Budworms on Petunias: Prevention and Treatment

I manage budworms at the end of summer—they appear, without fail, in my geraniums, petunias, and tomatoes. You’ll expect a full, lush garden only to find rotting veggies and flowers with tunneling holes full of frass, or budworm poop.

Because these larvae come from moth eggs, you can prevent them from reaching your petunias by discouraging the adult moths. If the worms are already present, various mechanical, biological, and chemical methods help reduce their populations. 

These targeted, routine, and effective treatments destroy budworms before they decimate your plants. We’ll first learn to identify and prevent the critters, then how to manage and reduce their populations. 

Budworm Overview

Budworms are moth larvae that tunnel into flowering buds, crops, and dense vegetation. Many budworms exist, though the most damaging for petunias are the tobacco budworms. Their botanical name is Chloridea virescens. The adult moth is whitish-brownish with three distinct stripes on its wings. It lays eggs on susceptible crops and garden plants.

Small, yellow-white caterpillars emerge from the eggs and begin tunneling into flowering buds and swelling vegetables. They have white stripes along their sides. As they eat, they shift from white to brown and green as they consume buds, leaves, and stems. When you squish them, you’ll see undigested plant matter ooze from their bodies!

The worms eat and eat until they gorge themselves, then they begin pupating in the soil. The pupae overwinter and emerge as adult moths the next growing season. 

How to Identify Budworms

You’ll notice the damaging symptoms these worms cause before you notice the worms themselves. They’re especially destructive to hemp crops, as they tunnel into the buds and prevent seeds from forming. If you notice budworm symptoms, inspect your petunia plants to see if the wormy larvae are present. 

How to Identify the Symptoms

The first sign of budworms is a lack of petunia flowers! As the worms eat at the buds, they cause them to wilt before they open. You’ll see brown, black, and dead buds on top of the plant, and new ones emerging from lower on the stems. 

Alongside wilted petunias, watch for tunneling holes and frass. The larvae create small, round holes in the flowers as they eat their way through the plants. If flowers are absent, the caterpillars may eat the tender leaves and stems. After eating, they poop out small brown and green waste particles that linger on the plants.

In severe infestations, the ample holes and tunnels create wounds where pathogens can fester. Bacteria and fungi may cause further symptoms, like rotting, withering, and wilting.  

How to Identify the Pest

The wormy pest itself is easy to identify, if you can find it! The budworms thrash and writhe when disturbed, making their capture cumbersome. After noticing symptoms of their presence, look closely at the infested buds to see if they’re still there.

Budworms, especially the tobacco budworm, resemble corn earworms—the two wormy larvae are almost identical! They both prefer eating the same crops, they look alike, and they cause the same damage. Treatment is similar for the two types of caterpillars, so don’t worry if you can’t identify them.

Look for segmented caterpillars with white lines on their sides. They’ll have small, leg-like stubs on their undersides and tiny black spots on their backsides. You may also see their eggs on flower buds; they’re white and oval-shaped. 

How to Prevent Petunia Budworms

Prevention is the best way to avoid budworm damage, and it helps reduce the likelihood of infestations. Keep your petunias happy and healthy, as the healthiest specimens are the most resistant to pest damage. Their perky, vigorous leaves are difficult for insects to chew on. 

Aside from cultivating healthy petunias, these other prevention strategies can discourage the moths from laying their eggs.

Remove Garden Debris

Because budworms pupate in the soil, they rely on petunia debris to cover and hide them from view. Old stems, dead leaves, and thick layers of mulch protect them from predators, winter frosts, and upset gardeners! 

Lower the chances of pupae surviving the winter by removing as much debris as possible without harming your garden. Debris, like mulch, insulates and protects the ground, though it also houses harmful pests that eat tender veggies and flowers.

Pull Nearby Weeds

Just as debris covers the pupae, so too do weeds. These pesky volunteer plants have ample roots and shoots that cover the ground, creating small pockets where pests can hide. 

Winter weeds protect the ground, while spring and summer weeds provide additional food sources for the adult moths and juvenile caterpillars. Lower the pests’ success rates by removing all the weeds near your petunias. Pull them with your hands, or use a tool like the CobraHead weeder. 

If you’re growing petunias in containers, this is especially important! Keep the pots weed-free, and remove excess debris from the soil. 

Add Row Cover

Row cover is helpful when the adult moths are actively laying eggs. It’s a mesh material that covers plants while still allowing air and moisture to pass through it. Because the budworm moths lay eggs in the evening, you can cover your petunias each afternoon to prevent eggs from being laid on the emerging flower buds. 

Row covers can boost humidity and heat levels, which is why it’s important to remove them during the day. Drape them over your petunias in the afternoon, then remove them first thing in the morning to let the plants breathe and photosynthesize.

Greenhouse plastic does the job, too, though it traps much more humidity and heat than mesh row covers. Use row covers in the summer and greenhouse plastic in the fall—the plastic will protect the petunias and also extend their growing season. 

Move Potted Petunias

Sometimes, moving the petunia flowers to a new location is all you’ll need to do! The adult moths land on blooms in the open, and porches, patios, and greenhouses can prevent them from finding the flowers. If you can enclose them in a new space, you’ll definitely prevent the moths from laying eggs!

A simple roof or patio covering can do wonders, especially if it’s far away from the rest of your garden. The budworms will pop up in the dense vegetation, while your petunias will sit safe and protected near your home. 

Budworms love geraniums, so consider planting some as “trap crops” far from your petunias. The trap crops lure the moths so they don’t fly onto your potted petunias. 

How to Manage Budworms

Prevention methods may not work all the time! Budworms are pesky caterpillars, and they’ll pop up when you least expect them. Try these management techniques to reduce budworm populations and protect your tender petunia blooms.

Squish Em!

You’ll have to get up close and personal with these critters to squish them. I recommend wearing gloves so you don’t have to touch them. Start by inspecting your plants, looking closely at each flower and unopened bud. 

The caterpillars may be inside the unopened flowers, or they’ll be traveling near them on stems, leaves, and petals. Catch them with your fingers, then squish them! If you’d rather not squish them, you can throw them inside a bucket full of soapy water. 

Encourage Predatory Wasps

Rather than relying on chemical sprays, lean on nature itself! The food chain is a wonderful thing—each creature eats another or is eaten by others. This is true for tobacco budworms. Parasitic wasps target the larvae, while birds target the moths. 

Paper wasps prey on budworms, and so too do two other species. Look for the species Campoletis sonorensis to target the worms when they’re small. The wasps lay eggs on the worms, which hatch into baby wasps that eat them from the inside out. 

If the infestation has existed for a few weeks and the worms are large, encourage the wasp species Cardiochiles nigriceps with ground cherry and flowering tobacco plants. It’ll come to the ground cherry, and then target the thick caterpillars before they reduce your petunias to bare stems. 

Add Biological Controls

Other biological controls aside from wasps can help manage these wormy pests. A fungus-like parasite, Nosema heliothidis, infects and kills them before they destroy your flowers. Find it in pesticides, and follow their labels for proper dosage and application rates. 

Aside from wasps and this parasite, many other predatory bugs eat budworms. Encourage pirate bugs, spiders, and damsel bugs to your garden by planting more native plants and flowering shrubs; provide a water source for the thirsty bugs to drink from, like a bird bath or jar full of water. 

Last Resorts

Though many pesticides kill budworms, they’re particularly damaging to pollinators that frequent flowers. Frequent pesticide applications can upset the natural pest-predator balance that’s already present. If you are using pesticides, select specific ones that target budworms; avoid broad-spectrum insecticides that kill at will.

Though some sources recommend using the bacterium Bt, Bacillus thuringiensis, it’s not that effective on budworms. They don’t eat enough of the bacteria to suffer damage. The pesticide will also kill beneficial caterpillars that frequent petunias. 

Follow the pesticide’s label, as the label is the law! It’ll have instructions for use, dosage rates, and necessary warnings.

Frequently Asked Questions