Bay Laurel Black Blotches
Answered by: Inge Poot
Question from: Jennifer Fung
Posted on: June 22, 1999

I purchased a bay laurel plant from you several years ago, and for the most part, it has been doing well. I have had a problem with the edges of the leaves turning brown, but once I changed soil, everything was OK.

I have a new problem and I hope you can help. The surfaces of some of the leaves are turning black. There is a bit of discolouration on the underside but most of it is in the form of black blotches on the surface. I’ve been growing the bay in a large terracotta pot which I bring in for the winter and grow outside in the summer. I usually change the soil every fall before I bring it inside. What is causing this problem and what can I do?

The black blotches could be caused by sunburn. Is sun coming directly at young foliage and perhaps getting distorted and focused by the glass or water on the leaves when the sun strikes them ? A sheer curtain would be the solution there. For plants moved from indoors too suddenly into full sun this could be a severe problem. Full sun up north where Richters is located is also not the same as full sun closer to the tropics.

It could also be a fungus or bacterial infection blown onto damp leaves from some source removed from the growing area. Always remove suspicious leaves from the plant so that spores cannot infect new leaves. Also try to have leaves dry by mid-morning so that when temperatures drop and humidity increases, causing more microorganisms to release their spores, they won’t find a congenial environment on your plants. Increasing air movement helps as well, because it won’t allow any airborne spores to settle. If you are pretty sure that the blotches are caused by an infection, spray the whole plant with a suspension of flower of sulphur to discourage spread of the infection. Remove and burn any old and dead leaves or debris in the vicinity of the plant, in case the spores are being produced there.

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