Although hellebores are usually easy to grow, they can be affected by a number of specific pests and diseases.
Hellebore aphid
Whitish-green aphids (Macrosiphum hellebori) sometimes form dense colonies on the underside of hellebore leaves and flowers in early spring. The sugary honeydew they excrete can also encourage unsightly sooty moulds on the foliage.
It is possible this aphid may also be responsible for spreading the serious virus disease known as hellebore black death.
Aphids can be controlled by using the systemic insecticides imidacloprid (Provado Ultimate Bug Killer), acetamiprid (Scotts Bug Clear Ultra) or thiacloprid (Provado Ultimate Bug Killer Ready to Use). These insecticides may also give incidental control of hellebore leaf miner (see below) if applied in August. Pesticides based on bifenthrin (Scotts Bug Clear Gun, Doff All In One Garden Pest Killer, Sprayday Greenfly Killer Plus) can also be used for aphid control. If plants are in flower, spray in the evening when bees are not active.
Hellebore leaf miner
This small fly (Phytomyza hellebori) was first discovered in Britain in 1999 but is now widespread in England. It is a specific pest of Helleborus foetidus. The larvae begin feeding inside the leaves during August and the mines are not fully developed until the new year. The mines are initially brownish-black blotches, but later become sinuous, whitish-brown tunnels. Pupation takes place within the leaf mines. Although the mines can be unsightly, H. foetidus plants are not greatly harmed and so the damage can be tolerated. Heavily mined leaved can be cut off and destroyed during the winter before the adult flies emerge.
Slugs
These often remain active in winter and can damage hellebore foliage and flowers, especially of Christmas rose (Helleborus niger). If necessary, scatter some slug pellets around the plants.
Other means of protecting plants
More hellebore problems
Hellebore leaf spot and root problems