First Report of Curvularia Leaf Spot of Corn ( Zea mays ), Caused by Curvularia lunata , in Iowa

In August 2025, small (1 to 3mm), oval lesions with dark brown margins surrounded by chlorotic halo, primarily affecting leaves in the mid to upper canopy were observed on approximately 5% corn (Zea mays L. growth stage R3) hybrid Golden Harvest G10L16-DV plants at the Iowa State University Agricultural Engineering and Agronomy Farm, Boone, IA. Disease severity on the ear leaf ranged from 5 to 30%. Symptomatic leaf sections were placed in a moist chamber and kept at 25ºC with a 12 h photoperiod for 4 to 7 days. Conidia arising from the lesions were transferred to Difco potato dextrose agar (PDA) amended with 100mg neomycin and 10mg chloramphenicol per liter. Resulting colonies were dark brown to black with orange margins. Colony appearance on other media types differed. Microscopic examination (400x) revealed curved, three-septate, melanized phragmospores, 17 to 27.5 x 9 to 15 µm in size, typically with one of the center cells enlarged, resulting in a curved spore shape. Phragmospores were produced on straight to flexuous, septate conidiophores through blastic mono or polytretic conidiogeny, resulting in a genticulate shape to the overall conidiophore (Seifert at al. 2011).. Molecular identification was performed by amplifying and sequencing the internal transcribed spacer (ITS) and the translation elongation factor 1-alpha (TEF1) regions of isolate AR74, and DNA sequences were deposited into the GenBank database (ITS, PZ502928; TEF 1, PZ511917). BLAST analysis of the ITS and TEF1 showed >99% similarity with C. lunata reference sequences NR_138223.1 (564/568 bp) and MG979800.1 (921/923 bp), respectively. Koch’s postulates were completed in growth chamber experiments. Corn hybrid Golden Harvest G10L16-DV was grown in one seed per pot in 0.95L containers filled with Sungro-Resilience SS#1-FP potting mix. Plants were maintained in a growth chamber at 25ºC with a 12-h photoperiod. Eight plants at growth stage V4 were inoculated with 1.5 ml of a conidial suspension of C. lunata AR74 isolate (1 x 104 conidia/ml sterile distilled water) using a handheld spray bottle. Eight control plants were sprayed with 1.5 ml sterile deionized water. All plants were returned to the growth chamber and kept under separate airtight plastic bags for 24 h to promote infection. Eight days after inoculation, symptoms consistent with prior field observations were recorded on all inoculated plants and no symptoms were observed on control plants. The pathogen was successfully reisolated from symptomatic inoculated leaves and colony morphology, conidial characteristics, and ITS and TEF1 sequences of the reisolated fungus matched the original C. lunata isolate. This process was repeated twice using methods described above. This is the first confirmed report of Curvularia leaf spot in Iowa. Within the United States (U.S.), the disease has also been reported in Louisiana (Garcia-Aroca et al. 2018), Kentucky (Anderson et al. 2019), Mississippi (Jimenez Madrid et al. 2022), Delaware (Henrickson and Koehler 2022) and Minnesota (Solórzano and Malvick 2026). Because the potential impact of Curvularia leaf spot on corn yield in Iowa and the U.S. is currently unknown, unknown. it will be important to monitor the impact of this disease in Iowa.