Yucca Leaf Spot
Yucca adds dramatic architectural effect to borders and courtyards with its bold sword-shaped leaves and panicles of bell-shaped flowers. Tender species make good house or conservatory plants. Until recently it had been largely free from foliar disease problems but a fungal disease causing leaf spots on outdoor plants has now become common and widespread.
Scientific name: Predominantly Coniothyrium concentricum (syn. Microsphaeropsis concentrica)
Plants affected: Yucca and some other succulents including Agave and Dracaena
Main symptoms: Brown leaf spots, scorched appearance to leaves
Main causes: Fungi
Timing: Year round, as Yucca retain their leaves
What is Yucca Leaf spot?
Coniothyrium concentricum (syn. Microsphaeropsis concentrica) is the most common cause of Yucca leaf spots in the UK. Others have been recorded, including Colletotrichum species, but they are much less common. All of these fungal species cause grey-brown spotting on the upper surface of leaves, and leaves can often appear scorched.
- The infection first appears as tiny clear spots in the older leaves. The lesions initially turn yellow and finally purple/brown as they mature. The lesions are generally oval and scattered across the upper leaf surface.
- With a Coniothyrium concentricum infection, after about 4 months, tiny black fruiting bodies of the fungus form in concentric rings on the sunken lesions.
- Leaves can often appear scorched, especially at the tips.
- Remove heavily infected leaves if feasible to prevent the spread of spores to new foliage.
- Reduce overhead watering and/or provide protection from rain which can help to reduce spores being splashed to new leaves.
- The fungus most likely persists on fallen leaf debris, so clear the area of fallen leaves, and destroy the leaves rather than adding them to your compost.
- Many plants suffer from more severe leaf spot infections when they are under general stress. Ensure that the plant is appropriately watered and fed to help improve its' overall health.
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. Additionally, 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 Yucca (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 damaging invertebrates and disease: 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 invertebrate damage is not a problem on the plants treated.
There is no specific information available as to the efficacy of these products against yucca leaf spot, however. It would be prudent to apply a small amount of the chosen fungicide first, at a solution suggested on the packet for other problems, to ensure that the product will not cause plant damage.
Success is more likely if it is combined with cutting out of the worst affected leaves.
Inclusion of a fungicide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.