How to avoid new generations of whiteflies on soybeans

Crops Successive successions are highly favorable to infestations of pests such as whiteflies, which in the proportion of 10 nymphs per leaf have led to losses of the order of 12 bags per hectare in soybeans. Insecticide applications, always combined with other integrated management strategies, must be carried out in the first culture implanted in the countryside, in order to break the cycle and avoid new generations of the insect.

The Brazilian cerrado region is characterized due to the presence of extensive and highly mechanized areas. The agroecosystem used is highly favorable to the multiplication of pests, as A production system prevails in which soybeans are the main crop to be grown. establish in the vast majority of areas, being rotated many times with cotton or corn in certain regions and years. This successive cultivation caused many pests adapted to the system. In addition to this, other factors, such as conditions Favorable climates, with high temperatures and mild winters, become ideal for the multiplication of insects. Among the pests, the whitefly, bemisia tabaci biotype b, have caused great concern and losses for some producers of soybean, cotton, beans, etc.     

The whitefly, bemisia tabaci biotype b (Gennadius, 1889), is a polyphagous insect, whose reproduction has already been observed in more than 500 different plant species, belonging to different botanical families. It belongs to the order Hemiptera and family Aleyrodidae. The whitefly's biological cycle can vary from 17 days to 45 days, being influenced mainly by temperature.

Adults are around 2mm in size long with four white membranous wings. The female can lay more than 200 eggs. The light green to light brown eggs are placed on the underside of the leaves. Hatching, the nymphs are mobile in their first stadium. After selecting a location, they insert their stylet and fix it, not moving anymore. Adults emerge after four instars.

As it is a sucking insect, during sucking of nutrient-rich substances and water from plants, whiteflies can introduce toxins that cause uneven development in the plant and fall in productivity. Furthermore, it secretes a sugary substance on the leaves that favor the growth of opportunistic fungi, in the case of the genus capnodium spp. leading to coverage of the leaf by this fungus, commonly called  Fumagina. This leads to a reduction in leaf area and photosynthetic rate, and consequently productivity.

Another characteristic is the ability to transmission of viruses, especially of the genus Begomovirus – Geminiviridae, in addition to the genus Carlavirus  Cowpea mild mottle virus – CpMMV (which leads to stem necrosis and subsequent death of plants).

Some areas in Brazil have presented plants with viruses, which lead to small losses. However, it is It is necessary for technicians, when noticing the presence of abnormal plants, to carry out collection and sending to laboratories to identify possible viruses. This one problem in soybeans must be treated with great importance since it is the main commodity Brazilian in agribusiness.

The Q or Mediterranean biotype is already found in Brazil, being the subject of studies by entomologists from IAC and Embrapa Arroz e Bean. The states of Rio Grande do Sul and São Paulo have already had this occurrence reported. This biotype was introduced in the USA around 2004 and the occurrence identified in Uruguay and Argentina in 2012.

In soybean crops, whiteflies can start its occurrence in the first few days, in some regions with greater pest pressure. Its damage is commonly only noticed during the grain filling phase, as the Plants tend to finish their cycle before the normal deadline, with smaller grains and consequently reducing production. This often occurs due to the presence of sooty mold.

High infestations in soybeans when not controlled or maintained in populations that do not compromise productivity, they may migrate to adjacent crops or even in succession. It is the case that some regions where the production system is more intensive, such as Chapadões and even in the irrigated areas of Mato Grosso, Goiás, Tocantins, Minas Gerais, Bahia and Maranhão, with crops such as beans, soybeans and cotton.

In cotton cultivation, whiteflies can still cause the problem of stains on the fibers, with the occurrence of fiber sugar (caramelization), causing a decrease in quality, especially in type. Its dispersion can occur by winds, which leads to large distances. It presents uneven distribution in crops, and the technician must pay attention to the borders that may receive migrant populations from other plots/crops.

Monitoring this pest at the beginning of infestations may focus on the presence of adults and with the development of the crop, attention must be paid to pest nymphs and eggs, depending on the colonization. At this stage, the aid of magnifying glasses of 20X or more should be inside the tools to be taken to the field or even the collection of sheets to send to the laboratories.

With the advent of soy Bt A certain amount of carelessness has been observed due to the lower occurrence of caterpillars, leading the technician and the producer to a false sense of tranquility in in relation to pests, which end up reaching high populations, being perceived in form late for its management.

Normally, control measures for whiteflies should be intensified during hot periods, when they occur insect population increases. The producer and his technician, when present common pest in the region, or even on the property, must draw up strategies to reduce the population. Integrated management of this important pest makes It is necessary to avoid staggered planting of crops as this tends to increase populations in final plantings. It is recommended to eliminate cultural remains, removing plants with viruses and hosts, such as weeds. The use of yellow traps with oil for monitoring can also reduce the population.

The control index for this pest is still part of studies from several institutions in Brazil. However, it is worth highlighting that in work on soybean cultivation, the plant coexists with an average of 10 nymphs per leaf led to losses in the order of 12 bags per hectare (TOMQUELSKI et al 2011).

The most used and practical alternative is the chemical control in which neonicotinoids such as Acetamiprid, Clothiadinim, Imidacloprid, Thiacloprid and Thiamethoxan, insecticides with greater successfully, used with action on adults and young forms. On the market there are also growth regulators that act on young forms such as cyantraniliprole, pyriproxyfen, spiromesifen and buprofezin with action on eggs and nymphs. New insecticides are being developed as ready-mixes (neonicotinoids+juvenoids) for the producer, in addition to new molecules. It's possible mention dinotefuran, in addition to flupyradifurone, with excellent action on nymphs.

Biological control is a tool interesting for management, since there are few active insecticides in the control of this pest. beauveria bassiana It is the species most used to control whiteflies. Insecticides must be applied at the end of the day and with humidity for satisfactory control of the insect.

Biological insecticides can also be used within management programs, interspersed with chemicals or even associated at certain times. It is worth noting, in this case, that the Producer must consult the manufacturing company about compatibility. In some work carried out at Fundação Chapadão has seen efficiencies interesting.

What is often observed is the application late in controlling this pest, in some cases due to lack of knowledge or poor sampling. Some applications in high infestations may not produce the desired effect depending on the application technology and other factors. In this In this case, the remains of the pest in the system must be analyzed, leading to reapplications for control.

When there are successive crops on the property, applications must be carried out on the first crop planted in the field, in order to prevent last plots will show high infestations. This practice of attacking Eggs and nymphs must often be analyzed as the pest cycle breaks, avoiding new generations.

In this battle, the knowledge of the whitefly, good sampling and definitions of integrated control strategies are tools that help the producer in control and consequently provide the increased productivity in soybean cultivation.

Percentage efficiency of some insecticides on the nymph population of B.tabaci biotype B in soybean cultivation. Chapadão Foundation. Chap.Sul/MS. 2016.G.39.

Article published in issue 215 of Cultivar Grandes Culturas, April 2017.