(1) Downy mildew
The lesions on the leaves are oval or cylindrical, with different sizes, yellow-green, inconspicuous edges, and white or lavender downy mildew on the affected parts. The leaves above the diseased area are drooping and dry, and the pseudostems often bend to the injured side and are easy to break.
Key points of prevention and control:
① Rotation with non-onion crops for 2-3 years.
② Spraying with 600 times solution of 75% chlorothalonil, 500 times solution of 50% dichlorvos or 1 ~ 2mg/kg cycloheximide at the 5th to 6th leaf stage for 7 ~ 10 day 1 time for 3 ~ 4 times.
(2) purple spot disease
The lesions mostly start from the middle of the blade tip and can spread to the lower part after a few days. The initial lesion is small, slightly concave, yellowish brown to brown. When the humidity is high, the lesion is covered with brown to black powdery mildew, which is often arranged in a concentric ring. The diseased spots will always heal and grow into strip-shaped large spots, leading to the death of leaves.
Key points of prevention and control:
(1) Clean rural areas and implement rotation for more than 2 years.
(2) Strengthen management, apply sufficient base fertilizer, apply topdressing reasonably, and drain water after rain to make plants grow healthily and enhance disease resistance.
(3) Control thrips allii in time to avoid wound.
④ Spraying 75% chlorothalonil wettable powder 500-600 times, or 64% antiviral alum wettable powder 500 times, and 58% metalaxyl manganese zinc wettable powder 500 times at the initial stage of the disease, and continuously controlling it for 3-4 times every 7- 10 day.
(3) Rust
Occurred in leaves and green stems, slightly raised brown sores and blisters appeared in the early stage of the affected part, which were oval or spindle-shaped, and then longitudinally split in the later stage, and the surrounding epidermis turned up, releasing orange powder. Finally, a long oval or spindle-shaped, dark brown and slightly raised lesion is formed in the affected part, and dark brown powder is released after the lesion ruptures.
Key points of prevention and control:
① Select disease-free onion seedlings.
② Remove the diseased leaves in time at the initial stage of the disease, and bury them deeply or burn them.
③ Apply sufficient fertilizer and pay attention to the coordination of nitrogen, phosphorus and potassium fertilizer.
④ Spraying 15% triadimefon wettable powder 2000 times, 7 ~ 10 day 1 time, 2 ~ 3 times in a row.
(4) yellow dwarf disease
The damaged leaves are mottled with yellow-green, or striped yellow spots, the leaves shrink unevenly, the leaf tube is deformed, the tip of the leaf is gradually yellowing and drooping, the growth of new leaves is inhibited, the plants are short, clustered or atrophied, and in severe cases, the whole plant dies. Most diseases occur at the seedling stage. After the disease, the seedlings grow slowly or stop, and cannot form scallion, which seriously affects the yield and quality.
Key points of prevention and control: ① agricultural prevention and control: choose healthy, virus-free seedlings and disease-resistant varieties; The onion field should not be adjacent to the onion seedling or seed collection field; Strengthen fertilizer and water management to enhance plant disease resistance; Check the fields frequently, pull out the diseased plants in time, and bury or burn them in a centralized way; Hands and furniture that have been exposed to infected plants should be disinfected, otherwise they can't touch healthy plants; It is necessary to strengthen pest control and reduce transmission routes; Be careful not to damage onion seedlings during farming operations to avoid virus invasion from the wound.
② Chemical control: spray 100 times of 83 antiallergic agent solution, 500 times of 20% virus A wettable powder solution or 300 times of 1 antitoxic agent solution in time at the initial stage of onset.
(5) Soft rot of Welsh onion
Soft rot of onion will harm the leaves and pedicels of onion. At the early stage of the disease, the first to second leaves appear soft spots along the veins. As the lesion spread to the base of the leaf sheath, the base of the leaf sheath softened and rotted, giving off stench, and the outer leaves fell off.
Key points of prevention and control:
① Agricultural control: select varieties with strong disease resistance and stress resistance, and select full, fresh and disease-free seeds; Rotation with non-onion and garlic crops for more than 2 years; Clean up the fields before planting and after harvesting, remove dead branches and diseased bodies in the fields, and burn or bury them deeply; Cultivate strong seedlings and sow them in time to prevent high temperature in the field; Increase the application of organic fertilizer and timely topdressing to promote plant growth and health, accelerate wound healing and enhance disease resistance; Strengthen water management, light watering and timely drainage in rainy season to reduce field humidity; Regularly check field diseases and pull out diseased plants in time; Strengthen the prevention and control of pests and diseases, pay attention to the early prevention and control of underground pests, prevent and control all kinds of chewing mouthparts pests at seedling stage, and reduce insect damage.
② Chemical control: At the initial stage of the disease, 72% agricultural streptomycin soluble powder is 4000 times, neophytomycin is 4000-5000 times, antibacterial is 40 1 500-600 times, 77% gram is 500 times of wettable powder, 500 times of 50% copper succinate wettable powder, or 800 times of 56% water dispersible granule. The above drugs should be used alternately.
③ Prevention and treatment of storage diseases: harvesting in sunny days and fully airing to dry and harden wounds and accelerate healing; Choose healthy, disease-free, insect-free and disability-free green onions for storage, pay attention to ventilation during storage, and keep the low temperature at about 0℃.
(6) Gray mold
At the early stage of the disease, white spots, oval or nearly round in shape, with a diameter of 65438±0 ~ 3mm, grow downward from the top of the green onion leaves. With the development of the disease, the lesion expanded into one piece until half or all of the leaves curled and died, and the internal tissue of the leaf sheath rotted. When wet, the disease grows a gray mold layer.
Key points of prevention and control:
① Agricultural control: select varieties with strong disease resistance and stress resistance, select full, tender and disease-free seeds, and rotate them with non-onion and garlic crops for more than 2 years; Thoroughly eliminate diseased plants and reduce the source of bacteria in the field; Select plots with good drainage, and use high ridges or ridges for reasonable close planting to make them well ventilated; Strengthen water management, prevent flooding, drain water in time after planting, and reduce field humidity; Formulated fertilization, don't apply too much nitrogen fertilizer, avoid plants growing in vain and reduce disease resistance; After harvesting, clean up the sick and disabled bodies in the field in time, and then dig deep into the soil.
② Chemical control: At the initial stage of the disease, spray 1000 ~ 1500 times of 50% chlorpheniramine wettable powder, or 2000 times of 50% prochloraz wettable powder, or 65% Wanmeiling wettable powder, or 500 times of 50% Hui Mei Ning wettable powder. Choose one of the above drugs and use them alternately. Spray every 10 day 1 time, and spray continuously for 2 ~ 3 times.
(7) Epidemics
Leaves and pedicels of Phytophthora infestans. When the leaves are damaged, they are dark green water spots at first, and then become gray spots after expansion, which surround the leaves, causing the leaves to collapse and wither from the diseased parts. When the rain is continuous or the humidity is high, the disease grows sparse white mold. When the weather is dry, the white mold disappears, and cotton-wool white mycelium can be seen when the epidermis is torn open. When the disease is serious, the diseased leaves rot and the whole plant dies.
Key points of prevention and control:
① Agricultural control: select varieties with strong stress resistance and disease resistance, select full, fresh and disease-free seeds, and rotate them with non-onion and garlic vegetables for more than 2 years; Choose strong seedlings when planting, and eliminate sick seedlings, weak seedlings and residual seedlings; Thoroughly clean the field, remove sick and disabled plants, and reduce the source of bacteria in the field; Choose plots with good drainage and high dry terrain for planting, and use high ridges or ridges for planting, and plant them reasonably and densely to make them well ventilated; Strengthen water management, drain water in time after rain, and reduce field humidity; Formulated fertilization is adopted to promote the robust growth of plants and enhance the disease resistance; Timely intertillage weeding.
② Chemical control: firstly, seed treatment before sowing, and seed dressing with 25% thiram which is equivalent to 0.3% of the seed weight. Second, at the initial stage of the disease, 75% chlorothalonil wettable powder 500 times, 50% carbendazim wettable powder 500 times, 25% toxomyl wettable powder 800 times, 64% antiviral alum wettable powder 500 times, 1500 ~ 2000 times, 50% quick killing powder or 58% cream can be used. The above chemicals should be used alternately, and sprayed every 7 ~ 10 day/time for 2 ~ 3 times continuously.
(8) White rot
The disease can occur at seedling stage and adult stage. The seedling tips turned yellow after injury, and the whole leaves died in the later stage, and finally the seedlings withered and died. When the adult plant is sick, the leaves turn yellow from the tip and then die, the plant is dwarfed and withered, the stem base tissue becomes soft, then it dries up and decays, and it is slightly concave and gray-black, expanding upward along the stem base, and the underground part turns black and decays. When the humidity is high, there are many white molds on the surface or tissue of leaf sheath, which turn gray-black and quickly form a large number of black spherical sclerotia. Sclerotinia is round and small, often overlapping each other to form sclerotia blocks, and the thickness of sclerotia blocks can sometimes reach about 5 mm.
Key points of prevention and control:
① Agricultural control: select varieties with strong disease resistance or stress resistance, and select full, fresh and disease-free seeds or disease-free onion seedlings; Rotation with non-onion and garlic vegetables for more than 2 years; Select plots with good drainage and dry terrain for planting; Strengthen the management of fertilizer and water, drain water in time after rain, and reduce the humidity in the field; Thoroughly clean the countryside, remove the sick and disabled, and reduce the source of germs in the field; Strengthen field inspections, burn or bury uprooted plants in time, and sprinkle lime or plant ash on diseased plants for disinfection; Formula fertilization should be carried out, instead of partial application of nitrogen fertilizer, more phosphorus and potassium fertilizer should be applied to enhance the disease resistance of plants.
② Chemical control: In addition to seed dressing with 50% chlorpheniramine wettable powder equivalent to 0.3% by weight before sowing, 500 times of 50% carbendazim wettable powder, 800 times of 70% thiophanate-methyl wettable powder, or 50% chlorpheniramine wettable powder 1000 ~ 1500 times of liquid, or 68 times of liquid.
(9) Anthracnose
Anthracnose mainly occurs on leaves and pedicels. When the leaf is damaged, the primary lesion is nearly spindle-shaped or irregular grayish brown to brown, with no edge. Later, with the development of the disease, the lesions were scattered with small black spots, that is, the umbilical points of the pathogen. When the condition is serious, the upper leaves die.
Key points of prevention and control:
① Agricultural control: select disease-resistant varieties and leave seeds on disease-free or disease-free plants to prevent seeds from carrying bacteria; Rotation with non-onion and garlic vegetables for more than 2 years; Choose plots with good drainage and high dry terrain for planting, with reasonable planting density and good ventilation. Choose strong seedlings when planting, and eliminate sick seedlings, residual seedlings and weak seedlings; Implement formula fertilization to enhance plant disease resistance; Strengthen water management, water properly, drain water in time after rain, and reduce the humidity in the field; Thoroughly clean the field after harvest, often check the situation of the field, and remove the diseased plants in time.
(2) chemical control: soak the seeds in 300 times formalin solution for 3 hours before sowing, take them out, rinse them, dry them and sow them; Spraying 75% chlorothalonil wettable powder 600 times, 80% anthrax thiram wettable powder 800 times, 70% mancozeb wettable powder 500 times, 64% antiviral alum wettable powder 500 times, or 50% thiophanate-methyl wettable powder 500 times at the initial stage of the disease. Any of the above chemicals can be used alternately, spraying 1 time every 10 day and preventing 1 ~ 2 times.
(10) mesophyllum
This disease harms leaves. At the early stage of the disease, there are water-soaked yellowing spots on the leaves. With the development of the disease, irregular dark green spots of different sizes are formed, which are slightly concave. In the later stage, a thick layer of black velveteen grows on the diseased spot. When the disease is serious, the leaves will dry up and die.
Key points of prevention and control:
① Agricultural control: rotation with non-onion and garlic vegetables for more than 2 years; Choose plots with good drainage, fertile soil and high and dry terrain for planting; Choose strong seedlings when planting, and eliminate sick and disabled seedlings and weak seedlings; Reasonable close planting, keep good ventilation and light transmission between plants; Strengthen water management, drain water in time after rain, and reduce field humidity; Formulated fertilization can prevent plants from growing white and enhance plant disease resistance; Regular field inspection, timely removal of diseased plants; Thoroughly clean the field after harvesting to reduce the source of germs in the field.
② Chemical control: 500 times of 50% carbendazim wettable powder, 500 times of 40% polysulfide suspending agent, 500 times of 50% mixed sulfur suspending agent, 600 times of 80% mancozeb wettable powder or 50% benomyl wettable powder 1500 times were sprayed at the initial stage of the disease. Choose one of the above chemicals, and use it alternately, and spray it every 7 ~ 10 day/time, and spray it continuously for 2 ~ 3 times.
(1 1) black dot
It mainly harms leaves and pedicels. When the plant is damaged, the primary white spot is soaked in water, and with the development of the disease, it becomes gray or light brown oval or spindle-shaped lesion, slightly depressed. In the later stage, the lesions were enlarged, surrounded by yellow halo, and dark or dark gray molds were arranged in concentric circles. When the disease is serious, the disease spots are connected with each other or spread around the leaves or pedicels for a week, so that the leaves or pedicels are broken or the whole leaves die.
Key points of prevention and control:
(1) Agricultural control: select disease-resistant varieties and plump, fresh and pest-free seeds; Rotation with non-onion and garlic vegetables for more than 2 years; Choose a well-drained plot and plant it in a reasonable density to make the plants ventilated and transparent; Implement formula fertilization to prevent premature aging of plants and improve plant disease resistance; Reasonable irrigation, timely drainage after rain, reduce field humidity; Regular field inspection, timely removal of diseased plants; After harvesting, all the sick and disabled bodies in the field are transported away, buried or burned in a centralized way.
② Chemical control: spraying 1500 times of 50% chlorpheniramine wettable powder, 500 times of 64% antiviral alum wettable powder, 800 times of 58% metalaxyl manganese zinc wettable powder, 600 times of 75% chlorothalonil wettable powder or 600 times of 70% mancozeb wettable powder at the initial stage of the disease. Choose one of the above chemicals to use alternately, and spray it every 10 day/time, and spray it continuously for 2 ~ 3 times.