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Research Progress 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Note: this information is considered unpublished work and should not be used as final or finished results.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 nematodes.

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.
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FIELD 1     Pretreat.Sept. 7     Posttreat. Sept. 15     Posttreat. Sept. 18
                 # Live MRB/ft²         # Live      # Dead         # Live      # Dead
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                         1.1                       0             1.5                 0               1.5
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FIELD 2    Pretreat. Sept. 14    Posttreat. Sept. 18      Posttreat. Sept. 26
                # Live MRB/ft²         # Live       # Dead          #Live     # Dead
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Treatment         1.5                      0.3            1.5                0               1.5
Check                  -                        2.7              0               2.6                0
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