Live to Plant

Most Common Mahonia Plant Pests:
Identification and Treatment Guide

Updated: July 2, 2023

Mahonia plants, also known as Oregon grapeholly or simply mahonias, are beautiful evergreen shrubs that add a touch of elegance to any garden. However, like any other plant, mahonias are susceptible to various pests that can damage their leaves, stems, and roots if left untreated.

In this article, we will discuss some of the most common pests that affect mahonia plants, how to identify them, and the best treatment methods to keep your mahonia healthy and thriving.

Aphids (Order: Hemiptera)

Aphids are small sap-sucking insects that can quickly multiply and infest your mahonia plants. These pests usually gather on the undersides of leaves and new growth, causing leaf curling, yellowing, and stunted growth.

Identification: Aphids are tiny insects ranging in color from green to black. They have pear-shaped bodies with long antennae.

Treatment: You can control aphids by spraying your mahonia with a strong jet of water to dislodge them. Alternatively, you can use insecticidal soap or neem oil spray to eliminate them. Ladybugs and lacewings are natural predators of aphids and can be introduced to your garden to help control their population.

Spider Mites (Family: Tetranychidae)

Spider mites are another common pest that can infest mahonia plants. These tiny arachnids feed on plant sap, leaving behind yellow stippling on the leaves. Severe infestations can cause leaf discoloration, premature leaf drop, and even plant death.

Identification: Spider mites are difficult to see with the naked eye but can be identified by their fine webbing on the undersides of leaves. Infested leaves may appear speckled or stippled.

Treatment: Regularly spraying your mahonia with water can help deter spider mites. Introducing predatory mites or applying insecticidal soap can also control their population. Avoid using broad-spectrum insecticides, as they can harm beneficial insects.

Scale Insects (Order: Hemiptera)

Scale insects are small, immobile pests that attach themselves to the stems and leaves of mahonia plants. They feed on plant sap, causing yellowing, leaf drop, and stunted growth. Heavy infestations can weaken the plant and make it more susceptible to other diseases.

Identification: Scale insects appear as small, round bumps that can be black, brown, or white in color. They often blend in with the plant’s bark or leaves.

Treatment: For light infestations, you can scrape off the scales with a gentle brush or your fingernail. Applying horticultural oil or insecticidal soap directly to the affected areas can also help control scale insects. If the infestation is severe, consult with a professional for targeted treatment options.

Leaf Miners (Order: Diptera)

Leaf miners are the larvae of various fly species that burrow into the leaves of mahonia plants, creating distinctive trails or tunnels. These pests feed on the leaf tissue, causing visible damage and weakening the overall health of the plant.

Identification: Leaf miners leave visible trails or tunnels on the surface of leaves, which may appear as white, brown, or winding lines.

Treatment: If you notice leaf miners infesting your mahonia plants, it’s best to remove and destroy the affected leaves immediately. Applying neem oil spray or introducing beneficial parasitic wasps can also help control leaf miner populations.

Root Knot Nematodes (Family: Heteroderidae)

Root knot nematodes are microscopic roundworms that infest the roots of mahonia plants. They cause galls or knots to form on the roots, interfering with nutrient uptake and water absorption. Infested plants may show symptoms of stunted growth, wilting, and yellowing leaves.

Identification: Root knot nematodes cannot be seen with the naked eye. However, the presence of galls or knots on the roots is a clear indication of their infestation.

Treatment: If you suspect root knot nematodes in your mahonia plants, it’s best to remove and destroy the affected plants to prevent the spread of the pests. Crop rotation, solarization, and soil fumigation can also help reduce nematode populations in the soil.


Protecting your mahonia plants from pests is essential to maintain their health and beauty. Regular inspection and early detection are crucial in preventing pest infestations from becoming severe. By identifying the most common pests that affect mahonias and applying appropriate treatment methods, you can keep your plants thriving and enjoy their vibrant foliage all year round.