**Application Technologies for Asian Soybean Rust Management**

Carlos Gilberto Raetano, Denise Tourino Rezende and Evandro Pereira Prado *São Paulo State University "Julio de Mesquita Filho", FCABO Brazil* 

### **1. Introduction**

116 Soybean Physiology and Biochemistry

Kerridge, P. C. (2001). A historical perspective of agropastoral system research in the savannas of South America. J*IRCAS Working Report*: **19**: 3-17, ISSN 1341-710X Kokubun, M. (2002) Soybean. *In* Encyclopedia of crop science, ed. Crop Science Society of

Macedo, M.C.M., Bono, J. A., Zimmer, A., Miranda, C. H. B., Costa, F. P., Kichel, A. N. &

Miranda, C.H.B., Macedo, M.C.M., Kanda, K. & Nakamura, T (2004) Soil organic residue

Ogawa, Y. & Mitamura, T. (1982) Studies on cessation of grazing on permanent pasture

Salton, J. C. & Lamas, F. M. (2007) Integration of farming-livestock and cultivation of the

Schwinning, S. (1988) Summer and winter drought in a cold desert ecosystem (Colorado

Seki, Y., Hoshiba, K. & Bordon, J. (2001) Root distribution of soybean plants in no-tillage

Shimoda, K., Horita, T., Hoshiba, K. & Bordon, J. (2010) Evaluation of an agropastoral

Shimoda, K., Horita, T., Hoshiba, K. & Bordon, J. (2011) Evaluation of an agropastoral

production under intensive grazing. *JARQ*, 45: in press, ISSN 0021-3551 Uwasawa, M. (2002) Management of organic matter and fertilizers. *In* Encyclopedia of plant

Japanese)

1341-710X

summary)

566, ISSN 0140-1963

C3561 (in Japanese)

*Report*, **36**: 29-33, ISSN 1341-710X

Brasilia, Brazil, 379-402, (in Portuguese)

ISSN 0021-5260 (in Japanese with English summary)

wheat production. *JARQ*, 44: 25-31, ISSN 0021-3551

Japan, Asakura Publishing, Tokyo, Japan, 370-377, ISBN 4-254-41023-9 C3561 (in

Kanno, T. (2001). Preliminary results of agropastoral systems in the cerrados of Mato Grosso do Sul-Brazil. *JIRCAS Working Report*, **19**: 35-42, ISSN 1341-710X Macedo, M.C.M., Zimmer, A., Miranda, C. H. B., Costa, F. P., Kanno, T., Bono, J. A. &

Fukuda, A. (2004) Results of soybean production, animal liveweight gain and soil fertility changes in agro-pastoral systems. *JIRCAS Working Report,* **36**: 15-18, ISSN

accumulation in agro-pastoral systems in the cerrados of Brazil. *JIRCAS Working* 

ecosystem: 5. Effect of cessation of grazing on some chemical characteristics in the soil. *J. Japan. Grassl. Sci.*, **27**: 407-412, ISSN 0447-5933 (in Japanese with English

cotton plant in savannahs. *In* Cotton in the savannah of Brazil, ed. Ferire E. C.,

Plateau). I. Effects on soil water and plant water uptake. *J. Arid Environ*., 60: 547-

fields in Yguazau district of Paraguay. *Nettai Nougyou* (*Jpn. J. Trop. Agr.*), 45: 33-37,

system introduced into soybean fields in Paraguay: Positive effects on soybean and

system introduced into soybean fields in Paraguay: Effects on soybean and animal

nutrition and fertilizers, ed. Editorial committee of encyclopedia of plant nutrition and fertilizers, Asakura Publishing, Tokyo, Japan, 436-439, ISBN 978-4-254-43077-6

#### **1.1 Occurrence**

Soybean rust is a foliar disease which initially surfaced and remained for many years in Asian countries such as Taiwan, Thailand, Japan and India (Ozkan et al., 2006). After that, the disease was detected in Uganda and South Africa and more recently in South America. Asian Soybean Rust (ASR) is caused by the *Phakopsora pachyrhizi* Sydon & P. Sydon fungus and has been the worst disease in soybean culture. The disease has been present on the American continent, in Paraguay and southern regions of Brazil since 2001 (Yorinori et al., 2010). The importance of ASR disease in Brazil can be evaluated by its rapid expansion and severity and the subsequent economic losses. Over three years (2001 to 2003), ASR dispersed to all soybean producing regions of Brazil, reached the whole of the American continent and was detected in the United States of America in November, 2004 (Yorinori, 2010). ASR disease, when not controlled, can cause a total loss of production (Yorinori et al., 2004). In Brazil, crops free of disease can have an average productivity of 3,300 kg ha-1. However, with the production cost included for a return, net profits of 2,436 kg ha-1 have been seen, thus it is recommendable to control the causal agent of the disease (Yorinori, 2005). In the 2007/08 season, ASR showed the lowest severity level since the 2002/03 season, due to farmer awareness of the necessity to obey the "period of sowing interruption", instituted by many of states of the Brazilian Federation. Another cause for improvement was the predominance in the planting of earlier varieties and the improved monitoring system of the disease (Yorinori et al., 2010).

#### **1.2 Severity of ASR disease**

The permanence of the pathogen inoculum in the fields the whole year around, due to the post-harvest sowing of the summer season and due to sowing carried out under irrigation during the winter/spring crop season, it was difficult to control the disease between the 2003 and 2005 seasons. During this control period, in the western region of Brazil, the first symptoms of rust were already visible 18 to 30 days after emergence began (V3/V4) and, therefore, some crops received up to seven applications of fungicides. In 2005, with the liberation of the genetically modified soybean culture Roundup Ready (RR), between harvests, the situation became even more serious due to the permanence of the pathogen in the fields all year round (Yorinori et al., 2010). With the "period of sowing interruption", when only the cultivation of soybeans used in research and for increasing generations provided by breeding lines is permitted under severe rust control conditions and subject to government control organs (MAPA), the severity of the disease has diminished. Nevertheless, the use of control practices of low efficiency, with inadequate fungicides, the use of reduced doses for lowering costs and inadequate number and duration of applications, unfortunately, contribute to persistence of the disease resulting in significant production losses. Continuous monitoring programs, adequate handling practices and appropriate application technology are necessary in order to guarantee the production of soybean culture. The relationship between lateness in the control of ASR and the severity of the disease is 0.25% for each day in which control is not carried out. The relationship between the return rate of the soybean and the severity of ASR is of -36 kg ha-1 for each severity percentage point (Calaça, 2007).

#### **1.3 Control of the pathogenic agent**

In order to define the strategies to be used for ASR control, regarding application technology, there must be an awareness of the way systemic fungicides move into plants after application and absorption has been carried out. In the present-day market, the majority of fungicides recommended for ASR control move from the base to the top of each leaf, with little chance of moving in the other direction and without the possibility of dislocation from one leaf to another (Antuniassi, 2005). Amongst the fungicides available at present for pathogen control, the triazole fungicides, when used alone, have not presented good performance, as can be seen with ciproconazole, propiconazole and meticonazole (Yorinori et al., 2010). The consistency shown in programmes for chemical control applied in a curative and preventive manner on different soybean varieties and growth stages of the crop has been evaluated by Navarini et al. (2007). The authors established that there was a tendency that higher profit rates were related to preventive applications between the R1 and R3 stages. They also established a low efficiency rate in the control of the pathogen when the fungicide propiconazole was applied in a preventive manner. A deficiency in the control of *P. pachyrhizi* was also observed 30 days after the spraying of the fungicide difeconazole on this crop, in a comparative evaluation of fungicides carried out by Soares et al. (2004). It therefore, becomes evident that triazole fungicides have some limited systemic activity (moving through the plant, especially to newly developed leaves) and are thus somewhat forgiving if the application is less than perfect. When triazole fungicides are mixed with strobilurin fungicides, they show better performance in the control of rust disease. In Brazil, it is believed that the causes of control failures may be related to technical failures in application, predominantly in a population shift which is more tolerant to triazole fungicides in some regions (*Fungicide Resistance Action Committee – FRAC*), instead of developing a tolerance or resistance to the triazole fungicides through genetic mutation of the fungus. As a precautionary measure, class representatives of the producers recommend the use of triazoles only when mixed with other groups of fungicides.

#### **1.4 Economic impact of ASR in Brazil**

An estimate of the volume of grain losses and of the economic impact of ASR in the period between 2002 and 2009 reached 34.2 million tons, a value equivalent to more than half a full soybean harvest. On the other hand, the economic impact of ASR, adding up grain losses (US\$ 7.95 billions), control costs (US\$ 5.76 billions) and intake losses (US\$ 1.55 billions) during the same period, totalled US\$ 15.25 billion (Yorinori et al., 2010). If we consider that the world demand for soybeans is strongly linked to population increase, to world riches and to bioenergy, the necessity to minimise losses in all stages of soybean processing becomes evident. These demand indicators generate worries, particularly in Brazil, where the biofuel program has demanded a mixture of 4% biodiesel in the final fuel formulation since 2009, especially since the main source of biodiesel is soybean oil (Barros & Menegatti, 2010).
