An Observation of Corn Tar Spot Dispersal from Agricultural Fields to an Isolated Urban Plot

Tar spot of corn is a fairly new disease to the United States, and since its introduction in 2015 it has spread to over 310 counties across nine states. Little is understood of the biology and epidemiology of the causative agent of tar spot of corn, Phyllachora maydis. Published research from Latin America indicates that spores can only travel a distance of 75 m; however, rapid progression and spread in the United States, in addition to widespread observations of top-down infection, indicate distal dispersal is likely more important. We observed an isolated plot of decorative corn in an urban setting, isolated from agricultural fields. We assessed nearby fields for crop, tar spot, cropping history, and distance from the urban site. Based on our observations, the propagules infecting the urban plot arrived from at least 560 m if from corn residue, and from at least 1,249 m if from active infections from nearby corn. Although this observation is not replicated, it does indicate that dispersal values from Latin America may not reflect the potential dispersion in Midwest topographies.