Knowledge on weed biology and ecology is fundamental to provide suitable control practices in weed management systems. The objective of this research was to understand the effect of light and temperature on germination of Chamaesyce hirta, as well as to evaluate the effect of depth of seed placement in the soil in the emergence of the plant. Two experiments were conducted. In the first one, in the laboratory, the seeds were placed to germinate in plastic boxes and kept in a B.O.D. germination chamber, under constant temperatures of 20, 25, 30 and 35 ºC, either in the dark or under continuous light. Daily germination assessments were performed. The percentage of germinated seeds in the 10-day period and the germination speed index (GSI) were calculated. In the second trial, carried out in greenhouse conditions, 100 seeds were planted, under six levels of seeding depth (0, 1, 2, 3, 4 and 5 cm) and three soil cover conditions: no straw, under black oats (Avena strigosa) straw and under corn (Zea mays) straw. Daily plant emergence was counted along 30 days and total emergence and GSI were calculated. Germination of C. hirta seeds occurs both in the presence and absence of light. For the highest temperature, both increased germination and GSI were reported in the presence of light. The highest levels of emergence were obtained with the absence of plant cover and under corn straw at 0 cm depth. The presence of black oat straw on the soil reduced the emergence of C. hirta.
Chamaesyce hirta is a troublesome weed in producing regions of Brazil; however, little is knownabout the control of adult plants. We evaluated the control of adult Chamaesyce hirta plants in the field. Theexperiment was installed at COACEN, municipality of Sorriso - MT, in a randomized complete block design, withfour replicates. Treatments were arranged in a split plot factor, where plots received the application of 19 herbicidesin burndown and subplots received the sequential application of paraquat, glufosinate ammonium, or no herbicide,nine days after the first application. Visual control evaluations were performed at 7, 14, 21 and 28 days after thefirst application and at 5, 12 and 19 days after the second application. Sequential applications increased the levelof control of most treatments. Isolated glyphosate applications, without sequential application did not control C.hirta. The addition of saflufenacil to glyphosate + 2,4-D mixture provides effective control with a single application.The mixture of glyphosate + 2,4-D provided better control than glyphosate + chlorimuron-ethyl and was efficientin controlling adult C. hirta plants, when used with sequential application of paraquat and ammonium glufosinate.
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