Prevalence Characteristics of Rice Black-streaked Dwarf Virus Disease and Continuous Control Strategies

Deyou LIU, Yangang LIU, Lijuan LIU, Xiaomei CUI, Zhaotang SHEN, Jinqian LIU, Xiugang YU, Zhouliang WANG, Shengfeng ZHANG, Qingquan MU, Xiushan ZHAO

1.Linyi Academy of Agricultural Sciences, Linyi 276012, China; 2.Shizilu Neighbourhood Agricultural Comprehensive Service Center of Ju’nan County, Ju’nan 276600, China; 3.Guichang Township Agricultural Comprehensive Service Center of Tancheng County, Tancheng 276122, China; 4.Pulianji Town Agricultural and Rural Service Center of Cao County, Cao County 274400, China

Abstract Through summarizing the prevalence characteristics of rice black-streaked dwarf virus disease(RBSDVD)in Linyi City of Shandong Province, this paper analyzed its prevalence is related to changes in farming and cultivation systems, the increase in the population of venomous Laodelphax striatellus Fallén and its own migration and spread, the poor disease resistance of cultivated varieties, and inadequate time of prevention and control.Besides, based on the practice of local control, it came up with some comprehensive control measures including strengthening monitoring, early warning and forecasting, planting resistant(tolerant)rice varieties according to local conditions, appropriately delaying the sowing(planting)period, supplemented by insect nets to cover seedlings, and making scientific use of chemical control.It is expected to provide a reference for the prevention and control of RBSDVD.

Key words Rice black-streaked dwarf virus disease(RBSDVD), Characteristics, Prevalence reasons, Monitoring and early warning forecast, Comprehensive prevention and control measures

1 Introduction

Rice is the largest food crop of China and its stable yield directly concerns China’s food security.The rice black-streaked dwarf virus disease(RBSDVD)is a viral disease caused by

Laodelphax

striatellus

Fallén(Homoptera: Delphacidae)as the main virus carrier.It is mainly distributed in East Asian countries and regions such as China, North Korea, South Korea, and Japan, causing damage to such cereal crops as rice, barley, wheat, and maize.Once rice is infected with this virus, there is currently no direct and effective method to cure.In 1941, the RBSDVD had a major outbreak in Japan, and became an epidemic disease in Korea, Japan, and China in the 1960s.After the 1960s, the RBSDVD was mild in China.However, in the late 1990s, it occurred in the lower reaches of the Yangtze River, including Jiangsu, Zhejiang and Shanghai, Anhui and northern Fujian, cause huge economic losses.In recent years, due to various factors such as changes in farming and cultivation systems, continued warm winters, and increased overwintering hosts, the population density of

L.

striatellus

has increased, and their overwintering zone has moved northward, the RBSDVD is spreading quickly in northern Jiangsu and southern Shandong, and the epidemic was rampant in some areas.In order to effectively control the RBSDVD damage, we carried out an extensive survey, we clarified the prevalence characteristics of the RBSDVD in Linyi City, analyzed the causes of its epidemic, and came up with pertinent strategies, so as to provide reference for the prevention and control of the RBSDVD.

2 Occurrence characteristics of the RBSDVD

2.1 Occurrence area showing a trend of increasing first and then decreasing

In 2008 and 2009, the RBSDVD was accompanied by sporadic occurrence of rice stripe leaf blight, and the general diseased plant rate was 0% to 1%.In 2010, the incidence of the RBSDVD increased significantly.The area with a diseased hole rate greater than 5% was nearly 0.07 million ha, mainly involving Lindao 10, Lindao 11, and Yangguang 200, and the affected areas were mainly concentrated in Luozhuang District and Tancheng County of Linyi City.In 2011, the occurrence area was further expanded.The occurrence area of Linyi City reached 36 900 ha.Among them, the paddy field area with diseased plant rate between 1% and 5% was 20 100 ha, the paddy field area with diseased plant rate between 5% and 10% was 10 000 ha, the paddy field area with diseased plant rate between 10% and 20% was 4 200 ha, the paddy field area with diseased plant rate between 20% and 30% was 1 800 ha, and the paddy field area with diseased plant rate between 30% and 50% was 700 ha, and the area with diseased plant rate greater than 50% was 100 ha, showing that the occurrence area was all over the city.In 2012, the occurrence area was reduced to 16 800 ha, the area with diseased hole rate greater than 5% was only 0.15 ha.In 2013, the occurrence area was reduced to 7 700 ha, the area with diseased hole rate greater than 5% was only 0.09 ha.

2.2 Big difference in incidence of different rice varieties

Linyi City mainly planted conventional japonica rice.In order to prevent rice stripe disease, Linyi City planted the resistant variety Lindao No.16 in a large area from 2009 to 2013, and the incidence of the RBSDVD was different from year to year and the diseased plant rate was in the range of 1%-45%.The survey results also showed that among the main rice varieties planted in Linyi City, no variety of immune or highly resistant black-streaked dwarf disease has been found, and the RBSDVD occurred in all rice varieties.However, there is a big difference in disease resistance(tolerance)between different rice varieties.Specifically, varieties such as Lindao 11, Lindao 16, Yangguang 200, and Jinyuan 45 had an average diseased hole rate of about 40%, and they were susceptible to RBSDVD, with serious disease and large yield loss.In comparison, varieties of Daliang 203, Suxiu 867, and Yanfeng 47 had the average diseased hole rate generally below 10%, and the incidence was relatively mild.

2.3 Different cultivation methods having large difference in disease severity

2.3.1

The disease in scattered seedling cultivation field is worse than in contiguous seedling cultivation field.Due to the promotion of dry rice-nursery technology, the area of seedling fields has been greatly reduced, and some farmers often use idle land outside the fields as seedling fields.The planting situation of this kind of seedling field is very complicated.The surrounding weeds are often overgrown, and the occurrence of

L.

striatellus

is large, which makes the seedlings vulnerable to concentrated migration, and accordingly the RBSDVD in scattered seedlings fields is obviously worse than that of contiguous seedling field.According to the survey in 2010, the average diseased plant rate of Lindao 16 in scattered seedling fields was 11.2%, which was significantly worse than the average diseased plant rate of 5.5% in contiguous seedling fields.

2.3.2

Early sowing hand-planted paddy fields are worse than late sowing machine-planted paddy fields.The field area for early sowing and early planting is small, and the adults of the first generation of

L.

striatellus

migrate early, the relative migration is large, and the virus propagation time is long, so the chance of being infected is much greater than that of late planting, and the disease is obviously worse.Take the hand-planted and machine-transplanted Lindao 16 in 2011 as an example, the diseased plant rate of hand-planted dry seedlings in the field on May 5 was 15%-35%(average 25.0%); while the diseased plant rate of the machine-transplanted seedlings on May 25 was 1%-5%(average 2.5%).

2.4 Unbalanced prevention and control leading to large differences in the control effect

Since 2000, the population base of the local

L.

striatellus

has been increasing year by year.Through measures such as the selection of resistant varieties, chemical soaking(mixing)seeds, seedling field control, and field control, the rice stripe leaf blight has basically been controlled, and people’s awareness of prevention and control has gradually weakened.As a result, the control of RBSDVD is unbalanced, resulting in different incidences.Taking Lindao 16 in 2011 as an example, in strict accordance with the requirements of the prevention and control technical advice, the paddy field was controlled 4-5 times in stages.The occurrence of RBSDVD was relatively mild, and the diseased hole rate was 1.5%-6.5%(average 4.0%); for paddy fields where only the early control of the seedling field was carried out without the application of pesticide before rice seedling transplant and the transplanting of small seedlings in the fields that were not controlled in the field, the diseased hole rate was 3.5%-15.5%(average 9.5%); the seedling field was controlled 3 times, and the diseased hole rate of the transplanted field of the uncontrolled seedlings in the field was 7.5%-26.5%(average 17.0%); the diseased hole rate of the field without the control of

L.

striatellus

was the most serious, with the diseased hole rate of 35.5%-56.5%(average 46.0%).

3 Analysis of prevalence reasons

3.1 High amount and virus rate of virus-transmitting mediators

3.1.1

Outbreak of

L.

striatellus

.In recent years, affected by the warm winter climate, the overwintering population base of

L.

striatellus

in wheat fields is high, the mortality rate is low, and the population of

L.

striatellus

is increasing year by year.According to the survey in late April 2011, the first generation of

L.

striatellus

in wheat fields reached 700 000-270 000/ha, which was 1.58 times that of 2010; the number of

L.

striatellus

in rice seedlings on June 3 was 11.13 million/ha, 1.033.50 million/ha on June 6, and it reached more than 186.0 million/ha on June 9, hitting a new high.

3.1.2

L.

striatellus

has a high virus carrying rate.The amount of venomous

L.

striatellus

is the basis for the incidence of the RBSDVD.

L.

striatellus

can carry the virus for life by sucking on virulent strains.The virus carrying rate of

L.

striatellus

is increasing and the absolute number of virus carrying insects is increasing.In late April 2011, tested by the Institute of Plant Protection of the Chinese Academy of Agricultural Sciences and the School of Plant Protection of Shandong Agricultural University, the black-streaked dwarf virus carrying rate of

L.

striatellus

overwintering in wheat fields was 23.3%, and the carrying rate of

L.

striatellus

migrating into the wheat field increased significantly, showing sufficient source of virus.

3.2 Extensive hosts of

For many years, Linyi City always practices a single cultivation mode of continuous cropping of rice and wheat, and the cultivation area of wheat and rice is relatively large, which provides a suitable place for

L.

striatellus

to survive the winter safely.

L.

striatellus

not only eats rice, but also hosts other gramineous crops and weeds.The planting of infected varieties increased the spread of the host and virus of

L.

striatellus

.In the past, Lindao 11, Yangguang 200, and Jinyuan 45, which were planted in large areas, were resistant to rice stripe disease but not resistant to the RBSDVD.These varieties are conducive to the accumulation of

L.

striatellus

, leading to a large occurrence of the RBSDVD.

3.3 Effects of cultivation factors

3.3.1

Farming mode of rice intercropping with wheat.Intercropping with rice and wheat is conducive to the overwintering of

L.

striatellus

, it not only increases the overwintering population base, but also provides a large number of host conditions for the annual circulation of the virus acquisition of

L.

striatellus

.According to a survey, in 2011, the average population of

L.

striatellus

in rotary tillage wheat fields was 705 000/ha, and the average population in rice-intercropped wheat fields was 2.73 million/ha.The difference in the population of

L.

striatellus

between the two cultivation methods was nearly 4 times.

3.3.2

Sowing and planting period.The growth period when rice is most susceptible to the RBSDVD is the seedling stage before the tillering stage and the pre-tiller stage.In the past, rice was sown in early May.By early June, the seedlings grew green and luxuriant, providing ample food supply for the first generation of

L.

striatellus

, practice has proved that

L.

striatellus

occurs in early sowing and early planting fields.

3.3.3

Prevention and control technology is not in place.Continuous use of organic phosphorus and pyrethroid pesticides in rice and wheat fields significantly stimulated the proliferation of

L.

striatellus

.At present, imidacloprid, the main agent used to control

L.

striatellus

, has a poor control effect on

L.

striatellus

, and resistance(tolerance)may have appeared, which is conducive to the accumulation of insect sources.In addition, farmers are not sufficiently aware of the control of the RBSDVD, neglect the pest control in the wheat field, and the control is not effective during the seedling stage.The pesticides are used only when the disease appears in the field, which increases the cost of pesticide use and fails to achieve the control effect.During the field stage, most farmers did not use the medicine timely and uniformly, the dosage of the medicine was insufficient, and the medicine could not reach the base of the rice plant.As a result,

L.

striatellus

was not killed in time, and the effect of preventing and controlling the RBSDVD could not be achieved.

4 Continuous control measures

The RBSDVD is a viral disease caused by

L.

striatellus

.The degree of disease occurrence is related to variety resistance, cultivation methods, the amount of

L.

striatellus

and the level of virus carrying rate.Considering the current and future structural adjustments in the rice planting industry, the cultivation system, and the prevalence of the RBSDVD in Linyi City, we came up with the prevention and control measures controlling the insects and diseases, cutting off the virus sources, and eliminating

L.

striatellus

before migrating to the rice seedlings, and taking agricultural ecological control as the basis, and attaching great importance to scientific application of pesticides.Besides, it is recommended to promote comprehensive prevention and control measures of "resistance, avoidance, interruption and treatment" to reduce the occurrence of

L.

striatellus

and the risk of virus transmission, prevent or reduce the occurrence of the RBSDVD.In addition, it is recommended to strengthen publicity and training, popularize scientific prevention and control knowledge and prevention technology, improve plant protection service level and the initiative of farmers in prevention and control, improve diagnosis and identification, pest control and disease prevention technology, and strictly prevent the recurrence of RBSDVD on a large scale.

4.1 Strengthening monitoring, early warning and forecasting

The RBSDVD is a viral disease transmitted by

L.

striatellus

.Once the viral mediator is transmitted, it will carry the virus for life, but it will not be transmitted through eggs.Therefore, it is necessary to do a good job of forecasting

L.

striatellus

.The agricultural plant protection department should do a good job in the general survey of the overwintering population of

L.

striatellus

, and accurately forecast whether

L.

striatellus

occurs in combination with the winter and spring climate of the year.If the overwintering population of

L.

striatellus

is large and the winter is warm, and the temperature in spring is high and the rainfall is low, the possibility of the occurrence of

L.

striatellus

is very high.It is necessary to issue forecasts through various media in time to enable grassroots agricultural technology departments to cooperate with the local government to prepare for the prevention and control of

L.

striatellus

and the RBSDVD.

4.2 Agricultural ecological prevention and control

4.2.1

Planting resistant(tolerant)varieties in accordance with local conditions.It is recommended to select the disease-resistant varieties and take advantage of their own resistance to achieve the purpose of active control, which is the most economical, effective, easy and environmentally safe control measures for the RBSDVD.In the selection of rice varieties, it is necessary to adhere to the principles of high quality, high yield and multiple resistance, and popularize varieties that have been resistant(tolerant)in production in recent years, such as Lindao 21, Daliang 203, Yangguang 800, Ningjing 4, Suxiu 867 and Yanfeng 47which have obvious disease prevention and control effects.In addition, government departments at all levels should increase their investment in rice breeding, and agricultural scientific research organizations should concentrate their efforts on collaborative research, and select and breed excellent varieties that are resistant to the RBSDVD as soon as possible on the basis of existing breeding materials.

4.2.2

Properly postponing the sowing(planting)period.It is recommended to vigorously promote the application of cultivation techniques such as dry seedling raising and machine transplanting seedlings, reduce conventional water raising seedlings, and keep the rice seedling fields away from the wheat fields as far as possible, in order to facilitate management and unified control of

L.

striatellus

.Production practice shows that in the suitable sowing period, appropriately postponing the rice sowing(planting)period can significantly reduce the occurrence of plant diseases.Dry seedlings should be sown around May 15 to avoid the damage period of

L.

striatellus

and reduce the duration of the virus transmission.The transplanting period should be postponed to after June 20, avoiding the peak number of

L.

striatellus

emigration, which can effectively reduce the early migration of the first generation of

L.

striatellu

adults and reduce the incidence of the RBSDVD.

4.2.3

Cutting off the source of

L.

striatellus

.(i)Promoting mechanical rotary cultivation of wheat to reduce the overwintering population of

L.

striatellus

.For many years, most of the rice stubble in Linyi City has been sown with no-tillage.Due to less changes in the ecological environment, it is very favorable for the survival and overwintering of

L.

striatellus

, which increases the incidence of the RBSDVD in the next year.Therefore, it is necessary to vigorously promote mechanical rotary tillage to eliminate stubble and grow wheat, destroy the suitable environment of

L.

striatellus

, reduce and control the overwintering population, and reduce its harm.(ii)Removing weeds on the sides of ditches and roads to reduce the source of infection.Weeds are an important place for the activity of

L.

striatellus

and the intermediate host of the RBSDVD.Weeds in wheat fields, rice seedling fields and the surrounding fields should be removed to worsen the living environment of

L.

striatellus

and reduce the transition host, cut off the host chain, and reduce the incidence of the RBSDVD.(iii)Covering the seedling fields with insect-proof nets.Covering rice seedlings with insect nets is an effective measure to actively control the RBSDVD.After rice sowing, 40-mesh white polyethylene special-shaped insect nets can be used to cover the seedlings throughout the entire process.In this way, it can prevent

L.

striatellus

from entering the seedlings and transmitting viruses.The efficiency can reach more than 90%.(iv)Strengthening the field management.During the seedling period, it is necessary to balance the fertilization, and organic fertilizer should be applied as much as possible, and the amount of chemical fertilizer should be appropriately controlled.In particular, do not apply nitrogen fertilizer, increase the application of phosphorus, potassium and silicon fertilizers,

etc.

, and strictly control the over-tenderness and over-greenness of the seedlings, to avoid the transmission of the virus-carrying

L.

striatellus

.It is recommended to carry out moisture management in the field.Never conduct deep water irrigation, promote the steady growth of seedlings, and enhance the ability of plants to resist diseases and insects.During transplanting, it is necessary to appropriately increase the number of plants per hole to ensure the number of basic seedlings, and promptly remove diseased plants from diseased fields to reduce the virus sources.Besides, taking advantage of the characteristics of strong tillering power and strong compensatory ability of rice, it is feasible to transplant 1/2 of the healthy plants from the surrounding disease-free rice plants to the holes left by the diseased plants.At the same time, it is recommended to spray 0.136% VitaCat WP or 2% Junkeduke(ningnanmycin)AS and other virus inactivating agents, and appropriately increase foliar fertilizer to restore the growth of rice with mild disease and reduce the damage.

4.3 Scientific and chemical prevention and control of

, and control of virus-carring hazards

4.3.1

Conducting comprehensive seed dressing.Seed dressing with 50% pymetrozine WG or 60% imidacloprid suspension seed coating agent(Gaoqiao)can inhibit the transmission of

L.

striatellus

in the seedling stage, thereby effectively controlling the occurrence of the RBSDVD and reducing the frequency of application, save medicine and labor, and avoid environmental pollution.

4.3.2

Control of

L.

striatellus

in wheat field.It is necessary to control insects every other day or continuously, the control of

L.

striatellus

in wheat fields is an effective method to cut off the mediator of the RBSDVD.For the wheat field, it is necessary to spray pesticide in the young nymph stage of the first generation of

L.

striatellus

.It should be applied twice in the year when

L.

striatellus

occurs on a large scale.In Linyi City, it should be used on May 15 and May 20, including the weeds on the ditches, canals, and field ridges.For the first time, it is necessary to combine the wheat "one spray and three prevention" technology, spray 25% pymetrozine WP 300 g/ha or 10% nitenpyram SL 300 mL/ha; for the second time, use 80% dichlorvos EC 4 500 mL/ha with water and mix an appropriate amount of dry fine soil and sprinkle it into the wheat field for fumigation at a later date.

4.3.3

Seedling field and field prevention and control.It is necessary to choose the proper pesticide, use adequate pesticide, and cooperate with the long-acting pesticide and quick-acting pesticide, and use different pesticide formulas alternately to improve the control effect and delay the resistance.The seedling stage is a critical period for the prevention and control of

L.

striatellus

infection.The amount of

L.

striatellus

in the seedling field in Linyi City in 2011 was a rare year in history.The adult

L.

striatellus

in wheat fields continuously rushed to the seedling fields.In early June(before the wheat harvest), the number of insects in the seedling field increased rapidly.Despite continuous control, the number of insects continued to stay high.The control strategy must be a combination of rapid killing and long-acting pesticides, and it is necessary to make preparation for continuous application.For example, dichlorvos fumigation can be used to kill the

L.

striatellus

quickly.Besides, it is recommended to empty the seedling field water and leave the ditch water, use 80% dichlorvos EC 1 500-1 950 mL/ha, spray 675 kg of water evenly, after 5 h, it can kill more than 85% of

L.

striatellus.

After June 15(wheat harvest), apply 5% pymetrozine + toxic EC 375 g/ha or 40% Xinnongbao(chlorpyrifos)EC 1 125 g/ha to the shallow water layer to spray 675 kg of water evenly.Around June 20(before transplanting)during the egg incubation period of the second generation of

L.

striatellus

, it is required to concentrate on controlling the second-generation

L.

striatellus

, spray 50% Tuosheng WP 375 g/ha and 675 kg of water evenly.In order to delay the resistance of

L.

striatellus

to chemical pesticides, the selected pesticide varieties should be used alternately, combined with practical experience to rationally match(mix)pesticides, and treat other diseases and insect pests simultaneously to reduce the frequency of pesticide application, so as to save labor and cost, and increase efficiency and reduce resistance.

It is recommended to establish a suitable control period that focuses on the 2-7 leaf stage of the seedlings with the early field stage as supplement, and appropriately increase the dosage.In epidemic and prevalent areas, the frequency of prevention and control should be appropriately increased, and if the residual insects still reach the prevention and control target after each prevention and control, it is required to continue implementing the prevention and control.In addition, in order to effectively control the disease prevalence, single-family prevention and control should be changed to unified prevention and control, and implement the unified prevention and control at a unified time, so as to ensure effective control in the entire region.