Henrique Fabricio Placido

Different Glyphosate Susceptibility in Chloris polydactyla Accessions

Abstract Glyphosate is now the most widely used herbicide; after years of frequent utilization, resistant weeds were selected, mainly due to widespread adoption of glyphosate-resistant crops and no-tillage sowing system. Increasing difficulty in controlling Chloris polydactyla with glyphosate has been noticed in agricultural areas. Here, the susceptibility level of various C. polydactyla accessions from Brazil is examined. Two whole-plant studies were conducted to confirm the presence and extent of glyphosate susceptibility among accessions, which involved the application of seven glyphosate doses on four accessions. The four accessions showed different glyphosate susceptibilities. The “Matão” accession presented major tolerance for glyphosate compared to “Palotina” accessions. “Jaboticabal” plants showed an intermediary susceptibility. The resistance factor (RF) was 3.76 between the “Matão” and “Palotina” accessions. All biotypes died at 2,880 g ae ha−1 glyphosate. Nomenclature: Glyphosate; Chloris polydactyla (L.) Sw. Resumen Glyphosate es actualmente el herbicida más ampliamente usado. Después de años de uso frecuente, malezas resistentes fueron seleccionadas, principalmente debido a la amplia adopción de cultivos resistentes a glyphosate y de sistemas de siembra con labranza cero. En áreas agrícolas, se ha notado el incremento en la dificultad para controlar Chloris polydactyla con glyphosate. Aquí, se examinó el nivel de susceptibilidad de varias accesiones de C. polydactyla de Brasil. Dos estudios de plantas enteras fueron realizados para confirmar la presencia y la magnitud de la susceptibilidad a glyphosate entre accesiones, los cuales involucraron la aplicación de siete dosis de glyphosate sobre cuatro accesiones. Las cuatro accesiones mostraron diferentes susceptibilidades a glyphosate. La accesión “Matão” presentó una tolerancia mayor al compararse con la accesión “Palotina”. Las plantas de “Jaboticabal” mostraron una susceptibilidad intermedia. El factor de resistencia (RF) fue 3.76 entre las accesiones “Matão” y “Palotina”. Todos los biotipos murieron al ser expuestos a 2,880 g ae ha−1 de glyphosate.

Behavior of RR soybeans subjected to different formulations and rates of glyphosate in the reproductive period

Recent studies indicate that glyphosate applied in post-emergence in RR soybean can eventually cause phytotoxic effects. However, there are many questions that need to be clarified in the scientific and technical contexts, involving the issue of RR soybeans regarding the use of glyphosate. This study has assessed the impact of the application of different doses and formulations of glyphosate in the reproductive period of RR soybean (R1 stage). For that purpose, an experiment in the field was conducted in two harvests (2011/12 and 2012/13), in which a 2 x 5 factorial design was used (formulations versus doses) totaling 10 treatments. In these two experiments the variables related to agronomic performance were: phytotoxicity (7, 14, 21 and 28 days after application), plant height, number of pods per plant, yield and weight of 100 grains (end of soy cycle). The results obtained allowed characterizing phytotoxicity and damages to the height and yield in RR soybean, with increasing rates of glyphosate applied in the reproductive period.

Rates of Chlorimuron Applied in Glyphosate-Tolerant and Sulfonylurea-Tolerant Soybean

Susceptibility to chlorimuron varies according to soybean genotype. STS® (sulfonylurea-tolerant soybean) presents a high tolerance to some sulfonylureas; this feature is determined by semi-dominants alleles, Als1 and Als2. Experiments were conducted in the field for four seasons with two cultivars for season to evaluate the selectivity of chlorimuron rates in post-emergency (V4) of glyphosate-tolerant and sulfonylurea-tolerant soybean. Data analysis made it possible to infer that there was no significant effect on the productivity of the cultivars when they received application in post-emergency, of chlorimuron at the doses used (0, 15, 30, 45, 60, 75, and 90 g ai ha-1). The maximum recommended rate for non-STS cultivars of chlorimuron is 20 g ai ha-1, or 4.5 times less than the maximum rate employed in this study. The soybean cultivars CD 250 RR/STS, CD 236 RR/STS, CD 2630 RR/STS, and BMX Turbo RR/STS were tolerant to the application, in post-emergency (V4) of the herbicide chlorimuron, until the rate of 90 g ai ha-1.