WSU Extension

Hortsense

Caption: Adult root weevil damage
Photo by: E.P. Breakey
  
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Photinia : Root weevils
(revision date: 3/10/2017)


Biology
Root weevil larvae feed on the roots and bark of plants. Feeding typically occurs near the crown region. The white grubs are found in the soil around the roots. Heavy feeding by root weevil larvae can cause girdling of roots or crown, resulting in decline or death of the plant. Adults may feed on leaves, causing minor to severe notching of leaf margins. Adult root weevils range in size from 1/4" to 1/2" long. They are brownish to black, flightless beetles which climb into the foliage to feed at night.
Management Options

Non-Chemical Management
  • Hand-pick and kill night-feeding adults.
  • Apply beneficial nematodes which kill weevil larvae. The nematodes are used as a soil drench in moist soils over 52 degrees F (late summer to early fall in western Washington). Read and follow the label directions carefully.
Select non-chemical management options as your first choice!

Chemical Management


Apply when first signs of notching are noticed on new leaves. Monthly applications may be necessary if infestation is serious. Cease when first hard frost occurs in late fall/early winter. Night time applications are more effective. Beneficial nematodes can be ordered from certain nurseries. They can be applied to control the larval stage if soil temperatures are warmer than 52 F. Do not apply nematodes in direct sunlight and be sure the soil is saturated with water before application. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Bonide Systemic Insect Control
    Active ingredient: acephate  |  EPA reg no: 239-2461-4
  • Naturalis L
    Active ingredient: Beauveria bassiana  |  EPA reg no: 53871-9
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • Safer Brand Garden Defense Multi-Purpose Spray Conc [Organic]
    Active ingredient: clarified hydrophobic extract of neem oil  |  EPA reg no: 70051-2-42697
  • This list may not include all products registered for this use.
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Caption: Adult root weevil damage
Photo by: E.P. Breakey
Caption: Root weevil larval damage
Photo by: A.L. Antonelli
Caption: Root weevil larvae
Photo by: A.L. Antonelli