Problems With Flowering Mock Orange (Philadelphus Lewisii)
Lewis mock orange (Philadelphus Lewisii) is a 6-foot deciduous flowering shrub that grows in U.S. Department of Agriculture plant hardiness zones 5 through 10. The shrub is named for the orange-scented white blooms that can appear between May and July. Mock orange is adaptable to most soil conditions, although it will produce more flowers in drier soil that gets occasional water. The problems associated with the shrub are mostly moisture- and insect-related.
Aphids are tiny insects, often white although they may also be green, yellow, brown, black or red. Aphids suck the sap from the leaves and branches of plants such as the mock orange. Visual signs of aphids include yellow or curled leaves, stunted branch growth and black moldy spots caused by honeydew excretions. Inspect the undersides of leaves for the tiny insects. Wash the aphids from the leaves weekly in the morning. If the population doesn't diminish with washing, an insecticidal soap treatment may be used.
Leaf miners are the larvae of many different insects, such as flies or beetles, that lay eggs on the undersides of leaves. When the eggs hatch, the larvae feed on the leaves, tunneling through the leaf surface, leaving holes. Visible symptoms include holes and furrows in the leaves, browning or curling leaves and black specks on the leaf surface. Prune the infested stems and foliage. Prevent a recurrence of leaf miners with insecticidal soap applications. Remove leaves, mulch and debris from the ground below the shrub in the fall and turn over the soil to expose any larvae to predators.
Powdery mildew is a fungus that appears as a white dust on affected leaves. Warm humid days and cool humid nights cause the mildew to flourish. The best way to prevent powdery mildew is to avoid overhead watering, to water in the mornings and to make sure your mock orange is in a place that gets plenty of air movement. Spray the shrub with copper fungicides or sulfur to help keep the fungus from growing on the leaves. If powdery mildew is present, prune off and destroy the affected limbs.
Leaf blight, or leaf spots, is caused by bacteria that develop during wet springs and overwinter in the shrub to re-appear the next year. Visible signs of leaf blight include wet spots on leaves that turn brown and rot away and crooked, stunted branch ends. Prune away and destroy affected foliage and branches. Help prevent blight from infecting your mock orange by protecting it from frosts or wet weather in the early spring. Plastic sheeting over the shrub will provide adequate protection. Make sure the shrub is planted where it gets good air movement.
- U.S. Forest Service: Philadelphus Lewisii Pursh
- Pacific Horticulkture: Fragrance in the Wild Western Garden: Philadelphus
- Pacific Northwest Plant Disease Management Handbook: Mock Orange (Philadelphus Sp.)-Bacterial Blight
- Missouri Botanical Garden: Powdery Mildew - Outdoors
- Horticulture: Plants We Love: Mock Orange (Philadelphus Lewisii)
- Montana Native Plant Society: Philadelphus Lewisii Lewis’s Mockorange
- Fine Gardening: Philadelphus Coronarius "Aureus" (Mock Orange)
- Missouri Botanical Garden: Philadelphus "Miniature Snowflake"
- The Connecticut Agricultural Experiment Station: Mockorange (Philadelphus)
- Missouri Botanical Garden: Flies - Leaf and Stem Miners
Jill Kokemuller has been writing since 2010, with work published in the "Daily Gate City." She spent six years working in a private boarding school, where her focus was English, algebra and geometry. Kokemuller is an authorized substitute teacher and holds a Bachelor of Arts in English from the University of Iowa.