Aspectos da biologia e manejo de três espécies daninhas do gênero Euphorbia na cultura da cana-de-açúcar

Abstract

The culture of sugarcane is going through a renewal process management. The traditional harvest with burns, has been replaced by mechanized harvest, without the need for firing. In this process the soil is covered with 25 t ha -1 of straw, forming a physical barrier modifying the physical, chemical and biological conditions of soil amending the phytosociology of weeds. The control of weeds in sugarcane fields is indispensable, but to be effective it’s necessary to know the biological aspects of the species and the effectiveness of the herbicide. However, the aim of this work was to evaluate germinative behavior of seeds, the effects of concentration of straw in the soil, analyzing the growth and development, evaluate the effectiveness of herbicides® Front and match® in control after periods without rain of weeds of the genus Euphorbia occurring raw cane systems State of Alagoas. The experiments were developed at the Center for agricultural sciences/UFAL in lab and vegetation with seeds of three species, Euphorbia heterophylla, Euphorbia hyssopifolia and Euphorbia hirta, collected in producing areas. The seeds were placed in germination type BOD under temperature 20- 30° C, under different conditions, light white, red light, red extreme and absence of light. Where were the percentage and germination speed index (IVG) and dry mass. Also, emergency percentage were evaluated, height and dry mass of plants under different levels of post. The two trials were conducted under a completely randomized design, with 4 repetitions. For growth analysis was used the experiment in completely randomized factorial arrangement (species x periods) with five repetitions. In each assessment were measured plant height, leaf area, the number of green leaves and total dry matter. Were also calculated the absolute growth rate, relative growth rate, the ratio of leaf area and leaf weight ratio. The data were subjected to analysis of variance and non-linear regression to model the growth of the species. The chemical control experiments were conducted in a greenhouse, using the completely randomized experimental design, willing on plots subdivided in time (four periods without rain 0, 15, 30 and 45 days), with three repetitions. We used two herbicides® Front and match®, each composed a herbicide experiment. The application of herbicide treatments, was held in pre-emergence on chaff. The data were subjected to analysis of variance and all the data were adjusted for the linear equation model for E. hirta and squared for E. heterophylla and E. hyssopifolia. The species E. heterophylla was presented the further development when submitted to the effect of chaff against the other species studied, and greater when submitted to twinning red light then the white lights and dark did not differ statistically. The red light presented the best IVG for this species. E. hirta and E. hyssopifolia presented greater values for germination percentage and IVG in the white light of red and red lights followed, which did not differ among themselves, in the absence of light was observed the smallest value of IVG. E. heterophylla was greater in height until the 63 days after sowing, being surpassed by E. hyssopifolia who obtained the largest height of the studied species. E. heterophylla was having greater accumulation of dry mass and absolute growth rate. The species E. hirta was 100% controlled by the two herbicides in all periods without rain. The Front® was effective in the control of E. hyssopifolia and Combine® wasn’t effective in the control of E. heterophylla and E. hyssopifolia after 45 days without rain. The presence of straw doesn't control E. heterophylla, with germination in the presence of 25 t ha-1. On the other hand the E. hyssopifolia and E. hirta have it’s suppressed germination in the presence of chaff. E. heterophylla showed the highest growth and development among the species studied, followed by E. hyssopifolia and E. hirta. The maximum point of growth of species occurred at 77 days after sowing. The Front® herbicide is effective on the control of three species of Euphorbia even being applied on the straw and after the 45 day period for to be leached.