Graduate Thesis Or Dissertation
 

Development and evaluation of sequential sampling plans for redbacked cutworm larvae, Euxoa ochrogaster (Guenée), in Oregon peppermint

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  • Field studies were conducted in 1975 and 1976 to evaluate sequential sampling plans for the redbacked cutworm, Euxoa ochrogaster (Guenee), in Oregon peppermint. Sequential sampling resulted in reliable decisions concerning whether or not cutworm densities were high enough to justify treatment with insecticides. The use of sequential sampling reduced the time required to sample fields when compared with stratified-random sampling. Results indicated that location of samples was simpler and less time was required with a systematic pattern of sequential sampling than with a random pattern of sequential sampling. There was no advantage in taking a predetermined minimum number of samples before decisions regarding the need for insecticide treatment were reached by sequential sampling, and all decisions were made before the maximum number of samples were taken (25). Significant correlations were found between the number of damaged plants/ft² and the number of cutworm larvae/ft²in most fields in 1975 and 1976. Results suggest, however, that variation in the correlations between 1975 and 1976 may preclude the use of damaged plants to estimate cutworm densities. Larvae were contagiously dispersed and larval counts fit the negative binomial distribution when population densities were above 0.50 larvae/ft². Negative correlations were found between peppermint oil yields and cutworm larval densities in artificially-infested newlyplanted peppermint plots (class I) and naturally-infested 8-year-old peppermint plots (class III). Significant correlations were not found between larval densities and peppermint oil yields in artificially- and naturally-infested 2-year-old fields (class II). Modified sequential sampling plans were formulated using revised k-values and tentative estimates of economic injury levels for fields of the three age classes: I (< 1- year -old), II (2- to 5- years -old), and III (≥6-years-old).
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