ABSTRACT
The effect of adjuvants on the spread of Xanthomonas axonopodis pv. citrumelo applied to nursery plots of citrus (Citrus spp.) rootstock trees in simulated wind-blown rain was studied. Commercial adjuvants tested included a penetrant-surfactant, the penetrant or surfactant components of the penetrant-surfactant alone, an antitranspirant, a surfactant, or 1 of 3 formulations of a spreader-binder. Individual rows were treated with the adjuvants or water alone as a control. Bacterial dispersal gradients in all rows were similar and extended the entire 7 m of the nursery rows. Disease incidence, number of lesions per plant, and lesion diameters were determined at selected assay points in each row 28 days after the event. The penetrant-surfactant and its surfactant component significantly increased the total number of lesions per plant and mean lesion diameters compared to the water control. The disease gradient slopes associated with the penetrant-surfactant and its surfactant component were significantly flatter and more extensive than the water control. The penetrant component of the penetrant-surfactant, the antitranspirant, and two spreader-binders adjuvants did not significantly alter the disease gradient compared to the water control. Lesion sizes and numbers were also increased by a surfactant product and the surfactant component of the penetrant-surfactant, but not by the penetrant component of the penetrant-surfactant, the antitranspirant, or the three spreader-binder formulations. These results suggest that surfactants which induce stomatal flooding may enhance infection and exacerbate citrus bacterial epidemics.
ABSTRACT
An accurate measurement of a gas concentration in air by diffusive sampling requires knowing the sampling rate. Both the boundary layer between turbulent ambient air and the sampler and the stagnant air layer inside the sampler impose resistance to the transport of analyte into the sampler. As the boundary layer mass transfer resistance is a function of the air speed and direction of the air movement, the sampling rate also depends on these variables. By the procedure developed here, the boundary layer mass transfer resistance was accurately measured as a function of wind speed and direction, and from these data a basic correlation with dimensionless parameters describing mass transfer was obtained. Deviation of air incidence angle and speed during sampling from the calibration conditions may produce a small positive bias, probably not in excess of 10%. Random variation of incidence angle and air speed while the sampler is in use may also contribute to the variability of this sampling method.
