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Mountain Laurel: Plant Heath Care Recommendations


A Technical Report from The Bartlett Tree Research Laboratories

Mountain laurel (Kalmia latifolia) is a popular native broadleaf evergreen shrub which is widely used in shrub borders and natural areas. Mountain laurel is highly prized for its flowers in mid-to-late spring and its attractive foliage. More than forty-five varieties of mountain laurel have been selected based primarily on flowering characteristics or foliage traits.

Mountain laurel is closely related to Rhododendron and azalea and have similar cultural requirements and share many of the same pest problems. Mountain laurel requires acid, well drained soils. Root disease and nutrient deficiencies typically occur on poorly drained or alkaline soils. Mountain laurel is quite tolerant of shade but flowering is most profuse where there is sun for part of the day. On exposed sites, foliage desiccation can occur especially during winter.

Common foliage feeding pests include lacebugs, weevils and foliage feeding caterpillars. Lacebugs feed by removing sap from cells resulting in a speckled leaf appearance. Weevils and caterpillars remove notches in the blade margins which severely disfigures the leaf. Scale insects and borers occasionally infest branches and stems of mountain laurel.

Leaf spots caused by the fungus Cerospora significantly reduce the attractiveness of the foliage and may cause defoliation. Leaf spot disease is severe on laurels grown in dense shade and with sprinkler irrigation which frequently wets the foliage. Phytophthora root disease causes decline and death of Kalmia especially on wet, poorly drained sites.

Mountain laurel is seldom damaged significantly by deer. Rodents may feed on stem tissue in winter especially if mulch is against the root crown.

Recommended Monitoring for Mountain Laurel

Timing Treatment
Late Winter Sample soil for nutrient and pH levels especially if deficiency symptoms are present. If plants exhibit decline, sample roots for Phytophthora root rot. Apply horticultural oil for overwintering pests (whiteflies, scale). Prune out any winter injured (dead) stems. Excavate mulch from root collars and add additional mulch to root zone as needed.
Early Spring Apply fungicide soil treatment on plants with Phytophthora root rot. Apply first fungicide spray to leaves to suppress leaf spot1. Inspect for lacebug, weevils and caterpillar defoliators. Treat as needed. Install pheromone trap for monitoring borers.
Mid Spring Apply second fungicide spray to suppress leaf spot disease. Inspect for lacebug, weevils, caterpillar defoliators and borers. Treat as needed. Apply fertilizers and soil amendments to adjust pH as needed.
Late Spring Apply third fungicide spray to suppress leafspot disease. Inspect for lacebug, weevils, caterpillar defoliators and borers. Treat as needed. Corrective prune plants after blooming. Inspect irrigation and soil moisture levels to minimize water stress and prevent root disease.
Early Summer Inspect for lacebug and weevils. Treat as needed. Corrective prune plants after blooming. Inspect irrigation and soil moisture levels to minimize water stress and prevent root disease.
Mid Summer Monitor for lacebug and weevils. Treat as needed. Corrective prune plants after blooming. Inspect irrigation and soil moisture levels to minimize water stress and prevent root disease. Apply second fungicide soil treatment on plants with Phytophthora root rot.
Late Summer Monitor for lacebug and weevils. Treat as needed. Corrective prune plants after blooming. Inspect irrigation and soil moisture levels to minimize water stress and prevent root disease.
Late Fall Apply fertilizer and soil treatments to adjust pH as needed. Erect burlap screens to protect against winter injury. Ensure adequate soil moisture levels before soil freezes to minimize winter injury. Remove mulch and soil from stems to reduce risk of rodent injury and Phtotophthora root disease.

1 Leaf spot treatments should be applied to plants with a history of this disease.

 




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