How to Identify and Control Southern Rice Black-Streaked Dwarf Virus

Southern rice black-streaked dwarf virus is a rice viral disease occurring in southern rice-growing areas, with characteristics of strong explosiveness, rapid spread, great difficulty in prevention and control, and heavy damage losses. Rice and corn infected at the seedling stage will basically suffer total crop failure. In 2011, after comprehensive prevention and control, a total of about 8,500 mu of southern rice black-streaked dwarf virus occurred in Lianyuan City, of which the affected area of middle-season rice was 6,500 mu, the affected area of late rice was 1,600 mu, and the affected area of corn and other crops was 400 mu. A total of 25.93 tons of rice was lost, of which the loss rate of the most severely affected patches did not exceed 3%.

I. Identification:

1. Typical symptoms

(1) Affected rice plants have dark green leaf color, and the upper leaves show uneven wrinkling on the leaf surface (mostly seen at the leaf base).

(2) The aboveground nodes of diseased plants have adventitious roots growing upside down and branching at high nodes; the stem surface of diseased plants has milky white tumor-like protrusions (noticeably rough to the touch), and the tumor protrusions are arranged longitudinally in a row like wax spots, milky white in the early stage and brown-black in the later stage; the node position where the tumors appear varies depending on the infection period. In rice plants infected early, the tumors appear at the lower nodes; the later the infection period, the higher the node position where the tumors appear.

2. Symptoms at the seedling stage: diseased plants are short and small, dark green in color, with slow emergence of the central leaf, and the central leaf blade is short, small and stiff, with shortened leaf sheath pulvinus spacing.

3. Symptoms at the tillering stage: diseased plants have increased tillering and grow in dense clumps, the leaf pulvini of the upper several leaves overlap, and the leaf tips are slightly twisted and deformed. The plants are short and small; the main stem and early-born tillers can still head, but the panicles are difficult to fill, or the panicles remain enclosed, or the panicles are small, resembling dwarf disease.

4. Symptoms at the heading stage: manifested as dwarfing and dense clumping of the whole plant, with the flag leaf short, small and stiff; longitudinal wrinkles can be seen at the base of the middle and upper leaves, and waxy white or black-brown raised short vein swellings can be seen on the lower internodes and nodes of the stem. On the stems of susceptible japonica and glutinous rice, waxy white raised vein swelling spots can be seen. This is currently the most prominent symptom of the disease. The root system of infected plants is not well developed, with few and short fibrous roots, and in severe cases the root system turns yellow-brown.

II. Prevention and control:

The pathogen of southern rice black-streaked dwarf virus is southern rice black-streaked dwarf virus, and its main virus-transmitting vector is the migratory pest white-backed planthopper. The main process is that viruliferous white-backed planthoppers migrating in feed on early rice or weeds and transmit the virus; viruliferous white-backed planthoppers migrating in or local white-backed planthoppers feed on viruliferous hosts and then transmit the virus to middle-season rice, late rice seedling beds and paddy fields. To prevent and control southern rice black-streaked dwarf virus and other rice viral diseases, a comprehensive prevention and control strategy should be adopted that is "based on agricultural control, focused on 'controlling planthoppers to prevent dwarfing', and supplemented by emergency remedial measures."

The key is to do a good job in preventing and controlling virus-transmitting vector insects such as rice planthoppers, and to grasp three key periods for control during the rice seedling stage and early field stage: first, the stage from one leaf and one heart to two leaves and one heart; second, 3-5 days before transplanting the seedlings; third, the beginning of the peak tillering stage of rice. Apply one pesticide spray each time to control rice planthoppers, eliminating them before the virus-transmitting vector insects transmit the virus and controlling virus spread. On this basis, fertilizer and water management should also be strengthened to improve the rice's own resistance, so as to achieve the goal of preventing and controlling southern rice black-streaked dwarf virus.

1. Do a good job with chemical seed dressing. For seed soaking, use 10% imidacloprid wettable powder at 300-500 times dilution and soak the seeds for 12 hours, or after the seeds are germinated until the white sprout appears, mix 15-20 g of 10% imidacloprid wettable powder evenly with 1-2 kg of seeds (calculated as dry seeds), and sow after the chemical is fully absorbed.

2. 3-5 days before transplanting rice seedlings, apply a "send-off pesticide" once. Use 25% pymetrozine wettable powder 40 g/mu or 25% buprofezin wettable powder 50 g/mu plus 48% chlorpyrifos emulsifiable concentrate 80-100 ml/mu, add plant gene activator 20 g/mu (or antiviral agents such as ningnanmycin) and foliar fertilizer, mix with 30-45 kg of water and spray evenly.

3. Strengthen field inspection and adopt emergency remedial measures: First, for affected seedling beds, promptly remove diseased plants (bury them concentrated in mud); second, for fields at the tillering stage with a clump incidence rate below 2%, promptly tread them directly into the mud; for fields with an incidence rate of 2-20%, promptly pull out the diseased plants (clumps) and tread them into the mud on the spot for deep burial, then split tillers from healthy clumps to fill in the seedlings. At the same time, strengthen fertilizer and water management to promote early growth and ensure the number of effective tillers and effective panicles. Third, for patches with particularly severe incidence, it is recommended to promptly plow and change to planting the next crop of rice or other crops.