Determination of foliar uptake of water droplets on waxy leaves in controlled environmental system

Authors: GAO, J - Jiangsu University; Zhu, Heping; Horst, Leona; Krause, Charles

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2015
Publication Date: 8/11/2015
Publication URL: http://handle.nal.usda.gov/10113/61830
Citation: Gao, J., Zhu, H., Horst, L., Krause, C.R. 2015. Determination of foliar uptake of water droplets on waxy leaves in controlled environmental system. Transactions of the ASABE. 58(4):1017-1024.

Interpretive Summary: Improving foliar uptake of pesticides is an appropriate approach for foliar applied systemic agents to be efficient and effective. These agents require absorption of their active ingredients into the plant for sites of action. However, foliar uptake mechanism of agrochemicals still remains unclear or unknown due to lack of techniques for accurate measurements. In this research, a sophisticated system that was integrated with a controlled environment chamber, a single droplet generator and a stereo microscopic imaging unit was constructed to measure foliar uptake rates of spray droplets with respect to variables of ambient temperature, droplet size, diurnal time, stoma density, osmotic pressure and droplet deposition locations on waxy leaf surfaces. This innovative technique will provide a better understanding of the transcuticular uptake mechanism of systematic compounds, and establish disciplined approaches to improve pesticide application efficacy to control target pests. This understanding will also improve efficiency for other spray applications such as plant hormones to regulate plant growth, liquid fertilizers to add supplemental nutrients to plants, and water to relieve foliar water stress during the growing season.

Technical Abstract: 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.