11 hours ago
Ask the head gardener: My buddleia is diseased – can I save it?
Dear Tom,
I have several buddleia plants in my garden, some big, and they are all exhibiting signs of being diseased. Crinkly, mottled leaves and flower spikes failing to develop. I am in west Cornwall but a friend in east Devon mentioned that she had a similar problem. Any advice much appreciated!
– Liz
Dear Liz,
Your question is really timely for me. As I sat out in my garden the other evening, enjoying the relatively cool temperatures with a glass of something even cooler, I noticed that a couple of my buddleia were showing the same symptoms. I have experienced unusually high numbers of pests at West Dean this year, exacerbated by the warm, dry spring.
This was clarified with a visit from a local fruit group who described an unusually successful year for aphids on fruit trees too. A plant's response to an insect attack will involve a degree of leaf curl – although there may be no insects visible, that doesn't mean that your plant has not been got at.
Over the past few years, more and more gardeners are reporting issues with distorted, curled leaves that appear to be virused on their buddleias, and in severe cases, flowers are aborted. From its research and high numbers of member enquiries, the RHS has concluded that the culprit is most likely to be the melon-cotton aphid.
Originally thought to be an issue for plants that grow in greenhouses, the distribution of these aphids in gardens is causing some excitement among entomologists at the RHS, so much so that they'd like us to report any damage with photographs to a survey found on this link.
When it comes to tackling this issue, the good news is that buddleia is repeat flowering, so by pruning out the worst of the damage at the extremities of the stems, you'll promote fresh growth and flowers in a few weeks' time. These sap-sucking pests will have weakened the plant, so a handful of Growmore or fish, blood and bone around the feeder roots (not the base of the trunk) and a thorough watering will help to encourage that new growth.
I have always considered buddleia to be bombproof garden shrubs, with very few pest and disease issues. I would hope that this pest does not change my opinion over the coming years, but my advice would be to stay vigilant.
Once you have removed the damaged growth, and fed and watered the shrub, spray the new growth with SB Plant Invigorator, which is soap-based. Spray the new growth only, no need to spray the entire plant, as the aphids are more likely to be found on the soft growth at the tips; do this once a week as a preventative until the end of September and continue to do so as new growth emerges next spring.
You may simply remove the damaged growth and hope that the new shoots are not affected; I appreciate that this new level of commitment to your buddleia might not be for everyone. Encouraging more aphid predators into your garden will also help to lessen the damage in future years: ladybirds, earwigs and birds will all help to control numbers. A few blue tit boxes around the garden will not only give you great pleasure but also help to maintain more of a balance.
