A complete guide to the basics of southern rice black-streaked dwarf disease
Rice seedling rot is the collective term for seed rot, bud rot and dead seedlings that occur at the seedling stage. Rice seedling rot can be divided into two types: physiological and infectious. Physiological seedling rot is mainly caused by low temperatures and mistakes or poor management practices in the seedling nursery; infectious seedling rot is caused by pathogen infection, and the main diseases include rice cottony rot, rice putrefactive disease and rice...
I. Overview of occurrenceSouthern rice black-streaked dwarf disease was first discovered in late rice in Guangdong in 2001. In recent years, the affected area has expanded rapidly in Vietnam and the rice-growing regions of southern China. In 2009, it occurred in 9 provinces including Guangxi, Guangdong and Hunan, with an affected area of 5 million mu, and it is expected to exceed 10 million mu in 2010 (accurate statistics are not yet available). In August of this year, diseased plants of black-streaked dwarf disease were found in Funing, Guangnan, Yanshan and other counties, with a general diseased clump rate of 1-35%. In our county, 3,000 mu were affected in 2010, with a diseased clump rate of 5%-10%. The disease can infect rice at all growth stages. Generally, affected fields suffer losses of 5-30%, and particularly severe cases can lead to total crop failure.
II. Disease characteristics
The symptoms vary depending on the stage at which infection occurs. Rice plants infected at the seedling stage are severely dwarfed (less than 1/3 the height of normal plants), cannot joint, and severely diseased plants die early; rice plants infected in the early field stage are noticeably dwarfed (about 1/2 the height of normal plants), do not head or only produce incompletely emerged panicles, and cannot set grain; rice plants infected at the jointing stage are not noticeably dwarfed and can head, but the panicles are small, have few filled grains and light grain weight.
The common features of diseased rice plants are: 1. The leaves of diseased rice plants are dark green, and uneven wrinkling can be seen on the surface of the upper leaves (mostly at the leaf base); 2. Adventitious fibrous roots grow from the nodes of several aboveground internodes of diseased plants; 3. Diseased plants branch at high nodes; 4. The surface of the culm of diseased plants has milky-white wart-like protrusions about 1-2 mm in size (clearly rough to the touch), and the warts are arranged longitudinally in rows like wax dots, milky white early on and brown-black later; the node positions where the warts appear vary with the infection period. In plants infected early, the warts appear at lower nodes; the later the infection period, the higher the node positions where the warts appear. 5. The root system of infected plants is poorly developed, with few and short fibrous roots, and in severe cases the root system turns yellow-brown.
III. Occurrence pattern
Southern rice black-streaked dwarf disease is a serious viral disease. Besides rice, it can also infect more than 20 hosts including wheat, corn, sorghum, barnyardgrass and foxtail. The virus mainly overwinters on diseased plants of wheat, corn and gramineous weeds. The migratory pest white-backed planthopper is a highly efficient virus-transmitting vector (once the vector acquires the virus, it carries it for life). When white-backed planthoppers feed on diseased plants, they immediately acquire the virus. When viruliferous planthoppers move to healthy plants and feed, they transmit the virus to the healthy plants. Once a healthy plant is infected with the virus, the virus attacks the rice growing point and the rice immediately stops growing. Rice can be infected throughout its entire growth period; the younger the seedling age, the more susceptible it is and the shorter the incubation period; the earlier the infection, the more severe the disease and the greater the yield loss.
IV. Control measures
The key to controlling southern rice black-streaked dwarf disease is to do a good job of preventing and controlling rice planthoppers. The control measures mainly adopt the "control insects to prevent disease" strategy of "focus on the early stage to protect the later stage, focus on the seedling nursery to protect the field," with priority on protecting the seedling nursery and the early stage of the main field. Before heading of early and middle rice, and during the seedling nursery and tillering stages of late rice, preventive and control work should be done well before viruliferous white-backed planthoppers transmit the virus. At the same time, fertilizer and water management should be strengthened, with balanced fertilization, to improve the crop's own resistance.
1. Eradicate gramineous weeds, rice ratoon seedlings and volunteer seedlings in fields and along ditches to reduce the source of virus in the field.
2. Select and promote good insect-resistant and disease-tolerant varieties.
3. Strengthen seedling management and avoid excessive nitrogen fertilizer, so as to prevent seedlings from becoming too green and triggering severe damage by rice planthoppers.
4. Vigorously control rice planthoppers, especially during the seedling nursery and tillering stages. Use 30 grams of 25% pymetrozine suspension concentrate per mu, or 50 grams of 25% buprofezin wettable powder, mixed with 50 kg of water for spraying.