Spray deposition and distribution in a bay laurel crop as affected by nozzle type, air assistance and spray direction when using vertical spray booms

Abstract

In Flanders, greenhouse growers predominantly use handheld sprayers instead of spray boom equipment. Nevertheless, handheld sprayers have several drawbacks. Growers increasingly recognize the advantages of spray boom equipment, which has resulted in increasing adoption of spray boom systems. Some growers still doubt the efficacy of spray boom systems, however, while others have questions about their use. In this study, we aimed to address both doubts and questions by optimizing a vertical spray boom application for a bay laurel crop using air support and spray angling. Spray deposition on the stem and the upper and lower side of the leaves was measured using mineral chelates as tracers at twenty collector positions in the top and bottom as well as in the front, back, left and right zone of the plant. Four plant repetitions were used for every spray event. Nine different application techniques were tested in three repetitions in laboratory conditions using a fully automated spray system. The effect of nozzle type, angled nozzles, air support and spraying in two passes with an opposite direction was evaluated. The experiments showed that collector position and application technique had a significant effect on deposition. However, angling the spray, using air support or spraying in two consecutive passes with an opposite direction did not result in a higher deposition or penetration capacity compared with the standard vertical spray boom. Nevertheless, some techniques might still result in a higher bio-efficacy due to a more homogenous liquid distribution. The use of a vertical spray boom is a promising technique for safe and efficient application of plant protection products in a vertical crop. Nozzle choice, spray boom setting, spray distance and the air speed of air assisted sprayers require careful consideration, however. Of the tested techniques, the applications made with an extended range standard flat fan nozzle without air support, directed straight toward the crop and used with a fixed spray distance of 30 cm to the stem generally produced the best spray results in the considered, conically pruned bay laurel crop.