||Mint Root Borer Control with
Report - 1990
Note: this information is considered unpublished work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 use of parasitic nematodes to control soil insects is presently being investigated on
a number of different crops. In mint, Mark Morris has demonstrated that parasitic
nematodes provide excellent control of strawberry root weevil and mint flea beetle larvae.
During fall 1990, the efficacy of parasitic nematodes against mint root borer larvae was
evaluated in two field experiments.
The first field was treated on September 7, 1990 by
injecting 3 billion parasitic nematodes/acre through sprinkler irrigation. Since the
parasitic nematodes are sensitive to ultraviolet light, all plots were treated in the
evening. Following treatment, an additional 1 3/4 inches of water was applied. Prior to
treatment, soil samples indicated that there was an average of 1.1 MRB larvae/ft². Post
treatment soil samples were taken September 15 and September 18, 1990. On September 15, 37
dead MRB larvae were found inside rhizomes in 25 samples (1.5 dead larvae/ft²), no live
larvae were found (Table 1). On September 18, 6 dead MRB larvae were found inside rhizomes
in 4 samples (1.5 dead larvae/ft²), no live larvae were found (Table 1). All affected
larvae were collected and dissected to positively verify the presence of parasitic
The second field was treated September 14, 1990 by injecting 3 billion parasitic
nematodes/acre through a sprinkler irrigation system. Following treatment, an additional 1
3/4 inches of water was applied. Prior to treatment, soil samples indicated that there was
an average of 1.5 MRB larvae/ft². Prior to injection, check areas were covered with 125
ft² tarps which were removed immediately after injection of the nematodes. Post treatment
soil samples, taken September 18, showed that there was an average of 1.5 dead MRB
larvae/ft and 0.3 live MRB larvae/ft . No dead larvae were found in the check plots (Table
1). Additional samples were taken September 26 and showed an average of 0 live MRB/ft²
(1.5 dead MRB/ft²) in the treated plots and an average of 2.6 live MRB/ft² in the
untreated plots (Table 1).
These studies indicate that parasitic nematodes injected through sprinkler irrigation
significantly reduced MRB larvae compared with check plots. All dead larvae were found
inside the rhizomes suggesting that the nematodes are capable of attacking larvae within
rhizomes. The presence of parasitic nematodes was verified in dead larvae collected from
the treated plots. At the present time, the cost of applying 3 billion parasitic
nematodes/acre is $300 However, lower rates may be equally effective which would
substantially reduce the cost. In addition, parasitic nematodes have been shown to control
strawberry root weevil and flea beetle larvae and are biological and non toxic which would
add to the benefits of using parasitic nematodes.
Table 1. Efficacy of parasitic nematodes injected through a sprinkler irrigation system on
mint root borer (MRB) larvae. Western Oregon, September 1990.
FIELD 1 Pretreat.Sept. 7 Posttreat. Sept.
15 Posttreat. Sept. 18
# Live MRB/ft² # Live
# Dead # Live
FIELD 2 Pretreat. Sept. 14 Posttreat. Sept. 18
Posttreat. Sept. 26
# Live MRB/ft² # Live
#Live # Dead