogen invasion.
(2) Improve environmental conditions
Increase indoor light to improve host disease resistance. Do not water or fertilize too much. Avoid sprinkler irrigation; watering is best injected from the edge of the flower pot to avoid high leaf surface humidity that promotes disease. Avoid watering on cloudy and rainy days, and ventilate to remove moisture at the end of watering. After disease onset, control watering, and if necessary, irrigate around the roots and stems. It is best not to mix different flowers in the same greenhouse. Reduce humidity and reduce condensation on the greenhouse roof and leaf surfaces. The humidity in the greenhouse should be reduced to below 80%, especially when the weather turns sunny and temperatures rise after consecutive cloudy days; this work should be done even more promptly. Pay attention to operational hygiene to prevent disease transmission during management. The suitable temperature for the onset of gray mold is between 20°C and 25°C. Above 32°C, the pathogen stops infection, growth, development, and reproduction. Using this characteristic, protected cultivation can control the development and infection of the pathogen by increasing temperature. This measure is obviously effective in autumn. Generally, ventilation is delayed in the morning, but in the afternoon the temperature needs to be maintained at 20°C to 25°C. When it drops to 20°C, the vents must be closed, keeping the nighttime temperature between 15°C and 17°C. If this method is mastered well, it can prevent gray mold without using chemicals.
(3) Timely chemical control
At present, there is no specific pesticide, so prevention should be the main approach, and chemical control should be carried out at the right time. Foliar spraying can be used, as can fumigation and dusting.
Before disease onset and in the early stage of disease, spray with 1:200 Bordeaux mixture once every two weeks.
After disease onset, promptly prune diseased leaves and spray chemicals for control. Generally, protective fungicides are used, such as 50% procymidone 1000 to 2000 times solution, 50% duomeiling 1000 times solution, 50% carbendazim 500 to 800 times solution, 65% zineb wettable powder 500 to 800 times solution, etc., usually sprayed once every 7 to 10 days. Spraying should be meticulous and thorough. The best time to apply chemicals is after 9 a.m., and avoid applying chemicals under high temperature and cloudy or rainy weather. It is advisable to alternate multiple chemicals to prevent resistance.
Chemical fumigation. Light formed smoke agent tablets or powdered smoke agents, and use heating to disperse the effective ingredients of the chemical into small particles, which can quickly fill the entire planting area and evenly reach all object surfaces, so that places difficult to reach by spraying liquid can also be treated with the chemical, achieving a good pathogen-killing effect.
Optional chemicals include 10% procymidone smoke agent (200 to 250 grams/667 sq m) and 20% baisu smoke agent (250 grams/667 sq m). After smoking for 3 to 4 hours, ventilate. This can be done on cloudy and rainy days or after watering, preferably in the evening after closing the vents. It works well when air humidity is high and unsuitable for spraying liquid chemicals.
Dusting. It can be used in dense plots with no wind and in closed greenhouses. It mainly uses a duster to disperse chemicals with small particles and strong floating ability into the air, allowing them to slowly settle and spread from top to bottom to achieve a sterilizing effect.
Effective chemicals include 10% meike compound powder, 5% chlorothalonil compound powder, 6.5% wanmeiling dust, 10% shameiling dust, and 5% meimeiling dust. Apply once every 9 to 10 days, used continuously or alternately with other methods 2 to 3 times. The application rate is 1 kilogram per mu. Spray toward above the plants, and after spraying, close the greenhouse to prevent the dust from drifting under airflow. Application is best done in the evening or during the peak disease period on cloudy and rainy days.
Symptoms and control of gray mold in flowers
Gray mold in flowers is one of the most common diseases in production. It frequently occurs during the flower growing season, especially during the growth period of flowers in greenhouses in winter and spring. The pathogen can infect any aboveground part of the plant. If cultivation management is neglected, it is even more conducive to the occurrence and epidemic of the disease. In severe cases, it can cause a large number of fallen flowers and leaves, affect plant flowering, reduce ornamental value, cause great harm to flower quality and yield, and seriously restrict the economic benefits of flower production.
I. Flower species harmed
Gray mold harms many kinds of herbaceous and woody flowers, such as Rieger Begonia, New Guinea Impatiens, Cyclamen, Cineraria, Phalaenopsis, Poinsettia, Primula obconica, China Aster, Begonia, Dahlia, Fuchsia, Calceolaria, Gloxinia, Pelargonium, Gladiolus, Strelitzia, and 50 flower species.
II. Damage symptoms
The disease harms leaves, flowers, flower stalks, petioles, and tender stems, and also harms fruits. It causes leaves and flowers to rot and tender stems to break, reducing or losing the commercial value of flowers. When Botrytis infects leaves, dark green water-soaked spots (like scalding by boiling water) often appear at the leaf margin or leaf tip and continuously expand inward. When humidity is high, it causes brown rot, covered with gray moldy material. When humidity decreases, the diseased parts become brown, light brown, withered yellow, and other dry and withered states (varying with flower species). On petals, brown, light brown, white, and other water-soaked patches appear (varying with flower species), followed by rot. On tender stems or stems with high water content, brown patches appear. If temperature and humidity are suitable, the lesions expand very quickly, causing brown rot in the diseased parts. Branches and stems break or lodge, and the parts above the diseased area wilt, wither, and die. In severe cases, the entire plant dies. No matter which part of the flower is affected, under high-humidity conditions, the growth of gray moldy material on the diseased part is their common feature and also an important symptom of the disease.
III. Pathogen and disease occurrence pattern
The pathogen is Botrytis cinerea, a fungus of the genus Botrytis in the order Moniliales of the class Deuteromycetes. The gray powdery substance appearing on diseased parts consists of the conidiophores and conidia of the pathogen. The conidiophores are slender, upright, branched, 1.3 mm long, with terminal cells swollen like spheres, bearing many small sterigmata on which conidia are produced. The conidia gather into grape-like clusters. The conidia are oval or elliptical, a few spherical, colorless to pale. The pathogen overwinters as mycelium, conidia, or sclerotia attached to diseased plant residues or left in the soil. The suitable temperature for the development of this fungus is 10-32°C, with a minimum of 4°C, and the relative humidity should remain at 90%.
When moist, the large number of conidia produced on diseased parts is the main source of secondary infection. Warmth and humidity are the main conditions for the epidemic of gray mold. The pathogen overwinters on diseased plant residues in the soil. Mature conidia are spread by airflow, rainwater, 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 be directly infected from faded flowers, necrotic tissue, and the epidermis. Healthy and robust plants are not easily infected. Under conditions of about 90% relative humidity and a temperature of 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, it develops slowly and there is less gray mold. When flower pots are placed too densely and ventilation is poor in a greenhouse, the occurrence is severe. When there is excessive nitrogen fertilizer and plant tissues are tender and weak, the disease is severe. Continuous rain, insufficient light, excessive nitrogen fertilizer, poor soil drainage, and many years of continuous cropping all make infection by the pathogen more likely and the disease more severe. After consecutive cloudy and low-temperature days, when the weather turns sunny and humidity rises, gray mold is prone to outbreak. The old leaves of some flowers are relatively sensitive to gray mold. Decaying leaf layers and flowers are often places where gray mold pathogens multiply in large numbers. Large numbers of spores fly into the air and cause disease when suitable temperature and humidity conditions are encountered. The use of sprinkler irrigation in greenhouses also helps spread the pathogen. When raising seedlings by cuttings, because film is used as an arched shed, the humidity inside is very high. If too much condensation appears on the film, it will also aggravate the occurrence of the disease. In poorly ventilated, shaded, and humid environments, plants are prone to the disease. Generally, in northern China in winter and spring, when the temperature in greenhouses is not high enough and humidity is high, plants are more severely affected.
IV. Technical control measures
Technical control measures include cultivar selection, disease prevention through cultivation techniques, and chemical protection.
1. Cultivar selection
Choosing disease-resistant cultivars for cultivation is the most economical means of controlling gray mold in flowers. For example, red-flowered carnation cultivars are more disease-resistant than yellow-flowered cultivars. Under the same conditions, red-flowered cultivars are less affected than yellow-flowered cultivars.
2. Pre-treatment
(1) Seed disinfectionTo kill fungi attached to the surface of flower seeds, the seeds can be soaked in a 10% trisodium phosphate solution for 20 minutes, rinsed with running water for 40 minutes, and then used. They can also be soaked in 52°C warm water for 30 minutes, then dried for later use.
(2) Substrate disinfectionThe pathogen mainly overwinters in the soil. Therefore, whether for garden planting or pot planting, the soil is always required to be disease-free new soil, and flower pots and bulbs must be disinfected.
(3) Reduce infection sourcesTo 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 treatmentsWhen planting with bulbs or seedlings, remove diseased plants first 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 enhance resistance. Apply fully decomposed organic fertilizer as much as possible, increase phosphorus and potassium fertilizer, and at the same time pay attention to controlling the amount of nitrogen fertilizer to prevent excessive vegetative growth and aggravate the disease, so as to keep plants robust and improve disease resistance. In the early stage of the disease, promptly remove diseased parts. They must not be directly piled in the greenhouse or placed on garbage heaps; they 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. Watering should be "see dry, see wet"; the pot soil should not be too wet, and water accumulation should be prevented. In the field, attention should be paid to ventilation and light transmission between plants, and drainage should be done promptly after rain. During management, plant damage should be minimized, avoid causing wounds, and prevent pathogen invasion.
4. Improve environmental conditions and control disease occurrence.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, prevent sprinkler irrigation, and watering is best injected from the edge of the flower pot to avoid high leaf surface humidity that favors disease. Avoid watering on cloudy and rainy days. At the end of watering, ventilate to remove moisture. After disease onset, control watering, and if necessary, irrigate around the roots and stems. It is best not to mix different flowers in the same greenhouse. Reduce humidity and reduce condensation on the greenhouse roof and leaf surfaces. Greenhouses should be ventilated and aired in a timely manner to reduce humidity below 80%, especially when the weather turns sunny and temperatures rise after consecutive cloudy days; this work should be done even more promptly. Pay attention to operational hygiene to prevent disease transmission during management.
The suitable temperature for the onset 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 increasing temperature. This measure is obviously effective in autumn. Generally, ventilation is delayed in the morning to raise the temperature in large sheds and greenhouses to between 31-33°C. When it exceeds 33°C, start ventilation. If it is still above 25°C near noon, ventilation can continue, but in the afternoon the temperature needs to be maintained at 20-25°C. When it drops to 20°C, the vents must be closed, and the nighttime temperature should be kept between 15-17°C. If this method is mastered well, it can achieve the purpose of preventing and controlling gray mold without using chemicals. 5. Chemical control At present, there is still no specific pesticide for controlling this disease, so prevention should be the main approach, and chemical control should be carried out at the right time. Foliar spraying can be used, as can fumigation and dusting.
(1) Before disease onset and in the early stage of disease, spray with 1:200 Bordeaux mixture once every two weeks.
(2) After disease onset, promptly prune diseased leaves and spray chemicals for control.
(3) Chemical fumigation.
(4) Dusting.