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Detection of Maize Dwarf Mosaic Onset in Northern Ohio. Raymond Louie, Research plant pathologist and adjunct professor, Corn and Soybean Research Unit, Agricultural Research Service, U.S. Department of Agriculture, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691; J. K. Knoke, research entomologist (retired), Departments of Plant Pathology and Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Phytopathology 81:760-765. Accepted for publication 13 February 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/Phyto-81-760.

An ability to detect maize dwarf mosaic virus (MDMV) infections will help explain how MDM epidemics develop. Trap plant plots with and without diseased source plants, successive maize plantings, and grass weeds in tile plots were used to monitor MDM onset in northern Ohio. This area is outside the natural distribution of johnsongrass (Sorghum halepense), the overwintering host of MDMV-A. The average incidence of MDM in trap plants increased from 44 to 52% as the number of source plants placed at a 0.6-m distance from the trap plants increased from 25 to 100 plants. At a constant level of 100 source plants, the average incidence of MDM decreased from 52 to 33% as the distance between source plants and trap plants increased from 0.6 to 4.9 m. The decrease in MDM incidence averaged –4.8%/m of the distance from source plants and averaged +0.5% MDM for each unit increase in source plants. Successive plantings at location 2 detected MDM onset 42 and 12 days earlier in 1986 and 1987, respectively, than did the trap plant plots without source plants. MDMV was not detected in 832 weed samples collected from the field or in the six grass weed hosts grown in tile plots. Aphid populations were monitored with yellow-pan water traps. Rhopalosiphum maidis was significantly related to MDM onset. Aphid migration, seed transmission, and infected weed host hypotheses were evaluated as initial sources of MDMV. The weed host hypothesis best explained MDM onsets in northern Ohio.