Effect of Fungicide and Timing of Application on Soybean Rust Severity and Yield

Abstract

Soybean rust, caused by Phakopsora pachyrhizi, is a devastating foliar disease of soybean that may cause significant yield losses if not managed by well-timed fungicide applications. To determine the effect of fungicide timing on soybean rust severity and soybean yield, field trials were completed in Paraguay (four locations), the United States (two locations), and Zimbabwe (one location) from 2005 to 2006. Treatments at each location included applications of tebuconazole, pyraclostrobin, or a combination of azoxystrobin + propiconazole, and in some locations pyraclostrobin + tebuconazole at the following soybean growth stages (GS): (i) GS R1 (beginning flowering), (ii) GS R3 (beginning pod), (iii) GS R5 (beginning seed), (iv) GS R1 + R3, (v) GS R3 + R5, and (vi) GS R1 + R3 + R5. Soybean yields from plots treated with fungicides were 16 to 114% greater than yields from no fungicide control plots in four locations in Paraguay, 12 to 55% greater in two locations in the United States, and 31% greater in Zimbabwe. In all locations, rust severity measured over time as area under the disease progress curve (AUDPC) was negatively correlated (r = –0.3, P < 0.0001) to yield. The effectiveness of any given treatment (timing of application and product applied) was often dependent on when rust was first detected and the intensity of its development. For example, when soybean rust was first observed before GS R3 (two locations in Paraguay), the plants in plots treated with a fungicide at GS R1 had the lowest AUPDC values and highest yields. When soybean rust was first observed after GS R3, plants treated with a fungicide at GS R3 and/or GS R5 had the lowest AUDPC values and highest yields with a few exceptions.

Effect of the interaction between fungicide application time and rainfall simulation interval on Asian Soybean Rust control effectiveness

“…The data suggest that the rainfall simulations after the application at 0400 h, with the occurrence of dew, further reduces the fungicide, providing lower ASR control effectiveness than application at 2300 h, without dew. This lower control effectiveness in treatment with application at 0400 h reduced the productivity as compared with the application at 2300 h. Mueller et al (2009) reported that soybean rust is a devastating foliar disease of the soybean plant that may cause significant yield losses if not managed by welltimed fungicide applications.…”

From Select Agent to an Established Pathogen: The Response to Phakopsora pachyrhizi (Soybean Rust) in North America

“…Previous to 2005, foliar fungicide use on soybean in the United States was limited primarily to the Southeast and midSouth to manage late-season foliar diseases such as frogeye leaf spot and Cercospora leaf blight. With the occurrence of soybean rust, producers would have to apply fungicides earlier in the season (Mueller et al 2009;Schneider et al 2009b). Soybean rust epidemics often are explosive and effective fungicide use relies on when fungicide is applied (before or after rust observation) and the type of product (curative or protectant) (Fig.…”

Taxa de aplicação e uso de surfactante siliconado na deposição da pulverização e controle da ferrugem da soja

“…Diferenças entre aplicações com e sem surfactante foram encontradas apenas quando se utilizou a taxa de 160 L ha -1 , com valor médio menor da AACPD detectado na presença do surfactante. A redução nos valores de AACPD é considerada um fator importante no controle da FAS, pois existem correlações negativas entre AACPD e produtividade da soja (MUELLER et al, 2009;PRADO et al, 2010;TWIZEYIMANA et al, 2011). O uso de surfactante siliconado na calda fungicida pode ser uma alternativa viável na melho ria do controle químico da FAS, uma vez que a adição desse produto à calda fungicida proporcionou redução na intensidade da doença.…”