Answer: Aphids or other sucking insects can leave behind a sticky substance called honeydew. They cause wilting and yellowing of plants. If you look closely at the undersides of the leaves, you'll probably find these pests. You can rid your plants of these pests with a product called Insecticidal Soap. I wouldn't spray household detergent on the plants; it could kill them. Instead, use insecticidal soap and carefully spray the undersides of the leaves.
Best wishes with your petunias!
Q&A Library Searching Tips