Necessary integrated management measures against mites in cotton

The frequency of incidence of mites in several crops has increased over the last few harvests in Brazil. In cotton, the pest gains importance both due to the damage and the need for control measures. Monitoring, adoption of cultural practices, use of more selective pesticides against natural enemies and attention to application technology are among the measures for the necessary integrated management of these tiny but aggressive arthropods

The cotton crop stands out in Brazil for determining the development of many regions. The Chapadões region is one of those that was boosted due to agribusiness around this crop. Cotton cultivation in Brazil had an area of ​​approximately 1,017 million hectares, and production of around 1,532 million tons of cotton lint in the 2014/2015 harvest (Conab, 2015). In the Chapadões region, this area totals around 50 thousand hectares.

The agroecosystem used in the Center-West is an environment favorable to the multiplication of pests, as a production system prevails in which soybeans are the main crop to be established in the vast majority of areas, often being rotated with cotton or corn crops. in certain regions and years. In this way, the successive cultivation of these crops causes many pests to adapt to the system. In addition to this, other factors such as favorable climatic conditions, high temperatures and mild winters become ideal for the multiplication of insects.

Among the problems, mites have increased in frequency in Brazil, mainly in places or years with a higher incidence of summers, in addition to attacking different crops, and thus increasing their importance, both due to the damage caused and the need for actions to prevent your control.

Pest mites are arthropods belonging to the Arachinida class, phytophagous and polyphagous, that is, they are found in various habitats and feed on different plant species where they pierce the cells with their stylets and feed on the liquids leaked from the leaves. They differ from insects (class Insecta) because they do not have body segmentation and because they have four pairs of legs.

In the past, phytophagous mites were considered secondary pests in some crops, such as soybeans. However, the use of some pesticides to control pests in crops has resulted in a drastic reduction in natural enemies (such as predatory mites from the Phytoseiidae family), increasing the population of phytophagous mites considerably. And in this context, cotton cultivation is no different. The use of insecticides to control the boll weevil has led to an increase in the mite population.

Mites typically required two to four interventions per harvest. With the exit of molecules from the pesticide market, such as endosulfan, it was necessary to adjust new management strategies, with other insecticides to control various pests, in addition to the emergence of new ones (such as Helicoverpa armigera), which increased the number of insecticide applications on the crop. We can also mention the various applications of fungicides to control diseases, which tends to reduce the fungi that could attack this pest. This environment favors an increase in the population of mites, with producers having to carry out a greater number of interventions.

Currently in Brazil, the species that attack cotton are the spider mite Tetranychus urticae, the green mite Mononychellus planki, both Tetranychids, and the white mite Polyphagotarsonemus latus of the Tarsonemidae family.

In general, the mites pierce the cells and feed on the exuded liquid. Among the species, the two-spotted mite is considered by many researchers to be one of the most important in the system. Tetranychus urticae In adulthood, it presents spots on its back, which are the deposits of its food, retained in the ventricles. They lay spherical, yellowish eggs. They weave webs that shelter these eggs, providing protection from various factors (characteristic of the Tetranychidae family). They go through the stages of larvae and nymphs, being divided into proto and deutonymphs. It is possible to notice the change in the leaves after the phase change. The cycle can be processed under Chapadão do Sul conditions, in around 15 days. The first populations in cotton crops begin from host plants or even from dispersal from neighboring areas, due to the wind, and associated conditions such as excessive application of pyrethroids or neonicotinoids in the crop. Plant colonization typically begins in the upper third.

This pest under favorable conditions can be highly tolerant to chemical control (Raizer et al 1985). Cases of resistance to acaricides have already been observed in Brazilian conditions (Sato et al 2009).

The green mite (Mononychellus planki) is another species found, less frequently in crops. It tends to stay close to the veins, or even when the population increases between the veins, normally starting on the lower side and then, when in high populations, it attacks the upper side of the leaves, causing physiological changes in the plants, premature defoliation. , and decreasing crop productivity. This species normally presents greater occurrence in the reproductive stages, especially when the crop is more leafy, which provides better survival conditions for the mites, and also occurs at the end of the crop cycle. This species Mononychellus planki It is a mite that occurs most frequently inside plants, colonizing first the middle third and then the upper third, causing early defoliation of the crop and consequently reducing production.

The white mite (Polyphagotarsonemus latus) presents an important occurrence in several cultures. In cotton, its incidence is mainly linked to the period after nitrogen fertilization, in addition to other nutrients applied foliarly, in addition to coinciding factors such as humid, cloudy and hot days. It attacks the young tissues of plants, causing the leaves to develop abnormally, remaining small or deformed. The presence can initially be observed by a shiny appearance on the underside of the leaf accompanied by slight waviness, the margins of which fold upwards. Subsequently, they fold downwards, and the limbus becomes leathery and brittle. Commonly found in new shoots and new leaves.

This plague has increased in recent years due to phenomena such as El Niño, which provides rain in May and June. Therefore, another issue to be considered is the practice of nitrogen fertilization at 90 days, which can provide a population increase if coincided with other factors. When the rains stop, this pest tends to decrease.

Sampling, in this scenario, plays a fundamental role in the successful management of pest mites. It must be judicious in order to verify the beginning of infestations and, as a result, be able to outline the best management alternatives. Infestations normally begin in reboleiras, and with the increase in population they tend to spread throughout the plot, due to their dispersion, which can be by wind, as well as other means.

It is essential to be aware of the population increase, as if any measure is taken under these conditions, it may be too late, requiring the use of a sequence of strategies to better suppress the population.

After identification, the technician must analyze the culture, the stadium, the weather conditions and thus use the available Integrated Pest Management (IPM) strategies. Chemical control is the most commonly used tool, however, without observing these criteria it may not be possible to control this pest satisfactorily. Some pesticides also present a certain selectivity towards natural enemies in this crop, and within the adverse scenario of a large number of applications, this must be considered in order to improve IPM.

Within the MIP, cultural management is a recommended measure. In work carried out by the Chapadão Foundation, a high frequency of this pest has been observed in poorly destroyed ratoons, from one harvest to another. Other weeds such as Commelina benghalensis (trapoeraba) in surveys in 2012 and 2013 showed a high frequency of mites (Figure 1). It is worth noting that crops used as cover can also host mites, in addition to other tigueras such as corn.

Another sensitive point is the stimulation of mite reproduction, called hormoligosis, which causes an increase in the population of individuals, caused by pyrethroid, neonicotinoid and other insecticides.

The use of acaricides is a quick and efficient alternative to prevent outbreaks of these pests. However, there are some differences in the action of these products. Some only act on adults, not controlling stages such as eggs and nymphs. It is also worth highlighting the residual power of certain acaricides, which provides interesting suppression in the different stages of the plague.

These differences in the action of acaricides must be taken into account, and in some cases, reapplication to the crop is necessary in order to avoid damage. Dose adjustment for each mite species cannot be forgotten. Examples of acaricides include spiromesifene, abamectin, chlorfenapyr, propargite and diafenthiuron, with interesting efficiencies within the management strategies for this pest. For some of these acaricides, a specific adjuvant (often vegetable oil) is recommended, which provides greater efficiency.

As they are difficult to control pests, application technology also plays an important role in combating this important pest for cotton farming.

Germison Tomquelski, Gabriella Manna, Josiane Oliveira, Chapadão Foundation

Article published in issue 198 of Cultivar Grandes Culturas.