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Perspectives on Sampling for Lygus in Cotton: Applications of Quadrat-based Sampling Schemes

Jeffrey L. Willers


Objective assessments of row crop attributes are necessary for optimal crop management. This study primarily demonstrates the use of line-intercept sampling (LIS) to estimate two row crop attributes; namely, stand counts and populations of Lygus spp. in cotton. For either type of count, prior to canopy closure, transect lines of known length are randomly positioned at right angles to imaginary reference baselines that lie parallel to the rows. Ideally, the transect line and baseline lengths are selected to define a reference area that comprises one land acre, or for enhanced brevity of sample effort, quarter-fractions thereof. Sample information is collected from constant size quadrats intercepted by the transect lines. A quadrat is a small, rectangular area centered on a row that is bisected (i.e., encountered) by the transect line and corresponds to either the length of a yardstick or drop cloth. Attention is directed toward estimating crop attributes measured from a series of adjacent quadrats having fixed row distances; therefore, several transect statistics may be estimated using simple formulae. One particular statistic of interest discussed here is the attribute totals (i.e, the number of plants or plant bugs) per acre. Alternately, a visual technique for sampling plant bugs after canopy closure is also described. This method uses non-adjacent quadrats where the size of each is now two adjacent rows, each 9 ft long. Sub-samples of 5 randomly drawn plants per quadrat are visually examined, using terminal scouting or whole plant visual samples. Each terminal or plant is counted as infested if at least one plant bug life stage is found. A simple ‘pen and paper'computer is described that provides the estimate of percent infested plants with this ‘2 x 9' or ‘stop' sampling method. For both sampling methods, for either plant bugs or stand, the user should stratify the samples where crop phenology are similar. Estimates of each strata should not be combined, in most instances, into a final average.

Reprinted from Proceedings of the 1998 Beltwide Cotton Conferences pp. 928 - 933
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998