Petunias are popular ornamental plants used in residential and commercial landscapes. There are hundreds of varieties of petunias planted in flower beds, hanging baskets and window baskets throughout the United States. This hardy plant is not bothered by nearly as many insects as most plants, but aphids and cutworms have both been known to infest petunia plants.
Aphids are small insects green, yellow, brown, red or black in color, depending on the specific species. Aphids are identified by tube-like structures (cornicles) that extend from the back of the body. These insects use their sender mouths to suck the fluids out of the stems and leaves of the plant. Adult aphids are wingless but younger aphids do have wings.
Damage by Aphids
Aphids generally do not cause severe damage to petunias unless they occur in extreme numbers. Symptoms that aphids are present include the yellowing and curling of leaves along with stunted growth of shoots. Aphids also are known to leave behind a sticky substance called honeydew, which grows a black mold. As they feed, some types of aphids inject a toxin into the part of the plant they are feeding on, which can prevent proper growth of the stem or leaf.
Although aphids do not normally threaten the life of the petunias, the damage caused can cause enough cosmetic problems that control methods are necessary. Ladybugs feed on aphids and can aid in the control. Limiting the amount of nitrogen in fertilizer can also help, as aphids prefer high-nitrogen soils. Pesticides available for retail purchase are also effective in killing and preventing aphids from damaging the petunia plant.
Cutworms are the larvae or caterpillar forms of certain types of moths, including Agrotis, Amathes, Peridroma and Prodenia. These insects got their name because of the way that they are able to cut down a petunia as they eat the stem. The adult moths feed on nectar at night. Cutworms can cause significant damage at worms and larvae but they do not cause damage as adults.
Damage Caused by Cutworms
The damage caused by cutworms is much greater than the amount of the plant they consume because they cut off plants at the soil line The varieties of cutworms that are capable of climbing eat the leaves, fruit, and buds.
Plowing fields in the summer or fall can uproot eggs buried by cutworms and prevent them from damaging the next season's crop. Toads are a natural control method for cutworms. Chemical treatments are available at retail stores that can be applied to the soil to help control these pests.