How to manage begomovirus or geminivirus in tomato crops

Currently, one of the most worrying diseases in tomato is begomovirus (also known as geminivirus). This virus is naturally transmitted through the feeding of the insect vector, known as whitefly (species Bemisia tabaci). There have been reports of the presence of whiteflies in the country since 1950, and at that time severe epidemics of begomovirus were not reported. However, at the beginning of the 1990s, a new whitefly biotype was introduced into the national territory, identified as biotype B and different from the one previously present (biotype A). Biotype B whiteflies are more aggressive, produce more eggs, are highly adaptable, easily develop resistance to insecticides and are capable of feeding on a large number of hosts. Among the main hosts are soybean, bean, cotton and tomato plants. This biotype became the predominant one in Brazil and enabled the movement of viruses between plants. As a result, in just a few years, begomoviruses became important in several crops, especially tomatoes.

Begomoviruses are spread throughout Brazil. There are several species of begomovirus that cause disease in tomato plants in Brazil - at least 11 species have been reported. The main symptoms of begomovirus infection in tomato are: lightening of veins; chlorotic spots on the leaves, which vary from mottled to intense mosaic; deformation and curling of leaves; decrease in leaf area; dwarfism; although there is no expression of symptoms in the fruits, there is a reduction in the size and quantity of fruits; When infected early, the symptoms are more severe and the plant's growth stops.

The incidence of begomovirus in different regions of Brazil is highly dependent on the population of whiteflies present in the area. Furthermore, there is a difference in the incidence of begomovirus in industrial tomatoes and table tomatoes. In tomato plants of indeterminate growth (table tomatoes), whose fruits are intended for fresh consumption, there are cultivars that have a good level of resistance and these are mandatorily used in regions with a high incidence rate. On the other hand, for tomato plants with determined growth, intended mainly for agribusiness, the incidence of begomovirus is much more problematic, reaching 100%. Sometimes, total crop losses are observed. The supply of hybrids with resistance is small and there is great difficulty in controlling whiteflies in large areas.

Infection caused by begomoviruses in tomato plants can cause serious damage, especially when plants become infected early, within three weeks of transplanting. Efficient control of begomovirus is based on delaying plant infection. The first 30 days after transplantation are decisive for the success or otherwise of disease management. However, delaying the onset of infection is not an easy task, which is why control of the disease must be started even before transplanting the tomato plant. For the management of begomovirus, the first point to be considered is to define the planting schedule throughout the harvest, avoiding staggered (successive) planting of tomato plants in neighboring areas. When this is not possible, the age between crops and plants within the same crop must not exceed 60 days. The next step is to select cultivation areas without a history of begomovirus occurrence, although this is a complex task nowadays. Planting time is also important. You should avoid periods with high populations of whiteflies, multiplied in other crops, such as soybeans, cotton and beans. A fundamental recommendation for a good tomato producer is to control whiteflies in neighboring crops, especially those that act as whitefly multipliers (soybeans, cotton, beans and cucurbits).

The area to be cultivated must be free of “tigueras” plants (volunteer plants from previous cultivation) and weeds, as they can host both the virus and multiply white flies. white flies such as begomovirus. The choice of cultivar is also essential for successful control. There are varieties that can withstand high pressure of viruliferous whiteflies (which carry the virus) without becoming infected or showing weaker symptoms. Another key factor is the use of healthy seedlings, which must be produced in closed screens that prevent insect vectors from entering and in a location far from production areas.In addition, these seedlings must be properly sprayed with insecticides before leaving the nursery.

It is necessary to make it clear that spraying any insecticide in the cultivation area may not be as efficient in controlling viruses as imagined, as viruliferous whiteflies are capable of transferring the viruses in a few minutes, before the insecticide kills the insect. Spraying with insecticides prevents these whiteflies from transmitting the viruses to other plants around the one initially visited by the vector. Therefore, periodic control of the vector must be carried out mainly until the first month of transplantation. After this period, the infection is not as severe, but control of whiteflies must continue in order to avoid direct damage caused by the attack of this pest and prevent the movement of large numbers of viruliferous individuals to new areas. A high population of insects can cause uneven ripening and isoporization of the fruits, in addition to multiplying the vector for the next crops. It is worth remembering that controlling whiteflies with insecticides must be done with products duly registered for the crop, in addition to planning the sequence of insecticides, considering the rotating use of active ingredients belonging to different chemical groups and mechanisms of action to reduce the risks of selection of insecticide-resistant insects. It is not enough to change the product based on its commercial name.

The elimination of crop residues immediately after the last harvest is also crucial for the management of begomoviruses on a farm scale, as the absence of live plants or the formation of a tomato seed bank in the area from abandoned fruits (the main cause of tigueras) drastically reduces the local whitefly population and the source (inoculum) of viruses in the field. In addition to this, a period of sanitary emptiness was proposed for implementation on a regional scale precisely to combat begomoviruses and their vector, the whitefly. This period strongly contributes to reducing the sources of begomovirus in nature and must be followed strictly. The sanitary void must be adopted, so that the cultivation area and all other areas close to it are, simultaneously, free from the crop and from plants that host tomato pests and viruses for at least 60 days. The sanitary void was instituted for creeping tomato plants in Goiás, in such a way that transplanting is only allowed between January 1st and June 30th. In staked tomato plants, the sanitary void period was instituted in some municipalities in Goiás, close to the main areas of trailing tomato production.

All control measures listed will not be efficient if they are not used jointly with neighboring producers, on a micro-region scale. Management carried out by a producer in isolation has a high cost and low return. To win the fight against whiteflies and begomoviruses in tomato plants, it is necessary to know the management strategies and these must be implemented in a conscious, planned and organized way among producers, to be carried out considering the entire agricultural system in the region.

Photo 1. Tomato plant infested with a high population of whiteflies. (photo: Alice K. Inoue-Nagata)

Photo 2. Tomato plant infected early with begomovirus showing severe symptoms. (photo: Mônica A. Macedo)

This article was published in issue 86 of Cultivar Hortaliças e Frutas magazine. Click here to read the edition.