The Purdue Tree Doctor app is a great tool for diagnosing any tree issues growers may have with diseases or pests. The app is specific to trees in the Eastern and Midwestern parts of the United States. It has hundreds of descriptions and images to help users identify the problem, including different stages of development for each separate diagnosis. The search engine can find results though either tree species, or pest type. This is a paid app and is available to Android and IOS operating systems.
Apps by Developer Purdue University