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Scouting Citrus for Pests - Page 7
Variables in Scouting for Rust Mites
Time constraints require that perhaps as few as 40 of the millions of fruit in a block actually get sampled for rust mite. Therefore, it is important to choose these samples in a way that will be most representative and yet do it efficiently. Frequency of sampling, number of sample locations per acre, path through the grove, number of sampled at each stop, location of fruit in the tree must all be determined. The lower the action threshold, the more samples must be taken for a given level of accuracy. Once a fruit is chosen, a hand lens is used to observe the mites. The number of lens fields per fruit and the way each is evaluated are additional factors. Mites may be either rated as exceeding a certain limit (one or more, three or more), rated to
estimate the actual number using an HB or Horsfall-Barrett system based on the fact that it is easier to visually perceive differences at extreme ends of a scale. An HB system of grouping rust mite population densities into 6 categories has been proposed*. Whatever system is used, trends over time are often more informative than the counts themselves, so it is important to scout regularly.
*Rogers, J. S et al. 1994. Standardized visual comparison keys for rapid estimations of citrus rust mite (Acari: Eriophyidae) populations. J. Econ Entomo. 87 p. 1507-1512.
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