Action of dwarf mucuna, pigeon pea and stylos anthes on weed under field and laboratory conditions

The quality and allelopathy properties of dwarf mucuna, dwarf pigeon pea and stylosanthes as cover crops on corn and weed species were evaluated. Seeds were sown in October 2007, with a control treatment, in 20 plots of 4×5m, with five replicates. Weed population was determined 30 and 60 days after sowing. At 90 days, plants were mowed and the residues left to remain on the plot. Fresh and dry mass of the cover crops were determined and the allelopathic potential of aqueous extract of their aerial part was tested. The extract was chemically characterized and applied on seeds of weeds and corn. The experimental design was completely randomized and averages compared by the Scott-Knott test at 5% significance. The cover crops showed to be effective in the control of weeds. The highest values in fresh and dry mass were obtained for dwarf pigeon pea, followed by dwarf mucuna; fresh mass increased 72 and 34%, respectively, compared to the control. The extract with dwarf mucuna affected arrowleaf sida germination. The use of green manure in the summer or between harvests ensures that crop rotation is carried out properly and warrants its benefits.

Chemical control of morning glory as a function of water restriction levels

Among the herbicides recommended for the dry season and registered to sugarcane crop, amicarbazone, isoxaflutole and the association diuron + hexazinone + sulfomethuron-methyl can be highlighted. These are pre-emergence herbicides efficient against broad-leaved weeds. Morning glory causes large losses in infested sugarcane fields by bending the stalks and interfering in harvesting. In this study the effectiveness of pre-emergence herbicides for two species of morning glory (Ipomoea hederifolia and Ipomoea grandifolia) was evaluated. Treatments were arranged in completely randomized factorial design (4 x 7). There were four periods of water restriction (0, 30, 60 and 90 days), seven chemical treatments [diuron + hexazinone + sulfometuron-methyl (1387 + 391 + 33.35 g a.i. ha-1), diuron + hexazinone + sulfometuron-methyl (1507.5 + 425 + 36.25 g a.i. ha-1), diuron + hexazinone + sulfometuron-methyl (1658.25 + 467.5 + 39.87 g a.i. ha-1), diuron + hexazinone + sulfometuron­methyl (1809 + 510 + 43.5 g a.i. ha-1), amicarbazone (1190 g a.i. ha-1), amicarbazone + isoxaflutole (840 + 82.5 g a.i. ha-1)] and a control with no application. At 7, 14, 21 and 28 days after the restoration of moisture, control was visually evaluated. After the final evaluation, the dry mass of morning glories was measured. At 90 days of water restriction, diuron + hexazinone + sulfometuron-methyl was more effective to control I. hederifolia than the amicarbazone + isoxaflutole tank mixture. The four diuron + hexazinone + sulfometuron­methyl doses have reduced morning glory dry mass to zero; whereas treatments with amicarbazone have not. The most effective treatment for morning glory control was diuron + hexazinone + sulfometuron-methyl. This result may be due to a possible synergistic interaction.

Action of rain on the efficiency of herbicides applied post-emergence in the control of Senna obtusifolia

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)