Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

First report of tar spot of corn caused by Phyllachora maydis in Minnesota.

Abstract

Commercial corn hybrids with typical signs and symptoms of tar spot were observed and collected in fields from Fillmore and Winona Counties, Minnesota, USA, in late September and early October 2019. The disease in Fillmore County appeared to be focused in one area of the field about 10 m in diameter with incidence estimated at 90% and severity on individual leaves at and above the ear ranging from 1 to 34%. The field in Winona County had leaves with a similar level of severity on field edges. Signs and symptoms on the epidermis of leaves in both fields consisted of small black, raised, circular stroma (0.5 to 4 mm), primarily on the upper surfaces of leaves. All lesions were assessed, and less than 3% of tar spots were associated with fisheye lesions or chlorotic halos. The causal pathogen was isolated and identified as Phyllachora maydis based on morphological characteristics and sequence analysis of the internal transcribed spacer (ITS) region. This is thought to be the first report of tar spot of corn caused by P. maydis in Minnesota, USA.