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Billbugs

Pest

Billbugs are small weevils that cause damage primarily through their larvae, which tunnel into the stems and crowns of plants. This feeding activity disrupts the plant's ability to transport water and nutrients, often leading to stunted growth or death.

Billbugs on a plant
Photo: Will Linnard, CC BY

Symptoms by part

Stems

You will see small entry holes near the base of the stem, often accompanied by sawdust like frass, and the stems may become hollowed out or easily pull away from the crown.

Roots

The larvae feed on the crown and upper root zone, causing the roots to become detached from the base of the plant, which makes the plant loose in the soil.

Causes

  • Presence of adult weevils laying eggs in the lower stems.
  • High populations of larvae feeding within the crown area.
  • Dry soil conditions that stress the plant and make it more susceptible to damage.

Could be confused with

  • White Grubs · White grubs feed on roots deeper in the soil and do not typically tunnel into the stems or crowns like billbug larvae.
  • Drought stress · Drought causes uniform wilting without the presence of sawdust like frass or hollowed out stems.

Treatment

  1. 1. Tug gently on the affected stems to see if they pull away easily from the crown, confirming larval damage.
  2. 2. Dig up and destroy heavily infested plants to prevent the larvae from completing their life cycle.
  3. 3. Apply a targeted treatment to the base of the plant and surrounding soil to reach the larvae.

Without chemicals

  • Remove and dispose of infested plants immediately.
  • Maintain consistent soil moisture to help plants recover from feeding damage.
  • Encourage natural predators like birds that feed on adult weevils.

Chemical options

  • Spinosad, apply as a soil drench around the base of the plant to target larvae, follow the label.

Preventing it

  • Keep the area free of debris where adult weevils might hide.
  • Ensure plants are well watered to maintain vigor.
  • Rotate planting sites if possible to break the life cycle.

Season

The warm growing season.

Spread risk

Moderate

Severity

High

When to act

Act as soon as you notice wilting or loose stems during the warm growing season. If a large area is affected and the plants cannot be saved, remove them entirely.

Think it's Billbugs?

This guide covers the general picture. Pocket Botanist looks at your actual plant from a photo and tells you what's really going on, how serious it is, and what to try first. Identification and a health check are free.

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Questions people ask

How do I know if I have billbugs?
Look for sawdust like material at the base of the plant and stems that pull away easily when tugged.
Can my plants recover from billbug damage?
If the crown is hollowed out, the plant usually cannot recover and should be replaced.

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This guide was generated with AI and is general information, not horticultural advice. Read about how we build these guides.