agronomy Article Effect of Nozzle Type and Adjuvants on Spray Coverage on Apple Leaves Ryszard Holownicki * , Grzegorz Doruchowski , Waldemar ´ Swiechowski, Pawel Konopacki and Artur Gody ´ n   Citation: Holownicki, R.; Doruchowski, G.; ´ Swiechowski, W.; Konopacki, P.; Gody´ n, A. Effect of Nozzle Type and Adjuvants on Spray Coverage on Apple Leaves. Agronomy 2021, 11, 1790. https://doi.org/ 10.3390/agronomy11091790 Academic Editor: Antonio Rodríguez-Lizana Received: 17 August 2021 Accepted: 4 September 2021 Published: 7 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). The National Institute of Horticultural Research, 96-100 Skierniewice, Poland; Grzegorz.Doruchowski@inhort.pl (G.D.); Waldemar.Swiechowski@inhort.pl (W. ´ S.); Pawel.Konopacki@inhort.pl (P.K.); Artur.Godyn@inhort.pl (A.G.) * Correspondence: Ryszard.Holownicki@inhort.pl; Tel.: +48-508-000-218 Abstract: Three non-ionic adjuvants, Agral, Silwet, and Greemax, at three concentrations, were applied on apple leaves with the use of hollow cone nozzles (TR) and air-induction nozzles (ID) to verify the assumption that adjuvants may improve spray coverage obtained by coarse droplets, and thereby ensure both satisfactory application quality and an environmental advantage. Spray coverage and droplet density were measured on both sides of the leaves. The adjuvants enhanced the spray coverage when applied at a certain concentration level. In general, the adjuvant coverage produced by the ID nozzles equaled the pure water coverage produced by the TR nozzles, thereby showing the adjuvants’ potential to compensate for the lower spray coverage usually obtained by coarse spray. A higher spray coverage was obtained on the lower side of leaves, which is discussed in terms of leaf surface properties. In the experiment with the mixture of Silwet and the fungicide Delan (dithianon), the product interacted with the adjuvant, resulting in the reversed picture of spray coverage and droplet density on the upper and lower leaf sides compared to the results obtained for the adjuvant alone. The combination of coarse spray nozzles with adjuvants may reduce environmental pollution without compromising the quality of spray applications in fruit growing. Keywords: spray application; deposition quality; surface wetting; leaf surface property; droplet density 1. Introduction Pesticides are still intensively used in agriculture to protect crops and ensure the quality of products. One of the public concerns in this regard is the environmental impact of pesticides, mainly due to spray drift associated with the pesticide application [1]. Use of coarse spray nozzles to reduce the spray drift and emission of pesticides to the environment is a very common practice in fruit growing where, in modern orchards with small and open tree canopies, more than 80% of applied spray volume may be lost [2]. Previous studies showed that fine droplets usually result in a higher spray coverage and hence a better biological efficacy of treatments in favorable weather conditions than those obtained by coarse droplets, which are less prone to drift but more likely to rebound from the leaf surface [3]. The influence of droplet size on the biological efficacy of chemical protection has long been a subject of research; however, the obtained results are inconclu- sive. A lower biological effect of herbicides applied with coarse droplets, produced by air-inclusion nozzles, was observed in field crops [4,5]. The coarse spray also worsened the efficacy of insecticides and acaricides in orchard pest control [6,7]. However, coarse droplets resulted in similar disease control in orchards to that of fine droplets, produced by conventional hollow cone nozzles [8–13]. The incidents of lower biological efficacy ob- served for air-inclusion nozzles than for conventional hollow-cone nozzles can be explained by the poorer spray coverage and lower spray droplet density. Therefore, in general, fine spray nozzles are recommended for favorable weather conditions, whereas coarse spray nozzles are preferred in windy conditions. The concept of automatic adjustment of nozzles Agronomy 2021, 11, 1790. https://doi.org/10.3390/agronomy11091790 https://www.mdpi.com/journal/agronomy