Hairy fleabane (Conyza bonarienis) response to saflufenacil in association with different formulations of glyphosate subjected to simulated rainfall

Saflufenacil has been used to control glyphosate resistant weeds, including hairy fleabane. There are several glyphosate formulations, which are related to different salts and adjuvants. Differences between these formulations may result in variations in efficacy, especially in the face of unfavorable environmental conditions, such as the occurrence of unexpected rainfall after application. The objective of this study was to evaluate the control of hairy fleabane with saflufenacil in tank mix with different formulations of glyphosate subjected to simulated rainfall after application. The treatments evaluated were salts of glyphosate (isopropylamine, potassium and ammonium salt), different periods of simulated rainfall after herbicide application (30, 120 and 240 min, and no rainfall), and the presence or absence of saflufenacil and a non-ionic adjuvant. Absorption of saflufenacil by hairy fleabane is rapid, since simulated rainfall after 30 min after application did not result in loss of efficiency when the herbicide is applied with adjuvant. The association of isopropylamine and ammonium salts of glyphosate with saflufenacil increases the control of hairy fleabane and prevents the occurrence of regrowth when rainfall occurs at 30 min after the application. The occurrence of simulated rainfall after 240 min reduces the glyphosate efficiency by 30%, 15% and 60% for the isopropylamine, potassium and ammonium salt formulations, respectively. The addition of adjuvant improves the efficiency of glyphosate salt of potassium by 40%. The response of the mixture of glyphosate and saflufenacil is variable, mainly in situations of rainfall after application

Dose de injúria econômca do herbicida cyanazine na cultura do milho

The tolerance of the com crop to the herbicide cyanazine depends on the growth stage of the crop. An experiment was conducted in Eldorado do Sul, RS, Brazil, to evaluate the selectivity of cyanazine applied at different rates on com, and at different growth stages, to estimate the economic impact of crop injury caused by the herbicide. The com hybrid AG 501 was planted on a no-till system where the weed control was performed with preemergence herbicides. Treatments tested were combinations of cyanazine (rates of 0.0, 2.0 and 2.5 kglha) at different growth stages (V3, V6 and V). Cyanazine selectivity decreases after the com crop reaches the six leaf stage, and with herbicide rates superior to 2.0 kglha. The rate of economic injury, that is, the herbicide rate which the benefit of the weed control is equivalent to the yield loss due to weed competition, reduces with the reduction of the economic impact of the weed on the crop, and with increased com price. These results suggest that when the weed infestation is almost above the weed economic threshold, the economic impact of the herbicide injury is higher than at high weed densities.A tolerância de plantas de milho ao herbicida cyanazine é variável em função dos estágios de desenvolvido da cultura. Um experimento foi conduzido em campo, na UFRGS, em Eldorado do Sul, RS, com os objetivos de avaliar a seletividade de cyanazine aspergido nos diferentes estágios de desenvolvimento vegetativo do milho e com diferentes doses do herbicida, e verificar a resposta econômica de sua toxicidade na cultura. O milho híbrido AG50l foi implantado no sistema de semeadura direta, numa área com controle prévio das plantas daninhas com herbicida pré-emergente. Os tratamentos foram organizados num esquema fatorial representado por doses de cyanazine (0,0, 2,0 e 2,5 kglha) e pelos estádios de desenvolvimento vegetativo do milho (V3' Vfi e V9, indicando 3, 6 e 9 folhas expandidas, respectivamente). O delineamento experimental foi o de blocos casualizados com quatro repetições. A seletividade do cyanazine para a cultura do milho diminui a partir do estádio de 6 folhas expandidas (V 6) e com o incremento da dose além de 2,0 kg/ha. A dose de injúria econômica, ou seja, a dose de cyanazine onde o benefício do controle de ervas se iguala à perda de rendimento de grilos de grãos devido à injúria à cultura, se reduz com a diminuição do prejuízo econômico causado pelas infestantes e com o aumento do preço da cultura. Esses resultados indicam que quando a infestação de plantas daninhas for pouco superior ao nível de dano econômico, a injúria do herbicida à cultura pode causar mais impacto econômico do que em infestações elevadas.