Efeitos de herbicidas pré-emergentes no crescimento inicial da mamona

Abstract

The castor bean (Ricinus communis L.) is a crop of great socioeconomic relevance; however, its productivity is significantly limited by weed interference, especially in the initial development stage. Pre-emergence chemical control is a fundamental strategy to mitigate this competition, but there are no herbicides registered for this application method. This study aimed to evaluate the selectivity and efficacy of pre-emergent herbicides, commonly used in soybean and corn crops, when applied to the castor bean crop. The experiment was conducted in Uberlândia/MG, using the castor bean hybrid Kariel (Kaiima Seeds) in a randomized block design with 18 treatments and four replications. The treatments consisted of the pre-emergence application ("plant and apply") of 17 herbicides, either isolated or in mixtures, and a control without application. Evaluations of phytotoxicity and weed control efficacy were performed at 16, 26, and 32 days after application; plant stand was evaluated at 16 and 40 days after application; and height and number of leaves were evaluated at 16, 37, and 60 days after application. The weed community was mainly composed of Bidens pilosa, Ipomoea triloba, Euphorbia heterophylla, Digitaria insularis, and Eleusine indica. The results showed that the herbicides clomazone and s-metolachlor, both isolated and in mixtures (S-metolachlor + atrazine and S-metolachlor + clomazone), exhibited the lowest levels of phytotoxicity and were selective. These treatments did not negatively affect the stand, height, or number of leaves of the castor bean plants, indicating that the crop has the ability to metabolize the compounds. Furthermore, these options proved to be highly effective, with over 80% control of the weed community. On the other hand, treatments with oxyfluorfen, metribuzim, diuron, and imazetapyr caused high phytotoxicity, with severe symptoms of necrosis and chlorosis, resulting in a reduction in height, number of leaves, and even the death of seedlings, making them unviable for this application method in the castor bean crop. It is concluded that the herbicides clomazone and s-metolachlor, as well as their mixtures with atrazine and clomazone, are the most promising alternatives for pre-emergence weed management in the castor bean crop.