We have a holly tree growing in our garden for at least 20 years. In 2024, for the first time, in October, it produced red berries. These berries have remained on the tree, untouched by birds and now the tree is shedding. The drive is covered in holly leaves. This has never happened before, and we are mystified. Our garden is in rural Mayo, which has seen a lot of wind and rain this winter. A McNeely
You’re right to be concerned about your poor holly bush, which sounds like it’s suffering from a disease known as holly leaf blight (Phytophthora ilicis). It’s an increasing problem in Irish gardens in recent years. This spring I also spotted it on holly trees in the wild.
The symptoms are very much as you describe and are typically first noticed in winter or early spring following a spell of wet, cool weather. Once-healthy holly trees and hedges start to sicken, with their leaves blackening and then dropping. Sometimes you’ll also see partial blackening of the stems. Foliage close to the ground is most vulnerable as a result of splash-back from the soil, which helps to spread the disease back on to once-healthy growth.
This destructive but nonfatal disease, which thrives in cool, rainy weather that enables its spores to easily move on to suitable host plants, is technically an alga but is more easily described as fungal in nature. Those same spores can also be concealed on fallen leaves and in soil near an afflicted plant, so can be inadvertently carried on your boots, or even carried via wind or visiting wildlife. There is no effective chemical control available to gardeners.
The fact that your holly bush is producing berries for the very first time is interesting and may offer a useful clue as to why it’s recently become infected with holly leaf blight. Hollies are classed as either male or female. Only female holly trees produce berries, for which they typically require a male pollinating partner (the exception is self-pollinating varieties). It sounds like your female tree was without a male pollinating partner for many years until recently, which suggests that one has recently been planted nearby, either by you in your own garden, or possibly in a neighbouring garden. If so, then this male holly tree was possibly the carrier of the disease that subsequently infected your plant.
[ Why are my rubber plants looking so unhappy?Opens in new window ]
Unfortunately, young plants can sometimes be infected but asymptomatic. For this reason, the RHS also strongly recommends taking great care to quarantine recently purchased young holly plants for several months after purchase so they can be observed for any signs of the disease.
In the case of your already-diseased holly tree, the best approach is to limit its effects by studiously collecting and destroying or burning any fallen leaves repeatedly to help reduce the chance of them spreading it back on to new growth. The RHS also recommends selectively pruning out and burning badly affected sections for the same reason.
