Improved sampling and management strategies for the Banks grass mite, Oligonychus pratensis (Banks), infesting commercial field corn in the Texas High Plains.

摘要

Field studies were conducted on the Banks grass mite (BGM) infesting field corn in the Texas High Plains. Sampling methods were developed and integrated management strategies were studied from 1994 thru 1996. The research explored the influence of four predators on BGM as well as the impact of the currently used acaricide, propargite.; It was determined that mite densities on leaf 3 from the plant's base were highly correlated (r = 0.78) to whole plant mite densities allowing for reliable estimates on corn plants of different ages and sizes. Extensive sampling showed that the regression of log population variance on log population mean had a high coefficient of determination (r{dollar}sp2{dollar} = 0.95), meaning that Taylor's power curve is applicable to BGM on corn in the Texas High Plains. Taylor's coefficient 'a' was {dollar}-{dollar}0.18 and coefficient 'b' was 1.58 which indicated an aggregated distribution throughout the season. Eighteen random samples provide reliable estimates of BGM, even at low mite densities. Studies on the within-field distribution of BGM indicated that populations occurring on row 10 provide a reliable estimate of BGM densities for the first 80 rows of the southernmost edge of the field.; Close examination of BGM colonies indicated that propargite did not immediately kill the eggs since they continued to hatch; the active stages were observed to have an empty gut after 7 days and they died slowly thereafter. Field studies with propargite showed great control of BGM; however, rain proved to be as effective as an acaricide.; The natural enemy complex of BGM included Frankliniella occidentalis, Stethorus sp., Hippodamia convergens, and Orius sp. Present research indicated that all named predators played an important role in suppressing BGM. Propargite showed no detrimental effects on the predators.; A treatment threshold was developed for deciding when to take corrective action with propargite on early-season populations of BGM. Findings indicated that an early-season mite density of 6 per leaf can lead to plant damage if no predators were detected; at the same mite density, 0.5 predators per leaf are enough to suppress BGM populations without propargite-treatment.