Care - Diseases of Laurel

Laurel are very easy to grow and, generally, disease-free. Occasionally Laurel suffer from diseases that can spoil the look of the leaves but rarely threaten the life of the plant. Powdery mildew and Shot-hole disease are the two most common diseases of laurel and these are described below.

Powdery Mildew

Powdery mildew is a fungus that can infect the new young leaves on Prunus laurocerasus under humid conditions and between the temperatures of 6 to 30oC. Rainfall or drier conditions can interrupt the spread of the disease.

Powdery Mildew will not threaten the life of the plant but may look unslightly.

Symptoms

A white powdery coating on the leaf, particularly the underside of the leaf.

Shrivelling of the new leaves.

Once the powdery coating dies off, the leaf will have brown patches or be completely brown and withered.

Control

There is normally no need for chemical control as the plants will grow through the disease once the growing conditions change to become less humid.

If the leaves look particularly unsightly, you can prune them off with a pair of secateurs or a hedgetrimmer. Disinfect the tools before using them on other plants.  Clear up any diseased leaves to prevent re-infection and burn or dispose of them. Do not compost them.

Food-grade Potassium bicarbonate at a rate of 5 grams per litre of water sprayed until run-off has been shown to control powdery mildew on many plants and is now used commercially. A number of applications may be necessary.

Products such as Bayer Fungus Fighter should result in control of powdery mildew.

Shot-hole Disease

Shot-hole disease can affect all varieties of Prunus laurocerasus and Prunus lusitanica and is caused by a bacterial pathogen called Pseudomonas syringae pv syringae or the fungi Stigmina and Eupropolella.

Shot-hole disease tends to be more of a problem on nurseries that use overhead irrigation (sprinklers) to water their plants as the disease is spread from plant to plant by water splash on the leaves. Shot-hole is not a disease that will threaten the life of a laurel and most plants will grow out of the problem once the growing conditions change (i.e. the laurel are planted into the ground where they do not need to be watered with sprinklers or the weather becomes drier) and new leaves are produced that cover up the diseased leaves.

Symptoms

Brown leaf spots between 2 and 10mm in diameter that eventually drop out to leave the leaf looking like it has been shot with a shot-gun.

Control

Chemical control is not necessary. Laurel plants will grow through the disease when the weather or growing conditions change. When the plants put on new growth, it will cover up the disease.

Do not water the leaves, water the soil around the base of the plant when watering a plant.

 

copyright © 2014 Laurel Hedging | Terms and Conditions | Privacy Policy | Cookie Policy |  web design by teapot creative