This site will serve as a central resource for the Mint Pest Alert eNewsletter, which will be delivered from June through August with insect development information in the form of growing degree-day models.

CLICK HERE or use the tab above to access the most recent newsletter issue.

A few tips & reminders:

  • This information should be used in conjunction with samples collected from your fields to maximize efficacy of insecticide applications if they are needed.
  • The purpose of this newsletter is not to recommend an application be made in your fields, but to alert you to the development of these populations statewide.We use growing degree days to provide these estimates.
  • Populations of both Mint Root Borer (MRB) and Variegated Cutworm (VCW) are not identical among or within production regions, and the information in these pest alerts in no way confirms the presence or absence of treatable populations in your fields.
  • Specific application timing recommendations will be given with respect to the use of Coragen, but the insect development information will also be useful for the traditional approach of using Orthene or Lorsban.
  • Similarly, application timings recommended for monitored insect pests (MRB and VCW) will likely control loopers and armyworms.

What are degree-day models?

Degree-day models are based on rate of an insect’s growth at different temperatures. Insects have development threshold temperatures (e.g. 50°F for MRB), and only temperatures above this threshold result in growth. Because a specific amount of time spent above that temperature (called degree-days) is needed for an insect to complete development, the accumulation of these heat-units can be used to both track and predict insect growth. Degree-day models use both observed and predicted temperatures to calculate degree-day accumulation.


Coragen is an effective, narrow-spectrum insecticide for control of several pests on peppermint. Application timing for MRB and VC is based on degree-day insect development models to increase precision for maximum control. Timing is similar to in-season Orthene application for Cutworms, but differs from the traditional fall application of Lorsban for Mint Root Borer (MRB).

Control eggs and early instar larvae before damage occurs Control multiple insect pests with single application

  • MRB, Cutworm, Armyworm, Loopers

Environmentally Friendly:

  • Extremely low application rates (3.5 – 7.5 oz/acre)
  • 2 week residual control
  • Translaminar movement through leaf tissue
  • Control eggs & larvae feeding on both top and bottom of leaves
  • Selective activity on caterpillars and some sap-feeding pests
  • Easy on beneficial insects
  • 4 hour REI

Application Timing:

Based on degree-day insect development models for MRB and VC
Research on MRB indicates:

  • Application window of 10-14 days from peak flight to peak egg-laying
  • Target peak flight for most consistent control of MRB
  • Peak flight provides best control of both MRB and Cutworms with single application
  • Post-harvest control has been less effective than earlier application timings


Consult the PNW Insect Management Handbook

for other chemical control options and currently registered product information, application rates, etc.