How to Manage Pests

UC Pest Management Guidelines


Mint Root Borer

Scientific name: Fumibotys fumalis

(Reviewed 8/12, updated 8/12)

In this Guideline:


Wings are cream colored at the base and a mixture of rust-orange and dark brownish-gray toward the wing tip. Wings are also marked with dark lines. The wingspan is approximately 0.8 in (20 mm). Males and females appear nearly identical, although the front wings of females have slightly more orange patches.

Eggs are laid along the veins on either side of leaves. They are oval, flat, and transparent to white and turn greenish-brown prior to hatching. Depending on the temperature, eggs hatch in approximately 5 to 10 days.

Larvae feed on leaves for 2 to 4 days then drop to the soil surface and burrow into a rhizome. Mature larvae are white or tan with a reddish-brown head and are about half an inch long. In October, larvae leave the rhizomes to overwinter in hibernacula just below the surface (4/5 to 1 5/8 below). Larvae pupate in spring.

Adult mint root borers start emerging between early and mid-June, with peak emergence occurring from mid to late July. Mint root borers have one generation per year.


Larvae bore into and feed on rhizomes of peppermint. Economic loss is due to decreased oil yield, reduced quality of oil, and shorter productive expectancy of mint stands.


Biological Control
Parasitic nematodes can be released through irrigation at 2 billion infective juveniles per acre.

Cultural Control

Tillage can be effective in late fall or spring when the mint root borer is overwintering or before adults emerge in June. Rotation with a non-host crop is also a possibility.

Monitoring and Treatment Decisions
  1. Sample for mint root borer larvae from September through October.
  2. Take at least two, 1 ft2 x 3 inches deep, soil samples for every 2- to 3-acre area (minimum of 25 samples per field).
  3. Examine soil, roots, and rhizomes, and record the number of larvae found. In addition, roots and rhizomes can be placed in a Berlese funnel for approximately 24 hours or until dry to extract larvae.
  4. Consider a postharvest treatment if two or more larvae are found per sample.
Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
  (Coragen) 3.5-5.0 fl oz 4 3
B. CHLORPYRIFOS 2 lb a.i. 24 90
  (Lorsban Advanced)
  COMMENTS: Apply postharvest when field counts indicate damaging levels are present. If ground applied, incorporate insecticide into the soil with approximately one inch of overhead irrigation water immediately after application or apply by chemigation. Make only 1 application of Lorsban 75WG or other product containing chlorpyrifos during the growing season.
C. ETHOPROP 3 lb a.i. 48-72 225
  (Mocap 15G)

COMMENTS: Broadcast and incorporate to a depth of approximately two to four inches via mechanical means, or immediately incorporate insecticide into the soil with approximately one inch of overhead irrigation water. The 48 hour REI is increased to 72 hours in areas where average rainfall is less han 25 inches a year. Make only 1 application per growing season.
** See label for dilution rates.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Peppermint
UC ANR Publication 3457

Insects and Mites

K. E. Tollerup, Entomology, UC Davis

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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