When you're attempting to protect your geraniums (Pelargonium spp.) from pests, the most important thing is to keep the plants healthy. Strong, healthy geraniums will be less susceptible to certain insects, and they will also bounce back from pest infestations much easier. Common geranium pests include aphids, caterpillars, greenhouse whiteflies, mites, cottony cushion scale, mealybugs, thrips, weevils, slugs and subterranean termites. Aphids are usually the most common geranium pests, and you can control them naturally by releasing and encouraging ladybug populations in your garden to provide natural aphid predators.
Keep aphids, thrips, greenhouse whiteflies and mites away from your geraniums by spraying the plants with insecticidal soap or horticultural oils, such as neem oil.
Introduce a natural predator, such as the vedalia beetle or parasitic fly, to keep cottony cushion scale away from your geraniums.
Get rid of subterranean termites by removing the geraniums from the soil, destroying the termite tunnels and treating the soil in the affected area with an insecticide before replanting the geraniums. Follow the instructions on the insecticide label exactly.
Spray your geraniums with Bacillus thuringiensis to get rid of caterpillars, including the cabbage looper, obliquebanded leafroller, omnivorous leaftier and geranium plume moth larvae. Bacillus thuringiensis is a microbial insecticide that kills only foliage-eating caterpillars.
Introduce parasitic wasps or the mealybug destroyer to your garden to keep mealybugs away from your geraniums. You can also apply insecticidal soap or neem oil to the plants to minimize the infestation, but a systemic insecticide is necessary to completely rid your geraniums of mealybugs chemically.
Apply an appropriate insecticide to the leaves of your geranium plant to control weevil infestations. Follow the application instructions on the label.