Rice black-streaked dwarf virus is a rice virus disease mainly transmitted by Laodelphax striatellus. Affected by many factors, such as farming system, farmland climate, and the increase of insect source base, the disease has been aggravated year by year in our county, which has become a sudden disease of rice in our county and one of the important diseases in rice production, posing a serious threat to rice production in our county.
I. Harmful symptoms
The main symptoms of rice black-streaked dwarf disease are: short and clustered plants, increased tillering, twisted and shriveled heart leaves, stiff leaves, dark green leaves, short strip-shaped protrusions on veins, leaf sheaths and stems on the back of leaves, which are waxy white at first and then brown.
(1) At seedling stage, the leaves are dark green, the leaves of heart leaves are short and straight, and the leaf sheath is wrapped by the leaf sheath of lower leaves, which makes the heart leaves germinate slowly, the leaves bend and contract, the internode distance is shortened, the leaves and pillows overlap or dislocate, and the diseased plants are seriously dwarfed, making it impossible to heading.
(2) At tillering stage, tillers increased and clustered, the upper leaves overlapped, and the heart leaves broke out from the lower leaf sheath or spiraled out from the lower leaf pillow. Early tillering can heading, but the ears are small and numerous. Half a bag of ears? Or? Wrap your neck and ears? Such as dwarfism.
(3) At jointing stage, the diseased plants were slightly short, and they could head, but the number of grains set decreased.
(4) Heading date: the whole plant is short and withered, and some plants can head, but it is late and small. Flag leaves are short and straight, and longitudinal wrinkles can be seen at the base of middle and upper leaves. Waxy white or dark brown swollen short veins can be seen on the lower internodes and nodes of the stem. This is a prominent symptom of this disease at present.
Second, the pathogenesis and infection cycle
1. Pathogenesis
Rice black-streaked dwarf virus is infected by rice black-streaked dwarf virus, mainly overwintering in barley and gramineous weeds, and mainly spread by Laodelphax striatellus (a few are Laodelphax striatellus). After Laodelphax striatellus is on the diseased host crops, the virus first proliferates in the digestive tract, passes through body fluids to saliva, and then spreads to plants. Infected Laodelphax striatellus can spread the virus for life, through old nymphs and adults, but not through eggs. It usually takes 60. The younger the rice seedlings are, the more likely they are to get sick, and the incubation period is short, generally 20-25 days; The incubation period of seedlings with more than 7 leaves is as long as 40-50 days. There are two peaks of rice black-streaked dwarf disease in rice. The first peak was that the infection occurred after transplanting in the field 10- 15d, and the second peak was that the initial infection of Honda occurred around full heading.
2. Infection cycle
Laodelphax striatellus has 5-6 generations a year in the local area, and most of them overwinter in wheat fields, leisure areas, ridges, ditches and roadside weeds, causing diseases of related host plants. From March to April of the following year, the first generation nymphae propagated in wintering places gradually moved into rice fields in late April and mid-May, the second generation nymphae moved into rice fields from rice fields and grass in mid-June, the third generation nymphae moved into rice fields in mid-July, and the fourth generation (August) was relatively small affected by high temperature season.
Third, popular factors.
1. Source of poison
The source of the virus is the basis of the occurrence and prevalence of rice black-streaked dwarf virus. Due to the seasonal migration and spread of Laodelphax striatellus population, natural disasters such as floods and the artificial spread of infected seedlings, the source of the virus is constantly expanding.
2. Variety resistance
There are differences in resistance among varieties, and hybrid rice Shanyou 63 and Huajing 6 are both susceptible varieties.
3. Farming system
No-tillage cultivation of sowing wheat in rice field and double cropping system of rice and wheat are beneficial to the overwintering of Laodelphax striatellus. It is beneficial to the continuous transformation of Laodelphax striatellus, increases the overwintering base of Laodelphax striatellus and becomes an important source of insect population.
4. Infection rate of Laodelphax striatellus
Laodelphax striatellus is the main vector of rice black-streaked dwarf disease, and its virus-carrying rate is closely related to the incidence and epidemic. According to relevant research, in recent years, the average virus-carrying rate of rice seedlings in our county is 10.8%, and the incidence rate of Honda plants is 16.2%.
5. The coincidence degree between the sensitive period and the peak period of Laodelphax striatellus seedling.
The sensitivity of different growth stages of rice to rice black-streaked dwarf virus is quite different. According to the susceptibility test of rice at different growth stages, rice seedlings can be susceptible from 1 leaf stage to the end of tillering, but the sensitive stage is 1-6 leaf stage, and the loss of susceptibility after jointing stage is generally less. According to the investigation and analysis of the population growth and decline of Laodelphax striatellus, the seedling stage of rice is from the end of April to the middle of May, which is the peak period of 1 generation nymph. From mid-June to early July, it is the early stage of Honda, and it is the peak of the second and third generations of adults. Once the sensitive period of seedlings coincides with the peak period of Laodelphax striatellus, it will lead to the outbreak of black-streaked dwarf disease.
6. Climatic conditions
If the temperature was high from 65438+February last year to 65438+1October the following year, and the temperature was low in July that year, it would be beneficial to the epidemic of black-streaked dwarf disease. In recent years, the winter temperature in our region has become higher, and the overwintering Laodelphax striatellus has frequent activities, large base and high conversion rate. Less rainfall in spring is beneficial to the emergence and reproduction of nymphs after overwintering; Summer rainfall is more and the temperature is lower, which is beneficial to the development and reproduction of Laodelphax striatellus, and the population number increases rapidly, and the harm situation is aggravated year by year.
Fourth, prevention and control technology.
1. Agricultural control
(1) Select disease-resistant (disease-tolerant) varieties according to local conditions. Lianjing 7, Wulianjing 1, Shuangyou 205, Teyou 559 and other varieties with mild diseases can be selected in our region.
(2) Select the position of paddy field. The rice field should be far away from the diseased field, and centralized seedling raising should be advocated. Before sowing, Laodelphax striatellus on crops or weeds around the rice field should be prevented to block the migration and spread of diseases.
(3) Strengthen seedling management and popularize agricultural measures such as healthy cultivation to prevent the occurrence, migration and spread of Laodelphax striatellus.
(1) to actively test and popularize insect-proof net covering seedling raising, insect prevention and disease prevention technology. ② It is necessary to control the amount of nitrogen fertilizer, increase the amount of phosphorus and potassium fertilizer, strengthen the field management of seedlings, strictly control the growth of seedlings that are too fine, too tender and too green, and reduce the induced migration and virus transmission of Laodelphax striatellus. ③ Emphasis on rational close planting, reducing infection rate and disease harm. (4) Conditional farmers should reserve a certain number of seedlings. For the fields with poor quality of prevention and control at seedling stage and serious diseases in Honda stage, the diseased plants (clumps) should be pulled out in time within 20 days after rice transplanting, buried in the mud, and then half of the tillers should be broken off from the healthy clumps or supplemented with reserved seedlings, and appropriate quick-acting fertilizers should be applied to promote the growth and recovery of rice seedlings and reduce the damage losses. Be prepared for emergencies.
2. Chemical control
(1) Do a good job of seed dressing with chemicals. After the seeds germinate and are exposed, each kilogram of dry hybrid rice seeds can be mixed with 10% high-quality imidacloprid (such as bumper harvest) wettable powder 10- 15g, which can be directly seeded. This method can effectively control the spread of Laodelphax striatellus and the harm of rice thrips in seedling stage.
(2) At present, the most important means to control black-streaked dwarf disease is to master the appropriate control period, select the corresponding chemicals, control lice and prevent diseases, and achieve unified control.
(1) evenly spraying 20% acetamiprid 100mL and 25% fenobucarb 100mL and 40-50kg of water every 5-7 days; At the same time, weeds at the edge of the seedling field and the surrounding fields should be sprayed every time.
② Early field control 1-2 times. We should choose the chemicals that can knock down Laodelphax striatellus quickly and last for a long time. 5 grams of high-quality imidacloprid active ingredients (such as bumper harvest) or 300 grams of 25% metoclopramide wettable powder or 200 ml of 20% isoprocarb plus 50- 100 ml of 80% dichlorvos and 30-60 ml of foliar fertilizer can be sprayed evenly and finely. The above chemicals should be sprayed
refer to
[1] Liu Lei. Agricultural paper center. [09-09-1611:34: 00]. Editor: studa090420.