Effects of Diquat Doses and Spraying Timing on the Control of Eichhornia crassipes

Water hyacinth (Eichhornia crassipes) is a major weed in several water bodies in the tropical and sub-tropical regions of the world, causing different types of negative interference in the multiple use of water and water bodies and in the prevention of human diseases. The control of this macrophyte is required under these conditions. Aiming to evaluate the efficacy of the herbicide diquat in the control of water hyacinth, two trials were carried out under greenhouse conditions. In the first assay, a factorial design 2 x 2 x 4 was used comparing two diquat formulations (Reward (R) and Reglone (R)), two spraying times (day and night time) and four herbicide doses (0.1; 0.2; 0.3 and 0.4 kg ha(-1)). The plants were grown in 1L pots and the plots were arranged in a completely randomized experimental design with six replications. The Reward (R) formulation was more efficient than Reglone (R) in the control of water hyacinth, acting faster, especially at smaller doses. The night application promoted better control than the day spraying. In a second assay, only Reward (R) was evaluated in a factorial design experiment comparing two spraying times (day and night time) and four doses (0.1; 0.2; 0.3 and 0.4 kg ha(-1)). The plants were grown in 40 L square pots, arranged in a completely randomized block design, with four replications. The results confirmed that night application promoted better control of water hyacinth. The doses of 0.3 and 0.4 kg ha(-1) provided the best control at two months after spraying, preventing intense re-growth of water hyacinth shoots.