Geraniums are reliable plants grown as annuals in most parts of the country. They begin flowering in late spring and continue providing gardens with vivid colour until the autumn. Pest problems are minimal with geraniums, but there are a few garden invaders that can ruin your geranium blooms. While some of these pests cause only cosmetic damage, others can stunt plant growth and even kill the plant.
Aphids are among the most common geranium pests. These small insects have long, narrow mouthpieces that can pierce the leaves, stems and buds of geranium plants, draining them of their internal fluids. Low numbers of aphids don't damage the plants and even can go unnoticed, but larger aphid infestations may cause leaves to curl and discolour. Neem oil, narrow-range oil and insecticidal soap can all control aphid populations. For best results, mix the material you choose with water and spray the mixture thoroughly on the tops and undersides of geranium leaves.
Like aphids, mites are pests that can cause aesthetic damage to geraniums; they are so tiny that they are hard to see. Mite infestation symptoms include leaves developing light-coloured dots and a bronze or yellow discolouration. In severe cases, leaves can drop from the plants and mites can cover plant parts with webbing. Unlike aphids, mites are arachnids, the same class that includes spiders. One common type of mite that preys on geraniums is the two-spotted spider mite. To eliminate mites from geraniums, you can spray them with a hard blast of water every few days, which disrupts mite reproduction or you can treat your geraniums with a miticide, which is a chemical pesticide for mites.
Caterpillars can cause extensive damage to geraniums by chewing holes in their blossoms and leaves, as well as devouring entire buds, flowers, leaves, shoots and seedlings. Unlike aphids and mites, caterpillars can stunt plant growth and kill plants. To control caterpillar populations, remove them by hand. Also remove adjacent weeds and treat geraniums with the bacteria Bacillus thuringiensis.
Whiteflies are small, winged insects that are covered with a white wax. Like aphids, the whiteflies feed on the internal fluids of geranium plants. Symptoms of a whitefly infestation are dry leaves, yellowed leaves or dropping leaves. While pesticide oils and soaps can reduce whitefly populations, they will not eliminate them. For best results, remove infected leaves by hand, spray the geraniums with water and/or vacuum the geraniums with a small, hand-held vacuum cleaner.
To get rid of slugs, set out saucers filled with stale beer in the garden. The slugs will be attracted to the beer, climb inside and drown. Alternatively, you can control slug populations by putting diatomaceous earth on the soil surrounding geraniums or trap them under flat boards or newspapers.
Ants can be a useful addition to anti-pest armoury as they feed on pests, such as whitefly, aphids and caterpillars. Leave garden ant nests in place so that the insects can help control the pests feeding on your geraniums and other plants.