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Determination of foliar uptake of water droplets on waxy leaves in controlled environmental system
- J GAO, H. ZHU, L. HORST, C. R. KRAUSE
- Transactions of the ASABE 2015 v.58 no.4 pp. 1017-1024
- absorption, active ingredients, additives, ambient temperature, droplet size, droplets, foliar uptake, generators (equipment), glass, leaves, osmotic pressure, permeability, pesticide application, pests, plant cuticle, relative humidity, scanning electron microscopes, scanning electron microscopy, spraying, vapor pressure, water uptake
- Pertinent techniques for determination of plant cuticle permeability are needed to select proper doses of active ingredients and spray additives to improve pesticide application efficacy. A controlled environmental system with 100% relative humidity was developed for direct measurements of foliar uptake rates of sessile water droplets at various locations on waxy leaf surfaces during two diurnal periods between 10:30 and 13:00 (noon) and between 16:00 and 19:00 (evening) at ambient temperatures of 15 and 20°C. Sessile droplets of 340 and 540 µm in diameter were produced with a single-droplet generator. Stoma densities and osmotic pressures on leaves were also measured with a Scanning Electronic Microscope (SEM) and a vapor pressure osmometer, respectively. At 100% relative humidity inside the environmental chamber, droplets remained unchanged after they were deposited on a non-permeable glass but they penetrated leaf tissues after they were deposited on leaves. Foliar uptake time varied with droplet size, droplet deposition location on leaves, and diurnal period, but varied little with osmotic pressure and stoma density. An average uptake rate of 540 µm diameter droplets on a leaf surface at 20°C and 100% relative humidity was 0.000401 ±0.000063 µL/s which was 2.1 times the average absorption rate of 340-µm diameter droplets. The incorporation of the controlled environmental system with 100% relative humidity and the sessile droplet generator to measure foliar uptake rates of water droplets would provide a unique approach to elucidate the foliar uptake mechanism of spray droplets for efficient and effective control of target pests on specific plants.