Occurrence of whitefly in the 2021/22 soybean harvest in Mato Grosso is observed in crops planted earlier

According to guidelines from the MT Foundation, producers must now pay attention to newer areas, which are currently in the R3 and R4 stages and, mainly, with cultivars with a longer cycle; understand why

13.01.2022 | 09:14 (UTC -3)
Dayane Pozzer

It is not new that producers, not only of soybeans, but of various crops, need to control whiteflies (Bemisia tabaci Biotype B) or even dealing with infestations in crops. In addition to the direct damage that the plague causes, there is also indirect damage, such as the transmission of several viruses that use it as a vector. In Mato Grosso, in the 2021/22 soybean harvest, it is already possible to observe the insect's adults in areas planted earlier, but still with a low population of nymphs, as the eggs and the first stages of development are not visible to the naked eye.

With research on the management of whitefly in soybeans, carried out in the Middle North of the State, the Mato Grosso Agricultural Research Support Foundation (Fundação MT) guides producers and technicians to pay attention to the newest areas of the crop, which at the moment are in the R3 and R4 stages, especially those of cultivars with a longer cycle, as they can offer food and a place for development for insects that will migrate from older areas.

Infestations in soybeans

Lucia Vivan, PhD in Entomology and researcher at Fundação MT, explains that in soybean crops, whitefly infestations begin with low populations of adults, but if there are periods of summer the tendency is for an increase in population and colonization with the presence of nymphs.

Lucia Vivan, from Fundação MT
Lucia Vivan, from Fundação MT

Another important point is that severe attacks have been observed in areas close to cotton, bean and cucurbit crops in the off-season, under a central pivot. “These host plants that end their cycles or dry out already harbored the whitefly, they are crops that act as a bridge for the pest between soybean crops”, explains Lucia.

It is common for the borders to suffer the initial attacks, as these are the areas where the insect enters the crop and are drier, more ventilated and, almost always, dustier areas, which tends to favor the pest. Crops where natural enemies have been disturbed or eliminated are also ripe for pest population explosions.

Soybean damage

Whitefly nymphs and adults cause direct damage to the crop. When they settle on the underside of the leaf, they suck the sap, extracting carbohydrates and amino acids, which can cause chlorotic spots, wilting and leaf fall. With the extraction of sap, the plants are depleted, compromising their vegetative and reproductive development. “In more severe attacks, the cycle may be brought forward by up to 15 days” highlights the doctor.

The main indirect damage, which is another major problem with whiteflies, is the fact that it is a vector of viruses from the geminivirus, carlavirus, closterovirus and luteovirus groups, which cause very severe diseases in different crops. Around 120 species of viruses have been described and are transmitted by the whitefly B. tabaci.

According to studies by Fundação MT, losses in Mato Grosso, in soybean crops where effective control is not carried out, can reach 10 to 15 bags per hectare, in relation to an area with control. However, low infestations can already cause losses, as damage from feeding and excretion of honey-dew and the development of sooty mold will interfere with the photosynthetic capacity of the plant, with negative impacts on productivity.

sooty mold

During feeding, the whitefly insect, and especially the nymph, excretes a “honeydew” that favors the development of sooty mold. It is a black fungus that grows on the leaves, darkening them, impairing photosynthesis and, consequently, can interfere with productivity, depending on the stage of the plant and the pest population present. It is the nymphs that release a large amount of this sugary substance, allowing greater growth of sooty mold on the leaves which, when they turn black, absorb a lot of solar radiation, burn and fall.

Starting point for management

One of the doubts that producers and technicians have regarding pest control is the right time to carry out management. In the case of whiteflies, Lucia Vivan explains that it is important that the areas are monitored and the adult population is checked, and when knowing the incidence of adults it is necessary to evaluate the nymph population, as the products used for control are different.

“The decision to control adults should be made when the infestation is still initial and there are no occurrences of nymphs visible to the naked eye. At this time, it is possible to use products based on neonicotinoids and diafenthiuron. Once nymphs occur, it is necessary to use specific products for the young form, such as piriproxyfen, buprofezin, cyantraniliprole, spiromesiphene, fupiradifurone, sulfoxaflor and spiropidion”, informs the entomologist.

She also highlights that the control of young forms of the insect finds good products on the market, however, they must be positioned at low infestations. “For soybean cultivation, one of the recommendations is infestations with 5 to 10 fourth instar nymphs per leaflet. Generally, the infestation begins in the lower and middle third of the plant. This low population of nymphs is due to the difficulty of identifying the population in terms of number of eggs and in the earliest instars, which is not possible with the naked eye, requiring a table magnifying glass”, he says.  

Preventive actions

As there are still no cultivars resistant or tolerant to whitefly, in general terms it is important to carry out preventive measures that discourage the development of the insect in cultivation areas. The MT Foundation recommends eliminating host plants for the pest within the crop and in neighboring areas, that is, good weed management; survey and count the pest in the field; use selective products to keep natural enemies out; destroy cultural remains; avoid planting cultivars that are very attractive to the pest; monitor training to identify the first outbreaks of the insect; selection of products considering rotation of mode of action, effect on natural enemies and stage of development of the whitefly.

Another preventive action that can be a good strategy in situations where the pest is already present, according to Dr. Lucia, is seed treatment with the aim of reducing migration to the newly germinated crop, thus preventing its establishment in the area. “But for soybean crops it is not effective due to the absence of infestation at the time of planting, however, for cotton crops in succession to soybeans it is a good initial control strategy”, she states.

Work on the whitefly

The MT Foundation develops several chemical and biological control works for whiteflies in soybean crops, as well as the susceptibility of soybean cultivars to this pest. The institution is also a source of results on host plants and pest management in cotton crops.

For work on whiteflies in soybeans, the development region is in the middle north. For cotton, research takes place in the Serra da Petrovina region, in the south of the state, and in Sapezal, in the west of Mato Grosso.

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