A field study was performed to investigate the development of cannabinoids in flowers of industrial hemp using three day-length-sensitive and two day-length-neutral varieties. Flower samples were analyzed for cannabinoids on a weekly basis from 2 to 4 weeks postanthesis to plant senescence. Results indicate that total THC, CBD, and CBG significantly increased as flowers matured, reaching the greatest concentration during 6 to 7 weeks postanthesis. After a plateau stage of varied length for different varieties, the peak concentrations declined as plants senesced. Total THC was above the 0.3% threshold from 4 weeks postanthesis to the end of the growing season for day-length-sensitive varieties, but this only occurred during 6 to 7 weeks postanthesis for day-length-neutral varieties. The CBD/THC ratio in flowers dynamically changed during the entire reproductive stage for all of the evaluated varieties. The current study provides vital information for successful cultivation of industrial hemp.

Information regarding agronomic practices for field-scale industrial hemp (IH) production for cannabinoids is extremely limited. The objective of this study was to investigate how pinching practice (i.e., removing the apical meristem) and varied plant density affect yield and cannabinoid production of IH in open field conditions. A field trial was performed in northern Florida in 2019 and 2020. The pinching study included pinch and non-pinch treatments evaluated on two commercially available day-length-sensitive IH cultivars Cherry Blossom (CBL) and Cherry Wine (CW). Four plant densities (3,000, 4,000, 6,000, and 12,000 plants ha -1 ) were evaluated on CW. The experimental design was a randomized complete block design with four blocks. Total flower yield in 2019 was two times greater than in 2020. In 2020, total tetrahydrocannabinol and cannabidiol (CBD) in CBL was significantly greater than in CW. Pinching did not significantly improve flower yield, cannabinoid concentration, or CBD production. Flower yield per plant decreased as plant density increased, but a reversed trend occurred for total flower yield per hectare. Cannabinoid concentration was not affected by plant density, but CBD production increased with increased plant density. Due to the high cost of IH plant material and labor, greater plant density does not always guarantee greater economic return. This study provides valuable information for field-scale cultivation of IH for cannabinoids and supports the development of a large agricultural industry globally.

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Resumo -Objetivou-se neste trabalho avaliar as características fisiológicas da cana-de-açúcar após aplicação de herbicidas em pré-emergência. Para isso, foi conduzido um experimento em esquema fatorial 2x5, onde o fator A constituiu-se das cultivares RB 867515 e SP 81-3250, e o fator B da aplicação em pré-emergência do tebuthiuron, diuron, ametryn, a mistura formulada diuron + hexazinone e uma testemunha sem herbicidas. O delineamento utilizado foi inteiramente casualizado, com quatro repetições. As avaliações foram realizadas aos 90 dias após a aplicação dos herbicidas. A concentração interna de carbono (Ci), a relação carbono interno e externo (Ci/Ca) e o índice SPAD das cultivares de cana-de-açúcar não foram afetadas pela aplicação em pré-emergência dos herbicidas. No entanto, a condutância estomática (gs), a taxa respiratória (E) e a taxa fotossintética (A) da RB 867515 foram reduzidas quando tratadas com tebuthiuron. A A e a eficiência no uso da água (EUA) da cultivar RB 867515 foi alterada negativamente pela aplicação do ametryn. Conclui-se que existe diferença na sensibilidade dos genótipos de cana-deaçúcar aos herbicidas, sendo que a SP 81-3250 mostrou-se mais tolerante. A aplicação do ametryn e tebuthiuron reduz a A da RB 867515. Palavras-chaves: Seletividade, estresse químico, variedades, Saccharum spp.Abstract -The objective of this study was to evaluate the physiological characteristics of sugarcane after application of pre-emergence herbicides. For this, an experiment was conducted in a 2x5 factorial scheme, where the first factor consisted of cultivates RB 867515 and SP 81-3250, and factor B of the pre-emergence application of tebuthiuron, diuron, ametryn, a formulated mixture diuron + hexazinone and a control without herbicides. The experimental 1 Recebido para publicação em