Scouting and Reporting Tar Spot of Corn in Pennsylvania

By Paul D. Esker and Alyssa Collins

Since tar spot of corn was first found in Pennsylvania in late 2020, most initial reports of the disease have been received in mid-to-late July. Given this, we recommend scouting corn fields for this disease early to mid-July. 

To facilitate reporting tar spot finds in Pennsylvania, we created a simple app using Epicollect5, available on Android and iOS platforms. This scouting tool has advantages over our current reporting system, which primarily relies on text messages or emails. One main advantage is that you can use the app while scouting without a signal, meaning that if you are offline, the report will upload once you have connectivity.

Below, we outline the steps you must follow to submit a report. We developed this to be systematic using a series of simple questions or information that is requested. We want to emphasize that while we ask for GPS coordinates, these are only used to identify the county where an observation was submitted.

Steps to use the "Corn tar spot" tool in Epicollect5.

1. Download "Epicollect5" following the app tool based on your phone or tablet type.
2. Once downloaded, open Epicollect5 and select "+ Add Project."
3. Search for the project using "Corn tar spot."
4. Select "Corn tar spot" to open the project.
5. Identify the field location by selecting "Update location." 
6. Indicate the corn growth stage.
7. Indicate if tar spot is present. If you are unsure if you have tar spot, select that option, and information will be provided about what to look for to help determine if you think you have this in your field. If you are still unsure at this stage, please mark "yes," but provide an image.
8. Provide an estimate of the incidence or severity of the disease. If you use this for incidence, the value would be for the number of plants with tar spot divided by the number of plants examined (i.e., 10 plants with tar spot divided by 100 plants examined = 10% or a 1 in a 1-10 scale). For severity, this would be the area of the leaf covered by tar spot symptoms, and you should examine multiple leaves in the field to estimate the average severity on the same 1-10 scale.
9. Take a photo of a leaf with symptoms, or upload an image if you have already taken the picture.

10. Add relevant notes. Here, you can provide your name and contact information, the corn hybrid, other diseases noted in the field, or any other relevant information you would like us to know. We will follow up with you if we have any questions.

11. Save the entry and upload it to our database.