ABSTRACT The obstacles in Phakopsora pachyrhizi management result especially from susceptible soybean genotypes and resistant fungal strains. The objective of the current study was to evaluate the applicability of the emission of extremely low and specific frequencies by Effatha technology in the soybean Asian rust control, nutrition, and its impact on yield. The in-vivo test followed the detached leaves method, with six treatments: frequencies 1 and 2 individually and in association; the conventional chemical treatment (fungicide azoxystrobin + benzovindiflupyr); and witnesses in presence and absence of the fungus. Frequency 1 relates to inhibition of the enzyme succinate dehydrogenase and 2 to ubiquinone oxidase. In the field, frequencies 1 and 2 associated (with the same fungicidal action of the in-vivo study); nutritional frequency; application of azoxystrobin + benzovindiflupyr + mancozeb, and control without application were evaluated. In vivo, the fungicide provided 85% control of the disease symptoms, against 65% of frequencies 1 and 2 in association, which showed a higher efficiency compared to the isolated frequencies. In the field, the rate of increase of symptoms were reduced by all treatments compared to the control. At the end of the soybean cycle, the conventional fungicide resulted in 33% severity against 56% of frequencies 1 and 2 associated, and 69.2% of the control. The emission of the frequency for increased nutrient efficiency stood out positively on yield in relation to all the other ones. The conventional application provided the highest weight of 1,000 grains, possibly a direct reflection of the better control of the disease.

RESUMO O trabalho teve por objetivo avaliar a ação do fungicida sítio-específico carbendazim + tebuconazole e do fungicida multissítio clorotalonil, in vitro, sobre a germinação dos uredosporos de Phakopsora pachyrhizi, e in vivo sobre a severidade dos sintomas da doença em folíolos de soja. Os uredosporos de Phakopsora pachyrhizi empregados nos experimentos foram provenientes de Artur Nogueira-SP, coletados a partir de ensaios de campo realizados em três épocas de cultivo, dentro da safra 2016/17. Para cada época de semeadura foram utilizadas três cultivares distintas, obedecendo-se às recomendações segundo o grupo de maturação de cada uma (precoce, médio e tardio), todas suscetíveis à ferrugem asiática, perfazendo um total de 9 cultivares, ou seja, de 9 coletas. Avaliou-se a ação do fungicida multissítio clorotalonil e sítio-específico carbendazim + tebuconazole sobre a germinação in vitro de urediniosporos e a severidade da doença, pelo método de folhas destacadas, in vivo, tratadas preventivamente, antes da inoculação. Determinou-se as concentrações letais CL50 e CL95 pelo método Probit. O fungicida multissítio clorotalonil foi mais fungitóxico in vitro e in vivo que o fungicida específico carbendazim + tebuconazole para os uredosporos de P. pachyrhizi, em todas as coletas referentes, independente das safras e épocas de semeadura. A partir dos testes in vivo e in vitro, há indicação de haver interação significativa dos cultivares com cada fungicida.

ABSTRACT The present study aimed to evaluate the action of both the site-specific fungicide carbendazim + tebuconazole and the multisite fungicide chlorothalonil, in vitro, on the germination of Phakopsora pachyrhizi uredospores and, in vivo, on the severity of symptoms of the disease in soybean leaflets. The uredospores of Phakopsora pachyrhizi used in the experiments were collected from Artur Nogueira, São Paulo State, during field trials carried out in three growing periods within the 2016/17 season. For each sowing period, three different cultivars, susceptible to Asian soybean rust, were used according to the recommendations for their respective maturation group (early, medium and late), totaling 9 cultivars, i.e., 9 samplings. The action of both the multisite fungicide chlorothalonil and the site-specific fungicide carbendazim + tebuconazole was evaluated on the germination of urediniospores, in vitro, and on the disease severity, in vivo, by the method of detached leaves, preventively treated before inoculation. Lethal concentrations LC50 and LC95 were determined by the Probit method. The multisite fungicide chlorothalonil was more fungitoxic in vitro and in vivo than the specific fungicide carbendazim + tebuconazole to P. pachyrhizi uredospores in all samplings, regardless of seasons and sowing times. The in vivo and in vitro tests indicated significant interaction of the cultivars with each fungicide.