Submitted to: Acta Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/10/2002
Publication Date: N/A
Citation: Interpretive Summary: Primary factors in spray application of systemic nutrients or other bioregulating materials to fruit trees are formulation of the solution; atomization; transport to the target, impaction and deposition of spray; and formation of the spray droplet residue. Owing to the difficulties in obtaining uniform foliar coverage, specific attention was given to the effects of spray-solution additives on penetration rates for a number of organic and inorganic nutrient and bioregulating compounds. Among additives such as deliquescent salts, ammonium nitrate and urea have been found to enhance plant cuticular penetration of naphthalene acetic acid (NAA) as a model active ingredient, exhibiting clear interaction with atmospheric humidity. These findings have the potential to aid more rapid and effective delivery of applied systemic active ingredients to their sites of action, in turn reducing application dosages and possible risks to the environment.
Technical Abstract: Spray application factors are examined relative to effective delivery of foliar-applied nutrients to fruit trees. Application processes involve a complex series of interdependent events: 1]formulation of active ingredient; 2]liquid atomization; 3]spray-cloud transport to the tree; 4]droplet impact, retention, and residue formation; and 5]cuticular penetration by the nutrient. Any significant change in one event can profoundly affect another, each affected by application and plant/environmental factors. Data are limited on application effects on nutrient-spray performance. Thus, we draw heavily on application studies with aqueous pesticide solutions. Since nutrients are commonly dispensed with pesticide applications, additives used with pesticide sprays impact nutrient performance. Nonuniform coverage throughout the fruit-tree canopy can be a critical limitation, with the lower quadrant nearest the spray lane frequently being overdosed with the top and center under-sprayed. Fruit-tree surfaces, except for some fruit surfaces, are generally not difficult to wet so droplet reflection is not limiting. Surfactants, when used, may reduce reflection, improve coverage and, with high-volume spraying, reduce the total dose retained per unit surface area. Residues from earlier treatments and presence of natural substances, such as extra-floral nectar, on some plant surfaces modify spreading and retention. Droplet reflection, spreading, retention and nature of droplet residues are determined primarily by physicochemical properties of spray solutions and plant-surface morphology, fine structure and chemistry. The nature and distribution of spray droplet residues are important factors in performance of systemic compounds because penetration takes place from both the drying droplet and its residue.