Laboratory experiments were conducted to determine the effects of application factors and standing Triticum aestivum stubble on herbicide spray deposition and efficacy in a simulated no-till environment. Spray deposition on weeds was reduced in the presence of stubble, and deposition losses on Amaranthus hybridus were greater than those on Setaria faberi. Spray penetration through stubble was significantly enhanced with electrostatic charging of a fine hydraulic spray. The combination of 45 kV electrostatic charge and 50 cm nozzle spacing produced maximum spray deposition on weeds and resulted in a 96% and 345% increase in deposition on A. hybridus and S. faberi, respectively, compared to the uncharged controls. Deposit reduction from standing stubble was greater at travel speeds of 16 km h−1 (36 to 52%) than 8 km h−1 (9 to 38%). On a dry weight and plant density basis, weeds retained more spray than was retained by stubble, yet stubble, at average densities, was capable of capturing 9 to 12% of total applied spray dose per unit area. Bounce studies of individual droplets of water or imazethapyr plus adjuvant mixture demonstrated that T. aestivum straw had a general affinity for all spray droplets, exhibiting no rebound even for 800-µm water droplets. Setaria faberi foliage exhibited poor retention of droplets: both 350- and 800-µm water droplets as well as 800-µm droplets of imazethapyr plus adjuvant mixture rebounded. Only 350-µm herbicide mixture droplets were retained by S. faberi. Amaranthus hybridus retained all droplets. In broadcast spraying, British Crop Protection Council “Medium” quality sprays were poorly retained by S. faberi compared to “Fine” sprays, whereas A. hybridus retained both sprays equally well. However, imazethapyr spray deposits resulting from coarser sprays were more efficacious on S. faberi than fine spray deposits, a difference that was not observed for A. hybridus.
Apple (Malus domestica Borkh.) leaves were sprayed to runoff using a selection of pesticides, and subsequent spray retention was evaluated by weight. Timing, cultivar, leaf surface, and leaf type significantly influenced spray retention. Spray retention correlated significantly and positively with leaf hair density. The importance of these differences is considered in relation to the possible efficiency of the pesticide application process in apple orchards.
: A video motion analysis system was used with two di †erent monodisperse droplet generators to quantify droplet impaction and any consequent reÑection. By using di †erent magniÐcation/droplet generator combinations, droplet impaction was detailed at various stages. Low (7]) magniÐcation, together with a generator that produced a spray cloud, allowed determination of the height and numbers of droplets reÑected from plant surfaces. Higher (15]) magniÐcation and a single-drop generator enabled the trajectory, and changes in velocity, of a rebounding droplet to be followed. By using high (90]) magniÐ-cation and the single-drop generator, detailed measurements of a droplet deforming on impact could be made. Examples of how these techniques could be used are given.1998 SCI ( Pestic. Sci., 53, 291È299 (1998)
We present an integro-differential equation model which, combined with experimental measurements of an oscillating free surface jet, calculates dynamic surface tension and elongational viscosity of a fluid. Our model builds upon previous models due to Rayleigh and Bohr in that it self-consistently incorporates the effects of viscosity and gravity. Further, surface tension and viscosity are allowed to be non-constant. The principal result of this paper is a technique for the measurement of surface tension of newly forming surfaces on the millisecond timescale relevant for agricultural spray mixtures. Coincidentally, our model independently yields the elongational viscosity of the fluid, although our present experimental apparatus limits the accuracy of measurement of this material property.In this paper we take measurements from physical jet experiments and implement our inverse model to deduce these material properties. The model is first benchmarked against standard techniques on a well-characterized fluid with constant surface tension and Newtonian viscosity. We then apply our method to an agricultural spray mixture, with non-constant surface tension and non-Newtonian rheology. We measure (i) the rapid decay of surface tension from the newly formed surface (aged less than a millisecond) to the much lower equilibrium value, and (ii) the rate dependence of elongational viscosity.
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