HERBICIDAS E VOLUMES DE CALDA DE APLICAÇÃO NO CONTROLE DE BUVA

Abstract

Burrweed (Conyza spp.) is one of the main weeds in soybean crops in Brazil, notable for its high competitive potential and resistance to multiple herbicides. The chemical management of this plant has become challenging due to its staggered germination cycle and the spread of resistant biotypes, especially in no-till systems with glyphosate-resistant cultivars. This study aimed to evaluate the interaction between different spray volumes and contact herbicides in controlling burrweed under field conditions. The experiment was conducted in the field in Mandaguari-PR, using a randomized block design with a 4×5 factorial scheme, combining four contact herbicides (diquate, glufosinate-ammonium, saflufenacil, and tiafenacil) and five spray volumes (50, 100, 150, 200, and 250 L ha-1). Spray coverage was monitored with water-sensitive papers, and control efficiency was evaluated at 3, 10, 16, and 22 days after application. Results indicated a strong positive correlation between spray volume and leaf coverage, with maximum coverage recorded at volumes close to 200 L ha-1. However, this increased coverage did not necessarily result in more effective control of burrweed. The herbicide saflufenacil demonstrated higher efficiency across all tested volumes, while diquate was the least effective. The correlation between spray coverage and effective control was weak or nonexistent at the evaluated periods, indicating that the architecture of burrweed, characterized by hairy leaves and vertical growth, compromises the adhesion and penetration of the herbicide spray. Additionally, spray volumes below 100 L ha-1 showed lower efficacy, emphasizing the need for adjustments in application technology. Thus, effective chemical management of burrweed requires applications at early development stages (rosette phase), using volumes around 200 L ha-1, preferably with spray nozzles that ensure uniform drop distribution along the vertical length of the burrweed plants. Integration with cultural practices, such as crop rotation and soil cover, is essential to reduce the weed population and mitigate the risk of resistance evolution. These combined strategies are key to optimizing chemical control of burrweed and ensuring the sustainability of agricultural production.