Tar Spot is Starting to Appear in Maryland
By Andrew Kness, Senior Agriculture Agent, University of Maryland Extension, Harford County
Tar spot has started to pop up in corn fields and we have received several reports from Harford, Cecil, and Kent County, Maryland over the past couple of weeks. These reports are about one month earlier than we have first reported tar spot in years past, with the July 23 confirmation of tar spot in Cecil County being the earliest.
Fortunately, all reports and all of the fields I have scouted myself, tar spot is present but at very low levels. The predominant disease I am seeing right now remains gray leaf spot, which makes sense as this is a disease that prefers warmer temperatures and tar spot tends to favor cooler temperatures.
With tar spot being present in our region earlier than usual, growers should be vigilant with scouting and monitoring this disease. Most of the corn crop in Maryland is at or close to R3 or near even near black layer in southern Maryland, which is towards the tail end of major yield concerns associated with disease infection. Furthermore, acres treated with a fungicide between VT-R3 should have sufficient protection to get them through grain fill. If you have corn that is later tasseling you will want to pay special attention to these fields to monitor tar spot levels and other foliar diseases that could potentially reduce yields. These fields may warrant a fungicide pass if you were not planning it already.
As you are scouting your corn fields, be on the lookout for tar spot. With funding from the USDA-NIFA, we are conducting a survey of tar spot’s distribution in Maryland. If you have tar spot, or think you might, please report it to corn.ipmpipe.org or reach out to me at akness@umd.edu or (410) 638-3255. Reports are kept anonymous and individuals and/or farms are not identified in any public reports or publications.
This article appears in August 2025, Volume 16, Issue 5 of the Agronomy News.