Geranium Budworm: What Causes Holes in Geranium Flowers and How to Stop It

Written by Richard Flowers, ACCNP, Green Thumb Nursery Ventura

Ivy Geraniums and Zonal Geraniums are two of the most popular plants around, because they give you a lasting flower display in a multitude of colors throughout the year and they are easy to grow. If your beloved geranium flowers keep getting ruined, the culprit is almost certainly geranium budworm, a small caterpillar that feeds on the buds and petals.

What Is Eating Your Geranium Flowers and Leaving Holes?

If your geranium flowers are failing to open, your petals look chewed and ragged, or you see small round holes in the buds and specks of frass (worm droppings), the culprit is geranium budworm. You will often see irregular or round holes chewed in the leaves as well. This pest, commonly called geranium budworm or tobacco budworm (Chloridea virescens, formerly Heliothis virescens), feeds on the buds and petals of many commonly grown flowers, including geranium, petunia, and nicotiana. The most common harm is associated with geranium, which is how it earned the name. The damage shows up as flowers that fail to open, small holes in the buds, and emerged flowers whose petals are chewed into a ragged appearance.

To confirm it with your own eyes, look closely and you will see a yellow or greenish worm with a brown head. The body carries many tiny black microspines that make the caterpillar feel rough to the touch, and it can measure up to about 1 1/2 inches long depending on its age (newly hatched larvae start as small as 1/25 inch). In the early evening you may also spot the adult, a moth with a wingspan of about 1 1/2 inches. Its wings are light green with brown overtones and a few wavy, cream-colored bands. Washington State University’s HortSense fact sheet on geranium tobacco budworm describes the same damage and the caterpillar that causes it. If you want to compare varieties while you inspect, you can browse geraniums in our plant library.

Why Budworms Show Up on Geraniums

Budworms arrive with the moths, so the trouble starts on warm spring evenings. You will see the moths fluttering around your geraniums in the early evening with the onset of warm spring weather, and in our mild coastal climate they can be active almost year-round. The females lay single eggs on buds or leaves, and those eggs soon hatch into the worm, or caterpillar, that does the damage.

During daylight hours the worms often hide around the base of the plant, which is why you rarely catch them in the act until the flowers are already chewed. The caterpillars become full-grown in about a month, then drop to the soil and pupate in cocoons. Sometimes you can spot the cocoons attached to leaves or buildings. Because the budworm attacks the buds of developing flowers, the result is poor flowering or no flowering at all, and the damage builds through the growing season. It becomes most noticeable in late summer, and on a moderate coast the problem can persist almost year-round.

How to Get Rid of Geranium Budworms

Start with the gentlest methods and only escalate if you must. Here is the order I recommend, from least disruptive to last resort:

1. Handpick at dusk. If you have a small area or you would rather not spray, simply lift the worms off and drop them in a bucket of soapy water. The worms do not bite. This works best when the caterpillars are active, which is at dusk.
2. Prune and bag infested buds. Another organic approach is to prune off any buds that have visible entrance holes or small specks of frass, then seal them in a plastic bag or dispose of them away from the plant. This breaks the life cycle before the next generation emerges.
3. Spray spinosad (Captain Jack’s) at dusk. Spinosad is a natural insecticide derived from a soil organism, and I find it easier to remember by the Captain Jack’s name. I find it more effective on geraniums than Bt. Apply it at dusk and let it dry, because spinosad is toxic to bees until it has dried on the plant. More than one application may be necessary.
4. Know the Bt caveat. The insecticide containing Bacillus thuringiensis (Bt), often sold as Bt Worm Killer or Caterpillar Killer, is an effective biological control on some plants, but the worm has to eat it for it to work. On geraniums, where the caterpillars drill into the buds and eat little of the outside surface, I find Bt is often not effective, a limitation Colorado State University Extension notes for geranium budworm as well. Some gardeners still get satisfactory results, and more than one application may be needed.
5. Malathion only as a cautioned last resort. If you choose a synthetic insecticide, malathion is one option, but treat it strictly as a last resort. It is a broad-spectrum synthetic that is harsh on bees and other beneficial insects, so the organic options above are preferred. I personally resort to an insecticide only if it is absolutely necessary.
6. Read and follow the label. Before you apply any product, read, follow, and understand all of the printed instructions on the insecticide label.

In my own garden, I have Ivy Geraniums spilling over the sides of a large decorative pot, and I monitor them on a routine basis. If I start to see evidence of harm, I snip away the little damage I have at dusk and I am done, keeping the worm population down to a minimum. That light, regular attention usually spares me from ever reaching for a spray. For another common garden plant problem, see our guide to begonia powdery mildew.

Will Geranium Budworms Kill My Plant?

No, geranium budworm will not kill your plant. It is difficult to control if you have a large population, but oftentimes nature takes its course and the plant will re-bloom and recover on its own. The budworm does not kill the plant, it just ruins the current flowers and causes cosmetic damage to the leaves. In my garden the budworms feast on my plants, and it does not cause me concern, because I know geraniums are tough, durable, and resilient plants that will come back.

You can help your plants bounce back even faster by keeping them healthy and vigorous. Water properly and fertilize with an organic fertilizer so your plants grow stronger and thrive, which also helps minimize insect and disease pressure over time.

Geranium Budworm FAQ

What is eating my geranium flowers and making holes in the leaves?

The most common culprit is geranium budworm (tobacco budworm). The caterpillar bores into flower buds and chews petals and leaves, leaving round holes, ragged flowers, and small specks of frass (droppings).

What is the green caterpillar on my geranium?

It is almost certainly a geranium budworm larva. Look for a yellow to green caterpillar (sometimes brown, tan, or reddish when mature) with a brown head and tiny black spines that make it feel rough. It grows up to about 1 1/2 inches.

How do I get rid of geranium budworms?

Start with the gentlest methods: handpick the caterpillars at dusk into soapy water, and prune off and bag any buds with holes or frass to break the life cycle. For larger populations, spray spinosad (Captain Jack’s) at dusk so it dries before bees are active. Bt is often ineffective here because the caterpillars eat little surface tissue once inside the bud.

What eats geranium flowers in pots?

The same pest, geranium budworm, attacks potted and in-ground geraniums alike, along with petunias and nicotiana. Check potted plants at dusk, when the moths fly and the caterpillars feed, and inspect the base of the plant where larvae hide by day.

Does geranium budworm kill the plant?

No. Budworm damage is cosmetic. It ruins the current flowers and chews some leaves, but geraniums are tough, durable plants that will re-bloom and recover on their own, especially if you keep them well watered and fed.

Are geraniums poisonous to dogs and cats?

Yes. According to the ASPCA, geraniums (Pelargonium species) are toxic to dogs, cats, and horses; the toxic compounds are geraniol and linalool, and signs can include vomiting, loss of appetite, and skin irritation. Keep plants and clippings away from pets, and apply and dry any budworm treatment per the label before pets are near treated plants.

Sources:

• Colorado State University Extension, Tobacco/Geranium Budworm
• WSU HortSense, Geranium: Tobacco Budworm
• ASPCA, Geranium (Toxic to Dogs, Cats, and Horses)

Bring Us Your Bug and Plant Questions

If you have any bug or plant related questions, feel free to stop by your favorite Green Thumb Nursery and we will be happy to help you out. You can visit your nearest Green Thumb Nursery to bring in a sample and get a hands-on diagnosis.

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