I have some laurel bushes that are developing black or
dark brown leaves. It starts at the top and then works down.
Trimming them off seems to help but then another bush develops the
problem. I want to take care of this before it gets out of control.
A neighbor had an entire laurel die–it was probably 15 feet tall.
While I cannot diagnose a plant problem via e-mail,
it might be a bacterial or fungal problem, or an environmental
disorder. I am assuming your laurels are English laurels (Prunus
laurocerasus), not Mountain laurels (Kalmia). According to the
Oregon State University Extension’s Plant Disease database, English
laurel can suffer from leaf spots and shothole. Excerpt:
Cause: Shothole symptoms are commonly observed on Prunus sp. and
can be caused by a variety of factors. The bacterium Pseudomonas
syringae pv. syringae and several fungi including Cercospora sp.,
Blumeriella sp., and Wilsonomyces carpophilum (Coryneum blight) can
cause leaf spots and shothole on cherry laurel (English laurel,
Otto Luyken, or ‘Zabeliana’). Copper spray injury and boron
toxicity can also cause leaf spotting and shothole. When symptoms
are advanced, it is not possible to identify the cause
specifically.Cherry laurels (English laurel, Otto Luyken, or ‘Zabeliana’), P.
laurocerasus and sometimes other Prunus sp. including cherry and
plum, commonly show shothole symptoms resulting from cultural or
environmental stress. Research has failed to identify what specific
stress is responsible. Both container- and field-grown laurel can
develop symptoms.Symptoms: Necrotic leaf spots with circular to irregular margins.
Bacterial spots are brown surrounded by a reddish border with a
yellow halo. Abscission layers develop around necrotic leaf spots
causing the injured tissue to drop away, leaving holes and tattered
areas in the leaf (as if someone fired a shotgun at the leaf-thus
the name shothole). After tissues drop, most often it is difficult
to determine specifically what caused the initial injury.
Observations of early symptom development, signs, and symptoms on
other areas of the plant may help make an accurate diagnosis. Note the holes in the leaves.Cultural control: No management practices have been shown to help
reduce physiological shothole. For disease-induced shothole, try
the following cultural practices.
- Avoid overhead irrigation.
- Remove and destroy fallen leaves.
- Do not plant near other flowering or fruiting Prunus sp.
If the problem is shothole, this is usually an environmental
disorder, and infected parts of the plant should be removed and
destroyed.
Here is more information from U.C. Davis Integrated Pest Management on bacterial blight, which in laurels
usually affects only the leaves.
If you want to be sure of what the problem is, I suggest
bringing samples of the affected leaves to one of the Master
Gardener Clinics in our area.