Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/17/1998
Publication Date: N/A
Technical Abstract: This article reviews recent advances in instrument development and in measuring techniques for agricultural spray droplets impacting on leaf and artificial surfaces. In most cases, spray droplets that reflect from a plant leaf fall to the ground and are not useful in pest control. Two types of uniform droplet generators are described along with high-speed cinema and video techniques for observing droplet/leaf interactions. Studies of reflection of droplets from leaf surfaces have found variation in reflection from leaves of the same plant. Reflection from some plant leaves change with the age of the leaf, or the growing conditions of the plant (in a greenhouse or outdoors). Droplet reflection from some other leaves vary with position on the leaf, that is, droplets may be reflected in greater numbers from near the tip of the leaf, compared to reflection near the center of the leaf. For these reasons, random leaf sampling techniques and replication of trials are very important. The oscillating jet method for measuring dynamic surface tension (DST) at short surface ages is discussed and some measured results for typical surfactants are presented. The system described here is the best system known for measuring these fluid properties. We have found DST to be correlated to droplet reflection. Thus a careful measure of DST of the spray mixture will provide insight into the likelihood of spray reflection of loss from the leaf surface. A DST model based on thin-film diffusion of surfactant molecules to the liquid/air interface was developed. Measured DST values over a range of surface ages was used to compute model constants for several surfactants.