Abstract
The wettability of plant leaves directly reflects leaf hydrophilicity, which is the key factor that influences the adhesion of liquid pesticide as well as affects plant protection products (PPP) efficacy. Generally, the wettability of leaf surface is quantified by the contact angle and surface free energy (SFE), which are mainly dependent on leaf surface properties, liquid properties and other spraying parameters. Therefore, the aim of this paper was to investigate the SFE of rice and rape leaves with the variation of leaf status, leaf surface, and probe liquid as well as the influence of droplet falling height, solid surface, and PPP concentration on the wettability. The results showed that: (1) the dispersive components of SFE of rice and rape account for a large proportion which are closely related to their hydrophobicity—the abaxial of rape new leaf and the adaxial of rape old leaf are easier to wet comparing with rice and rape leaves in other statuses; (2) the increase of droplet falling height had a significant effect on improving the wettability between wax surface and adjuvant solution, while it had little improving effect on the wettability between wax surface and water; (3) the wettability of different solid surface varied greatly, and the order of wettability from good to bad is water-sensitive paper (WSP), wax, rape leaf, and rice leaf; (4) the effect of PPP concentration on the leaf surface wettability is significant, the contact angle decreased with the increase of PPP concentration, and the wettability of microemulsion is better than that of suspending agent and wettable powder. In conclusion, the SFE and wettability of crop leaf surface determine the suitable type of PPP, studying the influence of multiple factors on leaf surface wettability can provide a reliable reference for providing scientific guidance as well as improving the effective utilization of PPP.
Highlights
An efficacious and efficient spray application is an important goal to increase the benefits of plant protection products (PPP) used for crop pest and disease control [1]
Four types of solid surfaces were used for experimental process: water-sensitive paper (WSP), wax, rice and rape leaf; WSP represents hydrophilic surface, wax represents hydrophobic surface while the leaves of rice and rape are chosen because they are popular crops in China
The difference of surface free energy (SFE) and its components was investigated on rice and rape leaves, and the effects of droplet falling height, solid surface, and PPP concentration on wettability were studied
Summary
An efficacious and efficient spray application is an important goal to increase the benefits of plant protection products (PPP) used for crop pest and disease control [1]. The PPPs are sprayed on the surface of the crop with a water or oil solution, and the wettability of leaf surface, adhesion force, spreading and retention behavior of PPP solution on leaf surface are the key factors affecting the exertion of PPP efficacy [3]. The leaf surface wettability affects the water absorption, gas exchange, pathogen infection, and other functions of the plant leaf [5]. Improving the effective utilization of PPPs, reducing at the same time the pesticide losses, is the main goal in the field of chemical spray application for pest and disease control [6].
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