Harvest with higher whitefly pressure

The 2023/2024 harvest in the Brazilian Cerrado was characterized as one of the most challenging for rural producers, and, among the adversities faced, without a doubt the climate was what became the biggest challenge.

The harvest began with the so-called “el Niño”, classified as high intensity, which brings irregularities in the normal establishment of rainfall; and a strong alternation between heavy rains and prolonged summers. Added to this are high temperatures. In some regions of the state, an increase of around two to three degrees Celsius (°C) in average temperatures was noted compared to the previous year.

Naturally, due to the climate factor, changes occurred in the sowing schedule, mainly in crops such as soybeans and cotton. The condition also contributed to the decline in the performance of herbicides for controlling weeds and tigueras, leaving a high presence of “invasives” in the environment that became a source of multiplication and shelter for pests.

This scenario has become the perfect environment for the proliferation of some groups of insects considered pests, which at high rates of occurrence directly impact the increase in production costs. Among them, the whitefly, Bemisia tabaci, a sucking and highly polyphagous insect, stood out. During the harvest, the fly presented highly high population rates and consequently stood out as one of the main pests of the harvest. It has also occurred in corn, a crop that, when compared to soybeans and cotton, is a much less preferred host.

Whiteflies in years with milder climates have a development cycle of around 25 days. Under the conditions experienced in the current harvest, combined mainly with the increase in temperature, there was an acceleration in its development cycle to something around 18 days. Consequently, there were a greater number of generations throughout the harvest.

This factor was proven by the producer in the field, who promptly made a greater number of insecticide applications. These applications, depending on the timing, did not appear to reduce the pest population. And that raised some doubts. For example, which biotype is predominant in the region (B or Q)? Has there been a drop in performance of some molecules? Has biological management proven to be effective in these climatic conditions?

Results and observations

The whitefly Q biotype has a different toxicological profile than the B biotype. Molecules such as pyriproxyfen, acetamiprid and buprofezin, for example, widely used and with good performance for controlling whitefly biotype B, do not perform well against the biotype. Q. In other words, controlling biotype Q is much more complicated, as there are fewer options for structuring a management program.

Within the compilation of tests carried out by the Instituto Mato-grossense do Algodão (IMAmt) in the current harvest, it was observed that products based on pyriproxyfen, used in isolation, showed a decline in performance. This occurs due to high exposure to the molecule. In the current scenario, thinking about whitefly control, this is undoubtedly the most used molecule. Therefore, this sequential exposure without an adjusted resistance management plan is completely harmful to the molecule, as it impacts the selection of tolerant or resistant populations.

One of the essential points for the success of biological insecticides is correct positioning. Factors such as temperature, light, humidity, application time and compatibility with chemicals have a total influence on the microorganism. Therefore, when applying, they must be observed carefully.

Against whiteflies, most of the products used are fungus-based. Therefore, they should be applied in the late afternoon, as UV radiation can impact the germination of spores, altering the performance of the microorganism. In the current harvest, despite the high temperatures, the nights had high humidity, making the use of this tool viable.

In the current harvest, the areas in which the association between chemical and biological insecticides (compatible) was chosen were those that presented the least problems with the pest, highlighting the importance of integrating different tools for better control of the pest.

New molecules for control

A new molecule has been registered for the control of whiteflies in large crops. This is the chemical insecticide Elestal Neo, composed of a mixture of spiropidone (derived from tetramic acid) and acetamiprid (neonicotinoid). It is a new option for controlling this pest in agricultural crops.

Within the trials carried out last year, a high control efficiency of this insecticide was observed on whitefly populations occurring in Primavera do Leste and Campo Verde. It is, therefore, another option for building a good management program aimed at rotating active ingredients with different modes of action. This is with the aim of reducing the frequency of selection of resistant populations and giving survival to molecules already used.

By Jacob Crosariol Netto, Mato Grosso Cotton Institute (IMA)