Quantifying the effects of fungicides and tillage on Cercospora sojina severity and yield of soybean

Authors: Mengistu, Alemu; KELLY, HEATHER - University Of Tennessee; Bellaloui, Nacer; Arelli, Prakash; LIN, BINBIN - University Of Tennessee

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2018
Publication Date: 9/4/2018
Citation: Mengistu, A., Kelly, H., Bellaloui, N., Arelli, P.R., Lin, B. 2018. Quantifying the effects of fungicides and tillage on Cercospora sojina severity and yield of soybean. Plant Health Progress. 19:226-232. https://doi.org/10.1094/PHP-04-18-0017-RS.
DOI: https://doi.org/10.1094/PHP-04-18-0017-RS

Interpretive Summary: Frogeye leaf spot disease of soybean is caused by a fungus and is common in the southern and northern US, causing significant yield losses. A field study was conducted in 2014 through 2016 to determine fungicide effects on frogeye leaf spot epidemics and yield under no-till and till practices. The treatments evaluated included six fungicides applied at beginning of pod development and at the beginning of seed development. The result showed that tillage did not affect severity of the disease or yield. There were differences between years and between fungicides, and the control obtained with the fungicides was not consistent across years. Disease was worse in 2016 than in 2014 and 2015. All fungicide applications improved yield from 9 to 16%; 6 to 16%; and 4 to 20% in 2014, 2015 and 2016, respectively relative to plants not treated with any fungicide. Among the fungicides compared, Topsin and Quadris TOP had the highest percent yield increases of 15 and 16; 16 and 15; 20 and 18 in 2014, 2015 and 2016, respectively. The results from this study demonstrated that except for Topsin and Quadris TOP, suppression of frogeye leaf spot epidemics did not consistently coincide with increased yields in all years for the rest of fungicides. This suggests that yield information may be required to make appropriate recommendations as to the best fungicide to use for disease suppression.

Technical Abstract: A field study was conducted in 2014 through 2016 at the University of Tennessee, Research and Education Center, Milan, TN to determine fungicide effects on frogeye leaf spot (Cercospora sojina) epidemics and yield under no-till and till practices. The treatments evaluated were untreated check, six fungicides (Bravo, Headline, Priaxor, Quadris Top SB, Topsin and Topguard) that incorporate five fungicide groups applied at R3 and R5 growth stages. Analysis of variance indicated that there was no significant effect due to tillage for the maximum frogeye severity (MFS) recorded at the R6 growth stage and yield. However, there were significant effects from fungicide and year main effects and fungicide by year interactions. Among the three years, disease severity in 2016 was greater than the disease severity recorded in 2014 and 2015. Among the six fungicides, applications, Topsin, Topguard, Quadris TOP and Priaxor fungicides significantly reduced MFS (P=0.05) in 2016. All fungicides applications have improved yield from 9 to 16%; 6 to 16%; and 4 to 20% in 2014, 2015 and 2016, respectively relative to the untreated check. Topsin and Quadris TOP however, had the highest percent yield increases of 15 and 16; 16 and 15; 20 and 18 in 2014, 2015 and 2016, respectively. The results from this study demonstrated that except for Topsin and Quadris TOP, suppression of FLS epidemics did not consistently coincide with increased yields in all years for the rest of fungicides suggesting that fungicide program may require yield data to make appropriate recommendations.