The Otto Luyken (Prunus laurocerasus "Otto Luyken") is a dwarf English laurel cultivar that grows well in U.S. Department of Agriculture plant hardiness zones 6 through 8. This compact, broadleaf evergreen shrub only reaches about 3 feet tall with 6-foot spreads and is commonly used as a hedge, a specimen plant or in group plantings. Flower spikes featuring aromatic, white blossoms bloom profusely from late spring through early summer. It also bears small, black fruit and glossy, deep green leaves with paler green undersides. This easy-to-grow shrub presents gardeners with just a few common problems.
The Otto Luyken laurel may be one of the more pest-resistant members of the Prunus plant family, but shothole borers (Scolytus rugulosus) still occasionally overrun this shrub. This tiny, dark-colored beetle grows to about the size of a grain of rice and possesses strong jaws for chewing its way into the inner wood of branches and trunks. Adult females lay eggs just underneath the bark, and the larvae emerge to start mining little galleries. Signs of a shothole borer infestation include little, round holes oozing gummy sap mixed with sawdust. Boring damage typically causes twig dieback.
Pest Control Methods
Chemical control methods don't work once shothole borers infest your shrub since the pests live in the protected area just below the bark. Preventative treatment is also difficult because the pesticide products available to home gardeners don't work effectively. The University of California Statewide Integrated Pest Management Program website suggests pruning out and destroying all infested plant parts. If the borers attack the trunk, remove the entire shrub.
This English laurel cultivar sometimes suffers from root rot and powdery mildew diseases. Root rot pathogens (Phytophthora spp.) enter the roots and disrupt the transfer of water and nutrients. Although the fungi thrive in overly wet soil conditions, affected plants look drought stressed with wilted, discolored, stunted and prematurely dropping foliage. Infected branches and twigs typically suffer dieback while cankers or stains often appear on infected trunks. Various fungus species trigger powdery mildew, a disease that causes a white, powdery growth to form on leaf surfaces. Affected foliage may also appear stunted and misshapen.
Fungal Disease Solutions
Help prevent root rot by planting your Otto Luyken in a site with good drainage. Avoid saturating the soil around the base of your shrub, and water only when the soil feels dry to the touch. Planting your shrub in a full-sun location helps control fungal diseases since most pathogens prefer shady conditions and cooler temperatures. Severe powdery mildew infections may require fungicidal treatment. A horticulturist at the Oregon state University Extension Service suggests spraying your shrub with a 2 percent horticultural oil solution. Following the directions on the product's label, thoroughly spray the upper and lower sides of the laurel leaves for the best results.
The Otto Luyken occasionally suffers from shot hole, a disease caused by bacterial pathogens (Xanthomonas pruni). This disease typically starts in early summer with little, brown sores appearing on the undersides of leaves. The spots grow and develop red borders and yellow halos. The spots eventually fall out of the leaves, leaving behind gaping holes and tattered leaf tissue. Many infected trees look as though someone peppered them with buckshot.
Bacterial Disease Control
Because chemical control of shot hole disease is hard to achieve for home gardeners, help prevent this disease from occurring by planting the shrub in a well-draining location. Prune out and destroy any infected plant tissue as soon as you notice it. Rake up fallen plant litter to prevent pathogens from being attracted to the area near your shrub.
You must prune these fast-growing shrubs on a regular basis to control the overall size. In some areas, English laurel cultivars grow excessively to the point of invasiveness. Prune your shrub after it stops flowering. Use hand pruners to cut back individual stems to the desired length. Using hedge clippers results in a bunch of discolored, raggedy leaves. The foliage and berries contain toxic properties, so plant this shrub only in areas where pets and children don't wander.
- Washington State University Clark County Extension: Otto Luyken
- Washington State University Extension: High Maintenance and Problem Plants in the Pacific Northwest
- University of California Statewide Integrated Pest Management Program: Shot Hole Disease
- North Carolina State University Cooperative Extension: Prunus Laurocerasus
- University of California Statewide Integrated Pest Management Program: Bark Beetles
- University of California Statewide Integrated Pest Management Program: Collar, Root, Root, and Crown Rots -- Phytophthora Spp.
- University of California Statewide Integrated Pest Management Program: Powdery Mildew on Ornamentals
- Oregon State University Extension Service: Controlling Powdery Mildew with Horticultural Mineral Oil