Viruses are obligate parasites; that is, they require a living host in order to grow and multiply. These virus particles infect the plants are extremely small and can be seen with the help of electron microscope. The diverse climatic condition is endowed with large number of viral disease outbreak in various cropping systems. Management of viral disease is much more difficult than that of diseases caused by other pathogens as viral disease have a complex disease cycle, efficient vector transmission and no effective viricide. But integration of various approaches is important to reduce the yield loss caused by virus diseases. There are essentially two approaches to manage virus diseases, similar to other plant diseases. The first approach is to decrease the source of infection (reservoirs) and secondly to minimize the rate of spread by following some of the ways and means. Cultural practices play major role in preventing the spread of disease in the field.
- Physical barriers such as fine-mesh screens for the nursery to prevent the insect (vector) movement to protect crops from virus diseases. For example, in tomato, whitefly transmitted tomato leaf curl virus was successfully reduced by using houses covered with 50-mesh screens which have decreased dramatically the number of invading whiteflies into net or greenhouses.
- Growing of barrier crops which are taller in nature around the field will reduce the virus infection and vector multiplication; hence monocot plants were tried as barriers for dicot crops. Several kinds of crops like maize, sorghum, job’s tear and pearl millet were tried as barrier crops when the main crop was of dicot family against non-persistent aphid borne viruses in different crops like chilli, pepper, potato, french beans and soybean which were effective in reducing the virus incidence under field conditions.
- Field sanitation: Removal of virus infected symptomatic plants or known alternative weed or volunteer plants that may serve as a reservoir for a virus infection
- Use of clean or sanitized tools and equipment for agricultural operation. Virus particles can be transmitted to healthy material by contaminated knives and secateurs during the preparation of vegetatively propagated material for planting in infected field. In such situations, growers should avoid the infected field to prevent transmission of virus.
- Hand washing after farm operation with infected field
- Crop rotation with non-host crops reduces the soil borne nematode/fungus transmitting viruses. For example, tomato followed by maize/barley will reduce the incidence of tomato viral disease in next season.
- Hygienic measures: Deals with decontamination of plant material, storage rooms, packing material and tools, and established rules of conduct to prevent virus/viroid spread. Tobacco mosaic virus (TMV), Potato virus X (PVX), can be spread while handling, pruning or by contact with infected plant debris or contaminated implements.
- Selection of disease free planting materials from disease free field. For vegetatively propagated crops, tissue culture techniques may be necessary to obtain disease-free planting materials. Example- Tissue culture banana
- New plantings should not be located near old plantings. For example, new tomato, capsicum, leafy crops or cucurbits or any other vegetables should not be grown nearby old fields having the same or another susceptible crop harboring virus diseases. Spread of this disease tends to decrease with increasing distance from infected field.
- Adjusting the planting time based on the insect (vector) migration i.e. avoidance of vectors by sowing late if vector migrates early and vice-versa.
- Removal of the earlier crops of either tomato, capsicum, cotton, tobacco, cereals, brassicas, cucurbits or any other crop, should be enforced immediately after the harvest. Since the older plants are not ideally suited for insect vector multiplication, insects will leave in search of better quality hosts and enhance the chances for virus movement to adjacent or nearby young susceptible plantings.
- Removal of infected plants is a key strategy which is widely used especially if the crop plant is the primary or sole source of inoculum. For example, bunchy top of banana caused by banana bunchy top virus can be managed only if affected plants are identified frequently, removed from plantations, and destroyed.
- A well-balanced supply of soil nutrients will result in healthy and vigorous plants
