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Variegated Cutworm



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[Variegated Cutworm]

[Insect Management]


Control of Variegated Cutworm with Entomopathogenic Nematodes

Note: this information is considered unpublished work and should not be used as final or finished results.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

Research Progress Report - 1993
Ralph Berry, Joyce Takeyasu, and Mark Morris


Entomopathogenic nematodes are effective in controlling many soil insect pests; however, they do not have the same degree of success against foliar pests (Begley 1990). Adverse environmental conditions, i.e. lack of adequate moisture, temperature extremes and exposure to UV light, make the foliar environmental detrimental to nematodes. As a result, entomopathogenic nematodes often fail to control foliar pests to an acceptable level despite performing well in initial susceptibility tests in the laboratory.

Variegated cutworm larvae are susceptible to S. carpocapsae in the laboratory, but it was unknown whether it would be as susceptible in the field. Good control of sixth instars can be expected since they burrow in the soil preparing to pupate. Unfortunately, by this time, crop damage has already occurred. Control of variegated cutworm should target earlier instars but it is not clear if early instars are resistant to the nematodes by virtue of a foliar habit. In fact, a field population would have a mixture of developmental stages present at any given time and the question of whether to apply the nematodes as a foliar or ground application arises. To determine the effectiveness of variegated cutworm control with entompathogenic nematodes, two experiments were conducted in a peppermint field near Eugene, OR.

Materials and Methods

Experiment 1: A completely randomized design experiment with eight replicates was conducted using bottomless 5 gallon buckets ringed with Tanglefoot. On June 21, 1993, each bucket was infested with 10 variegated cutworm larvae (late 3rd to early 5th instars) and the foliage cut back below the top of the bucket. On June 25, 1993, eight buckets chosen at random were treated with a 3 billion IJs/acre rate of S. carpocapsae either at the beginning of the irrigation set (ground application of nematodes) or at the end of the irrigation set (foliar application of nematodes). The remaining eight buckets were left untreated. A CO2 backpack sprayer with a single nozzle boom was used to apply the nematodes. Each bucket was then fitted with a sleeve made of "no-see-um" netting to confine the peppermint inside the buckets. The experiment was evaluated on July 7, 1993 by examining the foliage and sifting the soil to a depth of 2 inches, recording the number of variegated cutworm larvae recovered.

Experiment 2: An experiment was conducted under field conditions on July 16, 1993. Six irrigation lines covering approximately 21/2 acres were randomly assigned to receive a 2 billion IJs/acre rate with either 1/8 or 1 inch of irrigation. Pre-treatment ground searches for cutworms and loopers were taken along the irrigation lines prior to nematode application. The predominant species present in the field was the variegated cutworm. On July 29, 1993, ground searches were again taken. For consistency, the same person did all the sampling. The number of larvae found on the two sampling dates were compared using the T-test.

Results and Discussion

Excellent control of variegated cutworms was achieved in the bucket trial. Both the foliar and ground application of nematodes resulted in 94.5% reduction. On the other hand, the field trial yielded only 43.9% and 45.8% reductions respectively for foliar and ground nematode applications. It did not seem to matter whether the nematodes were applied to the foliage or ground.

The results between the two experiments may be explained by the use of different nematode rates. A higher rate of 3 billion IJs/acre was used in the bucket trial while a 2 billion IJs/acre rate was used in the field trial. However, another thing to consider is whether the buckets created a favorable environment for nematode survival. In addition, whether the developmental stages used in the buckets represented the field population and whether all developmental stages are uniformly susceptible to the nematodes needs to be considered.

Table 2: Evaluation of foliar and ground applications of S. carpocapsae against variegated cutworm larvae.
                                  mean no. ¹ ( SEM)
            treatment     VC larvae in 0.6 ft2    % reduction
            untreated           9.1 ( 0.5) a                          --
            foliar                    0.5(0.3) b                         94.5
            ground               0.5 ( 0.3) b                       94.5

                                     mean no. ( SEM)
                                     larvae in one
            treatment        sample²                       % reduction
            foliar                    1.1 (0.03)                       43.9
            ground                0.8 (0.04)                      45.8

¹Means followed by the same letter are not significantly different. Separation of means by FPLSD, p = 0.05.

²1 ft² Of soil surface was examined for larvae of cutworms and loopers.