Tiguera plant management

Tigueras or volunteer plants are those of the cultivated species, those of economic interest, that spontaneously infest the next crop when the seeds of fruits left in the field after harvest germinate. In tomato crops, both for the industrial and consumer segments in natura, it is common for tigueras to occur between crop lines and between plants transplanted into the crop line. In general, they are observed in clumps, as a result of fruit left in the field after harvest.

Tickers are considered weedy or invasive plants because they are not desired in the new crop resulting from the establishment of a new cultivated species or even the same species. Tigueras compete with the newly installed crop of economic interest for water, light, nutrients and CO₂, such as common weeds such as black maria (Solanum americanum), joá-de-capote (Nicandra physaloides) and milkman (Euphorbia heterophylla), easily found in tomato crops. They are also important sources of initial inoculum for phytopathogens that can be transmitted by seeds and those transmitted through insect vectors, such as viruses. Thus, pathogens and insect vectors are perpetuated in crops with each cycle of the host crop, even when this crop is rotated with crops of different species of non-host plants. This is because the seeds of tiguera plants can remain viable in the soil, presenting several emergence flows over time.

Seed-borne pathogens

As xanthomonas that cause bacterial spot (Xanthomonas perforans, Xanthomonas gardneri, Xanthomonas vesicatoria e Xanthomonas euvesicatoria), an important crop disease due to its frequency of occurrence and destructive capacity, are susceptible to transmission by tomato seeds (Leite et al, 1995). This is perhaps the disease whose importance in tigueras is most evident in the tomato growing conditions in the country (Quezado-Duval et al, 2008; Quezado-Duval & Lopes, 2010), mainly for crops destined for industrial processing. Observations were made of tomato tigueras in commercial crops in Goiás and São Paulo showing symptoms of the disease, followed by sample collection, isolation and identification of the species at the Embrapa Hortaliças Phytopathology Laboratory. In this segment, the role of tigueras that occur in succession/rotation crops in increasing the local seed bank is still unknown. It is believed that, due to the shading of the main crop or the application of herbicides, these plants do not produce fruits/seeds in a significant way. Since then, the bacteria has been detected in tomato tigueras in both segments.

In general, when the initial inoculum sources are tigueras, the cultivated tomato plants are in good health at the beginning of cultivation and become generally infected in the area. This pattern differs from a condition where the source of inoculum is the cultivated plants themselves, for example, from infected/infested seeds, whose pattern due to the low initial incidence is in foci. The environmental conditions that favor the disease are high temperatures and high humidity, predominant in the rainy season or throughout the cultivation period under central pivot irrigation, conventional sprinkler or planting furrow irrigation conditions, the latter considered a common practice in agricultural crops. staked tomato for the table in Brazil. Water splashes (rain or irrigation) then carry the bacteria, spreading it from plant to plant, which can be from the tiguera tomato plant to the cultivated one.

Other phytopathogenic bacteria such as Pseudomonas syringae p.v. tomato that causes bacterial blight and Clavibacter michiganensis sub sp. michiganensis that causes bacterial cancer can be transmitted by seeds (Jones et al, 2014), as well as some fungi such as Septoria lycopersici (which causes septoria), Alternaria spp. (black spot) and Fusarium oxysporum f.sp. lycopersici (fusaria wilt), among others, and viruses such as ToMV (tomato mosaic) (Inoue-Nagata et al, 2005). Therefore, they are also pathogens with the potential to perpetuate themselves in tomato growing areas through tiguera plants. It is also worth remembering that not all tomato pathogens have the issue of infection and transmission through seeds well understood.

Pathogens transmitted by insect vectors

Most viruses that infect tomato plants are transmitted by insects. In this case, they are called vectors. Two groups of insects currently draw attention as important vectors that can find shelter in tigueras: whiteflies and thrips. Whiteflies are vectors of geminiviruses (or begomoviruses) and criniviruses in Brazil. There are several species of geminiviruses (for example, Tomato severe rugosis virus) reported in Brazil and a species of crinivirus (Tomato chlorosis virus – ToCV). Thrips are vectors of tospoviruses (Tomato spotted wilt virus, Tomato chlorotic spot virus e Groundnut ringspot virus) that cause the disease known as tomato leaf turner. Then aphids appear as vectors that can cause problems. Tomato plants have not been shown to be hosts for aphids, but there are reports of damage caused by viruses following flights of aphids in tomato crops. The viruses transmitted by aphids are potyviruses and a cucumovirus.

Airborne foliar pathogens

Pathogens that cause foliar diseases, such as xanthomonas and Pseudomonas, as well as those that are not known to be transmitted by seeds, such as the fungus Phytophthora infestans which causes late blight and powdery mildew (Leveilulla taurica, Oidium lycopersici e Oidiopsis sicula), can be carried by wind and water splashes and thus be transmitted from plant to plant. Thus, these pathogens can pass from undecomposed crop remains of old crops to the tomato bush plants that appear in these areas and from there to the transplanted tomato plants from the new commercial crop.

Soil pathogens

The role of tigueras for this group of systemic pathogens³, like bacteria Ralstonia solanacerarum (bacterial wilt) and Pectobacterium spp. (hollow stalk) and fungi Fusarium oxysporum f.sp. oxysporum and the Verticillium spp., which cause wilting, as well as root-knot nematodes (Meloidogyne spp.), is not well elucidated. However, potentially, the importance would be in increasing the inoculum in the area through multiplication in tigueras and transmission through soil transport in machinery or by people moving between areas of infected old crops and with infested soils and those of healthy new crops. and not yet infested.

Tigueras as weeds

Tomato tigueras compete for essential resources in the agroecosystem (water, light, nutrients and CO₂) with the crop of commercial interest implemented in succession or rotation (be it the tomato itself or another cultivated species such as soybeans, corn or beans). This causes a reasonable loss of productivity, which can vary depending on the distribution and density of plants emerging in the commercial crop. However, it is necessary to manage them in such a way that they do not cause harm to the farmer. It is worth mentioning that great genetic variability is expected among tomato tigueras, since they are successive generations of a hybrid (F1), increasing the adaptive capacity to the local environment.

Management of tiguera plants

crop rotation. This practice consists of planting different crops at the same time, only to return to planting the same crop after at least three cultivation periods. Crops in rotation should preferably belong to botanical families different from those of tomato, which can be hosts for the same pathogens, such as potatoes, peppers, tobacco and eggplant. Furthermore, care must be taken when choosing the species for rotation to avoid those that multiply insect vectors. The aim is also to reduce the soil seed bank and facilitate the management of tigueras, as well as weeds. However, crop rotation is beneficial because it allows the use of herbicides that are known to be effective in controlling tigueras and weeds that traditionally infest tomato plants during the cultivation of crops that make up the rotation system, making it possible to reduce infestation in their crops. cultivation cycle. In this context, crops such as soybeans, corn and beans are good alternatives to be included in a crop rotation program, as they have a wider range of registered herbicides. The application of herbicides with residual activity at the beginning of the rotational crop cycle, for example, makes it possible to control several emergency flows of tigueras that, in turn, could be infesting the tomato plant in succession. However, it is necessary to check the residual activity on the tomato plant of that herbicide used in the previous crop. Chemical control will be covered in a specific topic later.

Harvest care. One of the ways to reduce the problem of tomato tigueras in subsequent crops in succession is to prevent fruit losses from occurring during harvesting procedures. Thus, in the case of tomatoes for consumption in natura, workers must be properly oriented and trained to avoid leaving tomato fruits on the farm that could give rise to new plants. When growing tomatoes for industrial processing, the harvester must be adjusted so that fruit losses during harvest are minimized. To this end, it is essential that the harvest is carried out with the fruits at the recommended stage of maturity, which may vary depending on the tomato genotype cultivated, and that the harvester is properly adjusted so as not to drop fruits on the ground. Likewise, destroying cultural remains immediately after the end of the harvest phase, not abandoning tomato crops at the end of the cycle, helps to reduce the remaining seed bank and breaks the continuity solution between cultural remains-tigueras-new crop , on site or in adjacent areas.

Toilet void. Normative Instruction SDA 024 (15/4/03) published by the Ministry of Agriculture, Livestock and Supply, regulated the sanitary void of tomato plants. The measure focuses on the management of whiteflies and geminiviruses, establishing a period of two months without trailing tomato plants for processing and various integrated pest management measures, in an attempt to reduce the incidence of geminiviruses. The void was implemented in Goiás (largest producer of tomatoes for processing, Agrodefesa IN 005/07; IN 002/08; IN 006/11), but is informally followed in São Paulo and Minas Gerais (second and third largest tomato producing states for processing). The adoption of the phytosanitary void provides that the tomato cultivation area and all other areas close to it are simultaneously free from tomato bushes before the tomato harvest for at least the two-month period established by IN. Therefore, controlling tigueras is crucial to the success of the stipulated sanitary void.

Grooming. This practice will only have any effect in terms of managing crop diseases when carried out before contact occurs between the cultivated plants (closing the lines). If the tigueras already show symptoms, they should also be removed from the site, taking care to avoid movement between the plants when their leaves are wet from dew, rainwater or irrigation water.

Weeding. During the tomato harvest, it is recommended to mow around the production fields to reduce potential tiguera bushes, in order to reduce the sources of inoculum for the various pathogens that infect tomato plants.

chemical control. Before transplanting the tomato crop, both in the in natura As with industrial processing, the producer can use desiccant herbicides to control the tiguera plants present in the area. In addition to being important in contributing to the reduction of inoculum sources for tomato pathogens, the measure acts to suppress the infestation of insect vectors, as with the desiccation of the tigueras most of the insects that are in the immature phase (eggs and nymphs) cannot reach the adult stage, thus reducing the transmission of viruses to new tomato crops. The herbicides chosen cannot present residual activity that could compromise the tomato cultivation that will be implemented. To this end, it is recommended to apply glyphosate, paraquat or carfentrazone-ethyl in a single or sequential application. Sequential application is more suitable for a situation in which the interval between harvesting the previous crop and transplanting the tomato plant is at least 20 or 30 days, making it possible to control another emergency flow of tigueras. For example: the producer can make a first application with glyphosate two to three weeks before transplanting and a second application of paraquat or carfentrazone-ethyl a few days before or the day before transplanting. If the interval is short, the producer can make a single application of desiccant herbicide. It is important to mention that a new emergency flow of tigueras will only occur if there is rainfall or irrigation during this period to stimulate the germination and emergence of these plants. Thus, in the case of tomato plants for industrial processing transplanted in months with little rainfall, it will likely be necessary to apply irrigation sheets to stimulate the germination and emergence of tigueras for subsequent control before tomato plant transplantation. Research by Embrapa Hortaliças in partnership with Cargill Agrícola S/A and IF Goiano (Campus Morrinhos) has shown that some herbicides not registered for the crop, such as paraquat + diuron (300 + 150g a.i. ha^-1) and flumioxazin (25g a.i. ha^-1), present an excellent level of weed control in pre-transplantation (pre-emergence of weeds) without compromising tomato productivity (Cavalieri et al, 2012). These herbicides could be used as desiccants before transplanting to eliminate tomato scabs, also presenting residual activity for weed control after tomato transplantation. Both herbicides, in fact, present excellent control of important weed species: maria-pretinha, joá-de-capote, caruru (Amaranthus spp.), white poaia (Richardia brasiliensis), buttercup (Galinsoga parviflora) and black walleye (bidens pilosa) when applied three days before tomato transplantation and complemented with the sequential application of metribuzin (168g a.i./ha) at 15 and 30 days after seedling transplantation. It is also believed that they can be applied in a targeted manner between the rows of tomato crops to control tigueras, which emerge after transplanting, consequently helping to control weeds present at the time of application and new emergency flows due to of residual activity. These results are promising for the purpose of obtaining registration by companies that own these molecules, in order to expand management options for tomato producers.

Systemic pathogens: pathogens that reach plant vessels, causing vascular wilt.

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