Denis Fernando Biffe

Profundidade de semeadura afetando a emergência de plântulas de Alternanthera tenella

Understanding the basic aspects of the biology of weeds may substantially improve the construction of more suitable strategies for their control, as well as help develop non-chemical control tools. This work aimed to evaluate the effect of sowing depth and soil cover on Alternanthera tenella emergence. Treatments consisted of a 7x2 factorial scheme, with seven depth levels (0, 1, 2, 3, 4, 5 and 10 cm) and two soil cover levels (with and without straw mulch). Straw mulch was provided by the aerial parts of black oat (Avena strigosa), simulating a soil cover equivalent to 2 t ha-1. Sowing was performed in PVC columns (50 seeds per column). Plant emergence was recorded daily up to 28 days after sowing. At the end of this period, total emergence percentage and emergence speed index (ESI) were calculated for each treatment. Emergence of A. tenella was affected by soil depth above which seeds were placed. Both in the presence and absence of black oat straw mulch, emergence was reduced in depths > 4 and 5 cm, respectively. There was no emergence for seeds placed at a 10-cm depth Seeds placed at soil surface presented emergence speed index equal to or higher than other depths, regardless of soil cover.

Tolerância de híbridos de milho ao herbicida nicosulfuron

This work aimed to evaluate tolerance of thecorn hybrids to nicosulfuron and to relate selectivity studies carried out under greenhouse conditions to field studies. Greenhouse experiments were carried out in a randomized block design, in a 33 x 3 factorial scheme, with the first factor being the corn hybrids and the second factor, the herbicide rates (0, 30 and 60 g ha-1). The effect of the treatments was evaluated based on shoot biomass. Under field conditions, a randomized block design experiment was carried out in a factorial scheme 5 x 3 (five corn hybrids, selected from the greenhouse studies, and three herbicide rates (0, 30 and 60 g ha-1). Field results were evaluated based on crop development and yield. Based on the greenhouse experiments, corn hybrids were grouped according to tolerance to nicosulfuron. In relation to crop yield in the field, nicosulfuron at 60 g ha-1 decreased crop yield by 17.4% for the hybrid B 761. When evaluating nicosulfuron selectivity to corn hybrids, field stage is necessary to verify whether the herbicide treatments have influence on grain yield.

Temperatura e luz na germinação das sementes de apaga-fogo (Alternanthera tenella)

Biology of tropical weeds is still mostly unknown, especially in relation to facts that could be used as cultural tools for weed management. The present work was aimed at evaluating the infuence of temperature and light on germination of Alternanthera tenella seeds. Treatments consisted of four constant temperature regimes (20, 25, 30 and 35xa0oC) in absence of light, and constant temperature of 25xa0oC in the presence and absence of light. The germination test was conducted with four replicates of 100 seeds per treatment, placed in plastic boxes (gerbox) and kept in BOD Germinator. Germination evaluations were performed at the same time daily, by counting normal seedlings, with visible roots and cotyledons. Total germination and speed of germination velocity index (GVI) were calculated after 34 days and the experiment was run twice. Total germination and germination velocity increased as temperature increased up to 28.2xa0oC, decreasing from this temperature on. At 25xa0oC, germination and GVI of joyweed seeds increased when the seeds were kept under light.

Efeito residual de flumioxazin sobre a emergência de plantas daninhas em solos de texturas distintas

This work aimed to evaluate the residual effect of flumioxazin on weed emergence in soils of distinct textures. Treatments were constituted by the combination of four periods of application (14, 10, 7 and 0 days before sowing) with two rates of flumioxazin (25 and 40 g ha-1), and no herbicide application for each weed species in soils with distinct textures. Residual activity of flumioxazin was evaluated by counting the emerged weeds for each species at 35 days after sowing. Control of initial flows of weed emergence varied with soil type, period of time between herbicide application and weed sowing. A. tenella, D. horizontalis, D. insularis, D. tortuosum, E. heterophylla, N. physaloides and S. latifolia, in both soils, were the most susceptible species to flumioxazin, applied at 25 and 40 g ha-1.

Seletividade de amonio-glufosinate isolado e em mistura com pyrithiobac-sodium em algodoeiro transgênico LL®

Due to the recent introduction of transgenic cotton varities with resistance to ammonium-glufosinate (LL®) in Brazil, there is a lack of information related both to the selectivity of sequential reapplications of ammonium-glufosinate and to tank mixture with other herbicides. This work aimed to evaluate the selectivity of sequential applications of ammonium-glufosinate isolated or in associations with pyrithiobac-sodium in LL® cotton. A field experiment was installed in a randomized blockxa0design with eight replicates. Treatments were arranged in a factorial scheme (3x3)+1. Thexa0first factor consisted of herbicide treatments as follows: ammonium-glufosinate (500xa0gxa0ha-1), ammonium-glufosinate + pyrithiobac-sodium (500 +xa042 gxa0ha-1 and 500xa0+xa056xa0gxa0ha-1). The second factor was the number of sequential post-emergence applications (one, two, or three), and the additional treatment was a non-applied check. All treatments were manually kept free of weeds throughout the crop cycle. Associating pyrithiobac-sodium to ammonium-glufosinate increased initial crop injury although no significant injury differences were found two weeks after application. Cotton fiber quality was not affected by any herbicidal treatment. Use of isolated ammonium-glufosinate was selective to LL® cotton up to three sequential post-emergence applications. LL® Cotton yield was also sustained after one application of ammonium-glufosinate + pyrithiobac-sodium, with no effects on crop yield.

AMINO ACID APPLICATION CAN BE AN ALTERNATIVE TO PREVENT GLYPHOSATE INJURY IN GLYPHOSATE-RESISTANT SOYBEANS

Glyphosate-resistant (GR) soybeans have continuously increased; however, this expansion significantly increased the use of glyphosate and therefore, in some cases, has resulted in injury symptoms observed in GR soybean, known as “yellow flashing”. Previous reports of interference of glyphosate with nutrient availability and utilization by GR soybean may be linked to this injury symptom. Also, because glyphosate interferes with amino acid synthesis, supplementation with exogenous amino acids may help GR soybean recover from adverse effects of glyphosate. Therefore, an experiment was designed to evaluate different amino acid concentrations. Near-isogenic and GR soybean varieties were grown in the greenhouse in two soils with and without glyphosate at different rates and amino acids were foliarly applied with and without glyphosate. In general, the photosynthetic variables, nutrient contents, and shoot and root dry biomass parameters were affected by glyphosate, however, use of amino acid formulations suppressed harmful effects of glyphosate on these parameters.

Tolerância de híbridos de milho ao herbicida isoxaflutole

This research aimed to evaluate the tolerance of corn hybrids to isoxaflutole and to correlate greenhouse selectivity studies to field studies for this herbicide. Under greenhouse conditions, experiments were arranged in a randomized block design, in a 23xa0xxa03 factorial scheme, with the first factor being corn hybrids and the second factor herbicide rates (0, 60 and 120 g ha-1). Treatment effect was evaluated based on shoot biomass. Under field conditions, a randomized block design experiment was carried out, in a factorial scheme 5xa0xxa03 (five corn hybrids, selected from the greenhouse studies, and three herbicide rates (0, 60 and 120xa0gxa0ha-1). Field results were evaluated based on crop development and yield. Based on the greenhouse experiments, corn hybrids were grouped according to tolerance to isoxaflutole .No significant correlation was found between hybrids and corn rates in relation to grain yield in the field. Otherwise, average grain yield across all hybrids was decreased by isoxaflutole at 120 g ha-1. It was concluded that greenhouse experiments are not sufficient when evaluating selectivity of isoxaflutole to corn hybrids and that field trials should be taken into account to evaluate the effects on crop yield.