• On the leaves the infection starts as small red-brown spots (1-5 mm diameter) with dark purple borders and yellow haloes. Spots are visible on both leaf surfaces and sometimes number in the hundreds on a single leaf
• In wet conditions the spores of the fungus may be visible as white clusters in the centre of the spots
• As the infection progresses the spots coalesce and the leaves turn yellow through to brown and fall from the stems
• Stem lesions appear as purple-brown, slightly-sunken elliptical cankers which remain visible on the stems throughout the year. Cankers which girdle the stem result in extensive stem die-back

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

The disease is best managed by removing all infected plant material and either burning it or disposing of it at your local council composting facility. Home compost heaps rarely reach the temperatures achieved by large-scale facilities required to kill fungal spores. Clearing fallen leaves should help to reduce fungal inoculum in the following year.

Chemical control

There are no fungicides available to amateur gardeners with specific recommendations for use against Blumeriella kerriae. However, 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 Kerria (at the owner’s risk) to try and control the disease.

There is no specific information available as to the efficacy of these products against Kerria twig and leaf blight. It is likely that repeated sprays will be required where the disease is present, particularly during warm wet weather. Success is more likely if the plant is cut back hard to remove affected material, and then sprays applied to protect the new growth. It would be prudent to apply a small amount of the chosen fungicide first to ensure that the product will not cause plant damage.

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.

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

The cause of twig and leaf blight on Kerria japonica is the fungus Blumeriella kerriae.

The development of Kerria twig and leaf blight is likely to be favoured by wet weather conditions. In damp conditions Blumeriella kerriae produces large numbers of asexual spores from each spot/lesion. Spores are likely to be transferred between plants via rain splash, wind, and transfer on contaminated tools.

The fungus overwinters on fallen leaves and lesions on the stems then releases spores to reinfect new growth in spring. Spore production has been observed throughout the year on Kerria plants in the UK.  The sexual stage of the fungus has not yet been observed to occur in the UK.