Joint management of the boll weevil

Fight against the boll weevil, a key pest in culture of cotton, requires actions that go beyond monitoring and applications of insecticides. It is necessary to involve the entire production chain of a region, as the Standardization of strategies will be essential to achieve success in combating Anthonomus grandis, one of the worst torments of cotton farmers.

A Brazilian cotton farming, almost in its entirety, is developed in large strips of land, under a tropical climate, and such conditions favor the development and multiplication of various pests that damage the crop, which constantly demands control measures to keep the population below the level of economic damage. In this context, the boll weevil Anthonomus grandis Boh. stands out as key pest as it feeds and reproduces mainly on cotton, and due to its high capacity to cause direct damage and difficulty in control. These characteristics of the pest increased production costs by approximately 360 million dollars in the 2015/2016 harvest, in which 185 million dollars were spent adopting techniques for its control (Belot et al. 2016).

O boll weevil is very dependent on the climate and especially on management adopted. Therefore, favorable environmental conditions such as greater humidity/rainfall and inadequate management contribute to population increase of the plague. According to the Mato Grosso Cotton Institute (IMAmt), in Mato Grosso insect capture in traps increased by 8% compared to the last harvest and reached 50% in some regions.

O Boll weevil has complete metamorphosis (egg, larva, pupa and adult) (Figure 1). This one insect, both in its young and adult stages, is considered a key pest of cotton, due to their feeding and reproduction behavior, which occurs in reproductive structures (flower bud and apple) of cotton, causing direct damage for destroying the part of economic interest. The young phases remain protected within the reproductive structures and, in this way, only the adults are exposed to sprays. The adult is easily identified by be a beetle from the Curculionidae family, measuring four to ten millimeters long, has a long and curved rostrum (mouthparts), which normally measures half the length of its body, and its coloring can vary from light brown, greyish brown to dark brown.

For the detection and monitoring of the cotton boll weevil adult, phase extremely important for decision making in Integrated Pest Management (IPM), are traps developed and widely used in plague eradication in the United States. In addition to the use of these traps, the visualization of attacked reproductive structures, carried out by monitoring of agricultural technicians in the field, is of paramount importance. Monitoring a In general, it is a crucial activity for making correct decisions in controlling the weevil.

To the traps are lime green in color, baited with Glandlure pheromone and must be installed in the off-season as well as during the harvest. The spacing adopted for these traps is between 150m to 200m. Recent studies carried out with traps distributed across areas in the South and Central-West regions of Mato Grosso, demonstrated which individuals are captured more than 200 meters away from the border (from the interior of the plot), from the vegetative stage of cotton, even if in a small quantity, with a gradual increase according to cotton phenology, showing the power of pheromone traps in monitoring.

A initial phase of flower bud emission (B1) is the most critical period and demands greater attention regarding the boll weevil. Studies carried out in 1960s demonstrate that male boll weevils when feeding on buds florals emit pheromones, attracting females for mating; once Once mated, females can oviposit around 200 eggs. In this way, the efficient monitoring and control in this initial phase (from B1 onwards) are great importance for population reduction and good coexistence with the plague until the end of the crop cycle.

Important points for decision making for the pest control

1 - Monitoring: Carry out the monitoring throughout the entire crop cycle, including the final phase, and if necessary to carry out insecticide applications in the final phase, with the aim of population reduction of the pest during the off-season.

2 - Choice of insecticide: O insecticide to be used must have high efficiency and be registered in the Ministry of Agriculture, Livestock and Supply (Map). The producer must rotate the active ingredients/insecticides. Organophosphate-based products, carbamates, neonicotinoids and ready-made mixtures of neonicotinoids + pyrethroids and organophosphates + pyrethroids have been good options as they present control efficiency.

3 - Sequential spraying: O Effective boll weevil control is almost exclusively dependent on the application of insecticides and studies prove that the best option is to carry out applications sequential, with a minimum of three with a maximum interval of five days. That ensures control of overlapping generations (emergency flows), as well as how it controls individuals that escape previous spraying.

4 - Application technology: O producer must adopt good practices for both aerial and ground application (respect temperature, humidity, thermal inversion, mixtures, etc.).

Complex management

O management of the boll weevil is much more complex and involves several other activities that go beyond monitoring and applying insecticides. I
It includes, for example, the destruction of ratoons, cleaning of highways and information sharing. It should be noted that all these actions need be adopted jointly, involving the entire cotton production chain. a region, as the standardization of management actions is essential to achieve the success. 

As a good example of working together for efficient boll weevil management is possible to mention the Cotton Technical Groups (GTA) of Mato Grosso, which are coordinated by IMAmt and the cotton production chain in each region. You GTAs aim to promote dialogue between members of this chain productive and, therefore, exchange information, standardize actions, among other initiatives that contribute to the successful management of boll weevils and other pests and diseases. It is important to highlight that the more united the local group, the better the results, a fact observed in the different GTAs in Mato Grosso. One of the examples resides in the Sapezal GTA: before the formation of the group at this location, the boll weevil population was increasing, resulting in great losses and, fortunately, after the formation of the GTA in this region (from 2016), through strong joint work between the properties, there was a reduction of the Bicudo/Trap/Week (BAS) index of approximately 80%.

Recommended management measures when the crop is well developed

1- Joint actions between producers to organize applications insecticides between neighboring properties (dates, times and products), concentration on management activities and information exchange, for the standardization of these actions.

2 - Insecticide applications in end of cycle in order to keep the sprays targeted sequential treatments for the boll weevil even after the opening of the first bolls. Also apply insecticide together with defoliation, to reduce population at the end of the harvest.

3 - Prioritization of techniques recommended by Application Technology, carrying out insecticide applications with ideal and calibrated equipment, whether in hydraulic or rotating nozzles, spraying under suitable environmental conditions (e.g. wind, thermal inversion, relative humidity, temperature), and pay attention to tank mixes.

4 - Installation of Boll Weevil Tubes (TMB) initially in pre-harvest and maintain until 30 days before the next planting of the following cotton harvest. It is recommended to install around the entire perimeter of the plantation. of cotton or, at least, in areas considered entry and exit points (refuges) of insects.

5 - Charging and adequate transportation of bales, rolls and/or cottonseed with the aim of preventing the spread of plants to sides of highways, local roads, cotton gins, etc. Plants that grow and develop (tigueras) in these places they harbor numerous pests (especially the boll weevil), and as there is no management of these plants, phytophagous insects remain and multiply, migrating to commercial crops later.

6 - Efficient destruction of ratoons and good management of tiguera plants: one of the main factors that have contributed to population increase of the boll weevil is the regrowth of ratoon plants and the presence of tiguera plants in plots/planting areas. Because the pest develops and reproduces only in cotton, eliminating the plants in the off-season reduces the chance of the pest remain in the system.

7 - Harvest quick and well done, then the more concentrated in a short period, the longer the interval for destruction of cultural remains on properties.

8 - Compliance of sanitary emptiness, provided for by regulations, in which the cultivation and/or presence of plants at phytosanitary risk in the areas.

A Brazilian cotton farming has become increasingly dynamic and technological, and this contributes to the increase in production and the consolidation of Brazil in the world stage as a major producer. However, all this dynamism is accompanied the high complexity of cultivating in large areas, which often makes it difficult to carry out some essential actions for weevil management, such as monitoring, applications in short time intervals (with maximum five days between each application) and destruction of cultural remains. This way, the union of everyone involved in the cotton production chain is of utmost importance importance for effective control of the pest, through cooperation and exchange of information, and mainly ensure the adoption of management strategies in a rigid and uniform manner.

Eduardo Moreira Barros, Syngenta Crop Protection LTDA; Guilherme Gomes Rolim, Mato Grosso Institute of Cotton (IMAmt); Lucas Souza Arruda, Rural Federal University of Pernambuco (UFRPE); Jacob Crosariol Netto, Mato Grosso Cotton Institute (IMAmt)

Article published in issue 232 of Cultivar Grandes Culturas, September, 2018.