Phenology of the Twospotted Spider Mite Tetranychus urticae (Acari: Tetranychidae) in North Carolina Tomato Systems
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Date
2007-04-25
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Abstract
The twospotted spider mite, Tetranychus urticae Koch, is a cosmopolitan and highly polyphagous pest of many fruits, vegetables, ornamentals, and field crops. While twospotted spider mite is a well-documented pest of corn and peanuts in eastern North Carolina, only recently has it been recognized as a consistent and serious pest of vegetables in the piedmont and mountains of North Carolina. Mites infest a number of vegetables in North Carolina including tomato, pepper, eggplant, and sweet corn, but tomato is by far the most seriously affected crop. The objectives of this study were to 1) determine the effect of vegetation on the dispersal of twospotted spider mites from tomatoes to overwintering hosts, and 2) to investigate the potential importance of various factors, including location, planting date, field history, surrounding area, pesticide use, and mite populations in surrounding vegetation, that may affect mite infestations in tomato fields in different regions of North Carolina. Two vegetation management techniques (herbicide and cultivation) plus an untreated control plot were established around senescing tomato plants. Twospotted spider mite dispersal was monitored by planting chickweed trap plants at 2, 6, and 12 m from the tomatoes. Sampling took place in the fall of 2004 & 2005 and the spring of 2005 & 2006. Only a small number of mites were collected in the 2004-2005 sampling period, making it difficult to draw conclusions. The 2005-2006 sampling period showed that herbicide-treated soil facilitated mite dispersal in the fall, while there were no differences in mite populations among treatments in the spring, suggesting a high rate of overwintering mortality. Tomato fields in the mountains and piedmont region were sampled in a grid pattern on a bimonthly basis to determine the importance of year, location, planting date, previous crop, adjacent crop, insecticide use, acaricide use, and mite populations in surrounding vegetation on mite intensities in those fields. Based on samples from 80 tomato fields, previous crop, acaricide use, insecticide use, and mite intensity in the weeds were important factors that were associated with seasonal mite intensity in tomato fields. Acaricide use and mite intensity in the weeds were important factors associated with the maximum mite intensity in tomatoes. Year, location, planting date, and acaricide use were all important factors associated with the time it took for tomato fields to reach their maximum density. Upon further analysis, it was found that none of the dependent variables (year, location, previous crop, adjacent crop, planting date, acaricide use, insecticide use) were associated with seasonal mite intensity in weeds or mite intensity in weeds on the last two sample dates. However, previous crop and insecticide use were significant factors associated with mite intensity in weeds on the first two sample dates. Furthermore, seasonal mite intensity in weeds was significantly correlated with seasonal and maximum mite intensity in tomato fields. While previous crop, current season insecticide use, and mite intensity in weeds were factors associated with mite intensities in the field, a high overwintering mortality appeared to negate the effects of these factors; consequently it was not possible to predict in advance fields that were most susceptible to high mite infestations. Acaricides will likely remain a key management strategy in the near future, and the development of sampling plans and economic thresholds will be necessary to use these materials in a judicious manner.
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Keywords
twospotted spider mite, Tetranychus urticae, tomato
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Degree
MS
Discipline
Entomology
