Detection of a related difference in efficacy of azadirachtin treatments for the control of whiteflies on Gerbera jamesonii by testing for interactions in generalised linear models
2010
Menke, Sebastian | Gerhard, Daniel
BACKGROUND: Within a project cluster, systemical effects of two neem treatments (Neem Azal[trade mark sign] U and Neem Pellet) on the number of Trialeurodes vaporariorum (Westw.) in Gerbera jamesonii Flori Line Maxi were investigated. In order to minimise adverse ecological effects of a product, a new plant protection product can be declared as superior to a reference if it shows the same or a higher effect at a lower dosage.RESULTS: Based on a negative binomial model, the efficacy of the two treatments is compared by applying a user-defined interaction contrast in a multiple-contrast test framework. The corresponding calculation of simultaneous confidence intervals for the ratio of model parameters provides conclusions about statistical significance and biological relevance. The validity of the approach is shown by a small simulation study. As a result of the experiment, besides a significant difference between two negative control treatments, no significant difference between the efficiency of the two neem treatments (Neem Azal[trade mark sign] U and Neem Pellet) could be detected.CONCLUSIONS: Simultaneous confidence intervals for linear combinations of parameters of generalised linear models provide a useful way to compare the efficiency of two plant protection products. The results for the azadirachtin experiment indicate that large differences between any application effects of either Neem Azal[trade mark sign] U or Neem Pellet cannot be expected.
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