Fungicide Efficacy on Tar Spot and Yield of Corn in the Midwestern United States

Abstract

Tar spot of corn caused by Phyllachora maydis has recently led to significant yield losses in the eastern corn belt of the Midwestern United States. Foliar fungicides containing quinone outside inhibitors(QoI), demethylation inhibitors(DMI), and succinate dehydrogenase inhibitors(SDHI) are commonly used to manage foliar diseases in corn. To mitigate the losses from tar spot thirteen foliar fungicides containing single or multiple modes of action (MOA/FRAC groups) were applied at their recommended rates in a single application at the standard tassel/silk growth stage timing to evaluate their efficacy against tar spot in a total of eight field trials in Illinois, Indiana, Michigan, and Wisconsin during 2019 and 2020. The single MOA fungicides included either a QoI or DMI. The dual MOA fungicides included a DMI with either a QoI or SDHI, and fungicides containing three MOAs included a QoI, DMI, and SDHI. Tar spot severity estimated as the percentage of leaf area covered by P. maydis stroma of the non-treated control at dent growth stage ranged from 1.6 to 23.3% on the ear leaf. Averaged across eight field trials all foliar fungicide treatments reduced tar spot severity, but only prothioconazole+trifloxystrobin, mefentrifluconazole+pyraclostrobin+fluxapyroxad, and mefentrifluconazole+pyraclostrobin significantly increased yield over the non-treated control. When comparing fungicide treatments by the number of MOAs foliar fungicide products that had two or three MOAs decreased tar spot severity over not treating and products with one MOA. The fungicide group that contained all three MOAs significantly increased yield over not treating with a fungicide or using a single MOA.

An assay to reliably achieve Tar Spot symptoms on corn in a controlled environment

“…Tar Spot, caused by the fungus Phyllachora maydis (Maubl. ), is a foliar disease of corn ( Zea mays L.) threatening U.S. production (Telenko et al, 2022). Temperate corn germplasm has shown variable susceptibility to infection by Tar Spot, ranging from 1-50% of leaf area infected (Telenko et al, 2019).…”

“… Abstract Tar Spot continues to threaten U.S. corn production (Telenko et al, 2022). A reliable assay under controlled conditions is needed to study the epidemiology and management of Tar Spot.…”

Uncovering the environmental conditions required for Phyllachora maydis infection and tar spot development on corn in the United States for use as predictive models for future epidemics

“…Partial genetic resistance for tar spot has been identified in corn germplasm 13 , 14 , but many current commercial corn hybrids are considered highly susceptible. Fungicides are currently the most effective method for reducing tar spot development and yield losses, especially when two or three fungicide classes are used 15 .…”

Tar Spot of Corn: A Diagnostic and Methods Guide

“…Tar spot develops most reliably in field settings where corn is planted into residue infested with P. maydis, or where the infected residue is spread throughout the experimental area (Jiménez 2021;Lipps et al 2022). Overhead irrigation can help facilitate disease development (Lipps et al 2022;Telenko et al 2022). Other practices, such as delayed planting or the use of longer day hybrids, may further improve the likelihood of tar spot development in field settings.…”