More than 100 species of plants share the name geranium, with 422 in the actual Geranium (jer-AY-nee-um) genus, 280 in the Pelargonium (pe-lar-GO-nee-um) genus, and a little over 100 more in other genera.
Pelargoniums are the most popular choice of geranium for most growers. While less hardy than true geraniums, these South African plants are excellent heavy bloomers.
But pelargoniums are susceptible to many pests that don’t affect their mountain-born kin.
One of these is a particularly nasty pest often erroneously called the geranium worm.
What Are Geranium Worms?
Geranium worms are the caterpillars of Chloridea virescens (formerly Heliothis virescens), known as the tobacco budworm.
Generally appearing from late spring into early fall, these pests age faster in warmer weather. It allows them to have as many as 5 generations at the southernmost USDA hardiness zones in a single year.
A single adult will generally lay 300 to 500 eggs but may produce up to 3 times that amount under the right conditions.
These pests deposit their eggs on fruits, blooms, and the tips of new growth.
Upon hatching, the larvae need 5 to 7 instars to reach the pupal stage. At this point, they burrow into the soil for their metamorphosis.
These caterpillars can vary in color depending on the instar and resemble the cotton bollworm (Heliothis virescens). The latter doesn’t attack geraniums.
What Damage Do Geranium Worms Cause?
These nasty little critters chew holes into your geranium buds, which can prevent them from opening.
The petals will display a hole where the budworm chewed through when they do. The budworm can even cause the entire bud to fall off in some cases.
But the flowers aren’t the only thing these pests will attack, and the foliage can take on heavy damage with a large enough population.
It is a small comfort to know that tobacco budworms can become cannibalistic as they get older. This population’s self-control will be barely noticeable in a large infestation.
Even worse, the pupae can safely overwinter unless there’s a deep freeze, at which point your geranium will die.
While this pest is far more selective in which plants it attacks (and their coloration may even change depending on the host plant), it’s known to go after other garden and lawn plants such as:
- Abutilon theophrasti
- Geranium dissectum
- Jacquemontia tamnifolia
- Lespedeza bicolor
- Linaria canadensis
- Lonicera japonica
- Medicago lupulina
- Penstemon laevigatus
- Sida spinosa
- Various weeds
How To Control Geranium Worms?
Due to how prevalent this pest is, it’s developed a resistance to most chemical insecticides.
Pyrethroid insecticides seem the most effective, although only for a while. The budworm already has a resistance to these chemicals.
Yet, some natural options are still quite viable, especially when using more than one method.
The easiest method is to hand-pick the caterpillars and drop them into soapy water.
Neem oil is another helpful method that won’t harm beneficial insects.
Use a neem foliar spray every other day for 14 days or until the infestation is gone, then once every 2 weeks as a preventative.
Likewise, you can use a neem soil soak every 14 days until the infestation is gone, then once every 2 to 3 weeks as a preventative.
Neem soil soaks and neem cakes are both able to help combat these bugs when they enter or exit the pupal stage. But they’re not 100% percent effective.
Treating the soil is more complex but essential in eliminating a budworm infestation.
When using potted plants, repot and safely discard the soil. Sterilize the pots before reusing them.
In the garden, it may be more difficult to sterilize the soil, but you may be able to remove the dirt and sift out the bugs or replace it with organic compost.
The larvae will burrow down to 4″ to 6″ inches and create a packed wall around themselves. Excavation can destroy these walls.
Finally, you may wish to invest in pheromone traps. These are conical bug zappers that emit tobacco budworm pheromones to attract the adults, killing them on contact.
While this won’t eliminate any younger stages, it can help prevent more eggs from being laid.