Atividade residual de herbicidas aplicados em pré-emergência na cultura da soja sobre o algodoeiro cultivado em sucessão

Abstract

The constant application of herbicides with the same mechanism of action has allowed the populations of weeds to become resistant. Faced with this problem, it is indispensable to the rotation of herbicide action mechanisms for weed management. However, the persistence of these herbicides in the soil can generate a serious problem, including the phytointoxication of crops sown in succession, known as residual activity or carryover. Thus, the objective of this work was to evaluate the residual activity of the herbicides [imazapyr+imazapic], sulfentrazone and diclosulam applied in pre-emergence in the soybean crop and its possible effects on cotton in succession. The experimental design was a randomized block design with five replicates, using seven concentrations (0, 6.25, 12.5, 25, 50, 100 and 200%) of the recommended dosage of herbicides [imazapyr+imazapic] (26.25+78.75 g ha-1 ), sulfentrazone (600 g ha-1 ) and diclosulam (35 g ha-1 ). The cotton plant was sown 112 days after herbicide application, during which time accumulated rainfall of 637 mm occurred. The variables related to photosynthetic characteristics, phytointoxication, establishment, development, production components and productivity in both cultures were evaluated. None of the herbicides used affected the soybean crop to twice the recommended dosage. The residual activity of [imazapyr+imazapic] did not affect the cotton in succession to soybean. The residual sulfentrazone activity generated phytointoxication in cotton and affected the development, production components and productivity. At the dosages of 217.5 and 314.4 g ha-1 there is already a reduction of 5% and 10% in the Respectively. The residual activity of diclosulam on cotton resulted in phytotoxication of approximately 5% at 14, 20 and 27 DAS and 28% reduction in dry mass of the shoot at 80 DAS, however, the cotton did not present a reduction in the other variables. Caution should be exercised when sulfentrazone is applied in soybean-cotton succession, and herbicides [imazapyr+imazapic] and diclosulam may be recommended in the edaphoclimatic conditions of the study.