Laurel plants are becoming more and more popular in Ireland because they are very easy and fast to grow. However, Laurel plants suffer from some diseases such as Powdery mildew and Shot-hole disease. These diseases are popular in Laurel plants. Even though they cannot threaten the life of the plant, they might affect the look of the leaves.
1. 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 that can lead to unslight leaves.
- There are some white and powdery spreading patches of fungus on the leaf surfaces.
- New leaves can be dried up
- When the powdery patches of fungus die off, the leaf will change into a brown colour completely in the infected part and withered.
There are two ways to control this disease, particularly non-chemical and chemical control. However, according to experts, in this case, it is unnecessary to use chemical control because the plants will grow through the disease when the growing conditions change to become less humid. Thus, you should concentrate on the non-chemical control method.
First of all, you can check the location to see if there is enough sun for plants to grow. Secondly, soil is one of the important factors; hence, it is crucial to managing humidity and leaf wetness. Pruning the leaves off with a pair of secateurs or a hedge trimmer if they become particularly unsightly. After pruning, you should disinfect the tools in case you will use 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.
2. Shot-hole Disease
The shot-hole disease is caused by a bacterial pathogen called Pseudomonas syringae pv syringae or the fungi Stigmina and Eupropolella. This 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 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 have produced that cover up the diseased leaves.
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.
For the shot-hole disease that is not really serious; hence, chemical control is not essential. 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.
To find out further information about the disease, you can read on the website of the Royal Horticultural Society.