Mildew on Echeveria and Other members of Crassulaceae

: Howard Drury; Fact Sheets; 26 March 2022; Hits: 473

Echeveria Verugas

Echeverias infected with Echeveria Mildew © Howard Drury 2022

Mildew on Echeverias and Others

Introduction
I have for several years been growing various members of the family Crassulaceae. In late summer plants of the genus Echeveria were attacked by what appeared to be a form of Powdery Mildew. Discussions on social media groups quickly confirmed many growers in the UK were experiencing this for the first time. I also learned by November 2021 that commercial growers in the UK of succulents were also experiencing problems with mildew on certain succulents. This plus a revamp of my personal website allowed the opportunity to produce further information based on research.

Overview

Research indicates there have been several scientific papers reporting mildews on members of the Crassulaceae family over a number of years. The one noticeably documented incidence occurred at the Royal Horticultural Society’s garden at Wisley in Surrey. Here the plants infected included Echeveria gibbiflora, E. gibbiflora‘Carunculata’, E.‘Chantilly’, E.‘Afterglow’, E.‘Secunda’, E.‘Ballerina’, Crassula capitella‘Flame’, C. lactea, C. multicava, Dudleya palmeri and Cotyledon orbiculata. From samples taken and analysed all speciemens were suffering from the same infection, one of which did not match any records in the Powdery Mildew GenBank. This must mean his is a new species and later research confirmed it matched an infection found on Sedum alboroseum in Hungary. The characteristics were consistent with Oidium subgenus Pseudoidium, the anamorph of Erysiphe, This is the first record of this powdery mildew species on Crassula, Echeveria, Cotyledon and Dudleya in the UK. There are also scientific papers siting Powdery mildew on Pachypodium lamerei in the Czech Republic in 1999, again a new species of mildew was identified based on the pseudoidium anamorph, this fungus may be clearly assigned to Erysiphe emendation, probably to section Uncinula, since the cleistothecial appendages are non-mycelioid and occassionally circinate at the apex. The fungus is described as a new species Erysiphe pachypodiae sp. nov.
Others have reported Powdery mildew on Echeveria agavoides in India in 2008 The fungus has been identified as belonging to Oidium subgenus Pseudoidium. This is the first record of powdery mildew on Echeveria in India. This disease is also of significance since this part of India (North East) shares its boundaries with Nepal, China, Burma, Bhutan and Bangladesh, and this disease has not been reported from any of these countries.

Symptoms

From my own examples it was obvious the symptoms matched those seen in 2007 at the Royal Horticultural Society’s Garden at Wisley. Powdery white patches developed on the upper surface of leaves which left plants with foliage exhibiting corky lesions. This should not be confused with Farina which occurs on the foliage of certain Echeverias, for example E. ‘Cante’. As many of my plants are grown for their highly attractive ornamental foliage such as the Dick Wright cabbage type large leaved Echeverias they were completely spoiled but not killed as I had applied a systemic fungicide in an attempt to halt the spread of the disease and kill existing symptoms.

Economic Importance

The family Crassulaceae is large with some 1400 species in 33 genera. Whilst most are hugely popular house plants, with some being grown on very large commercial scales as florists pot plants such as Kalanchoe blossfieldiana hybrids, there are also numerous species highly cherished by collectors world-wide. This leads to an international movement of particularly newer introductions and so increases the risk of spreading the disease around the world very rapidly given today’s movements in plants. Some are valuable medicinal plants such as Cotyledon, where some species are used to produce treatments for problems such as warts and abscesses.

Life Cycle

Possible Controls

Cultural controls include:

Better air circulation, more ventilation, use of fans to move air, improved use of auto vents.

More attention to watering and nutrition levels to keep plants healthier. Keeping water off the foliage as this may spread spores

Giving plants more space. Avoid handling plants as it can be passed from one plant to another.

Chemical methods

Use of retail or amateur fungicides where it states for mildew on ornamentals.

The use of stimulants like SB Plant Invigorator promotes healthy growth and prevents pests and diseases from attaching plants.

New possible amateur products may become available such as Protac SF which is available to professionals and does not require a PA6 certificate to apply as it is a natural product but currently only available in 1litre containers from horticultural wholesalers at just over £80,00, and may be purchased by anyone.