Whole-plant bioassays using sugar beet, lettuce, cucumber, green bean, pea, and soybean as test crops were used to detect mesotrione residues in the soil. The test crops were planted in soil treated with mesotrione in the field the previous year at rates of 0 to 560 g ai ha−1 and in nontreated soil from the same field, with mesotrione added at concentrations of 0 to 320 μg kg−1. Experiments were conducted in the greenhouse for a 21-d period. Values for the dose giving a 50% response (I50) were predicted using a log-logistic nonlinear regression model. I50 values (mean ± SE) of 8.6 ± 1.8, 14.9 ± 2.0, 29.8 ± 11.0, 41.6 ± 7.3, 52.9 ± 6.4, and 67.9 ± 30.3 g ai ha−1 for sugar beet, lettuce, green bean, cucumber, pea, and soybean, respectively, indicate that these crops were effective bioassay test species for quantifying mesotrione residues. A greenhouse bioassay was a simple and sensitive tool to detect mesotrione at concentrations of less than 1.0 μg kg−1 with sugar beet and lettuce being the most sensitive test species. The I50 values for soil treated with known concentrations of mesotrione were lower than for field soil treated with mesotrione the previous year. Knowing the level of mesotrione residues in the soil, growers have flexibility in crop rotations following mesotrione use on corn. Growers can use this information to minimize risk of crop injury by choosing appropriate rotation crops that suffer little or no yield reduction.

Sulfentrazone is a phenyl triazolinone herbicide used for control of certain broadleaf and grass weed species. Sulfentrazone persists in soil and has residual activity beyond the season of application. A laboratory bioassay was developed for the detection of sulfentrazone in soil using root and shoot response of several crops. Shoot length inhibition of sugar beet was found to be the most sensitive and reproducible parameter for measurement of soil-incorporated sulfentrazone. The sugar beet bioassay was then used to examine the effect of soil properties on sulfentrazone phytotoxicity using 10 different Canadian prairie soils. Concentrations corresponding to 50% inhibition (I 50 values) were obtained from the dose–response curves constructed for the soils. Sulfentrazone phytotoxicity was strongly correlated to the percentage organic carbon (P = 0.01) and also to percentage clay content (P = 0.05), whereas correlation with soil pH was nonsignificant (P = 0.21). Because sulfentrazone phytotoxicity was found to be soil dependent, the efficacy of sulfentrazone for weed control and sulfentrazone potential carryover injury will vary with soil type in the Canadian prairies.

This paper presents a degree-two probability lower bound for the union of an arbitrary set of events in an arbitrary probability space. The bound is designed in terms of the first-degree Bonferroni summation and pairwise joint probabilities of events, which are represented as weights of edges in a Hamilton-type circuit in a connected graph. The proposed lower bound strengthens the Dawson–Sankoff lower bound in the same way that Hunter and Worsley's degree-two upper bound improves the degree-two Bonferroni-type optimal upper bound. It can be applied to statistical inference in time series and outlier diagnoses as well as the study of dose response curves.