What is hellebore leaf spot?

Hellebore leaf spot is caused by the fungus Microsphaeropsis hellebori and is a common disease on many hellebore species. You are most likely to see infections when new plant growth is occurring from late winter until summer.

It attacks most Helleborus spp. but is not so damaging on the tougher leaves of Helleborus argutifolius. H. niger is particularly badly affected by leaf spot.

Symptoms

You may see the following symptoms:

• On leaves: Infections cause more-or-less round, dead, brown patches on leaves and stems. Later, the dead leaf tissue may fall out, leading to a ragged appearance
• On stems: Infections on the stems may cause them to collapse
• On flowers: Dark spots and blotches can also develop on the flowers
• Tiny, black fruiting structures of the fungus may be visible in the dead plant tissue

Control

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

Non-chemical control

• Remove all affected leaves promptly and destroy
• Do not allow dead, infected material to remain around the plants, since this will be a source of infection in the following season

Chemical control

The fungicide tebuconazole with trifloxystrobin (Provanto Fungus Fighter Plus, Toprose Fungus Control & Protect) has a recommendation for the control of leaf spots on ornamental plants. Additonally, the fungicides tebuconazole (Provanto Fungus Fighter Concentrate) and triticonazole (Fungus Clear Ultra) are labelled for the control of other diseases on ornamental plants, and could therefore be used legally on hellebore (at the owner’s risk) to try and control the leaf spotting.

The following products contain a combination of both insecticide and fungicide, enabling the control of both insect pests and disease: myclobutanil containing cypermethrin (Resolva Rose 3 in 1, Rose Shield Bug & Fungus Killer, Roseclear Ultra Gun 2, Rosegarde) and triticonazole containing acetamiprid (Roseclear Ultra, Roseclear Ultra Gun).When a proprietary product contains an insecticide as well as a fungicide it would be preferable to use an alternative product if pests are not a problem on the plants treated.

Inclusion of a product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.

Download

Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: storing and disposing safely

Biology

The fungus causing hellebore leaf spot produces minute spores from small black fruiting bodies that form in the dead, affected tissues. The spores are spread in water and wind-blown rain and thus wet conditions are required to initiate disease. The fungus perpetuates on the plant over the summer and autumn and a new round of infections is intiated at times when new plant growth is occurring.