Petunias bring non-stop, colorful and often fragrant blooms to the landscape. They're available as bushy or trailing plants. Their flowers may be single and funnel-shaped, spherical with dense double petals or a variety of other forms. Petunia colors range from white and pale yellow to rich purples, clear blues and a host of pinks, reds and bi-colors. While this low-maintenance annual is generally pest-resistant, it sometime attracts small green bugs called aphids.
Aphids are tiny -- typically less than 1/8-inch long --, pear-shaped insects. Most aphids are green to yellow-green and wingless. Large populations on insects on a single petunia, however, grow wings and move to other plants. Aphids have long legs and antennae and mouthparts designed for piercing a plant to feed on its juices. They cling to the lower surface of new leaves or the undersides of stems. Aphids will often remain attached to the plants even when disturbed.
Aphids are most numerous in the spring, when petunias put out new growth. Infestations are possible, however, at any time during the growing season. Infested petunias develop wrinkled or curled leaves and misshapen flowers. Aphids also secrete a sweet, sticky waste product called honeydew. Ants flocking to your petunias to feed on the honeydew are a telltale sign of aphid infestations.
Small numbers of aphids seldom cause more than cosmetic damage to petunias. Large numbers of the insects, however, produce enough honeydew to attract a fungus called "sooty mold." As this fungus feeds on the honeydew, it covers the petunias'leaves with a powdery, black mold. A severe case of sooty mold may impair the petunia's photosynthesis, and deprive it of nutrients.
Petunias are vulnerable to aphid-transmitted cucumber virus. Signs of this disease include curled yellowed or spotted leaves and stunted plants. Even small aphid infestations can carry the virus. If you have a vegetable garden, plant your petunias well away from your cucumbers. Choose virus-resistant petunia varieties.
Track your petunias' aphid problem weekly during the growing season. Study the plants' new stems growth and their leaves' lower surfaces with a 10X magnifying glass. Place a white piece of paper beneath a plant before you examine it. A sharp tap on the foliage will loosen the insects' grip. The number of aphids landing on the paper indicates the severity of the infestation.
Homemade Aphid Control
Add 2 tbsp. of degreaser-free, liquid dish soap to 1gallon of water. Use the solution in a garden hose spray attachment. Spray your petunias' stems and the undersides of their foliage up to once a week, as necessary, to control aphids during the growing season.
Insecticidal Aphid Control
Use an insecticide formulated for aphids for sever infestations. Spray until the insecticide drips from the petunias. Use the manufacturer's recommended concentration. Repeat as new infestations appear. Bifenthrin-, carbaryl- and imidacloprid-based insecticides are some aphid-controlling insecticides.