Within-Plant Distribution of Spider Mites (Acari: Tetranychidae) on Cotton: A Developing Implementable Monitoring Program

The vertical distribution of spider mites, Tetranychus spp., on cotton is largely determined by the phenological stage of crop growth. Early in the season, plants have few leaves and the mites are located close to the mainstem terminal; during the rapid phase of vegetative growth, the mites are located increasingly farther from the terminal; as vegetative growth decreases late in the season, the mites are again found closer to the terminal. The small size and potentially large numbers of mites found on cotton make conventional monitoring procedures economically impractical. A presence-absence monitoring procedure is presented which relates the proportion of mite-infested mainstem node leaves at the most infested node to the number of mites per leaf which can in turn be converted to an area estimate. An optimized sampling program was developed by incorporating the spider mite distribution information into a presence-absence sequential sampling plan. Some monitoring shortcuts that result in incorrect treatment decisions are discussed.

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