 Herbicides work well when they're used correctly, but sometimes because of wind, rain, and other factors out of your control, they can cause injury to other plants. The trick is knowing if the plants were affected by the herbicide or something else. Gail Rule is a senior plant disease diagnostician at Purdue University. She says when diagnosing herbicide injury, the first step is to identify the plant species you're concerned about and then to look for similar symptoms on plants nearby.