An integrated study to improve spray deposition in a dense crop with a horizontal leaf position

Flemish greenhouse growers predominantly use handheld spray guns and spray lances for their crop protection purposes, despite the heavy workload and high risk for operator exposure associated with these techniques. These spray application techniques have shown to be less effective than spray boom equipment under many conditions. Handheld spraying techniques are less expensive, however, and they are more flexible in use. Many Flemish growers also erroneously believe that high spray volumes and pressures are needed to assure good plant protection.
This paper summarises the results of a whole series of laboratory trials to optimize the depositions of a horizontal spray boom system in a dense ivy crop with a horizontal leaf position. The effect of nozzle type, spray volume, spray direction, air assistance and the number of passes was evaluated. In total, seventeen spray application techniques were evaluated.
Overall, the use of air assistance resulted in the most uniform spray distribution because of an improved spray penetration and a good coverage of the lower sides of the leaves. The use of air assistance was most effective when combined with a medium droplet size extended range flat-fan nozzle at 3.0 bar with a 30° forward or a standard 0° spray angle and a spray volume of 1000 L ha^-1. Without air assistance, a 30° forward angle lead to higher spray depositions within the canopy as well.