Return to:

[Mint Root Borer]

[Insect Management]

[Home]

Note: this information is considered unpublished work and should not be used as final or finished results. It has been included in IPMP 3.0 because it may not be available from other sources, and in some cases may include information that may not reach final publication.

The purpose of this study was to determine what density of MRB larvae may require treatment in the fall to prevent significant economic injury. Different aged fields were selected fall 1989 (newly planted, 2 years old, 4 years old, 12 years old). First instar larvae were released inside cages (9 ft) at each location at densities of 0, 0.5, 1.1, 1.7, 2.2, and 2.8 larvae/ft². Plots were harvested fall l989 and 1990 to determine fresh hay weight and oil yield in the 2, 4, and 12year old fields only (plots were lost in the newly planted field). Results showed that the oil and fresh hay weights were significantly correlated with MRB density in 2- and 4-year old fields. Oil yield in the 12-year old field was not significantly correlated with MRB density. Based on these data, the estimated EIL for MRB ranged from 0.7 MRB/ft² in the 2year old field to 1.4 MRB/ft² in the 4-year old field. This estimated EIL was calculated using the formula T/P/b where: T is the cost of one application of Lorsban ($30/acre), P is the value of oil ($15/lb) and b is the regression coefficient. It is evident that additional replicated studies must be conducted to refine this estimate under different growing conditions and in different aged fields.