Late blight is a potentially devastating plant disease that affects potatoes and tomatoes. Other related plants such as petunia and hairy nightshade also are affected. Don’t let the name fool you. This plant menace can show up any time during the growing season on a susceptible plant when the right weather conditions and the pathogen are present. The pathogen that causes late blight is windborne and can devastate yields quickly in the garden and commercial fields if left unchecked. As a result, late blight is a community problem that affects everyone.