Hellebore leaf spot

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
• Tiny, black fruiting structures of the fungus may be visible in the dead plant tissue

Control

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

There are no fungicides with specific recommendations for the control of hellebore leaf spot. However, the fungicides tebuconazole (Bayer Fungus Fighter Concentrate), tebuconazole with trifloxystrobin (Bayer Fungus Fighter Plus), and triticonazole (Scotts Fungus Clear Ultra and Scotts Fungus Clear Ultra Gun) are labelled for the control of a number of other diseases on ornamental plants, and may give some control of hellebore leaf spot .

The following products contain a combination of both insecticide and fungicide, enabling the control of both insect pests and disease: myclobutanil containing cypermethrin (Bayer MultiRose 2, Doff Rose Shield, Vitax Rosegarde, Westland Rose Rescue); tebuconazole containing deltamethrin (Bayer Multirose Concentrate 2), and triticonazole containing acetamiprid (Scotts Roseclear Ultra and Scotts 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 which 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.

See also...

Hellebore aphid
Hellebore black death
Hellebore leaf miner
Hellebores
Shade gardening