Bay Laurel Tree and Black Mould
Answered by: Inge Poot
Question from: Nancy Hughes
Posted on: August 12, 2007

I have a bay laurel tree that is about 2 years old. It was doing wonderfully last year until I put it outdoors for the summer. The leaves and trunk became covered with a black film (mould?) I tried to cut it back and clean off what was left of it with a damp cloth. I brought it back in for the winter and now it is outside again. The new growth looks fine but the old leaves still have a black film. What can I do?

The black film is a mould that feeds off plant juices released by the leaves. Usually, this release occurs when some insect is putting holes into the leaf blade to suck its juices. The most common culprits are scale insects and spider mites. Since you have not noticed these pests it could be a species that is very hard to see with the naked eye. There are some very tiny and flat scale insects and some so called false spider mites that are very hard to detect, the latter because they are one tenth the size of ordinary spider mites and they don’t spin any webs. Use a cloth dipped in diluted dishwash detergent to wipe off the mould and while doing so check with a magnifying glass if you can see little scaly humps on the plant parts or tiny little translucent ovals -the insects. Spray with neem oil-2 tsp oil plus I tsp dishwash detergent per litre /quart of water. Repeat weekly for at least 3 to 5 times.

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