What Kinds of Pests Attack Petunias?

Caterpillars that turn into worms are the biggest potential petunia pests.

Petunias are known for their vividly colored flowers and frilly petals. Petunias perk up gardens from summer through the end of fall -- as long as they're not invaded by pests. The most damaging and common pests are moths that overwinter and transform into caterpillars. Take care to inspect your plants frequently and catch infestations early to rescue your petunias from potential damage.

Tobacco Budworm

You will notice if the tobacco budworm (Heliothis virescens) has invaded your petunia patch if you seed what looks like small black seed-like droppings on the flowers and leaves of the plant. The droppings will be more visible than the budworm caterpillar itself. That's because the budworm is sneaky about when it shows itself. The female will usually wait until dusk to lay her eggs and start chomping on the plant, leaving flowers with raggedy edges. If you can catch the budworm during a dusk inspection, remove it by hand. Otherwise, resort to an insecticidal warfare strategy with Bacillus thuringiensis (Bt), or insecticides with active ingredients such as spinosad, permethrin, esfenvalerate, cyfluthrin, bifenthrin or related compounds.

Cutworms

Cutworms are dingy gray-looking caterpillars that grow to a length of an inch and members of the Lepidoptera order of insects. They curl up into a ball in the shape of a "C" if you touch them. The good news about cutworms is that they typically only attack new petunia transplants and seedlings. The bad news is that this could mean having to start from seed again or repurchase new petunia transplants. Homemade and simple preventative solutions are to loosely wrap the plant stems with foil or paper to set up a barrier that keeps the cutworms away from the plant stems. Sprinkling cornmeal or bran on the soil is another option. Otherwise, dig the soil surrounding the plant, find the cutworms, remove and kill them or place chemical baits to trap them.

Hornworms

Hornworms are cousins of budworms and can wreak the same type of havoc on your petunias. They bore holes into the buds, and then, like their budworm cousins, leave black seed-like droppings. Inspect your petunia stems, flowers and leaves on the top and underneath for signs. Wait until dusk to look for the hornworm, and if you spot them, use tweezers or your hands to pluck them and plop them into a pail of soapy water. Otherwise, use a BT or an insecticide with carbaryl, permethrin or spinosad.

Leafminers

Leafminers are tiny, swarming black and yellow flies. When they land on petunias, they rupture the leaves and petals, leaving a sappy substance. The biggest leafminer culprits causing damage to petunias are the serpentine leafminer (Liriomyza trifolii) and the pea leafminer (L. huidobrensisa). The best solution is to keep petunias well irrigated and clip off infested leaves, since the damage caused by leafminers is largely "cosmetic."

References

• Colorado State University Extension: Tobacco Geranium Budworm
• UC Davis: Pests in Gardens and Landscapes, Petunia
• University of Rhode Island Extension: Petunias
• Botanical Journeys Plant Guides: Petunia Pests
• Garden Services: Petunia

Resources

• University of Florida Institute of Food and Agricultural Sciences: Tobacco Budworm
• Weidners: Caterpillar Information