What Causes Yellow Leaves on Petunias?

Fungal diseases often occur due to humid conditions caused by over-watering. Petunias should be watered to a depth of six inches and only watered again when the top one inch of soil is dry. Plenty of air circulation and well-drained soil are necessities.

Viral disease can only be prevented with disease-resistant soil and the elimination of weeds that harbor pests.

Aphids are treated with insecticidal soap spray, either commercially purchased or made by mixing 2 to 5 tablespoons of dish soap with a gallon of water. This spray should be applied on both sides of the leaves when conditions are cool every four to seven days until the aphids are gone.