I'm posting here as I didn't see a disease forum. Hope someone can help me identify the problem occurring with our laurel hedge. About January we noticed some discoloured leaves on the top and sides of our mature laurel hedge that borders an alley. The affected leaves display brown spots with a concentric circular pattern almost like rings on a log. This will be our third summer in this house and the first time we recall seeing this. We had the hedge professionally pruned last summer and there is some occasional local traffic in the alley. It seems to be spreading and I haven't had any luck identifying it in our books or online. I've attached a photo. I think it might be a fungus and would like to determine the most effective and natural treatment before it gets out of hand. Any help is appreciated. Daryl Harrison Nanaimo, BC
Necrosis at the tip of a cherry laurel (Prunus laurocerasus) leaf usually indicates winter injury (desiccation of exposed leaves in cold, windy weather) or salt damage (from de-icing salts, marine salt spray, excess fertilizer, etc.). The interesting pattern of concentric rings would suggest something else, possibly cristulariella leaf spot, caused by Cristulariella moricola. Disease development for C. moricola is favoured by cool, wet weather in mid summer. A serious infection may lead to partial defoliation of the plant. On the other hand, the damage may be a combination of abiotic stresses, such as winter injury or salt damage together with feeding by saprobic fungi (saprobes feed on dead or dying tissues). Positive identification of fungus diseases often requires laboratory analysis.
Thanks for the reply. Here's a bit more more detail in light of your response. The spots are not always at the tip of the leaf but usually appear connected to an edge of the leaf. We have had a somewhat colder and windier late winter this year although I think longer duration of cold periods last year. The alley doesn't get salted at all (let alone ploughed!) and the affected leave are also on the inside of the hedge exposed only to our yard. Neighbours laurel hedges don't appear to have the same problem that I've noticed. Attached is an image of the alley side to show the pattern of the leaf damage and other leaves. Any suggestions on measures to deal with this? I would assume that if it's winter injury, it will heal itself over the spring/summer. If it's a cristulariella leaf spot, should I be concerned about it spreading and can I spray to control it? Thanks for your help! Daryl
I wouldn't spray anything, particularly as a pathogen hasn't been identified. Even if one was positively identified, the chances of the same conditions that encouraged the disease being the same again are very slight. I say this because cherry laurel is very tough and generally disease resistant in this part of the world. Chances are that it's an abiotic problem. For example, if the hedge was pruned in the summer and regrowth not hardened off adequately, the soft tips could have been burned by the wind and cold. This situation would be exacerbated if the hedge or lawn adjacent was fertilized late in the season.
