Powdery mildew is a high-prevalence and more harmful disease in melon production, and occurs in northern solar greenhouses, plastic greenhouses and open-field cultivation of melons.
Powdery mildew is mainly harmful to melon leaves, and generally occurs during the expansion and ripening stages of the fruit. At the beginning of the disease, small white powder spots appear on the leaves, gradually expand into white powder mold spots, and in severe cases, the entire plant leaves are covered with white powder, and spread to the petioles, stems and even fruits, and the diseased leaves become yellow and dry, which seriously affects the yield and quality of melons.
Symptoms of powdery mildew
Powdery mildew is a fungal disease caused by infection of The Single Capsule Shell (Podosphaera xanthii) or Powdery Mildew (Golovinomyces cichoracearum) in the family Asteraceae. In the northern solar greenhouse, after the onset of the melon growth period, the pathogen spreads with the air flow in the asexual stage of the conidia produced by the disease part, causing repeated infection, causing aggravation of the disease, and completing the impregnation cycle.
However, the conidia of powdery mildew melon bacteria are less stress-resistant, and quickly lose their activity above 36 °C or below -1 °C. At the same time, when melon leaves have water droplets or water membranes, the conidia absorb too much water, and the increased expansion pressure will lead to the rupture of the cell wall, which is not conducive to spore germination. Therefore, through the method of high temperature and stuffiness, creating a limit condition that can kill conidia in a short period of time can effectively prevent and control powdery mildew of melon. At the same time, melon is a relatively high temperature resistant crop, if the high temperature shed at the same time a large amount of irrigation, to ensure the melon leaf transpiration of the water required, then the short-term high temperature will not cause harm to the leaves.
It has been proved through practice that in the cultivation of thin-skinned melon cranes in the northern solar greenhouse, timely and moderate high temperature shed is a more effective physical method to control the occurrence and development of powdery mildew. The specific operation process and precautions are as follows:
1. Prepare the thermometer
In the solar greenhouse, a thermometer is hung every 10 meters or so in the east-west direction, and the position of the suspension is in the middle of the planting row in the north-south direction. The lowest point of the thermometer is about 1.5 meters from the ground, pay attention to the thermometer not to be directly exposed to sunlight.
2． Irrigation and stuffiness
Select Sunny Morning to do it. While starting to fill the water, close the greenhouse to release the air outlet and close the sullen shed. At different times of melon growth, the maximum critical point of irrigation and the temperature of the shed is different.
At the late stage of melon elongation (10 days after slow seedlings to before flowering), the amount of irrigation is 40% of the amount of irrigation in the sullen shed during the expansion of the fruit (so that the soil reaches the maximum water holding capacity), and the maximum temperature critical point is 45 °C. By continuously hanging in the greenhouse with a thermometer in the greenhouse to closely observe the temperature rise, when the temperature reaches 45 ° C, the air is released immediately, so that the temperature in the shed gradually falls back to 30 ° C. This temperature critical point can initially inhibit the development of powdery mildew.
At the melon fruit stage (from after flowering pollination to melon egg size), the amount of irrigation is 60% of the amount of irrigation in the sullen shed during the expansion of the fruit, and the maximum temperature critical point is 48 °C. When the temperature rises to 48 ° C, the air is released immediately, so that the temperature in the shed gradually drops to 30 ° C. This temperature critical point can effectively control the further spread of powdery mildew, but it cannot eradicate the bacteria.
When the melon fruit is expanded (after the fruit and egg are large), a large amount of water should be irrigated to make the soil reach the maximum water holding capacity, and the maximum critical point of temperature is 50 °C. In some areas, dense planting cultivation (more than 3500 plants per mu) is adopted, and the maximum critical point of temperature can be increased to 52 °C. When the temperature rises to the highest critical point, the wind is released immediately, so that the temperature in the shed gradually falls back to 30 ° C. This temperature critical point can basically kill the powdery mildew bacteria in the shed.
Effect on the prevention and treatment of powdery mildew after high temperature stuffiness
Powdery mildew in the shed where the temperature is not high
3． Precautions
This method is prohibited during flowering pollination. The melon pollination period is very sensitive to temperature, and it is forbidden to carry out high temperature stuffiness during this period so as not to affect fruit set.
It should be operated at the beginning of the onset of powdery mildew, the earlier the better. To closely observe the growth of melon leaves, once there are white powdery dots on individual leaves (indicating that powdery mildew has begun to occur), high temperature shed operation should be carried out as soon as possible. Because the number of powdery mildew bacteria in the shed is still relatively small, it is easy to eliminate quickly. At the same time, the pathogen has not caused great damage to the leaves and will not affect the growth of the plant.
Strictly grasping the temperature critical point and irrigation volume is the technical key. At different stages of melon growth and development, the water absorption ability of roots, the heat resistance of plants, and the water requirements of fruit development are different. The root absorption ability of the root system is weak in the early stage of plant growth, and the tolerance of leaves to high temperature is poor, so the temperature critical point of different periods should be strictly grasped to avoid damage caused by excessive temperature. The purpose of irrigation is to reduce the leaf temperature to protect the leaf by increasing the transpiration effect, so the higher the temperature, the more the amount of irrigation water should be increased, which is the premise of ensuring the success of the high temperature shed operation.
Pay attention to clear the source of greenhouse disease to prevent secondary infection. When the high temperature shed operation in the greenhouse is carried out, it is necessary to pay attention to removing weeds and crop residues outside the greenhouse to prevent the powdery mildew bacteria from outside entering the greenhouse through the vent, causing secondary infestation.
This technique is suitable for thin-skinned melon solar greenhouse cranes and the cultivation method of submembrane drip irrigation. Thick-skinned melon has special requirements for moisture and temperature due to the presence of peel hardening or reticulation during fruit development, and it is recommended to use this technique with caution.
The application of high-temperature shed technology can not only effectively prevent and control thin-skinned melon powdery mildew, but also reduce the use of chemical pesticides and save production costs, so it has certain reference significance in the green prevention and control of melon diseases.
bibliography:
Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Chinese Society for Plant Protection. Crop Diseases and Pests in China (Third Edition)[M]. Beijing:China Agriculture Press,2015:1347-1353.]
Authors: He Ming, Sun Baixin (Liaoning Academy of Agricultural Sciences), Song Fengming (Zhejiang University), Zhao Tingchang (Institute of Plant Protection, Chinese Academy of Agricultural Sciences)