Holly Blight Disease

What is holly leaf blight?

Phytophthora ilicis is an incurable disease for hollies specifically, that was first discovered in the UK in 1989. It was not commonly seen until about 10 years ago when it really took off. Over the last 10 years holly leaf blight has been killing holly bushes at an alarming rate. It is still not fully understood but is said to be more like an algae rather than a fungus, therefore some fungicides can suppress it but none can kill it.

It is suspected that the disease is spread through infected water, whether it is ground water or rain splashing up on the plant, there are no clear answers. It is known that these outbreaks happen immediately after heavy rains and wet conditions occur. There are other possibilities for the spread of this disease as well, like birds and other animals.

What are the symptoms?

Blackening of leaves and stems will occur followed by premature leaf drop. Large sections of dead, leafless branches will appear.

How do you control Holly leaf blight?

Unfortunately fungicides and other chemicals have been ineffective on this disease. Non-chemical control is found to work best. Pruning off effected branches and removing all the leaves from the ground, will help slow the progression. You will need to burn any trimmed off branches and burn all leaves removed from the ground below.

Which hollies are resistant to this disease?

There are some varieties that show resistance to this disease. Many of these cultivars are heavily propagated by growers and some are more obscure cultivars.

Ilex cassine, Dahoon holly

Ilex ciliospinosa, Sichuan holly

Ilex crenata Convexa, Convexa Japanese holly

Ilex crenata “Hetzii”, Hetzi holly

Ilex glabra, Inkberry holly

Ilex latifolia, Mary Nell holly

Ilex perado, Canary Island holly

Ilex pernyi var. veitchii, Veitch’s Perny holly

Ilex sugerokii, Sugeroku holly

Ilex vomitaria, Yaupon holly

I have seen a healthy holly recover from a bad trim job but have never seen an infected holly actually rebound from this disease, as it is incurable. If you have an infected bush in a yard amongst some healthy holly bushes, I may recommend pulling up that bush and all of its leaves and burn it to kill the disease and monitor your other bushes to make sure the disease has not spread.

When pruning, use bypass pruners and dip the cutting blades in alcohol after each cut to avoid spreading the disease further.