One of the wettest and warmest years on record created ideal conditions for traditionally problematic plant diseases to thrive, but it is the emergence of new diseases into the top 10 that has attracted the attention of Royal Horticultural Society (RHS) scientists.
The discovery of four viruses in grapevines and one in wisterias, none of which had previously been reported in the UK, contributed to viruses securing 10th place among the top enquiries from gardeners in 2014 to the RHS Gardening Advice service. The use of advanced detection methods enabled the RHS to more readily identify the viruses.
The two most damaging viruses, which affect grapevines and are transmitted by mealybugs and scale insects, have the potential to affect the UK’s developing grapevine industry.
While viruses were a new addition to the top 10, honey fungus was the most commonly diagnosed garden disease for the 19th year running.
One reason why honey fungus is so destructive is its ability to affect a wide range of plants, particularly woody and herbaceous perennials. This silent killer not only infects and typically kills the host plant, a process that can take several years before symptoms of infection appear, but even after an infected plant has been removed the residues of the fungus in the soil can infect new plants.
As in previous years the weather played a major role in the proliferation of certain diseases. A combination of high temperatures and high rainfall last year created optimum conditions for diseases that attack the leaves of plants to thrive.
Enquiries about foliar diseases, which include rusts and leaf spots, increased significantly in 2014, pushing rust diseases up four places in the chart from 7th place in 2013 to 4th in 2014. Leaf spots maintained their position as the third most enquired-about disease.
Box blight caused by Cylindrocladium or Volutella continues to be a cause of concern for gardeners, as it can discolour and strip the leaves of architectural box plants creating a bald, brown effect. The disease maintains its position as the second most commonly diagnosed among samples received by the charity.
RHS Senior Plant Pathologist Matthew Cromey says: “Although the list may seem concerning to gardeners, they can be reassured that the RHS is looking for ways to manage the most damaging diseases. For example, we are investigating how to accelerate the breakdown of honey fungus residues to allow gardeners to replant susceptible plants more quickly in areas that have been affected by the disease.
“Although we have detected viruses that can seriously damage grapevines, there is no evidence that these have spread to commercial vineyards. Therefore the industry may be able to introduce control measures now to avoid significant losses in the future.”
The Top Ten enquiries of 2014
1. Honey fungus
2. Box blight (Cylindrocladium and Volutella)
3. Leaf spots
4. Rusts
5. Phytophthora diseases
6. Powdery mildews
7. Pythium diseases
8. Wilts
9. Root and stem rots (including damping off)
10. Viruses
