Planting Date of Cotton in the Brazilian Cerrado Drives Boll Weevil (Coleoptera: Curculionidae) Infestation

Simple Summary Cotton is cultivated in subtropical and seasonally dry tropical areas in the northern and southern hemispheres as the most common natural fiber used to make textiles. In the Americas, especially Central and South America, cotton is infested by a beetle named the boll weevil. This weevil feeds directly on the cotton reproductive structures, causing up to 70% yield losses. The flower buds and bolls damaged by weevils fall on the ground, becoming lost or are retained by the plants producing poor-quality fiber. Boll weevil is a target of 19-25 insecticide applications of broad-spectrum insecticides throughout the season, harming non-target organisms and growers. Therefore, alternatives to manage boll weevil need to be pursued. In this work, we studied how the planting dates of cotton could negatively affect boll weevil infestation. We studied three contrasting planting dates, monthly spaced, and looked at how the cotton plant and the boll weevil responded. We noticed that the middle-planting date was unfavorable to the boll weevil compared to the early and late-planting dates because cotton plants developed faster then and so escaped from pest infestation. Thus, cotton crop seeded late was more prone to receive numerous and fertile insects dispersing from surrounding cultivations while early planted cotton was more prone to receive dispersing adults from the refuge areas avid for infesting cotton reproductive structures. Although the boll weevil (BW), Anthonomus grandis grandis (Coleoptera: Curculionidae) has been attributed to the significant losses caused to cotton yield in the Americas, the categorization as a quarentenary pest in places where it is still not occurring has increased its relevance worldwide. In areas where it is widespread, pest suppression relies on many broad-spectrum insecticide applications. However, other control tactics are sought. Considering that early-flowering cultivars escape from boll weevil infestation, we investigated if three different planting dates (November, December, and January) could alter the plant life cycle, allowing the plants to escape from boll weevil infestation. Field trials were run in two seasons (2014/2015 and 2017/2018), and variables (days required to reach each flowering stage, fruiting plant structures-undamaged and damaged by the BW, and totals-number of boll weevils on plants and that had emerged from fallen structures on the ground) were assessed over 29 and 33 weeks, respectively. Based on the number of days required to initiate and terminate the flowering stage, the time to reach the economic threshold (ET), the number of undamaged, damaged, and the total reproductive structures, we concluded that planting dates in December for the Central Cerrado of Brazil should be preferred over the other two tested dates. Cultivations run at this planting date, anticipating the flowering period initiation and termination, reduced infested flowering structures, and delayed the decision making to control the pest, when compared to the other two planting dates.

Automated summary

Cotton is commonly cultivated in subtropical and seasonally dry tropical regions. The boll weevil, a beetle, poses a significant threat to cotton crops in the Americas, causing substantial yield losses. The planting dates of cotton plants can affect boll weevil infestation, with mid-planting dates being less favorable for weevil damage. Alternatives to broad-spectrum insecticide applications need to be explored for boll weevil management.