Symptoms and control methods of brown streak of lotus root

Brown streak of lotus root, because its lotus leaves show round to irregular faded green macula or brown dead spots, also known as black spot or lotus leaf spot, although it only harms the leaves, but in serious cases, the whole leaf except the veins of the lotus root field will be covered with disease spots, half-leaf or whole leaf dry, as if it had been burned. At present, the disease is one of the main diseases in lotus root production. When the disease is serious, the commodity value of the whole lotus root field will be reduced by more than 25%, which will greatly affect the interests of lotus root growers. Let's learn about the symptoms of lotus root brown streak and how to prevent and cure lotus root brown streak.

Symptoms of the disease

The disease mainly harms the leaves of lotus root, and there are few symptoms on the petiole. Needle-sized small round yellow-brown spots were initially produced on the front of the lotus root leaves, especially on the back of the leaves, and then gradually expanded into round or irregular brown spots or dark brown withered spots with a diameter of 0.5 cm to 2.0 cm. The color of the disease spot on the back of the leaf was slightly lighter than that on the front of the leaf, showing a large yellow spot of faded green. The disease spot is slightly sunken, with or without obvious brown concentric pattern on the disease spot, the edge of the disease is clear, and there is a narrow faded yellow halo around it. The disease spot on the front of the floating leaf is mostly dark brown, in the middle and later stage, the disease part is easy to rot, touch with the hand, the upper epidermis is easy to fall off, but not perforated; although the upper epidermis of the disease spot is necrotic, it is not easy to fall off. In the middle and later stages, several disease spots are often enlarged and fused into large irregular scorched disease spots. In severe cases, except for the veins of the leaves, the whole leaf surface is covered with disease spots, resulting in the drying up and death of the half leaf to the whole leaf. When there is a continuous epidemic in the field, overlooking the disease area of lotus root seems to be burning.

2. The route of transmission and the conditions of the disease

The pathogen survived and overwintered with mycelium and conidia on the diseased body or seed lotus root plant, and produced conidia in the following year, which were transmitted by wind and rain for primary infection. After 2-3 days of incubation, the disease part produced conidia and re-infection. The disease began in the middle of May in Hubei, and flourished in the high temperature and rainy season from July to September, especially after the storm or when the growth of lotus root was weak. The water temperature of lotus root field was higher than 35 ℃ or partial application of nitrogen fertilizer and aphids were rampant.

III. Prevention and control measures

1. Change crop rotation to avoid continuous cropping

The implementation of flood-drought rotation is the best way to prevent and cure the disease. Crop rotation must be carried out in diseased fields for more than 3 years, especially in lotus root fields with serious disease last year, changing stubble with gramineous crops such as rice or cash crops such as garlic and medicinal celery can effectively reduce the accumulation of germs in the field and reduce the harm of infection.

2.. Select disease-resistant and disease-tolerant varieties according to local conditions

Elian No. 4 and Elian No. 5 have strong disease resistance, good quality and high yield. The disease-free lotus root must be selected or left in the disease-free field. The whole lotus root with hypertrophic front end should be selected. Because of its rich nutrition, the lotus root leaves can stretch out of the water earlier, which is beneficial to enhance disease resistance and reduce the chance of initial infection.

3. Clean the lotus root field as soon as possible

Pick diseased leaves at any time in the middle and later stages of lotus root growth, take them out of the field and bury them or burn them, but be careful not to break their petioles, lest Rain Water or pond water pour into the petiole vents and cause underground stem rot. Remove the diseased leaves before harvesting the lotus root. After harvesting the lotus root, remove the remains of the lotus root in the field as far as possible, and immediately concentrate on burying or burning the lotus root outside the field. In addition, after the Beginning of Winter (November 7-8), the soil of the lotus root field was disinfected, mixed with 2kg of carbendazim wettable powder per mu and sprinkled with 100kg of fine dry soil, then turned deeply into the cultivated land and frozen in winter.

4. Sowing at the right time and reasonable close planting

The planting density per unit area should not be increased blindly in order to increase the yield, otherwise it is easy to cause field depression and disease. Only with reasonable close planting can the ventilation and light transmission in the field be good and the growth of lotus root plants be ensured. Shallow water should be irrigated after sowing in order to increase the temperature and make the seed lotus root sprout earlier.

5. Strengthen the management of fertilizer and water

Choose the fields with good soil quality and convenient irrigation to plant lotus root. Apply sufficient compost retted by enzyme bacteria or fully mature organic fertilizer as base fertilizer. During the growth of lotus root, we should pay attention to timely and appropriate amount of topdressing, combine organic fertilizer with chemical fertilizer, properly increase phosphorus and potassium fertilizer, and avoid partial application of nitrogen fertilizer.

The water layer management was carried out according to the growth and development stage of lotus root. In the early stage of lotus root growth, the temperature is low and the standing leaves are few, and the water layer should be shallow; in the middle high temperature season, the water layer should be deep; in the later stage, the water layer should be shallower, which is beneficial to the long lotus root and oxygen exchange. Note that the water temperature should be controlled below 35 ℃. The lotus root field water will be fully and deeply irrigated before the typhoon and storm, and drained in time after the wind and rain.

6. Disinfection of lotus root

The seed lotus root was disinfected before planting, and the seed lotus root was soaked in 50% carbendazim wettable powder 700-1000 times for 20 minutes. The seed lotus root can also be sprayed with 1000 times of carbendazim wettable powder + 75% chlorothalonil wettable powder, then covered with plastic film for 24 hours, dried and planted.

7. Planting lotus root field to prevent diseases

For lotus root fields that occurred last year, 0.5 kg of carbendazim wettable powder per mu, 10 kg of dry fine soil and 15 kg of dry soil were used before planting, or 100 kg of quicklime was used to disinfect the soil per mu.

8. Medication prevention and treatment

The floating leaves are generally damaged first, spraying on the front of the leaves, and mainly on the leaves in the middle and later stages, spraying on both sides of the leaves. In the early stage of the disease, 70% methyl topiramate wettable powder + 75% chlorothalonil wettable powder was mixed in a proportion of 1 ∶ 1 and sprayed with 800x water, or 0.5∶ 0.5∶ 100x Bordeaux solution was sprayed. Or use a 700x solution of 77% copper hydroxide wettable particulate powder, a 1500-fold solution of 50% imipramine wettable powder, a 2000-fold solution of 70% ethyl phosphine ·manganese zinc wettable powder, a 2000-fold solution of 20% difenoconazole microemulsion, a 2000-fold solution of 25% carbendazim suspension, a 5000-fold solution of 40% fluorosilazole EC, 58% nail cream manganese zinc (Redomir manganese zinc) wettable powder 600 times liquid or 64% oxidizing manganese zinc (antidote alum) 600 times liquid spray control. When spraying, first spray the middle plants of the field, and then spray the plants around. Because there is more wax on the leaves of lotus root, it is best to add a small amount of washing powder when spraying to enhance the adhesion of the liquid. It is better to spray on a windless sunny day. The medicine was sprayed every 7-10 days for 2-3 times in a row. If there is a rainy day after the application, it should be sprayed in time.

The above are the causes, symptoms and related prevention and control measures of lotus root brown streak disease. Through the prevention and control methods, we can see that the focus of this disease is prevention. Before planting lotus root, we have introduced the lotus root from the aspects of seed selection, lotus root field cleaning, sowing, fertilizer and water management, and there are also treatment measures in the early stage of the disease. I hope to provide you with some reference and help.